Bicuculline Research Papers - Academia.edu (original) (raw)

The present series of experiments had two main objectives: The first was to determine the conditions under which self-injection of the benzodiazepine diazepam would be optimal; the second was to identify neurochemical substrates which underlie the maintenance of diazepam selfadministration. Data from the first experiment indicated that rats maintained on an FI-1 (Fixed Interval of 1 min) schedule of food delivery self-injected significantly more diazepam than rats not maintained on this schedule. Results from the second experiment demonstrated that the benzodiazepine antagonist Ro 15-1788, and the GABA antagonist bicuculline, significantly reduced diazepam self-administration, but the opiate antagonist naloxone was without effect. Data from the third experiment showed that the dopamine antagonist haloperidol also significantly reduced the rate of diazepam self-injection. Thus, these findings indicate that the acquisition of diazepam self-injection occurs under an FI-1 schedule of food delivery, which has been shown to be middly stressful, while its maintenance depends upon the functional integrity of benzodiazepine and GABA receptors and upon the activity of deopaminergic pathways.

- by
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- Psychopharmacology, Dopamine, Self-administration, Haloperidol

Cannabinoids exert complex actions on neurotransmitter systems involved in cognition, locomotion, appetite, but no information was available so far on the interactions between the endocannabinoid system and histaminergic neurons that command several, similar behavioural states and memory. In this study, we investigated the effect of cannabimimetic compounds on histamine release using the microdialysis technique in the brain of freely moving rats. We found that systemic administration of the cannabinoid receptors 1 (CB1-r) agonist arachidonyl-2′chloroethylamide/N-(2chloroethyl)-5Z, 8Z,11Z,14Z-eicosatetraenamide (ACEA; 3 mg/kg) increased histamine release from the posterior hypothalamus, where the histaminergic tuberomamillary nuclei (TMN) are located. Local infusions of ACEA (150 nM) or R(+)-methanandamide (mAEA; 1μM), another CB1-r agonist, in the TMN augmented histamine release from the TMN, as well as from two histaminergic projection areas, the nucleus basalis magnocellularis and the dorsal striatum. When the endocannabinoid uptake inhibitor AM404 was infused into the TMN, however, increased histamine release was observed only in the TMN. The cannabinoid-induced effects on histamine release were blocked by co-administrations with the CB1-r antagonist AM251. Using double-immunofluorescence labelling and confocal laserscanning microscopy, CB1-r immunostaining was found in the hypothalamus, but was not localized onto histaminergic cells. The modulatory effect of cannabimimetic compounds on histamine release apparently did not involve inhibition of γ-aminobutyric acid (GABA)ergic neurotransmission, which provides the main inhibitory input to the histaminergic neurons in the hypothalamus, as local infusions of ACEA did not modify GABA release from the TMN. These profound effects of cannabinoids on histaminergic neurotransmission may partially underlie some of the behavioural changes observed following exposure to cannabinoid-based drugs.

- by Patrizia Giannoni
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- Psychology, Cognitive Science, Immunohistochemistry, Cannabinoids

Increased open field locomotion and decreased striatal GABAA binding after activity wheel running. PHYSIOL BEHAV 60 (3) 699-705, 1996.--Open-field behavior has been used to model reductions in anxiety-related behaviors in the rat after chronic physical activity. Plausible mechanisms for the increased open field locomotion observed after physical activity have not been studied. Open field locomotion is decreased by y-aminobutyric acid (GABA) and its agonists, and increased by GABA antagonists, in the ventral striatum. Hence, we tested the hypothesis that increased open field locomotion following chronic physical activity would be accompanied by a decrease in the number of GABAA receptors in the corpus striaturn. Young ( ~55 days) male Sprague-Dawley rats (N = 24) were randomly assigned to three conditions: 24-h access to an activity wheel (AW), running for 1 h without shock 6 days/week on a motorized treadmill (TM), or sedentary control (C). Open field locomotion (total and center squares traversed), defecation, and urination were assessed on each of 3 consecutive days prior to and again after 8 weeks of physical activity. Open field locomotion (total and center squares) increased after activity wheel running, decreased after treadmill training, and did not change for control animals. GABAA receptor density indicated by [3H] bicuculline binding (fmol/mg) was lower for activity wheel animals compared with treadmill animals and controls. GABA concentration (#mol/g) was not different between activity wheel and treadmill groups but was higher for both groups contrasted with controls. Our findings of decreased GABAA density in the corpus striatum concomitant with an increase in open field locomotion are consistent with an anxiolytic effect of chronic activity wheel running.

- by Shawn Youngstedt
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- Physiology, Physical Activity, Locomotion, Biological Sciences

substantially to the neuronal population of the adult dentate gyrus. We report here that the neurons located in the deep aspects of the granule cell layer, near the proliferative zone, have different properties from those located in the superficial layers. The former group of neurons, tentatively designated as young, can be readily identified in a standard hippocampal slice preparation by morphological, immunohistochemical, and electrophysiological criteria. Electrophysiological recordings and imaging with Lucifer yellow from these neurons in the standard hippocampal slice preparation showed one or two main dendrites and conically shaped branches possessing varicose protrusions. These features are in agreement with the appearance of the same population of young neurons immunopositive for TOAD-64, a marker for immature neurons. In disinhibited slices, these putative young neurons are distinguished from the mature neurons, located in the superficial granule cell layer, by showing paired pulse facilitation and having a lower threshold for induction of long-term potentiation. The putative young neurons are completely unaffected by GABA A inhibition and always display robust longterm potentiation. In contrast, the mature neurons never produce long-term potentiation when the GABA A inhibition is intact. We propose that the heterogeneity of the functional properties of the granule neurons is related to the ongoing neurogenesis in the adult animals.

