Govindan Dayanithi - Academia.edu (original) (raw)
Papers by Govindan Dayanithi
Progress in Brain Research, 2002
The interactions of the dendritically released neuropeptides vasopressin and oxytocin with co-rel... more The interactions of the dendritically released neuropeptides vasopressin and oxytocin with co-released neuroactive substances such as opioids and nitric oxide are reviewed. Endogenous opioids regulate magnocellular neurons at the level of the supraoptic nucleus and the relationship of dendritically released peptides and co-released opioids seems to be dependent on the stimulus given and the physiological state of the animal. Nitric
Brain Research, 1991
Ingestion of ethanol (EtOH) is known to result in a reduction of plasma arginine-vasopressin (AVP... more Ingestion of ethanol (EtOH) is known to result in a reduction of plasma arginine-vasopressin (AVP) levels in mammals. We examined the basis for this effect using a combination of biochemical and electrophysiological techniques. Release of AVP from nerve terminals isolated from the rat neurohypophysis was very sensitive to EtOH, with significant reductions in AVP release evident in 10 mM EtOH. However, EtOH did not affect the release of AVP from terminals which had been permeabilized with digitonin, suggesting that voltage-gated calcium channels might be the target of EtOH's actions. Patch clamping of these terminals indicated that both inactivating and long-lasting calcium currents were reduced in EtOH, but the long-lasting currents were more sensitive (significant reductions in 10 mM EtOH). EtOH-induced decreases in plasma AVP levels can be explained by EtOH's inhibition of calcium currents in the nerve terminals.
Neuroscience, 1990
The intracellular action on exocytosis of botulinum A toxin and constituent chains was studied us... more The intracellular action on exocytosis of botulinum A toxin and constituent chains was studied using permeabilized isolated nerve endings from the rat neural lobe. The release of the neuropeptide vasopressin was measured by radioimmunoassay. In the presence of the reducing agent dithiothreitol, the two-chain form of botulinum A toxin inhibited vasopressin release induced by 10 microM free calcium. Half maximal inhibition was obtained with 15 nM botulinum A toxin. In the absence of the heavy chain the light chain of the toxin strongly inhibited exocytosis with a half maximal effect of 2.5 nM. The inhibitory effects on secretion could be prevented by incubating the light chain with an immune serum against botulinum A toxin. The heavy chain of botulinum A toxin did not affect vasopressin release. However, it prevented the inhibitory effects of the light chain on stimulated exocytosis. It is concluded that botulinum A toxin inhibits the calcium-dependent step leading to exocytosis by in...
Cell calcium, 2015
Neurones in the supraoptic nucleus (SON) of the hypothalamus possess intrinsic osmosensing mechan... more Neurones in the supraoptic nucleus (SON) of the hypothalamus possess intrinsic osmosensing mechanisms, which are lost in transient receptor potential vanilloid 1 (Trpv1)-knock-out mice. The molecular nature of the osmosensory mechanism in SON neurones is believed to be associated with the N-terminal splice variant of Trpv1, although their entire molecular structures have not been hitherto identified. In this study, we sought for TRPV1-related molecules and their function in the rat SON. We performed RT-PCR and immunohistochemistry to detect TRPV1-related molecules in the SON, and patch-clamp and imaging of the cytosolic Ca(2+) concentration ([Ca(2+)]i) to measure responses to osmolality changes and TRPV-related drugs in acutely dissociated SON neurones of rats. RT-PCR analysis revealed full-length Trpv1 and a new N-terminal splice variant, Trpv1_SON (LC008303) in the SON. Positive immunostaining was observed using an antibody against the N-terminal portion of TRPV1 in arginine vasop...
Nature, Jan 4, 2002
Information in neurons flows from synapses, through the dendrites and cell body (soma), and, fina... more Information in neurons flows from synapses, through the dendrites and cell body (soma), and, finally, along the axon as spikes of electrical activity that will ultimately release neurotransmitters from the nerve terminals. However, the dendrites of many neurons also have a secretory role, transmitting information back to afferent nerve terminals. In some central nervous system neurons, spikes that originate at the soma can travel along dendrites as well as axons, and may thus elicit secretion from both compartments. Here, we show that in hypothalamic oxytocin neurons, agents that mobilize intracellular Ca(2+) induce oxytocin release from dendrites without increasing the electrical activity of the cell body, and without inducing secretion from the nerve terminals. Conversely, electrical activity in the cell bodies can cause the secretion of oxytocin from nerve terminals with little or no release from the dendrites. Finally, mobilization of intracellular Ca(2+) can also prime the rele...
