Thiago Moreira - Academia.edu (original) (raw)

Papers by Thiago Moreira

Research paper thumbnail of Clinical Response and Transfusion Reactions of Sheep Subjected to Single Homologous Blood Transfusion

The Scientific World Journal, 2014

Studies in relation to blood conservation and responses to transfusion are scarce for ruminants. ... more Studies in relation to blood conservation and responses to transfusion are scarce for ruminants. We evaluated the clinical manifestations of sheep that received a single homologous transfusion of whole blood, focusing on transfusion reactions. Eighteen adult sheep were subjected to a single phlebotomy to withdraw 40% of the total blood volume, which was placed into CPDA-1 bags and then divided into G0, animals that received fresh blood, and G15 and G35, animals that received blood stored for 15 or 35 days, respectively. Clinical observations were recorded throughout the transfusion, whereas heart rate, respiratory rate, and rectal temperature were assessed at the following times: 24 hours after phlebotomy and before transfusion; 30 minutes, six, twelve, 24, 48, 72, and 96 hours and eight and 16 days after transfusion. All groups presented transfusion reactions, among which hyperthermia was the most frequent (50% of animals). Tachycardia occurred most frequently in the G35 animals (50% of them). During transfusion G35 animals presented more clinical manifestation ( < 0.05). Transfusion of fresh or stored total blood improved the blood volume, but transfusion reactions occurred, demonstrating that a single transfusion of fresh or stored blood can cause inflammatory and febrile nonhemolytic transfusion reactions in sheep.

Research paper thumbnail of Respiratory deficits in a rat model of Parkinson's disease

Neuroscience, Jan 30, 2015

Parkinson's disease (PD) is a neurodegenerative disease characterized by loss of the dopamine... more Parkinson's disease (PD) is a neurodegenerative disease characterized by loss of the dopaminergic nigrostriatal pathway. In addition to deficits in voluntary movement, PD involves a disturbance of breathing regulation. However, the cause and nature of this disturbance are not well understood. Here, we investigated breathing at rest and in response to hypercapnia (7% CO2) or hypoxia (8% O2), as well as neuroanatomical changes in brainstem regions essential for breathing, in a 6-hydroxydopamine (6-OHDA) rat model of PD. Bilateral injections of 6-OHDA (24 μg/μl) into the striatum decreased tyrosine hydroxylase (TH(+))-neurons in the substantia nigra pars compacta (SN), transcription factor phox2b-expressing neurons in the retrotrapezoid nucleus and neurokinin-1 receptors in the ventral respiratory column. In 6-OHDA-lesioned rats, respiratory rate was reduced at rest, leading to a reduction in minute ventilation. These animals also showed a reduction in the tachypneic response to hy...

Research paper thumbnail of Contribution of excitatory amino acid receptors of the retrotrapezoid nucleus to the sympathetic chemoreflex in rats

In the present study, we evaluated the role of glutamatergic mechanisms in the retrotrapezoid nuc... more In the present study, we evaluated the role of glutamatergic mechanisms in the retrotrapezoid nucleus (RTN) in changes of splanchnic sympathetic nerve discharge (sSND) and phrenic nerve discharge (PND) elicited by central and peripheral chemoreceptor activation. Mean arterial pressure (MAP), sSND and PND were recorded in urethane-anaesthetized, vagotomized, sino-aortic denervated and artificially ventilated male Wistar rats. Hypercapnia (10% CO 2 ) increased MAP by 32 ± 4 mmHg, sSND by 104 ± 4% and PND amplitude by 101 ± 5%. Responses to hypercapnia were reduced after bilateral injection of the NMDA receptor antagonist d,l-2-amino-5-phosphonovalerate (AP-5; 100 mm in 50 nl) in the RTN (MAP increased by 16 ± 3 mmHg, sSND by 82 ± 3% and PND amplitude by 63 ± 7%). Bilateral injection of the non-NMDA receptor antagonist 6,7-dinitro-quinoxaline-2,3-dione (DNQX; 100 mm in 50 nl) and the metabotropic receptor antagonist (+/−)-α-methyl-4-carboxyphenylglycine (MCPG; 100 mm in 50 nl) in the RTN did not affect sympathoexcitatory responses induced by hypercapnia. Injection of DNQX reduced hypercapnia-induced phrenic activation, whereas MCPG did not. In animals with intact carotid chemoreceptors, bilateral injections of AP-5 and DNQX in the RTN reduced increases in MAP, sSND and PND amplitude produced by intravenous injection of NaCN (50 μg kg −1 ). Injection of MCPG in the RTN did not change responses produced by NaCN. These data indicate that RTN ionotropic glutamatergic receptors are involved in the sympathetic and respiratory responses produced by central and peripheral chemoreceptor activation.

Research paper thumbnail of Central moxonidine on salivary gland blood flow and cardiovascular responses to pilocarpine

Brain research, Jan 17, 2003

Peripheral treatment with the cholinergic agonist pilocarpine induces intense salivation that is ... more Peripheral treatment with the cholinergic agonist pilocarpine induces intense salivation that is inhibited by central injections of the alpha2-adrenergic/imidazoline receptor agonist moxonidine. Salivary gland blood flow controlled by sympathetic and parasympathetic systems may affect salivation. We investigated the changes in mean arterial pressure (MAP) and in the vascular resistance in the submandibular/sublingual gland (SSG) artery, superior mesenteric (SM) artery and low abdominal aorta (hindlimb) in rats treated with intraperitoneal (i.p.) pilocarpine alone or combined with intracerebroventricular (i.c.v.) moxonidine. Male Holtzman rats with stainless steel cannula implanted into lateral ventricle (LV) and anesthetized with urethane were used. Pilocarpine (4 micromol/kg of body weight) i.p. reduced SSG vascular resistance (-50+/-13% vs. vehicle: 5+/-3%). Pilocarpine i.p. also increased mesenteric vascular resistance (15+/-5% vs. vehicle: 2+/-3%) and MAP (16+/-3 mmHg, vs. vehic...

Research paper thumbnail of Central blockade of nitric oxide synthesis reduces moxonidine-induced hypotension

British journal of pharmacology, 2004

1. Nitric oxide (NO) and alpha(2)-adrenoceptor and imidazoline agonists such as moxonidine may ac... more 1. Nitric oxide (NO) and alpha(2)-adrenoceptor and imidazoline agonists such as moxonidine may act centrally to inhibit sympathetic activity and decrease arterial pressure. 2. In the present study, we investigated the effects of pretreatment with l-NAME (NO synthesis inhibitor), injected into the 4th ventricle (4th V) or intravenously (i.v.), on the hypotension, bradycardia and vasodilatation induced by moxonidine injected into the 4th V in normotensive rats. 3. Male Wistar rats with a stainless steel cannula implanted into the 4th V and anaesthetized with urethane were used. Blood flows were recorded by use of miniature pulsed Doppler flow probes implanted around the renal, superior mesenteric and low abdominal aorta. 4. Moxonidine (20 nmol), injected into the 4th V, reduced the mean arterial pressure (-42+/-3 mmHg), heart rate (-22+/-7 bpm) and renal (-62+/-15%), mesenteric (-41+/-8%) and hindquarter (-50+/-8%) vascular resistances. 5. Pretreatment with l-NAME (10 nmol into the 4t...