- by Sabrina Wang
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- Cognitive Science, Plasticity, Neurogenesis, Long Term Potentiation

Dried roots of Delphinium denudatum Wall. are a popular folk remedy for the treatment of epilepsy in the traditional Unani system of medicine in the sub-continent. We carried out anticonvulsant screening of the ethanolic extract (EE) and aqueous fraction (AF) of this plant utilising the maximal electroshock (MEST) and subcutaneous pentylenetetrazole (scPTZ), bicuculline (scBIC), picrotoxin (scPTX) and strychnine (scSTN) tests for anticonvulsant activity. EE had weak dose-dependent anticonvulsant effects on seizures induced by PTZ and BIC. AF exhibited dose-dependent activity against hind limb tonic extension phase (HLTE) of MEST and comparatively stronger anticonvulsant activity against seizures induced by PTZ and BIC. The results suggest the presence of potent anticonvulsant compounds in AF of D. denudatum and deserve further investigation for isolation of active compounds and elucidation of the mechanism of anticonvulsant action.

- by Mohsin Raza
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- Neurology, Water, Complementary and Alternative Medicine, Plant Biology

The onset of spontaneous seizures in the pilocarpine model of epilepsy causes a hyperpolarized shift in the voltage-dependent activation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channel-mediated current (I h ) in CA1 hippocampal pyramidal neuron dendrites, contributing to neuronal hyperexcitability and possibly to epileptogenesis. However, the specific mechanisms by which spontaneous seizures cause downregulation of HCN channel gating are yet unknown. We asked whether the seizure-dependent downregulation of HCN channel gating was due to altered phosphorylation signalling mediated by the phosphatase calcineurin (CaN) or the kinase p38 mitogen-activated protein kinase (p38 MAPK). We first found that CaN inhibition upregulated HCN channel gating and reduced neuronal excitability under normal conditions, showing that CaN is a strong modulator of HCN channels. We then found that an in vitro model of seizures (one hour in 0 Mg 2+ and 50 μM bicuculline at 35 -37 °C) reproduced the HCN channel gating change seen in vivo. Pharmacological inhibition of CaN or activation of p38 MAPK partially reversed the in vitro seizure-induced hyperpolarized shift in HCN channel gating, and the shift was fully reversed by the combination of CaN inhibition and p38 MAPK activation. We then demonstrated enhanced CaN activity as well as reduced p38 MAPK activity in vivo in the CA1 hippocampal area of chronically epileptic animals. Pharmacological reversal of these phosphorylation changes restored HCN channel gating downregulation and neuronal hyperexcitability in epileptic tissue to control levels. Together, these results suggest that alteration of two different phosphorylation pathways in epilepsy contributes to the downregulation of HCN channel gating, which consequently produces neuronal hyperexcitability and thus may be a target for novel antiepileptic therapies.

- by James Bullis
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- Neuroscience, Epilepsy, Chronic Disease, The

The activity-regulated cytoskeletal protein Arc/Arg3.1 is required for long-term memory formation and synaptic plasticity. Arc expression is robustly induced by activity, and Arc protein localizes both to active synapses and the nucleus. While its synaptic function has been examined, it is not clear why or how Arc is localized to the nucleus. We found that murine Arc nuclear expression is regulated by synaptic activity in vivo and in vitro. We identified distinct regions of Arc that control its localization, including a nuclear localization signal, a nuclear retention domain, and a nuclear export signal. Arc localization to the nucleus promotes an activity-induced increase in promyelocytic leukemia nuclear bodies, which decreases GluA1 transcription and synaptic strength. Finally, we show that Arc nuclear localization regulates homeostatic plasticity. Thus, Arc mediates the homeostatic response to increased activity by translocating to the nucleus, increasing promyelocytic leukemia levels, and decreasing GluA1 transcription, ultimately downscaling synaptic strength.

- by Erica Korb
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- Cognitive Science, Membrane Proteins, Brain, Mutation
- by Jaime E. C. Hallak
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- Cognitive Science, Chemistry, Animal Behavior, Fear
- by Kinga Borowicz
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- Drug interactions, Amygdala, Rats, Valproic Acid

Background This review discusses evidence that cells in the mesocortical dopamine (DA) system influence information processing in target areas across three distinct temporal domains. Discussions Phasic bursting of midbrain DA neurons may provide temporally precise information about the mismatch between expected and actual rewards (prediction errors) that has been hypothesized to serve as a learning signal in efferent regions. However, because DA acts as a relatively slow modulator of cortical neurotransmission, it is unclear whether DA can indeed act to precisely transmit prediction errors to prefrontal cortex (PFC). In light of recent physiological and anatomical evidence, we propose that corelease of glutamate from DA and/or non-DA neurons in the VTA could serve to transmit this temporally precise signal. In contrast, DA acts in a protracted manner to provide spatially and temporally diffuse modulation of PFC pyramidal neurons and interneurons. This modulation occurs first via a relatively rapid depolarization of fast-spiking interneurons that acts on the order of seconds. This is followed by a more protracted modulation of a variety of other ionic currents on timescales of minutes to hours, which may bias the manner in which cortical networks process information. However, the prolonged actions of DA may be curtailed by counteracting influences, which likely include opposing actions at D1 and D2-like receptors that have been shown to be timeand concentration-dependent. In this way, the mesocortical DA system optimizes the characteristics of glutamate, GABA, and DA neurotransmission both within the midbrain and cortex to communicate temporally precise information and to modulate network activity patterns on prolonged timescales.