Neuroscience, 1994
The tetanus toxin light chain blocks calcium induced vasopressin release from neurohypophysial ne... more The tetanus toxin light chain blocks calcium induced vasopressin release from neurohypophysial nerve terminals. Here we show that histidine residue 233 within the putative zinc binding motif of the tetanus toxin light chain is essential for the inhibition of exocytosis, in the rat. The zinc chelating agent dipicolinic acid as well as captopril, an inhibitor of zinc-dependent peptidases, counteract the effect of the neurotoxin. Synthetic peptides, the sequences of which correspond to motifs present in the cytoplasmic domain of the synaptic vesicle membrane protein synaptobrevin 1 and 2, prevent the effect of the tetanus toxin light chain. Our results indicate that zinc bound to the zinc binding motif constitutes the active site of the tetanus toxin light chain. Moreover they suggest that cleavage of synaptobrevin by the neurotoxin causes the inhibition of exocytotic release of vasopressin from secretory granules.
The peptides -melanocyte stimulating hormone (-MSH) and oxytocin, when administered centrally, pr... more The peptides -melanocyte stimulating hormone (-MSH) and oxytocin, when administered centrally, produce similar behavioral effects. -MSH induces Fos expression in supraoptic oxytocin neurons, and -MSH melanocortin-4 receptors (MC4Rs) are highly expressed in the supraoptic nucleus, suggesting that-MSH and oxytocin actions are not independent. Here we investigated the effects of -MSH on the activity of supraoptic neurons. We confirmed that -MSH
Journal of Physiology-london - J PHYSIOL-LONDON, 2002
The Journal of Physiology, 2010
Body fluid balance requires the release of arginine vasopressin (AVP) from the neurohypophysis. T... more Body fluid balance requires the release of arginine vasopressin (AVP) from the neurohypophysis. The hypothalamic supraoptic nucleus (SON) is a major site of AVP synthesis, and AVP release is controlled somatodendritically or at the level of nerve terminals by electrical activities of magnocellular neurosecretory cells (MNCs). Acid-sensing ion channels (ASICs) are neuronal voltage-insensitive cationic channels that are activated by extracellular acidification. Although ASICs are widely expressed in the central nervous system, functional ASICs have not been assessed in AVP neurons. ASICs are modulated by lactate (La − ), which reduces the extracellular calcium ion concentration. We hypothesize that ASICs modify neuronal function through La − that is generated during local hypoxia resulting from osmotic stimulation in the SON. In the present study, we used the whole-cell patch-clamp technique to show that acid-induced ASIC current is enhanced by La − in isolated rat SON MNCs that express an AVP-enhanced green fluorescent protein (eGFP) transgene. Immunohistochemistry and multi-cell reverse transcriptase-polymerase chain reaction experiments revealed that these neurons express the ASIC1a and ASIC2a subunits. In addition, increased La − production was specifically observed in the SON after osmotic stress. These results suggest that interaction between ASICs and La − in the SON plays an important role in the regulatory mechanism of body fluid homeostasis.