Research paper thumbnail of Role of pressor mechanisms from the NTS and CVLM in control of arterial pressure

American journal of physiology. Regulatory, integrative and comparative physiology, 2005

In the present study, we investigated the effects of inhibition of the caudal ventrolateral medul... more In the present study, we investigated the effects of inhibition of the caudal ventrolateral medulla (CVLM) with the GABA(A) agonist muscimol combined with the blockade of glutamatergic mechanism in the nucleus of the solitary tract (NTS) with kynurenic acid (kyn) on mean arterial pressure (MAP), heart rate (HR), and regional vascular resistances. In male Holtzman rats anesthetized intravenously with urethane/chloralose, bilateral injections of muscimol (120 pmol) into the CVLM or bilateral injections of kyn (2.7 nmol) into the NTS alone increased MAP to 186 +/- 11 and to 142 +/- 6 mmHg, respectively, vs. control: 105 +/- 4 mmHg; HR to 407 +/- 15 and to 412 +/- 18 beats per minute (bpm), respectively, vs. control: 352 +/- 12 bpm; and renal, mesenteric and hindquarter vascular resistances. However, in rats with the CVLM bilaterally blocked by muscimol, additional injections of kyn into the NTS reduced MAP to 88 +/- 5 mmHg and mesenteric and hindquarter vascular resistances below contr...

Research paper thumbnail of Antihypertensive responses elicited by central moxonidine in rats: possible role of nitric oxide

Journal of cardiovascular pharmacology, 2006

In the present study, we investigated the effects of pretreatment with NG-nitro-L-arginine methyl... more In the present study, we investigated the effects of pretreatment with NG-nitro-L-arginine methyl ester (L-NAME) (nitric oxide synthase inhibitor) injected intravenously (IV) on the hypotension, bradycardia, and vasodilation produced by moxonidine (alpha2-adrenergic/imidazoline receptor agonist) injected into the fourth brain ventricle (4th V) in rats submitted to acute hypertension that results from baroreflex blockade by bilateral injections of kynurenic acid (kyn, glutamatergic receptor antagonist) into the nucleus of the solitary tract (NTS) or in normotensive rats. Male Wistar rats (n=5 to 7/group) anesthetized with IV urethane (1.0 g kg(-1) of body weight) and alpha-chloralose (60 mg kg(-1) of body weight) were used. Bilateral injections of kyn (2.7 nmol 100 nL(-1)) into the NTS increased baseline mean arterial pressure (148 +/- 11 mm Hg, vs. control: 102 +/- 4 mm Hg) and baseline heart rate (417 +/- 11 bpm, vs. control: 379 +/- 6 bpm). Moxonidine (20 nmol microL(-1)) into the...

Research paper thumbnail of HCN channels contribute to serotonergic modulation of ventral surface chemosensitive neurons and respiratory activity

Journal of neurophysiology, Jan 15, 2015

Chemosensitive neurons in the retrotrapezoid nucleus (RTN) provide a CO2/H(+)-dependent drive to ... more Chemosensitive neurons in the retrotrapezoid nucleus (RTN) provide a CO2/H(+)-dependent drive to breathe and function as an integration center for the respiratory network, including serotonergic raphe neurons. We recently showed that serotonergic modulation of RTN chemoreceptors involved inhibition of KCNQ channels and activation of an unknown inward current. Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels are the molecular correlate of the hyperpolarization-activated inward current (Ih) and have a high propensity for modulation by serotonin. To investigate whether HCN channels contribute to basal activity and serotonergic modulation of RTN chemoreceptors, we characterize resting activity and the effects of serotonin on RTN chemoreceptors in vitro and on respiratory activity of anesthetized rats in the presence or absence of blockers of KCNQ (XE991) and/or HCN (ZD7288, Cs(+)) channels. We found in vivo that bilateral RTN injections of ZD7288 increased respiratory ...

Research paper thumbnail of Independent purinergic mechanisms of central and peripheral chemoreception in the rostral ventrolateral medulla

The Journal of physiology, 2015

The rostral ventrolateral medulla oblongata (RVLM) contains two functionally distinct types of ne... more The rostral ventrolateral medulla oblongata (RVLM) contains two functionally distinct types of neurons that control and orchestrate cardiovascular and respiratory responses to hypoxia and hypercapnia. One group is composed of the central chemoreceptor neurons of the retrotrapezoid nucleus, which provides a CO2 /H(+) -dependent drive to breathe and serves as an integration centre and a point of convergence of chemosensory information from other central and peripheral sites, including the carotid bodies. The second cluster of RVLM cells forms a population of neurons belonging to the C1 catecholaminergic group that controls sympathetic vasomotor tone in resting conditions and in conditions of hypoxia and hypercapnia. Recent evidence suggests that ATP-mediated purinergic signalling at the level of the RVLM co-ordinates cardiovascular and respiratory responses triggered by hypoxia and hypercapnia by activating retrotrapezoid nucleus and C1 neurons, respectively. The role of ATP-mediated ...

Research paper thumbnail of Morphine Spinal Block Anesthesia in Patients Who Undergo an Open Hemorrhoidectomy: A Prospective Analysis of Pain Control and Postoperative Complications

Annals of Coloproctology, 2014

This study evaluated the use of adding morphine to bupivacaine in spinal anesthesia for pain cont... more This study evaluated the use of adding morphine to bupivacaine in spinal anesthesia for pain control in patients who underwent an open hemorrhoidectomy. Forty patients were prospectively selected for an open hemorrhoidectomy at the same institution and were randomized into two groups of 20 patients each: group 1 had a spinal with 7 mg of heavy bupivacaine associated with 80 µg of morphine (0.2 mg/mL). Group 2 had a spinal with 7 mg of heavy bupivacaine associated with distilled water, achieving the same volume of spinal infusion as that of group 1. Both groups were prescribed the same pain control medicine during the postoperative period. Pain scores were evaluated at the anesthetic recovery room and at 3, 6, 12, and 24 hours after surgery. Postoperative complications, including pruritus, nausea, headaches, and urinary retention, were also recorded. There were no anthropometric statistical differences between the two groups. Pain in the anesthetic recovery room and 3 hours after surgery was similar for both groups. However, pain was better controlled in group 1 at 6 and 12 hours after surgery. Although pain was better controlled for group 1 after 24 hours of surgery, the difference between the groups didn&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;t achieved statistical significance. Complications were more common in group 1. Six patients (6/20) presented coetaneous pruritus and 3 with (3/20) urinary retention. A hemorrhoidectomy under a spinal with morphine provides better pain control between 6 and 12 hours after surgery. However, postoperative complications, including cutaneous pruritus (30%) and urinary retention (15%), should be considered as a negative side of this procedure.