- by Paul Phillips
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- Neuroscience, Electrochemistry, Immunohistochemistry, Prefrontal Cortex

We studied auditory thalamocortical interactions in vitro, using an auditory thalamocortical brain slice preparation. Cortical activity evoked by electrical stimulation of the medial geniculate nucleus (MGN) was investigated through field potential recordings and voltage sensitive dyes. Experiments were performed in slices obtained from adult mice (9-14 weeks). Stimulus evoked activity was detected in the granular and supragranular layers after a short latency (5-6 ms). In 9-14 weeks old mice infragranular activity was detected in 10 of 24 preparations and was found to be increased in younger mice (p 31-64). In 14 of 24 slices a prominent horizontal spread was observed, which extended into cortical areas lateral to A1. In these experiments, the shortest onset latencies and largest signal amplitudes were located in the supragranular layers of A1. In areas lateral to A1, shortest onset latencies were located in the granular layer, while largest signal amplitudes were found in the supragranular layers. Evoked cortical activity was sensitive to removal of extracellular Ca 2؉ or application of 6-cyano-7-nitroquinoxaline-2,3dione (CNQX, 10 M). Short repetitive stimulation, resembling thalamic burst activity (three pulses at 100 Hz), resulted in an increase of signal amplitude and excited area by ϳ25%, without changing the overall spatiotemporal activity profile. Blockade of N-methyl-D-aspartate receptors by 2-amino-5phosphonopentanoate (AP5, 50 M) reduced amplitudes and excited area by ϳ15-30%, irrespective of stimulation frequency. Application of bicuculline (10 M) greatly increased cortical responses to thalamic stimulation. Under these conditions, evoked activity displayed a pronounced horizontal spread in combination with a 2-3-fold increase in amplitude. In conclusion, afferent thalamic inputs primarily activate su-pragranular and granular layers in the auditory cortex of adult mice. This activation is predominantly mediated by non-NMDA receptors, while GABA A receptor-mediated inhibition limits the horizontal and vertical spread of activity.

- by E. Speckmann
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- Neuroscience, Psychology, Aging, Calcium

Aim of the study: Gamma-aminobutyric acid A receptors are the principal mediators of synaptic inhibition in striatal neurons and play an important role in preventing the spreading of seizures through the striatum. In the present study, effect of Bacopa monnieri (L.) Pennel and its active component bacoside-A on spatial recognition memory deficit and alterations of GABA receptor in the striatum of epileptic rats were investigated. Materials and methods: Total GABA and GABA A receptor numbers in the control and epileptic rats were evaluated using [ 3 H]GABA and [ 3 H]bicuculline binding. GABA A␣1, GABA A␣5, GABA A␥3 and GABA A␦ gene expressions were studied. Behavioral performance was assed using Y-maze. Results: Scatchard analysis of [ 3 H]GABA and [ 3 H]bicuculline in the striatum of epileptic rats showed significant decrease in B max compared to control. Real-Time PCR amplification of GABA A receptor subunits such as GABA A␣1, GABA A␣5 and GABA A␦ , were down regulated (p < 0.001) in the striatum of epileptic rats compared to control. Epileptic rats have deficit in Y-maze performance. Bacopa monnieri and bacoside-A treatment reversed these changes to near control. Conclusion: Our results suggest that decreased GABA receptors in the striatum have an important role in epilepsy associated motor learning deficits and Bacopa monnieri and bacoside-A has a beneficial effect in the management of epilepsy.

The present study was done to determine if estrogen interacts with excitatory and / or inhibitory amino acid neurotransmitters to alter neuronal excitability within the parabrachial nucleus (PBN) and modulate autonomic tone. First, the role of estrogen in modulating autonomic tone was investigated in male rats anesthetized with Inactin (100 mg / kg). Animals were instrumented to record blood pressure, heart rate, vagal parasympathetic and renal sympathetic nerve activities as well as baroreflex sensitivity. Direct, bilateral injection of 17b-estradiol (0.5 mM; 200 nl / side) into the PBN resulted in a significant decrease in blood pressure (1764 mmHg), sympathetic tone (2065%) and heart rate (2265 beats / min) while increasing parasympathetic tone (3464%) 30 min post-injection. These estrogeninduced effects were completely blocked by the co-injection of estrogen with the estrogen receptor antagonist, ICI 182,780 (20 mM; 200 nl / side). Co-injection of the NMDA receptor antagonist, (6)-3-(2-carboxypiperazine-4-yl) propyl-1-phosphonic acid (CPP; 10 mM; 200 nl / side), with estradiol resulted in complete blockade of the estrogen-induced decrease in heart rate and increase in parasympathetic tone only. Co-injection of estradiol with the GABA receptor antagonist, (1)-bicuculline (0.1 mM; 200 nl / side), resulted in complete blockade A of the estrogen-induced decrease in blood pressure and sympathetic nerve activity only. These results suggest that estrogen acts on estrogen receptors on neurons in the PBN to modulate GABA -receptor mediated inhibitory neurotransmission to alter sympathetic tone A and blood pressure and on neurons in a separate, parallel pathway to modulate NMDA-receptor mediated neurotransmission to alter parasympathetic tone and heart rate. 

- by Tarek Saleh
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- Cognitive Science, Drug interactions, Autonomic Nervous System, Estrogen Receptor

Hippocampal g oscillations, as a form of neuronal network synchronization, are speculated to be associated with learning, memory and attention. Nicotinic acetylcholine receptor a7 subtypes (a7-nAChRs) are highly expressed in hippocampal neurons and play important roles in modulating neuronal function, synaptic plasticity, learning and memory. However, little is known about the role of a7-nAChRs in hippocampal g oscillations. Here, we examined the effects of selective a7and non-a7-nAChR antagonists on tetanic g oscillations in rat hippocampal slices. We found that brief tetanic stimulation-induced g oscillations (30e80 Hz) and pharmacological blockade of a7-nAChRs using the relatively selective a7-nAChR antagonists, methyllycaconitine (10 or 100 nM) or a-bungarotoxin (10 nM), significantly reduced the frequency spectrum power, the number of spikes, and burst duration of evoked g oscillations. Neither mecamylamine nor dihydro-b-erythroidine, which are selective antagonists of non-a7-nAChRs, demonstrated significant effects on tetanic g oscillations. Nicotine exposure promotes hippocampal g oscillations in a methyllycaconitine-sensitive manner. It is concluded that a7-nAChRs in hippocampal slices play important roles in regulation of g oscillations, thus potentially helping to explain roles of nAChRs in cognitive functions such as learning, memory and attention.