The Journal of Physiology, 2002
Effects of adenosine on voltage-gated Ca 2+ channel currents and on arginine vasopressin (AVP) an... more Effects of adenosine on voltage-gated Ca 2+ channel currents and on arginine vasopressin (AVP) and oxytocin (OT) release from isolated neurohypophysial (NH) terminals of the rat were investigated using perforated-patch clamp recordings and hormone-specific radioimmunoassays. Adenosine, but not adenosine 5‚-triphosphate (ATP), dose-dependently and reversibly inhibited the transient component of the whole-terminal Ba 2+ currents, with an IC 50 of 0.875 mM. Adenosine strongly inhibited, in a dose-dependent manner (IC 50 = 2.67 mM), depolarization-triggered AVP and OT release from isolated NH terminals. Adenosine and the N-type Ca 2+ channel blocker v-conotoxin GVIA, but not other Ca 2+ channel-type antagonists, inhibited the same transient component of the Ba 2+ current. Other components such as the L-, Q-and R-type channels, however, were insensitive to adenosine. Similarly, only adenosine and v-conotoxin GVIA were able to inhibit the same component of AVP release. A 1 receptor agonists, but not other purinoceptor-type agonists, inhibited the same transient component of the Ba 2+ current as adenosine. Furthermore, the A 1 receptor antagonist 8-cyclopentyltheophylline (CPT), but not the A 2 receptor antagonist 3, 7-dimethyl-1-propargylxanthine (DMPGX), reversed inhibition of this current component by adenosine. The inhibition of AVP and OT release also appeared to be via the A 1 receptor, since it was reversed by CPT. We therefore conclude that adenosine, acting via A 1 receptors, specifically blocks the terminal N-type Ca 2+ channel thus leading to inhibition of the release of both AVP and OT.
Stress: The International Journal on the Biology of Stress, 2010
Stem Cells and Development, 2013
Human embryonic stem cell-derived neural precursors (hESC NPs) are considered to be a promising t... more Human embryonic stem cell-derived neural precursors (hESC NPs) are considered to be a promising tool for cellbased therapy in central nervous system injuries and neurodegenerative diseases. The Ca 2 + ion is an important intracellular messenger essential for the regulation of various cellular functions. We investigated the role and physiology of Ca 2 + signaling to characterize the functional properties of CCTL14 hESC NPs during long-term maintenance in culture (in vitro). We analyzed changes in cytoplasmic Ca 2 + concentration ([Ca 2 + ] i ) evoked by high K + , adenosine-5¢-triphosphate (ATP), glutamate, g-aminobutyric acid (GABA), and caffeine in correlation with the expression of various neuronal markers in different passages (P6 through P10) during the course of hESC differentiation. We found that only differentiated NPs from P7 exhibited significant and specific [Ca 2 + ] i responses to various stimuli. About 31% of neuronal-like P7 NPs exhibited spontaneous [Ca 2 + ] i oscillations. Pharmacological and immunocytochemical assays revealed that P7 NPs express L-and P/Q-type Ca 2 + channels, P2X 2 , P2X 3 , P2X 7, and P2Y purinoreceptors, glutamate receptors, and ryanodine (RyR1 and RyR3) receptors. The ATP-and glutamate-induced [Ca 2 + ] i responses were concentration-dependent. Higher glutamate concentrations (over 100 mM) caused cell death. Responses to ATP were observed in the presence or in the absence of extracellular Ca 2 + . These results emphasize the notion that with time in culture, these cells attain a transient period of operative Ca 2 + signaling that is predictive of their ability to act as stem elements.
Proceedings of the National Academy of Sciences, 1992
We have investigated the role of endothelin (ET) in the stimulus-secretion coupling mechanism in ... more We have investigated the role of endothelin (ET) in the stimulus-secretion coupling mechanism in the posterior pituitary. We report that isolated nerve endings contain immunoreactive endothelin, the level of which is regulated by homeostatic mechanisms involved in control of water balance. ET-1 and ET-3 potentiate vasopressin release induced by depolarization through interaction with specific receptors of the ETA subtype and this response is antagonized by sarafotoxin S6b. The second messenger for this effect, however, remains unknown since the potentiation of depolarizationinduced vasopressin release occurs in the absence of an increase in cellular calcium.
Proceedings of the National Academy of Sciences, 1987
The free Ca2+ concentration in isolated rat neurohypophysial nerve endings was measured using the... more The free Ca2+ concentration in isolated rat neurohypophysial nerve endings was measured using the Ca2+ indicator fura-2. Depolarization with high K, veratridine, or electrical stimulation induced an increase in intracellular Ca2+ concentration that was abolished by agents known to block voltage-sensitive Ca channels. Electrical stimulation of the isolated nerve endings with a pulse pattern similar to that recorded in vivo from the hypothalamic magnocellular neurons showed that the increase in intracellular Ca2+ concentration was not only a function of the applied frequency but also of the duration of the silent interburst intervals. The relationship between the cytoplasmic free Ca concentration and the release of neuropeptides is discussed.