Research paper thumbnail of New advances in the neural control of breathing

The Journal of physiology, 2015

Research paper thumbnail of Combined oral midazolam-ketamine better than midazolam alone for sedation of young children: a randomized controlled trial

International Journal of Paediatric Dentistry, 2012

BACKGROUND. There is a lack of clinical trials on paediatric dental sedation. AIM. We investiga... more BACKGROUND. There is a lack of clinical trials on paediatric dental sedation. AIM. We investigated whether young children&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s behaviour improves during dental treatment with oral ketamine/midazolam compared with midazolam alone or no sedation. DESIGN. Healthy children under 36 months of age, presenting early childhood caries were randomly assigned to receive protective stabilization plus: combined oral midazolam (0.5 mg/kg) and ketamine (3 mg/kg) (MK), or oral midazolam (1.0 mg/kg) (MS), or no sedative (PS). One observer scored children&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s behaviour using the Ohio State University Behavior Rating Scale (OSUBRS) at determined points in a dental exam (no sedative) and treatment session. Data were analysed using nonparametric bivariate tests. RESULTS. Forty-one children were included. In the dental exam session, the sum of OSUBRS scores was similar for the three groups (P = 0.81). In the treatment session, the MK produced more cooperative behaviour than MS and PS (P = 0.01), longer sessions (P = 0.04), and a pattern of homogeneous OSUBRS scores from the reception area (before sedative administration) to the end of the session (P = 0.06). No immediate and post-discharge side effects were observed in groups MK and MS. CONCLUSIONS. The combination of oral midazolam and ketamine is efficacious for guiding the behaviour of children under 3 years old.

Research paper thumbnail of Inhibitory input from slowly adapting lung stretch receptors to retrotrapezoid nucleus chemoreceptors

The Journal of Physiology, 2007

The retrotrapezoid nucleus (RTN) contains CO 2 -activated interneurons with properties consistent... more The retrotrapezoid nucleus (RTN) contains CO 2 -activated interneurons with properties consistent with central respiratory chemoreceptors. These neurons are glutamatergic and express the transcription factor Phox2b. Here we tested whether RTN neurons receive an input from slowly adapting pulmonary stretch receptors (SARs) in halothane-anaesthetized ventilated rats. In vagotomized rats, RTN neurons were inhibited to a variable extent by stimulating myelinated vagal afferents using the lowest intensity needed to inhibit the phrenic nerve discharge (PND). In rats with intact vagus nerves, RTN neurons were inhibited, also to a variable extent, by increasing positive end-expiratory pressure (PEEP; 2-6 cmH 2 O). The cells most sensitive to PEEP were inhibited during each lung inflation at rest and were instantly activated by stopping ventilation. Muscimol (GABA-A agonist) injection in or next to the solitary tract at area postrema level desynchronized PND from ventilation, eliminated the lung inflation-synchronous inhibition of RTN neurons and their steady inhibition by PEEP but did not change their CO 2 sensitivity. Muscimol injection into the rostral ventral respiratory group eliminated PND but did not change RTN neuron response to either lung inflation, PEEP increases, vagal stimulation or CO 2 . Generalized glutamate receptor blockade with intracerebroventricular (I.C.V.) kynurenate eliminated PND and the response of RTN neurons to lung inflation but did not change their CO 2 sensitivity. PEEP-sensitive RTN neurons expressed Phox2b. In conclusion, RTN chemoreceptors receive an inhibitory input from myelinated lung stretch receptors, presumably SARs. The lung input to RTN may be di-synaptic with inhibitory pump cells as sole interneurons.

Research paper thumbnail of Retrotrapezoid nucleus and central chemoreception

The Journal of Physiology, 2008

The 'distributed chemoreception theory' attributes the central chemoreflex (the stimulation of br... more The 'distributed chemoreception theory' attributes the central chemoreflex (the stimulation of breathing by CNS acidification) to the cumulative effects of pH on multiple classes of respiratory neurons as well as on their tonic sources of drive. Opinions differ as to how many classes of pH-sensitive neurons contribute to the central chemoreflex but the number of candidates is high and growing fast. The 'specialized chemoreceptor theory', endorsed here, attributes the chemoreflex to a limited number of specialized neurons. These neurons (the central chemoreceptors) would drive a respiratory pattern generator that is not or minimally activated by acidification. In this review we first describe the properties of the retrotrapezoid nucleus (RTN) and argue that this nucleus may contain the most important central chemoreceptors. Next, we subject the assumptions that underlie the distributed chemoreception theory to a critical analysis. We propose several explanations for the apparent contradiction between the two competing theories of central chemoreception. We attribute much of the current controversy to premature extrapolations of the effects of acidification on neurons recorded in vitro (chemosensitivity) and to a semantic confusion between chemosensitivity and chemoreception (the mechanism by which CO 2 or pH activates breathing in vivo).

Research paper thumbnail of Central chemoreceptors and sympathetic vasomotor outflow

The Journal of Physiology, 2006

Research paper thumbnail of Peripheral chemoreceptor inputs to retrotrapezoid nucleus (RTN) CO2-sensitive neurons in rats

The Journal of Physiology, 2006

The rat retrotrapezoid nucleus (RTN) contains pH-sensitive neurons that are putative central chem... more The rat retrotrapezoid nucleus (RTN) contains pH-sensitive neurons that are putative central chemoreceptors. Here, we examined whether these neurons respond to peripheral chemoreceptor stimulation and whether the input is direct from the solitary tract nucleus (NTS) or indirect via the respiratory network. A dense neuronal projection from commissural NTS (commNTS) to RTN was revealed using the anterograde tracer biotinylated dextran amine (BDA). Within RTN, 51% of BDA-labelled axonal varicosities contained detectable levels of vesicular glutamate transporter-2 (VGLUT2) but only 5% contained glutamic acid decarboxylase-67 (GAD67). Awake rats were exposed to hypoxia (n = 6) or normoxia (n = 5) 1 week after injection of the retrograde tracer cholera toxin B (CTB) into RTN. Hypoxia-activated neurons were identified by the presence of Fos-immunoreactive nuclei. CommNTS neurons immunoreactive for both Fos and CTB were found only in hypoxia-treated rats. VGLUT2 mRNA was detected in 92 ± 13% of these neurons whereas only 12 ± 9% contained GAD67 mRNA. In urethane-chloralose-anaesthetized rats, bilateral inhibition of the RTN with muscimol eliminated the phrenic nerve discharge (PND) at rest, during hyperoxic hypercapnia (10% CO 2 ), and during peripheral chemoreceptor stimulation (hypoxia and/or I.V. sodium cyanide, NaCN). RTN CO 2 -activated neurons were recorded extracellularly in anaesthetized intact or vagotomized rats. These neurons were strongly activated by hypoxia (10-15% O 2 ; 30 s) or by NaCN. Hypoxia and NaCN were ineffective in rats with carotid chemoreceptor denervation. Bilateral injection of muscimol into the ventral respiratory column 1.5 mm caudal to RTN eliminated PND and the respiratory modulation of RTN neurons. Muscimol did not change the threshold and sensitivity of RTN neurons to hyperoxic hypercapnia nor their activation by peripheral chemoreceptor stimulation. In conclusion, RTN neurons respond to brain P CO 2 presumably via their intrinsic chemosensitivity and to carotid chemoreceptor activation via a direct glutamatergic pathway from commNTS that bypasses the respiratory network. RTN neurons probably contribute a portion of the chemical drive to breathe.