- by Ronald Lukas and +1
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- Psychology, Electrophysiology, Neuropharmacology, Synaptic Plasticity

Cue-induced drug-seeking in rodents progressively increases after withdrawal from cocaine, suggesting that cue-induced cocaine craving incubates over time. Here, we explored the role of the medial prefrontal cortex (mPFC, a brain area previously implicated in cue-induced cocaine seeking) in this incubation. We trained rats to self-administer cocaine for 10 d (6 h/d, infusions were paired with a tone-light cue), and then assessed after 1 or 30 withdrawal days the effect of exposure to cocaine cues on lever presses in extinction tests. We found that cue-induced cocaine-seeking in the extinction tests was higher after 30 withdrawal days than after 1 day. The time-dependent increases in extinction responding were associated with large (ventral mPFC) or modest (dorsal mPFC) increases in ERK phosphorylation (a measure of ERK activity and an index of neuronal activation). After 30 withdrawal days, ventral but not dorsal injections of muscimol+baclofen (GABAa+GABAb receptor agonists that inhibit neuronal activity) decreased extinction responding. After 1 withdrawal day, ventral but not dorsal mPFC injections of bicuculline+saclofen (GABAa+GABAb receptor antagonists that increase neuronal activity) strongly increased extinction responding. Finally, muscimol+baclofen had minimal effect on extinction responding after 1 day, and in cocaineexperienced rats, ventral mPFC injections of muscimol+baclofen or bicuculline+saclofen had no effect on lever presses for an oral sucrose solution. The present results indicate that ventral mPFC neuronal activity plays an important role in the incubation of cocaine craving.

- by Jennifer Bossert and +1
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- Psychology, Animal Behavior, Neuropharmacology, Prefrontal Cortex

1. Intracellular recordings were made from rat CA3 hippocampal neurones in vitro during the first eighteen days of postnatal life. The cells had resting membrane potentials more negative than -51 mV, action potentials greater than 55 mV and membrane input resistances of 117 + 12 MQ. An unusual characteristic of these cells was the presence of spontaneous giant depolarizing potentials (GDPs) which were observed during the first eight postnatal (P) days in over 85 % of neurones. They were less frequent between P9 and P12 (48 %) and disappeared after P12.

- by Renato Corradetti
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- Biological Sciences, Hippocampus, Evoked Potentials, Ketamine

Progabide inhibited male rat sexual behavior at a dose of 200 mg/kg. This dose had only modest effects on ambulatory activity and no effect at all on motor coordination as evaluated by a rotarod test. The GABAA antagonist bicuculline, at a dose of 1 mg/kg, blocked the effects of progabide on sex behavior. In contrast, the GABAB antagonist CGP 35348, at doses of 50 and 100 mg/kg, was ineffective. These doses have previously been shown to block the actions of baclofen on sexual behavior. It was concluded that the GABAA but not the GABAB receptor is important for the inhibitory effects of progabide on that behavior. The actions of progabide on ambulatory activity were not blocked by bicuculline or CGP 35348 at any of the doses used (up to 2 and 200 mg/kg, respectively). Even the combination of both antagonists was ineffective. This suggests that the motor effects of progabide are mediated by either a non-GABAergic receptor or by a subtype of the GABAA or the GABAB receptor that is not sensitive to the antagonists. Present results show that the effects of progabide on motor functions depend on mechanisms different from those involved in its effects on sexual behavior. They further suggest that the GABAA receptor may be important for drug actions on male sexual behavior.

The dopamine D 4 receptor (D 4 R) is predominantly expressed in the frontal cortex (FC), a brain region that receives dense input from midbrain dopamine (DA) neurons and is associated with cognitive and emotional processes. However, the... more

In patch clamp experiments the b-amino acid uptake inhibitor guanidinoethyl sulphonate (GES) activated currents in intact cultured murine cerebellar granule neurones. These responses could be attenuated by the g-aminobutyric acid A (GABA A ) receptor antagonists bicuculline and picrotoxin. With intracellular chloride concentrations of either 20 or 130 mM, GES-induced current responses reversed polarity near the chloride equilibrium potential. When fast applications of agonist were made to excised granule cell macropatches GES responses were dose-dependent and exhibited signi®cant outward recti®cation. Like taurine (but unlike GABA and b-alanine) responses, macroscopic desensitisation of GESinduced currents was slow. Our data indicate that care should be exercised when using GES as a taurine uptake inhibitor in systems that also contain GABA A receptors. q

- by John Mellor
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- Psychology, Cognitive Science, Electrophysiology, Patch-clamp and imaging techniques

We evaluated the effectiveness of intrathecal antagonists of a1-(WB4101) and

- by Wiliam Prado
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- Biophysics, Pain, Pain Management, Multivariate Analysis

1 Alfaxalone (1-100nM) potentiated y-aminobutyric acidA (GABAA)-receptor-mediated contractile responses in the guinea-pig isolated ileum, with a leftward shift of the GABA concentrationresponse curve, and a significant potentiation of the GABA-induced contractions over the lower concentration-range for GABA (3-30pM). Alfadalone on the other hand, did not affect contractile responses to GABA.

- by Graham Johnston
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- Smooth muscle, Anesthetics, Muscle contraction, Bicuculline

Daily peak plasma glucose concentrations are attained shortly before awakening. Previous experiments indicated an important role for the biological clock, located in the suprachiasmatic nuclei (SCN), in the genesis of this anticipatory rise in plasma glucose concentrations by controlling hepatic glucose production. Here, we show that stimulation of NMDA receptors, or blockade of GABA receptors in the paraventricular nucleus of the hypothalamus (PVN) of conscious rats, caused a pronounced increase in plasma glucose concentrations.

- by Andries Kalsbeek
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- Neuroscience, Autonomic Nervous System, Hyperglycemia, Blood Glucose

Medetomidine, a new selective a,-adrenoceptor agonist, potentiated bicuculline seizures in mice. In vivo pretreatment with medetomidine in mouse cerebral cortex reduced dose-dependently (2.5-100 pg/kg) GABA-potentiated 'Hflunitrazepam binding. The affinity of 3H-muscimol was also reduced by medetomidine. This effect of medetomidine on GABA-potentiated benzodiazepine binding was reversed by pretreatment with atipamezole (1 mg/kg), a specific a,antagonist. In an elevated plus-maze model of anxiety medetomidine (0.540 pg/kg) was inactive both in rats and mice and did not antagonize the behavioural effects of an anxiogenic P-carboline, DMCM. However, at lower doses medetomidine (10 but not 50 pg/kg) antagonized the swimming stress caused increase of central benzodiazepine binding sites (labeled with 'H-Ro 15-1788) in mouse cerebral cortex. The increase of peripheral benzodiazepine binding sites on brain and heart cryostat cut slices caused by stress was also antagonized by pretreatment with medetomidine. The behavioural and biochemical data obtained in this study are evidence that medetomidine does not have anxiolytic effect but may have, in lower doses, stress-protective activity.