Ophthalmic Genetics, 2010
Purpose: The regulation of Ca 2+ entry and removal is a fine-tuned process which remains not well... more Purpose: The regulation of Ca 2+ entry and removal is a fine-tuned process which remains not well understood in mouse retinal ganglion cells (RGCs). The latter are known to be sensitive to dysfunctions of mitochondria, organelles playing a pivotal role in Ca 2+ reuptake.
Neuroscience Letters, 1989
The role of Cl- and Mg+ ions has been studied on the secretory mechanism leading to the release o... more The role of Cl- and Mg+ ions has been studied on the secretory mechanism leading to the release of vasopressin from digitonin permeabilized nerve endings isolated from the rat neurohypophysis. Secretion was triggered by challenging the permeabilized nerve endings with 1.1 microM free Ca2+. Magnesium enhances secretion and its maximal effect occurred at a concentration of about 2 mM. Further increase of this divalent cation concentration however led to an inhibition of secretion. Chloride ions are necessary for the final steps in exocytosis and this effect of Cl- was inhibited by the chloride channel antagonist N144. It is concluded that in neurosecretory nerve endings magnesium and chloride ions are crucial components for exocytosis to occur.
Nature, 1987
The hormone relaxin has recently been shown to inhibit not only uterine muscle contraction, but a... more The hormone relaxin has recently been shown to inhibit not only uterine muscle contraction, but also the release of oxytocin into the plasma. Intravenous injection of porcine relaxin in anaesthetized lactating rats inhibits milk ejection and injection of relaxin into the cerebral ventricles disturbs the pattern of the milk ejection reflex. Recent experiments performed in vivo indicate that relaxin might act not only in the uterus, but also in the hypothalamus and possibly in the neurohypophysis. We tested this hypothesis in vitro by studying the effect of relaxin on hormone release from isolated neural lobes of the pituitary and isolated neurosecretory nerve endings of the neurohypophysis from the rat. We report here that relaxin has a dual effect on neurohypophysial hormone secretion. Under basal conditions, vasopressin and oxytocin release was inhibited by relaxin but, when the nerve endings were depolarized, vasopressin and oxytocin secretion was potentiated. We also found that relaxin acts at a stage before the increase in cytoplasmic free Ca2+ that is necessary for inducing hormone release, possibly by gating the calcium channel.
Journal of Veterinary Medical Science, 2010
Adult rat dorsal root ganglion (DRG) neurons cultured in the presence of 100 ng/ml NGF show spont... more Adult rat dorsal root ganglion (DRG) neurons cultured in the presence of 100 ng/ml NGF show spontaneous action potentials and fluctuations in their cytosolic Ca 2+ concentrations ([Ca 2+ ] i ). In the present study, the Ca 2+ sources of the [Ca 2+ ] i fluctuations and the types of neurons whose excitability was affected by NGF were examined. In the subpopulation of NGF-treated neurons, obvious fluctuations of [Ca 2+ ] i were observed. The [Ca 2+ ] i fluctuations were inhibited by Ca 2+ removal or inhibitors of voltage-gated Ca 2+ channels. Regardless of the treatment with NGF, about half of the neurons responded to capsaicin and 10% of the neurons responded to icilin, and almost all icilin-responding neurons also responded to capsaicin. Fluctuations of [Ca 2+ ] i with large amplitudes were observed in 12 out of 131 NGF-treated neurons. Among these 12 neurons, 10 neurons responded to both capsaicin and icilin. The degree of the [Ca 2+ ] i fluctuations in the NGF-treated neurons responding to both capsaicin and icilin was significantly larger than in other neurons. These results suggest that neurons expressing both capsaicin-and icilin-sensitive TRP channels are susceptible to NGF and become hyperexcitable and that Ca 2+ influx through voltage-gated Ca 2+ channels is the major source contributing to the [Ca 2+ ] i fluctuations. Since such DRG neurons could play a physiological role as nociceptors, the NGF-induced spontaneous activity of DRG neurons may be the underlying mechanism of neuropathic pain.