Research paper thumbnail of Serotonergic Neurons Activate Chemosensitive Retrotrapezoid Nucleus Neurons by a pH-Independent Mechanism

Journal of Neuroscience, 2007

Serotonin activates respiration and enhances the stimulatory effect of CO2 on breathing. The pres... more Serotonin activates respiration and enhances the stimulatory effect of CO2 on breathing. The present study tests whether the mechanism involves the retrotrapezoid nucleus (RTN), a group of medullary glutamatergic neurons activated by extracellular brain pH and presumed to regulate breathing. We show that the RTN is innervated by both medullary and pontine raphe and receives inputs from thyrotropin-releasing hormone (TRH) and substance P-expressing neurons. Coexistence of serotonin and substance P in terminals within RTN confirmed that lower medullary serotonergic neurons innervate RTN. In vivo, unilateral injection of serotonin into RTN stimulated inspiratory motor activity, and pH-sensitive RTN neurons were activated by iontophoretic application of serotonin or substance P. In brain slices, pH-sensitive RTN neurons were activated by serotonin, substance P, and TRH. The effect of serotonin in slices was ketanserin sensitive and persisted in the presence of glutamate, GABA, glycine, and purinergic ionotropic receptor antagonists. Serotonin and pH had approximately additive effects on the discharge rate of RTN neurons, both in slices and in vivo. In slices, serotonin produced an inward current with little effect on conductance and had no effect on the pH-induced current. We conclude that (1) RTN receives input from multiple raphe nuclei, (2) serotonin, substance P, and TRH activate RTN chemoreceptors, and (3) excitatory effects of serotonin and pH are mediated by distinct ionic conductances. Thus, RTN neurons presumably contribute to the respiratory stimulation caused by serotonergic neurons, but serotonin seems without effect on the cellular mechanism by which RTN neurons detect pH.

Research paper thumbnail of Expression of Phox2b by Brainstem Neurons Involved in Chemosensory Integration in the Adult Rat

Journal of Neuroscience, 2006

Central congenital hypoventilation syndrome is caused by mutations of the gene that encodes the t... more Central congenital hypoventilation syndrome is caused by mutations of the gene that encodes the transcription factor Phox2b. The syndrome is characterized by a severe form of sleep apnea attributed to greatly compromised central and peripheral chemoreflexes. In this study, we analyze whether Phox2b expression in the brainstem respiratory network is preferentially associated with neurons involved in chemosensory integration in rats. At the very rostral end of the ventral respiratory column (VRC), Phox2b was present in many VGlut2 (vesicular glutamate transporter 2) mRNA-containing neurons. These neurons were functionally identified as the respiratory chemoreceptors of the retrotrapezoid nucleus (RTN). More caudally in the VRC, many fewer neurons expressed Phox2b. These cells were not part of the central respiratory pattern generator (CPG), because they were typically cholinergic visceral motor neurons or catecholaminergic neurons (presumed C1 neurons). Phox2b was not detected in serotonergic neurons, in the A5, A6, and A7 noradrenergic cell groups nor within the main cardiorespiratory centers of the dorsolateral pons. Phox2b was expressed by many solitary tract nucleus (NTS) neurons including those that relay peripheral chemoreceptor information to the RTN. These and previous observations by others suggest that Phox2b is expressed by an uninterrupted chain of neurons involved in the integration of peripheral and central chemoreception (carotid bodies, chemoreceptor afferents, chemoresponsive NTS neurons projecting to VRC, RTN chemoreceptors). The presence of Phox2b in this circuit and its apparent absence from the respiratory CPG could explain why Phox2b mutations disrupt breathing automaticity during sleep without causing major impairment of respiration during waking.

Research paper thumbnail of Chemosensory control by commissural nucleus of the solitary tract in rats

Respiratory Physiology & Neurobiology, 2011

The commissural nucleus of the solitary tract (commNTS) is a main area that receives afferent sig... more The commissural nucleus of the solitary tract (commNTS) is a main area that receives afferent signals involved in the cardiovascular and respiratory control like those related to chemoreceptor activation, however, the importance of the commNTS for the cardiorespiratory responses to chemoreceptor activation is still controversial. In the present study, we investigated the cardiorespiratory responses to hypoxia or hypercapnia in anesthetized and conscious rats treated with injections of the GABA-A agonist muscimol into the caudal portion of the commNTS. Male Holtzman rats (280-300 g) were used. In conscious rats that had a stainless steel cannula previously implanted into the commNTS, the injection of muscimol (2 mM) into the commNTS reduced the pressor response (16±2 mmHg, vs. saline: 36±3 mmHg) and the increase in ventilation (250±17 ml/min/kg, vs. saline: 641±28 ml/min/kg) produced by hypoxia (8-10% O(2)). In urethane anesthetized rats, the injection of muscimol into the commNTS eliminated the pressor response (5±2 mmHg, vs. saline: 26±5 mmHg) and the increase in phrenic nerve discharge (PND) (20±6%, vs. saline: 149±15%) and reduced the increase in splanchnic sympathetic nerve discharge (sSND) (93±15%, vs. saline: 283±19% of baseline) produced by hypoxia. However, muscimol injected into the commNTS did not change hypercapnia (8-10% CO(2)) induced pressor response or the increase in the sSND or PND in urethane anesthetized rats or the increase in ventilation in conscious rats. The present results suggest that the cardiorespiratory responses to hypoxia are strongly dependent on the caudal portion of the commNTS, however, this area is not involved in the responses to hypercapnia.