- by Mauno Airaksinen
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- Pharmacology, Animal Behavior, Brain, Kidney

Extracellular electrophysiological recordings in freely moving cats have shown that serotonergic neurons from the dorsal raphe nucleus (DRN) fire tonically during wakefulness, decrease their activity during slow wave sleep (SWS), and are nearly quiescent during paradoxical sleep (PS). The mechanisms at the origin of the modulation of activity of these neurons are still unknown. Here, we show in the unanesthetized rat that the iontophoretic application of the GABA A antagonist bicuculline on dorsal raphe serotonergic neurons induces a tonic discharge during SWS and PS and an increase of discharge rate during quiet waking. These data strongly suggest that an increase of a GABAergic inhibitory tone present during wakefulness is responsible for the decrease of activity of the dorsal raphe sero-tonergic cells during slow wave and paradoxical sleep. In addition, by combining retrograde tracing with cholera toxin B subunit and glutamic acid decarboxylase immunohistochemistry, we demonstrate that the GABAergic innervation of the dorsal raphe nucleus arises from multiple distant sources and not only from interneurons as classically accepted. Among these afferents, GABAergic neurons located in the lateral preoptic area and the pontine ventral periaqueductal gray including the DRN itself could be responsible for the reduction of activity of the serotonergic neurons of the dorsal raphe nucleus during slow wave and paradoxical sleep, respectively.

D6 is a promoter/enhancer of the mDach1 gene that is involved in the development of the neocortex and hippocampus. It is expressed by proliferating neural stem/ progenitor cells (NSPCs) of the cortex at early stages of neurogenesis. The differentiation potential of NSPCs isolated from embryonic day 12 mouse embryos, in which the expression of green fluorescent protein (GFP) is driven by the D6 promoter/enhancer, has been studied in vitro and after transplantation into the intact adult rat brain as well as into the site of a photochemical lesion. The electrophysiological properties of D6/GFP-derived cells were studied using the whole-cell patch-clamp technique, and immunohistochemical analyses were carried out. D6/GFPderived neurospheres expressed markers of radial glia and gave rise predominantly to immature neurons and GFAPpositive cells during in vitro differentiation. One week after transplantation into the intact brain or into the site of a photochemical lesion, transplanted cells expressed only neuronal markers. D6/GFP-derived neurons were characterised by the expression of tetrodotoxin-sensitive Na ?currents and K A -and K DR currents sensitive to 4-aminopyridine. They were able to fire repetitive action potentials and responded to the application of GABA. Our results indicate that after transplantation into the site of a photochemical lesion, D6/GFP-derived NSPCs survive and differentiate into neurons, and their membrane properties are comparable to those transplanted into the non-injured cortex. Therefore, region-specific D6/GFP-derived NSPCs represent a promising tool for studying neurogenesis and cell replacement in a damaged cellular environment.

Wernicke-Korsakoff syndrome (WKS), a form of diencephalic amnesia caused by thiamine deficiency, results in severe anterograde memory loss. Pyrithiamine-induced thiamine deficiency (PTD), an animal model of WKS, produces cholinergic abnormalities including decreased functional hippocampal acetylcholine (ACh) release and poor spatial memory. Increasing hippocampal ACh levels has increased performance in PTD animals. Intraseptal bicuculline (GABA(A) antagonist) augments hippocampal ACh release in normal animals and we found it (0.50 microg/microl and 0.75 microg/microl) also increased in-vivo hippocampal ACh release in PTD animals. However, the 0.75 microg/microl dose produced a greater change in hippocampal ACh release in control animals. The 0.50 microg/microl dose of bicuculline was then selected to determine if it could enhance spontaneous alternation performance in PTD animals. This dose of bicuculline significantly increased hippocampal ACh levels above baseline in both PTD and control rats and resulted in complete behavioral recovery in PTD animals, without altering performance in control rats. This suggests that balancing ACh-GABA interactions in the septohippocampal circuit may be an effective therapeutic approach in certain amnestic syndromes.

- by Jessica Roland
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- Animal Behavior, Spatial Memory, Hippocampus, Amnesia

13 C nuclear magnetic resonance (NMR) experiments have previously shown that glutamatergic neurotransmitter flux (V cycle(Glu/Gln)) changes proportionately with neuronal glucose oxidation (CMR glc(ox)N) in the nonactivated cortex of anesthetized rats. Positron Emission Tomography measurements of glucose and oxygen uptake during sensory stimulation had shown that the incremental glucose utilization is greater than oxygen leading to the suggestion that the energy required for stimulated neuronal activity arises from nonoxidative glucose metabolism. In this study, the authors used spatially localized 1 H-observed, 13 C-edited NMR spectroscopy during an infusion of [1,6-13 C 2 ]glucose to assess the relationship between changes in V cycle(Glu/Gln) and glucose utilization (CMR glc(ox)N and CMR glc(nonox)) during the intense cortical activity associated with bicuculline-induced seizures. Metabolic fluxes were determined by model-based analysis of the 13 C-enrichment time courses of glutamate-C4 and glutamine-C4 (CMR glc(ox)N , V cycle(Glu/Gln)) and lactate-C3 (CMR glc(nonox)). The exchange rate between ␣-ketoglutarate and glutamate was found to be significantly faster than TCA cycle flux both for control (41 mol•g −1 •min −1 ; 95% CI, 5 to 109 mol•g −1 •min −1) and during seizures (21 mol•g −1 •min −1 ; 95% CI, 4.4 to 51.8 mol•g −1 •min −1). During seizures, total glucose utilization (CMR glc(ox+nonox)) increased substantially (466% between 0 and 6 minutes; 277% between 6 and 55 minutes). Glucose oxidation (CMR glc(ox)N) also increased (214%; from 0.26 ± 0.02 to 0.57 ± 0.07 mol•g −1 •min −1) but to a lesser degree, resulting in a large increase in cortical lactate concentration. V cycle(Glu/Gln) increased 233% (from 0.22 ± 0.04 to 0.52 ± 0.07 mol•g −1 •min −1), which was similar to the increase in glucose oxidation. The value of V c y c l e (G l u / G l n) and CMR glc(ox)N obtained here lie on the line predicted in a previous study. These results indicate that neuronal glucose oxidation and not total glucose utilization is coupled to the glutamate/glutamine cycle during intense cortical activation.