Journal of Neuroendocrinology, 2005
ABSTRACT Oxytocin release from neurophypophysial terminals is particularly sensitive to inhibitio... more ABSTRACT Oxytocin release from neurophypophysial terminals is particularly sensitive to inhibition by the micro-opioid receptor agonist, DAMGO. Because the R-type component of the neurophypophysial terminal Ca2+ current (ICa) mediates exclusively oxytocin release, we hypothesised that micro-opioids could preferentially inhibit oxytocin release by blocking this channel subtype. Whole-terminal recordings showed that DAMGO and the R-type selective blocker SNX-482 inhibit a similar ICa component. Measurements of [Ca2+]i levels and oxytocin release confirmed that the effects of DAMGO and SNX-482 are not additive. Finally, isolation of the R-type component and its associated rise in [Ca2+]i and oxytocin release allowed us to demonstrate the selective inhibition by DAMGO of this channel subtype. Thus, micro-opioid agonists modulate specifically oxytocin release in neurophypophysial terminals by selectively targeting R-type Ca2+ channels. Modulation of Ca2+ channel subtypes could be a general mechanism for drugs of abuse to regulate the release of specific neurotransmitters at central nervous system synapses.
Journal of Neuroendocrinology, 2007
Arginine vasopressin (AVP) plays an important role in stress-induced activation of the hypothalam... more Arginine vasopressin (AVP) plays an important role in stress-induced activation of the hypothalamic-pituitary adrenal axis. In the present study, AVP-enhanced green fluorescent protein (eGFP) transgenic rats were used to investigate changes in AVP-eGFP expression in the hypothalamic paraventricular nucleus (PVN) and the median eminence (ME) upon exposure to stress conditions. The eGFP fluorescence in the parvocellular division of the PVN (pPVN) was markedly increased 5 days after bilateral adrenalectomy (ADX) and it was colocalised with corticotrophin-releasing hormone-like immunoreactivity in the pPVN. Peripheral administration of dexamethasone completely suppressed the increase of eGFP fluorescence in the pPVN and the external layer of the ME (eME) after bilateral ADX. Significant increases of eGFP fluorescence were observed in the pPVN 6, 12, 24 and 48 h after intraperitoneal (i.p.) administration of lipopolysaccharide (LPS). In the eME, eGFP fluorescence was significantly increased 48 h after i.p. administration of LPS. By contrast, eGFP fluorescence changed neither in the magnocellular division of the PVN, nor the internal layer of the ME after i.p. administration of LPS. Our results indicate that AVP-eGFP transgenic rats are useful animal model to study dynamic changes of AVP expression in the hypothalamus under stressful conditions.
Progress in Brain Research, 2002
The interactions of the dendritically released neuropeptides vasopressin and oxytocin with co-rel... more The interactions of the dendritically released neuropeptides vasopressin and oxytocin with co-released neuroactive substances such as opioids and nitric oxide are reviewed. Endogenous opioids regulate magnocellular neurons at the level of the supraoptic nucleus and the relationship of dendritically released peptides and co-released opioids seems to be dependent on the stimulus given and the physiological state of the animal. Nitric
Brain Research, 1991
Ingestion of ethanol (EtOH) is known to result in a reduction of plasma arginine-vasopressin (AVP... more Ingestion of ethanol (EtOH) is known to result in a reduction of plasma arginine-vasopressin (AVP) levels in mammals. We examined the basis for this effect using a combination of biochemical and electrophysiological techniques. Release of AVP from nerve terminals isolated from the rat neurohypophysis was very sensitive to EtOH, with significant reductions in AVP release evident in 10 mM EtOH. However, EtOH did not affect the release of AVP from terminals which had been permeabilized with digitonin, suggesting that voltage-gated calcium channels might be the target of EtOH's actions. Patch clamping of these terminals indicated that both inactivating and long-lasting calcium currents were reduced in EtOH, but the long-lasting currents were more sensitive (significant reductions in 10 mM EtOH). EtOH-induced decreases in plasma AVP levels can be explained by EtOH's inhibition of calcium currents in the nerve terminals.