Research paper thumbnail of Activation of α2-adrenoceptors in the lateral hypothalamus reduces pilocarpine-induced salivation in rats

Neuroscience Letters, 2009

Research paper thumbnail of Clinical Response and Transfusion Reactions of Sheep Subjected to Single Homologous Blood Transfusion

The Scientific World Journal, 2014

Studies in relation to blood conservation and responses to transfusion are scarce for ruminants. ... more Studies in relation to blood conservation and responses to transfusion are scarce for ruminants. We evaluated the clinical manifestations of sheep that received a single homologous transfusion of whole blood, focusing on transfusion reactions. Eighteen adult sheep were subjected to a single phlebotomy to withdraw 40% of the total blood volume, which was placed into CPDA-1 bags and then divided into G0, animals that received fresh blood, and G15 and G35, animals that received blood stored for 15 or 35 days, respectively. Clinical observations were recorded throughout the transfusion, whereas heart rate, respiratory rate, and rectal temperature were assessed at the following times: 24 hours after phlebotomy and before transfusion; 30 minutes, six, twelve, 24, 48, 72, and 96 hours and eight and 16 days after transfusion. All groups presented transfusion reactions, among which hyperthermia was the most frequent (50% of animals). Tachycardia occurred most frequently in the G35 animals (50% of them). During transfusion G35 animals presented more clinical manifestation ( < 0.05). Transfusion of fresh or stored total blood improved the blood volume, but transfusion reactions occurred, demonstrating that a single transfusion of fresh or stored blood can cause inflammatory and febrile nonhemolytic transfusion reactions in sheep.

Research paper thumbnail of Respiratory deficits in a rat model of Parkinson's disease

Neuroscience, Jan 30, 2015

Parkinson's disease (PD) is a neurodegenerative disease characterized by loss of the dopamine... more Parkinson's disease (PD) is a neurodegenerative disease characterized by loss of the dopaminergic nigrostriatal pathway. In addition to deficits in voluntary movement, PD involves a disturbance of breathing regulation. However, the cause and nature of this disturbance are not well understood. Here, we investigated breathing at rest and in response to hypercapnia (7% CO2) or hypoxia (8% O2), as well as neuroanatomical changes in brainstem regions essential for breathing, in a 6-hydroxydopamine (6-OHDA) rat model of PD. Bilateral injections of 6-OHDA (24 μg/μl) into the striatum decreased tyrosine hydroxylase (TH(+))-neurons in the substantia nigra pars compacta (SN), transcription factor phox2b-expressing neurons in the retrotrapezoid nucleus and neurokinin-1 receptors in the ventral respiratory column. In 6-OHDA-lesioned rats, respiratory rate was reduced at rest, leading to a reduction in minute ventilation. These animals also showed a reduction in the tachypneic response to hy...

Research paper thumbnail of Contribution of excitatory amino acid receptors of the retrotrapezoid nucleus to the sympathetic chemoreflex in rats

In the present study, we evaluated the role of glutamatergic mechanisms in the retrotrapezoid nuc... more In the present study, we evaluated the role of glutamatergic mechanisms in the retrotrapezoid nucleus (RTN) in changes of splanchnic sympathetic nerve discharge (sSND) and phrenic nerve discharge (PND) elicited by central and peripheral chemoreceptor activation. Mean arterial pressure (MAP), sSND and PND were recorded in urethane-anaesthetized, vagotomized, sino-aortic denervated and artificially ventilated male Wistar rats. Hypercapnia (10% CO 2 ) increased MAP by 32 ± 4 mmHg, sSND by 104 ± 4% and PND amplitude by 101 ± 5%. Responses to hypercapnia were reduced after bilateral injection of the NMDA receptor antagonist d,l-2-amino-5-phosphonovalerate (AP-5; 100 mm in 50 nl) in the RTN (MAP increased by 16 ± 3 mmHg, sSND by 82 ± 3% and PND amplitude by 63 ± 7%). Bilateral injection of the non-NMDA receptor antagonist 6,7-dinitro-quinoxaline-2,3-dione (DNQX; 100 mm in 50 nl) and the metabotropic receptor antagonist (+/−)-α-methyl-4-carboxyphenylglycine (MCPG; 100 mm in 50 nl) in the RTN did not affect sympathoexcitatory responses induced by hypercapnia. Injection of DNQX reduced hypercapnia-induced phrenic activation, whereas MCPG did not. In animals with intact carotid chemoreceptors, bilateral injections of AP-5 and DNQX in the RTN reduced increases in MAP, sSND and PND amplitude produced by intravenous injection of NaCN (50 μg kg −1 ). Injection of MCPG in the RTN did not change responses produced by NaCN. These data indicate that RTN ionotropic glutamatergic receptors are involved in the sympathetic and respiratory responses produced by central and peripheral chemoreceptor activation.

Research paper thumbnail of Central moxonidine on salivary gland blood flow and cardiovascular responses to pilocarpine

Brain research, Jan 17, 2003

Peripheral treatment with the cholinergic agonist pilocarpine induces intense salivation that is ... more Peripheral treatment with the cholinergic agonist pilocarpine induces intense salivation that is inhibited by central injections of the alpha2-adrenergic/imidazoline receptor agonist moxonidine. Salivary gland blood flow controlled by sympathetic and parasympathetic systems may affect salivation. We investigated the changes in mean arterial pressure (MAP) and in the vascular resistance in the submandibular/sublingual gland (SSG) artery, superior mesenteric (SM) artery and low abdominal aorta (hindlimb) in rats treated with intraperitoneal (i.p.) pilocarpine alone or combined with intracerebroventricular (i.c.v.) moxonidine. Male Holtzman rats with stainless steel cannula implanted into lateral ventricle (LV) and anesthetized with urethane were used. Pilocarpine (4 micromol/kg of body weight) i.p. reduced SSG vascular resistance (-50+/-13% vs. vehicle: 5+/-3%). Pilocarpine i.p. also increased mesenteric vascular resistance (15+/-5% vs. vehicle: 2+/-3%) and MAP (16+/-3 mmHg, vs. vehic...

Research paper thumbnail of Central blockade of nitric oxide synthesis reduces moxonidine-induced hypotension

British journal of pharmacology, 2004

1. Nitric oxide (NO) and alpha(2)-adrenoceptor and imidazoline agonists such as moxonidine may ac... more 1. Nitric oxide (NO) and alpha(2)-adrenoceptor and imidazoline agonists such as moxonidine may act centrally to inhibit sympathetic activity and decrease arterial pressure. 2. In the present study, we investigated the effects of pretreatment with l-NAME (NO synthesis inhibitor), injected into the 4th ventricle (4th V) or intravenously (i.v.), on the hypotension, bradycardia and vasodilatation induced by moxonidine injected into the 4th V in normotensive rats. 3. Male Wistar rats with a stainless steel cannula implanted into the 4th V and anaesthetized with urethane were used. Blood flows were recorded by use of miniature pulsed Doppler flow probes implanted around the renal, superior mesenteric and low abdominal aorta. 4. Moxonidine (20 nmol), injected into the 4th V, reduced the mean arterial pressure (-42+/-3 mmHg), heart rate (-22+/-7 bpm) and renal (-62+/-15%), mesenteric (-41+/-8%) and hindquarter (-50+/-8%) vascular resistances. 5. Pretreatment with l-NAME (10 nmol into the 4t...