- by Anant Patel
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- Chemistry, NMR Spectroscopy, Magnetic Resonance Spectroscopy, Medicine
- by J. Hablitz
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- Neurophysiology, Hippocampus, Evoked Potentials, Plant tissue Culture Techniques

The dorsal (DR) and median (MR) raphe nuclei contain 5-hydroxytryptamine (5-HT) cell bodies that give rise to the majority of the ascending 5-HT projections to the forebrain. The DR and MR have differential roles in mediating stress, anxiety and depression. Glutamate and GABA activity sculpt putative 5-HT neuronal firing and 5-HT release in a seemingly differential manner in the MR and DR, yet isolated glutamate and GABA activity within the DR and MR has not been systematically characterized. Visualized whole-cell voltage-clamp techniques were used to record excitatory and inhibitory postsynaptic currents (EPSC and IPSC) in 5-HT-containing neurons. There was a regional variation in action potential-dependent (spontaneous) and basal [miniature (m)] glutamate and GABAergic activity. mEPSC activity was greater than mIPSC activity in the DR, whereas in the MR the mIPSC activity was greater. These differences in EPSC and IPSC frequency indicate that glutamatergic and GABAergic input have distinct cytoarchitectures in the DR and MR. 5-HT1B receptor activation decreased mEPSC frequency in the DR and the MR, but selectively inhibited mIPSC activity only in the MR. This finding, in concert with its previously described function as an autoreceptor, suggests that 5-HT1B receptors influence the ascending 5-HT system through multiple mechanisms. The disparity in organization and integration of glutamatergic and GABAergic input to DR and MR neurons and their regulation by 5-HT1B receptors may contribute to the distinction in MR and DR regulation of forebrain regions and their differential function in the aetiology and pharmacological treatment of psychiatric disease states.

- by Azhar Rafiq
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- Neurology, Water, Complementary and Alternative Medicine, Plant Biology
- by Alain Artola
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- Electrophysiology, Long Term Potentiation, Multidisciplinary, Nature

The lateral amygdala (LA) is the key locus for synaptic changes that underpins the long-term memory of conditioned auditory fears. In this Pavlovian fear conditioning paradigm, a neutral auditory tone (conditions stimulus; CS) is paired with electric shock (unconditioned stimulus; US) and once the association between the CS and US is formed, the CS alone can then elicit a conditioned fear response. The LA receives sensory information from both the auditory thalamus and cortex, and serves as the first stage of processing of auditory inputs to the amygdala . CS and US inputs converge onto specific cells in the LA, and the association of CS and US leads to long-lasting alterations in synaptic efficiency . Depending on the stimulating protocols and the recording conditions used, bidirectional alterations of synaptic efficacy, long-term potentiation (LTP) and long-term depression (LTD) at these LA synapses have previously been reported ). Recent studies have provided some correlative evidence suggesting an important role for LA LTP in mediating the association between CS and US, and hence the formation and storage of the learned fear in the LA 1 These authors contributed equally to this work.

- by Lidong Liu
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- Long Term Potentiation, Neurochemistry, Synaptic Plasticity, Endocytosis
- by Bernd Sommer
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- Spatial Memory, Long Term Potentiation, Science, Calcium

Fast inhibitory synaptic transmission in the medial vestibular nucleus (MVN) is mediated by GABAA receptors (GABAARs) and glycine receptors (GlyRs). To assess their relative contribution to inhibition in the MVN, we recorded miniature inhibitory postsynaptic currents (mIPSCs) in physiologically characterized type A and type B MVN neurons. Transverse brain stem slices were prepared from mice (3–8 wk old), and whole cell patch-clamp recordings were obtained from visualized MVN neurons (CsCl internal; Vm = –70 mV; 23°C). In 81 MVN neurons, 69% received exclusively GABAAergic inputs, 6% exclusively glycinergic inputs, and 25% received both types of mIPSCs. The mean amplitude of GABAAR-mediated mIPSCs was smaller than those mediated by GlyRs (22.6 ± 1.8 vs. 35.3 ± 5.3 pA). The rise time and decay time constants of GABAAR- versus GlyR-mediated mIPSCs were slower (1.3 ± 0.1 vs. 0.9 ± 0.1 ms and 10.5 ± 0.3 vs. 4.7 ± 0.3 ms, respectively). Comparison of type A ( n = 20) and type B ( n = 32) ...

- by Aaron Camp
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- Drug interactions, Neurophysiology, Mice, Synaptic Transmission

In the present study, alterations of the General GABA and GABAA receptors in the hippocampus of pilocarpine-induced temporal lobe epileptic rats and the therapeutic application of Bacopa monnieri and its active component Bacoside-A were investigated. Bacopa monnieri (Linn.) is a herbaceous plant belonging to the family Scrophulariaceae. Hippocampus is the major region of the brain belonging to the limbic system and plays an important role in epileptogenesis, memory and learning. Scatchard analysis of [3H]GABA and [3H]bicuculline in the hippocampus of the epileptic rat showed significant decrease in Bmax (P < 0.001) compared to control. Real Time PCR amplification of GABAA receptor sub-units such as GABAAά1, GABAAά5, GABAAδ, and GAD were down regulated (P < 0.001) in the hippocampus of the epileptic rats compared to control. GABAAγ subunit was up regulated. Epileptic rats have deficit in the radial arm and Y maze performance. Bacopa monnieri and Bacoside-A treatment reverses all these changes near to control. Our results suggest that decreased GABA receptors in the hippocampus have an important role in epilepsy associated behavioral deficit, Bacopa monnieri and Bacoside-A have clinical significance in the management of epilepsy.