Research paper thumbnail of Role of pressor mechanisms from the NTS and CVLM in control of arterial pressure

American journal of physiology. Regulatory, integrative and comparative physiology, 2005

In the present study, we investigated the effects of inhibition of the caudal ventrolateral medul... more In the present study, we investigated the effects of inhibition of the caudal ventrolateral medulla (CVLM) with the GABA(A) agonist muscimol combined with the blockade of glutamatergic mechanism in the nucleus of the solitary tract (NTS) with kynurenic acid (kyn) on mean arterial pressure (MAP), heart rate (HR), and regional vascular resistances. In male Holtzman rats anesthetized intravenously with urethane/chloralose, bilateral injections of muscimol (120 pmol) into the CVLM or bilateral injections of kyn (2.7 nmol) into the NTS alone increased MAP to 186 +/- 11 and to 142 +/- 6 mmHg, respectively, vs. control: 105 +/- 4 mmHg; HR to 407 +/- 15 and to 412 +/- 18 beats per minute (bpm), respectively, vs. control: 352 +/- 12 bpm; and renal, mesenteric and hindquarter vascular resistances. However, in rats with the CVLM bilaterally blocked by muscimol, additional injections of kyn into the NTS reduced MAP to 88 +/- 5 mmHg and mesenteric and hindquarter vascular resistances below contr...

Research paper thumbnail of Antihypertensive responses elicited by central moxonidine in rats: possible role of nitric oxide

Journal of cardiovascular pharmacology, 2006

In the present study, we investigated the effects of pretreatment with NG-nitro-L-arginine methyl... more In the present study, we investigated the effects of pretreatment with NG-nitro-L-arginine methyl ester (L-NAME) (nitric oxide synthase inhibitor) injected intravenously (IV) on the hypotension, bradycardia, and vasodilation produced by moxonidine (alpha2-adrenergic/imidazoline receptor agonist) injected into the fourth brain ventricle (4th V) in rats submitted to acute hypertension that results from baroreflex blockade by bilateral injections of kynurenic acid (kyn, glutamatergic receptor antagonist) into the nucleus of the solitary tract (NTS) or in normotensive rats. Male Wistar rats (n=5 to 7/group) anesthetized with IV urethane (1.0 g kg(-1) of body weight) and alpha-chloralose (60 mg kg(-1) of body weight) were used. Bilateral injections of kyn (2.7 nmol 100 nL(-1)) into the NTS increased baseline mean arterial pressure (148 +/- 11 mm Hg, vs. control: 102 +/- 4 mm Hg) and baseline heart rate (417 +/- 11 bpm, vs. control: 379 +/- 6 bpm). Moxonidine (20 nmol microL(-1)) into the...

Research paper thumbnail of HCN channels contribute to serotonergic modulation of ventral surface chemosensitive neurons and respiratory activity

Journal of neurophysiology, Jan 15, 2015

Chemosensitive neurons in the retrotrapezoid nucleus (RTN) provide a CO2/H(+)-dependent drive to ... more Chemosensitive neurons in the retrotrapezoid nucleus (RTN) provide a CO2/H(+)-dependent drive to breathe and function as an integration center for the respiratory network, including serotonergic raphe neurons. We recently showed that serotonergic modulation of RTN chemoreceptors involved inhibition of KCNQ channels and activation of an unknown inward current. Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels are the molecular correlate of the hyperpolarization-activated inward current (Ih) and have a high propensity for modulation by serotonin. To investigate whether HCN channels contribute to basal activity and serotonergic modulation of RTN chemoreceptors, we characterize resting activity and the effects of serotonin on RTN chemoreceptors in vitro and on respiratory activity of anesthetized rats in the presence or absence of blockers of KCNQ (XE991) and/or HCN (ZD7288, Cs(+)) channels. We found in vivo that bilateral RTN injections of ZD7288 increased respiratory ...

Research paper thumbnail of Independent purinergic mechanisms of central and peripheral chemoreception in the rostral ventrolateral medulla

The Journal of physiology, 2015

The rostral ventrolateral medulla oblongata (RVLM) contains two functionally distinct types of ne... more The rostral ventrolateral medulla oblongata (RVLM) contains two functionally distinct types of neurons that control and orchestrate cardiovascular and respiratory responses to hypoxia and hypercapnia. One group is composed of the central chemoreceptor neurons of the retrotrapezoid nucleus, which provides a CO2 /H(+) -dependent drive to breathe and serves as an integration centre and a point of convergence of chemosensory information from other central and peripheral sites, including the carotid bodies. The second cluster of RVLM cells forms a population of neurons belonging to the C1 catecholaminergic group that controls sympathetic vasomotor tone in resting conditions and in conditions of hypoxia and hypercapnia. Recent evidence suggests that ATP-mediated purinergic signalling at the level of the RVLM co-ordinates cardiovascular and respiratory responses triggered by hypoxia and hypercapnia by activating retrotrapezoid nucleus and C1 neurons, respectively. The role of ATP-mediated ...

Research paper thumbnail of Morphine Spinal Block Anesthesia in Patients Who Undergo an Open Hemorrhoidectomy: A Prospective Analysis of Pain Control and Postoperative Complications

Annals of Coloproctology, 2014

This study evaluated the use of adding morphine to bupivacaine in spinal anesthesia for pain cont... more This study evaluated the use of adding morphine to bupivacaine in spinal anesthesia for pain control in patients who underwent an open hemorrhoidectomy. Forty patients were prospectively selected for an open hemorrhoidectomy at the same institution and were randomized into two groups of 20 patients each: group 1 had a spinal with 7 mg of heavy bupivacaine associated with 80 µg of morphine (0.2 mg/mL). Group 2 had a spinal with 7 mg of heavy bupivacaine associated with distilled water, achieving the same volume of spinal infusion as that of group 1. Both groups were prescribed the same pain control medicine during the postoperative period. Pain scores were evaluated at the anesthetic recovery room and at 3, 6, 12, and 24 hours after surgery. Postoperative complications, including pruritus, nausea, headaches, and urinary retention, were also recorded. There were no anthropometric statistical differences between the two groups. Pain in the anesthetic recovery room and 3 hours after surgery was similar for both groups. However, pain was better controlled in group 1 at 6 and 12 hours after surgery. Although pain was better controlled for group 1 after 24 hours of surgery, the difference between the groups didn&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;t achieved statistical significance. Complications were more common in group 1. Six patients (6/20) presented coetaneous pruritus and 3 with (3/20) urinary retention. A hemorrhoidectomy under a spinal with morphine provides better pain control between 6 and 12 hours after surgery. However, postoperative complications, including cutaneous pruritus (30%) and urinary retention (15%), should be considered as a negative side of this procedure.

Research paper thumbnail of New advances in the neural control of breathing

The Journal of physiology, 2015

Research paper thumbnail of Combined oral midazolam-ketamine better than midazolam alone for sedation of young children: a randomized controlled trial

International Journal of Paediatric Dentistry, 2012

BACKGROUND. There is a lack of clinical trials on paediatric dental sedation. AIM. We investiga... more BACKGROUND. There is a lack of clinical trials on paediatric dental sedation. AIM. We investigated whether young children&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s behaviour improves during dental treatment with oral ketamine/midazolam compared with midazolam alone or no sedation. DESIGN. Healthy children under 36 months of age, presenting early childhood caries were randomly assigned to receive protective stabilization plus: combined oral midazolam (0.5 mg/kg) and ketamine (3 mg/kg) (MK), or oral midazolam (1.0 mg/kg) (MS), or no sedative (PS). One observer scored children&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s behaviour using the Ohio State University Behavior Rating Scale (OSUBRS) at determined points in a dental exam (no sedative) and treatment session. Data were analysed using nonparametric bivariate tests. RESULTS. Forty-one children were included. In the dental exam session, the sum of OSUBRS scores was similar for the three groups (P = 0.81). In the treatment session, the MK produced more cooperative behaviour than MS and PS (P = 0.01), longer sessions (P = 0.04), and a pattern of homogeneous OSUBRS scores from the reception area (before sedative administration) to the end of the session (P = 0.06). No immediate and post-discharge side effects were observed in groups MK and MS. CONCLUSIONS. The combination of oral midazolam and ketamine is efficacious for guiding the behaviour of children under 3 years old.

Research paper thumbnail of Inhibitory input from slowly adapting lung stretch receptors to retrotrapezoid nucleus chemoreceptors

The Journal of Physiology, 2007

The retrotrapezoid nucleus (RTN) contains CO 2 -activated interneurons with properties consistent... more The retrotrapezoid nucleus (RTN) contains CO 2 -activated interneurons with properties consistent with central respiratory chemoreceptors. These neurons are glutamatergic and express the transcription factor Phox2b. Here we tested whether RTN neurons receive an input from slowly adapting pulmonary stretch receptors (SARs) in halothane-anaesthetized ventilated rats. In vagotomized rats, RTN neurons were inhibited to a variable extent by stimulating myelinated vagal afferents using the lowest intensity needed to inhibit the phrenic nerve discharge (PND). In rats with intact vagus nerves, RTN neurons were inhibited, also to a variable extent, by increasing positive end-expiratory pressure (PEEP; 2-6 cmH 2 O). The cells most sensitive to PEEP were inhibited during each lung inflation at rest and were instantly activated by stopping ventilation. Muscimol (GABA-A agonist) injection in or next to the solitary tract at area postrema level desynchronized PND from ventilation, eliminated the lung inflation-synchronous inhibition of RTN neurons and their steady inhibition by PEEP but did not change their CO 2 sensitivity. Muscimol injection into the rostral ventral respiratory group eliminated PND but did not change RTN neuron response to either lung inflation, PEEP increases, vagal stimulation or CO 2 . Generalized glutamate receptor blockade with intracerebroventricular (I.C.V.) kynurenate eliminated PND and the response of RTN neurons to lung inflation but did not change their CO 2 sensitivity. PEEP-sensitive RTN neurons expressed Phox2b. In conclusion, RTN chemoreceptors receive an inhibitory input from myelinated lung stretch receptors, presumably SARs. The lung input to RTN may be di-synaptic with inhibitory pump cells as sole interneurons.

Research paper thumbnail of Retrotrapezoid nucleus and central chemoreception

The Journal of Physiology, 2008

The 'distributed chemoreception theory' attributes the central chemoreflex (the stimulation of br... more The 'distributed chemoreception theory' attributes the central chemoreflex (the stimulation of breathing by CNS acidification) to the cumulative effects of pH on multiple classes of respiratory neurons as well as on their tonic sources of drive. Opinions differ as to how many classes of pH-sensitive neurons contribute to the central chemoreflex but the number of candidates is high and growing fast. The 'specialized chemoreceptor theory', endorsed here, attributes the chemoreflex to a limited number of specialized neurons. These neurons (the central chemoreceptors) would drive a respiratory pattern generator that is not or minimally activated by acidification. In this review we first describe the properties of the retrotrapezoid nucleus (RTN) and argue that this nucleus may contain the most important central chemoreceptors. Next, we subject the assumptions that underlie the distributed chemoreception theory to a critical analysis. We propose several explanations for the apparent contradiction between the two competing theories of central chemoreception. We attribute much of the current controversy to premature extrapolations of the effects of acidification on neurons recorded in vitro (chemosensitivity) and to a semantic confusion between chemosensitivity and chemoreception (the mechanism by which CO 2 or pH activates breathing in vivo).

Research paper thumbnail of Central chemoreceptors and sympathetic vasomotor outflow

The Journal of Physiology, 2006

Research paper thumbnail of Peripheral chemoreceptor inputs to retrotrapezoid nucleus (RTN) CO2-sensitive neurons in rats

The Journal of Physiology, 2006

The rat retrotrapezoid nucleus (RTN) contains pH-sensitive neurons that are putative central chem... more The rat retrotrapezoid nucleus (RTN) contains pH-sensitive neurons that are putative central chemoreceptors. Here, we examined whether these neurons respond to peripheral chemoreceptor stimulation and whether the input is direct from the solitary tract nucleus (NTS) or indirect via the respiratory network. A dense neuronal projection from commissural NTS (commNTS) to RTN was revealed using the anterograde tracer biotinylated dextran amine (BDA). Within RTN, 51% of BDA-labelled axonal varicosities contained detectable levels of vesicular glutamate transporter-2 (VGLUT2) but only 5% contained glutamic acid decarboxylase-67 (GAD67). Awake rats were exposed to hypoxia (n = 6) or normoxia (n = 5) 1 week after injection of the retrograde tracer cholera toxin B (CTB) into RTN. Hypoxia-activated neurons were identified by the presence of Fos-immunoreactive nuclei. CommNTS neurons immunoreactive for both Fos and CTB were found only in hypoxia-treated rats. VGLUT2 mRNA was detected in 92 ± 13% of these neurons whereas only 12 ± 9% contained GAD67 mRNA. In urethane-chloralose-anaesthetized rats, bilateral inhibition of the RTN with muscimol eliminated the phrenic nerve discharge (PND) at rest, during hyperoxic hypercapnia (10% CO 2 ), and during peripheral chemoreceptor stimulation (hypoxia and/or I.V. sodium cyanide, NaCN). RTN CO 2 -activated neurons were recorded extracellularly in anaesthetized intact or vagotomized rats. These neurons were strongly activated by hypoxia (10-15% O 2 ; 30 s) or by NaCN. Hypoxia and NaCN were ineffective in rats with carotid chemoreceptor denervation. Bilateral injection of muscimol into the ventral respiratory column 1.5 mm caudal to RTN eliminated PND and the respiratory modulation of RTN neurons. Muscimol did not change the threshold and sensitivity of RTN neurons to hyperoxic hypercapnia nor their activation by peripheral chemoreceptor stimulation. In conclusion, RTN neurons respond to brain P CO 2 presumably via their intrinsic chemosensitivity and to carotid chemoreceptor activation via a direct glutamatergic pathway from commNTS that bypasses the respiratory network. RTN neurons probably contribute a portion of the chemical drive to breathe.