- by Jobin Mathew
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- Animal Behavior, Motor Learning, Epilepsy, Saponins

Previous studies have outlined an important role for serotonin (5-HT) in the development of synaptic connectivity and function in the cerebral cortex. In this study, we have examined the effects of 5-HT on synaptic function in prefrontal cortex at a time of intense synapse formation and remodelling. Whole-cell recordings in slices derived from animals aged postnatal (P) days 16-20 showed that administration of 5-HT induced a robust increase in synaptic activity that was blocked by CNQX but not by bicuculline. This 5-HT-induced increase in glutamatemediated synaptic activity was pharmacologically heterogeneous as it was differentially inhibited by the receptor subtype-selective antagonists SB-269970, MDL 100907 and GR 113808 and thus involved 5-HT 7 , 5-HT 2A and 5-HT 4 receptors. These results, obtained in juvenile cortex, contrast with those seen in adults where the increase in spontaneous excitatory postsynaptic currents (sEPSCs) was mediated solely by 5-HT 2A receptors. In developing cortex, activation of 5-HT 7 , but not 5-HT 2A or 5-HT 4 receptors, elicited a robust inward current. However, the facilitation of synaptic activity mediated by all three of these receptors involved increases in both the amplitude and frequency of sEPSCs and was blocked by TTX. These results are best interpreted as indicating that all three receptor subtypes increase synaptic activity by exciting neuronal elements within the slice. No evidence was found for a postsynaptic facilitation of synaptic currents by 5-HT. Together, these results show that the repertoire of electrophysiologically active 5-HT receptors in prefrontal cortex is developmentally regulated, and that 5-HT 7 and 5-HT 4 receptors play a previously unsuspected role in regulating synaptic activity in this region.

A neurosurgical intervention that has shown potential for treating basal ganglia (BG) mediated motor tics involves high-frequency deep brain stimulation (HF-DBS) targeted to the output nucleus of the BG: the globus pallidus internus (GPi). This study used a nonhuman primate (Macaca fuscata) model of BG-meditated motor tics, and investigated the short-term neuronal mechanism that might underlie the beneficial effects of GPi-HF-DBS. In parallel with behavioral tic expressions, phasic alterations of neuronal activity emerged in the pallidum following focal disinhibition of the striatum with bicuculline. We delivered HF-DBS in the GPi in such a way that on-stimulation and off-stimulation conditions alternated every 30 s. Analysis of electromyographic (EMG) records showed that during on-stimulation, there were significant reductions in tic-related EMG amplitude.

- by K. McCairn
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- Neuroscience, Deep Brain Stimulation, Macaca, Electromyography
- by Udai Singh
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- Microbiology, Medical Microbiology, Medicinal Plants, Berberine

Introducing 3-methoxy or 3,5-dimethoxy substituents on the 4-hydroxyphenacyl (pHP) photoremovable protecting group has been explored with two excitatory γ-amino acids, L-glutamic acid and γ-amino butyric acid (GABA). These substituents significantly extend the absorption range of the pHP chromophore, e.g., the tail of absorption bands of 2a,b extend above 400 nm, well beyond the absorptions of aromatic amino acids and nucleotides. Irradiation releases the amino acids with rate constants of ∼10 7 s -1 and appearance efficiencies (Φ app ) of 0.03−0.04. The photoproducts are formed through the pHP excited triplet and are primarily products of photoreduction and photohydrolysis. 1a,b also rearranged to the phenylacetic acid 3.

- by Richard Givens
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- Ion Channels, Hippocampus, Light, Neurons
- by Tammy Sajdyk and +1
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- Multidisciplinary, Panic Disorder, Heart rate, Amygdala

In the adult rat hippocampus, granule cell mossy fibers (MFs) form excitatory glutamatergic synapses with CA3 principal cells and local inhibitory interneurons. However, evidence has been provided that, in young animals and after seizures, the same fibers can release in addition to glutamate GABA. Here we show that, during the first postnatal week, stimulation of granule cells in the dentate gyrus gave rise to monosynaptic GABA A-mediated responses in principal cells and in interneurons. These synapses were indeed made by MFs because they exhibited strong paired-pulse facilitation, high sensitivity to the metabotropic glutamate receptor agonist LAP -4, and short-term frequency-dependent facilitation. MF responses were potentiated by blocking the plasma membrane GABA transporter GAT-1 with NO-711 or by allosterically modulating GABA A receptors with flurazepam. Chemical stimulation of granule cell dendrites with glutamate induced barrages of GABA A-mediated postsynaptic currents into target neurons. Furthermore, immunocytochemical experiments demonstrated colocalization of vesicular GABA transporter with vesicular glutamate transporter-1 and zinc transporter 3, suggesting that GABA can be taken up and stored in synaptic vesicles of MF terminals. Additional fibers releasing both glutamate and GABA into principal cells and interneurons were recruited by increasing the strength of stimulation. Both the GABAergic and the glutamatergic component of synaptic currents occurred with the same latency and were reversibly abolished by LAP -4, indicating that they originated from the MFs. GABAergic signaling may play a crucial role in tuning hippocampal network during postnatal development. Low-threshold GABA-releasing fibers may undergo elimination, and this may occur when GABA shifts from the depolarizing to the hyperpolarizing direction.

- by fiorenzo conti
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- Neuroscience, Patch-clamp and imaging techniques, Reaction Time, The
- by Jose Antunes-Rodrigues
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- Oxytocin, Amygdala, Rats, Sodium

The main aim of the present study was to investigate the effects of local perfusion with the tridecapeptide neurotensin on extracellular GABA and dopamine levels in the nucleus accumbens of the halothane-anaesthetized rat, using in viuo microdialysis. In an initial set of characterization studies we examined the Na+ dependence of neurotransmitter release by local perfusion with ouabain, vefatridine and tetrodotoxin.