Research paper thumbnail of Serotonergic Neurons Activate Chemosensitive Retrotrapezoid Nucleus Neurons by a pH-Independent Mechanism

Journal of Neuroscience, 2007

Serotonin activates respiration and enhances the stimulatory effect of CO2 on breathing. The pres... more Serotonin activates respiration and enhances the stimulatory effect of CO2 on breathing. The present study tests whether the mechanism involves the retrotrapezoid nucleus (RTN), a group of medullary glutamatergic neurons activated by extracellular brain pH and presumed to regulate breathing. We show that the RTN is innervated by both medullary and pontine raphe and receives inputs from thyrotropin-releasing hormone (TRH) and substance P-expressing neurons. Coexistence of serotonin and substance P in terminals within RTN confirmed that lower medullary serotonergic neurons innervate RTN. In vivo, unilateral injection of serotonin into RTN stimulated inspiratory motor activity, and pH-sensitive RTN neurons were activated by iontophoretic application of serotonin or substance P. In brain slices, pH-sensitive RTN neurons were activated by serotonin, substance P, and TRH. The effect of serotonin in slices was ketanserin sensitive and persisted in the presence of glutamate, GABA, glycine, and purinergic ionotropic receptor antagonists. Serotonin and pH had approximately additive effects on the discharge rate of RTN neurons, both in slices and in vivo. In slices, serotonin produced an inward current with little effect on conductance and had no effect on the pH-induced current. We conclude that (1) RTN receives input from multiple raphe nuclei, (2) serotonin, substance P, and TRH activate RTN chemoreceptors, and (3) excitatory effects of serotonin and pH are mediated by distinct ionic conductances. Thus, RTN neurons presumably contribute to the respiratory stimulation caused by serotonergic neurons, but serotonin seems without effect on the cellular mechanism by which RTN neurons detect pH.

Research paper thumbnail of Expression of Phox2b by Brainstem Neurons Involved in Chemosensory Integration in the Adult Rat

Journal of Neuroscience, 2006

Central congenital hypoventilation syndrome is caused by mutations of the gene that encodes the t... more Central congenital hypoventilation syndrome is caused by mutations of the gene that encodes the transcription factor Phox2b. The syndrome is characterized by a severe form of sleep apnea attributed to greatly compromised central and peripheral chemoreflexes. In this study, we analyze whether Phox2b expression in the brainstem respiratory network is preferentially associated with neurons involved in chemosensory integration in rats. At the very rostral end of the ventral respiratory column (VRC), Phox2b was present in many VGlut2 (vesicular glutamate transporter 2) mRNA-containing neurons. These neurons were functionally identified as the respiratory chemoreceptors of the retrotrapezoid nucleus (RTN). More caudally in the VRC, many fewer neurons expressed Phox2b. These cells were not part of the central respiratory pattern generator (CPG), because they were typically cholinergic visceral motor neurons or catecholaminergic neurons (presumed C1 neurons). Phox2b was not detected in serotonergic neurons, in the A5, A6, and A7 noradrenergic cell groups nor within the main cardiorespiratory centers of the dorsolateral pons. Phox2b was expressed by many solitary tract nucleus (NTS) neurons including those that relay peripheral chemoreceptor information to the RTN. These and previous observations by others suggest that Phox2b is expressed by an uninterrupted chain of neurons involved in the integration of peripheral and central chemoreception (carotid bodies, chemoreceptor afferents, chemoresponsive NTS neurons projecting to VRC, RTN chemoreceptors). The presence of Phox2b in this circuit and its apparent absence from the respiratory CPG could explain why Phox2b mutations disrupt breathing automaticity during sleep without causing major impairment of respiration during waking.

Research paper thumbnail of Chemosensory control by commissural nucleus of the solitary tract in rats

Respiratory Physiology & Neurobiology, 2011

The commissural nucleus of the solitary tract (commNTS) is a main area that receives afferent sig... more The commissural nucleus of the solitary tract (commNTS) is a main area that receives afferent signals involved in the cardiovascular and respiratory control like those related to chemoreceptor activation, however, the importance of the commNTS for the cardiorespiratory responses to chemoreceptor activation is still controversial. In the present study, we investigated the cardiorespiratory responses to hypoxia or hypercapnia in anesthetized and conscious rats treated with injections of the GABA-A agonist muscimol into the caudal portion of the commNTS. Male Holtzman rats (280-300 g) were used. In conscious rats that had a stainless steel cannula previously implanted into the commNTS, the injection of muscimol (2 mM) into the commNTS reduced the pressor response (16±2 mmHg, vs. saline: 36±3 mmHg) and the increase in ventilation (250±17 ml/min/kg, vs. saline: 641±28 ml/min/kg) produced by hypoxia (8-10% O(2)). In urethane anesthetized rats, the injection of muscimol into the commNTS eliminated the pressor response (5±2 mmHg, vs. saline: 26±5 mmHg) and the increase in phrenic nerve discharge (PND) (20±6%, vs. saline: 149±15%) and reduced the increase in splanchnic sympathetic nerve discharge (sSND) (93±15%, vs. saline: 283±19% of baseline) produced by hypoxia. However, muscimol injected into the commNTS did not change hypercapnia (8-10% CO(2)) induced pressor response or the increase in the sSND or PND in urethane anesthetized rats or the increase in ventilation in conscious rats. The present results suggest that the cardiorespiratory responses to hypoxia are strongly dependent on the caudal portion of the commNTS, however, this area is not involved in the responses to hypercapnia.

Research paper thumbnail of Activation of α2-adrenoceptors in the lateral hypothalamus reduces pilocarpine-induced salivation in rats

Neuroscience Letters, 2009