- by Kjell Fuxe
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- Neuroscience, Psychology, Nucleus Accumbens, Dopamine

Physical exercise is known to reduce anxiety. The ventral hippocampus has been linked to anxiety regulation but the effects of running on this subregion of the hippocampus have been incompletely explored. Here, we investigated the effects of cold water stress on the hippocampus of sedentary and runner mice and found that while stress increases expression of the protein products of the immediate early genes c-fos and arc in new and mature granule neurons in sedentary mice, it has no such effect in runners. We further showed that running enhances local inhibitory mechanisms in the hippocampus, including increases in stress-induced activation of hippocampal interneurons, expression of vesicular GABA transporter (vGAT), and extracellular GABA release during cold water swim stress. Finally, blocking GABAA receptors in the ventral hippocampus, but not the dorsal hippocampus, with the antagonist bicuculline, reverses the anxiolytic effect of running. Together, these results suggest that running improves anxiety regulation by engaging local inhibitory mechanisms in the ventral hippocampus.

- by Timothy Schoenfeld
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- Neuroscience, Swimming, Mice, Dentate Gyrus

In some mammals, epileptic seizures have been induced in the cerebral cortex, hippocampus and other limbic structures after the sudden suppression of chronically infused GABA. This hyperexcitability state induced by the endogenous neurotransmitter resembles the withdrawal seizure-responses to other GABA A receptor agonists such as benzodiazepines, barbiturates and alcohol.

- by Teresa Montiel
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- Neuroscience, Psychology, Long Term Potentiation, Electroencephalography

Bilobalide, a constituent of Ginkgo biloba, has neuroprotective properties. Its mechanism of action is unknown but it was recently found to block GABA A receptors. The goal of this study was to test the potential role of a GABAergic mechanism for the neuroprotective activity of bilobalide. In rat hippocampal slices exposed to NMDA, release of choline indicates breakdown of membrane phospholipids. NMDA-induced choline release was almost completely blocked in the presence of bilobalide (10 μM) and under low-chloride conditions. Bicuculline (100 μM), a competitive antagonist at GABA A receptors, reduced NMDA-induced choline release to a small extent (−23%). GABA (100 μM) partially antagonized the inhibitory action of bilobalide. Exposure of hippocampal slices to NMDA also caused edema formation as measured by increases of tissue water content. NMDA-induced edema formation was suppressed by bilobalide and by low-chloride conditions. Bicuculline exerted partial protection (by 30%) while GABA reduced bilobalide's effect by about one third.

- by Vikas Kumar
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- Cognitive Science, Nonlinear dynamics, Drug interactions, Neuroprotection

The role of the nucleus basalis magnocellularis (NBM) in learning and memory has been demonstrated in different learning paradigms such as conditioned taste aversion (CTA) and inhibitory avoidance (IA). This participation has been related to the cholinergic system, but recent studies have reported the potential role of other neurotransmitters such as GABA. The effects of acute intracerebral administration of the GABAergic antagonist bicuculline (0.05 mg) and the GABAergic agonist muscimol (0.05 mg) into the NBM of male Wistar rats were assessed in CTA and IA learning. In both learning tasks, the drug administration was performed before the acquisition. Taste aversion learning was not affected by the infusion of any of the drugs administered. IA acquisition was not affected by the administration of bicuculline or muscimol, requiring similar number of trials to reach the learning criterion. However, when the rats were tested 24 h later, those injected with bicuculline or muscimol showed an impairment of the IA learning. The present results support a role of the GABAergic system in the consolidation process of IA learning. #

- by Milagros Lugo
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- Learning, Memory, Learning and Memory, Taste

PURPOSE. Intraocular pressure (IOP) fluctuation has recently been identified as a risk factor for glaucoma progression. Further, decreases in intracranial pressure (ICP), with postulated increases in the translaminar pressure gradient across the lamina cribrosa, has been reported in glaucoma patients. We hypothesized that circadian fluctuations in IOP and the translaminar pressure gradient are influenced, at least in part, by central autonomic regulatory neurons within the dorsomedial and perifornical hypothalamus (DMH/PeF). This study examined whether site-directed chemical stimulation of DMH/PeF neurons evoked changes in IOP, ICP, and the translaminar pressure gradient.

- by Anantha Shekhar
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- Biological Sciences, Glaucoma, Intraocular Pressure, Rats

The presubiculum (PrS) plays critical roles in spatial information processing and memory consolidation and has also been implicated in temporal lobe epileptogenesis. Despite its involvement in these processes, a basic structure-function analysis of PrS cells remains far from complete. To this end, we performed whole-cell recording and biocytin labeling of PrS neurons in layer (L)II and LIII to examine their electrophysiological and morphological properties. We characterized the cell types based on electrophysiological criteria, correlated their gross morphology, and classified them into distinct categories using unsupervised hierarchical cluster analysis. We identified seven distinct cell types: regularspiking (RS), irregular-spiking (IR), initially bursting (IB), stuttering (Stu), single-spiking (SS), fast-adapting (FA), and late-spiking (LS) cells, of which RS and IB cells were common to LII and LIII, LS cells were specific to LIII, and the remaining types were identified exclusively in LII. Recorded neurons were either pyramidal or nonpyramidal and, except for Stu cells, displayed spine-rich dendrites. The RS, IB, and IR cells appeared to be projection neurons based on extension of their axons into LIII of the medial entorhinal area (MEA) and/or angular bundle. We conclude that LII and LIII of PrS are distinct in their neuronal populations and together constitute a more diverse population of neurons than previously suggested. PrS neurons serve as major drivers of circuits in superficial (LII-III) entorhinal cortex (ERC) and couple neighboring structures through robust afferentation, thereby substantiating the PrS's critical role in the parahippocampal region. J. Comp. Neurol. 521: 3116-3132, 2013.

- by Bill Hansson
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- Engineering, Neuroscience, Physiology, Zoology