Neuroscience, 1990
The intracellular action on exocytosis of botulinum A toxin and constituent chains was studied us... more The intracellular action on exocytosis of botulinum A toxin and constituent chains was studied using permeabilized isolated nerve endings from the rat neural lobe. The release of the neuropeptide vasopressin was measured by radioimmunoassay. In the presence of the reducing agent dithiothreitol, the two-chain form of botulinum A toxin inhibited vasopressin release induced by 10 microM free calcium. Half maximal inhibition was obtained with 15 nM botulinum A toxin. In the absence of the heavy chain the light chain of the toxin strongly inhibited exocytosis with a half maximal effect of 2.5 nM. The inhibitory effects on secretion could be prevented by incubating the light chain with an immune serum against botulinum A toxin. The heavy chain of botulinum A toxin did not affect vasopressin release. However, it prevented the inhibitory effects of the light chain on stimulated exocytosis. It is concluded that botulinum A toxin inhibits the calcium-dependent step leading to exocytosis by in...
Cell calcium, 2015
Neurones in the supraoptic nucleus (SON) of the hypothalamus possess intrinsic osmosensing mechan... more Neurones in the supraoptic nucleus (SON) of the hypothalamus possess intrinsic osmosensing mechanisms, which are lost in transient receptor potential vanilloid 1 (Trpv1)-knock-out mice. The molecular nature of the osmosensory mechanism in SON neurones is believed to be associated with the N-terminal splice variant of Trpv1, although their entire molecular structures have not been hitherto identified. In this study, we sought for TRPV1-related molecules and their function in the rat SON. We performed RT-PCR and immunohistochemistry to detect TRPV1-related molecules in the SON, and patch-clamp and imaging of the cytosolic Ca(2+) concentration ([Ca(2+)]i) to measure responses to osmolality changes and TRPV-related drugs in acutely dissociated SON neurones of rats. RT-PCR analysis revealed full-length Trpv1 and a new N-terminal splice variant, Trpv1_SON (LC008303) in the SON. Positive immunostaining was observed using an antibody against the N-terminal portion of TRPV1 in arginine vasop...
Nature, Jan 4, 2002
Information in neurons flows from synapses, through the dendrites and cell body (soma), and, fina... more Information in neurons flows from synapses, through the dendrites and cell body (soma), and, finally, along the axon as spikes of electrical activity that will ultimately release neurotransmitters from the nerve terminals. However, the dendrites of many neurons also have a secretory role, transmitting information back to afferent nerve terminals. In some central nervous system neurons, spikes that originate at the soma can travel along dendrites as well as axons, and may thus elicit secretion from both compartments. Here, we show that in hypothalamic oxytocin neurons, agents that mobilize intracellular Ca(2+) induce oxytocin release from dendrites without increasing the electrical activity of the cell body, and without inducing secretion from the nerve terminals. Conversely, electrical activity in the cell bodies can cause the secretion of oxytocin from nerve terminals with little or no release from the dendrites. Finally, mobilization of intracellular Ca(2+) can also prime the rele...
Neuroscience, 1994
The tetanus toxin light chain blocks calcium induced vasopressin release from neurohypophysial ne... more The tetanus toxin light chain blocks calcium induced vasopressin release from neurohypophysial nerve terminals. Here we show that histidine residue 233 within the putative zinc binding motif of the tetanus toxin light chain is essential for the inhibition of exocytosis, in the rat. The zinc chelating agent dipicolinic acid as well as captopril, an inhibitor of zinc-dependent peptidases, counteract the effect of the neurotoxin. Synthetic peptides, the sequences of which correspond to motifs present in the cytoplasmic domain of the synaptic vesicle membrane protein synaptobrevin 1 and 2, prevent the effect of the tetanus toxin light chain. Our results indicate that zinc bound to the zinc binding motif constitutes the active site of the tetanus toxin light chain. Moreover they suggest that cleavage of synaptobrevin by the neurotoxin causes the inhibition of exocytotic release of vasopressin from secretory granules.
The peptides -melanocyte stimulating hormone (-MSH) and oxytocin, when administered centrally, pr... more The peptides -melanocyte stimulating hormone (-MSH) and oxytocin, when administered centrally, produce similar behavioral effects. -MSH induces Fos expression in supraoptic oxytocin neurons, and -MSH melanocortin-4 receptors (MC4Rs) are highly expressed in the supraoptic nucleus, suggesting that-MSH and oxytocin actions are not independent. Here we investigated the effects of -MSH on the activity of supraoptic neurons. We confirmed that -MSH
Journal of Physiology-london - J PHYSIOL-LONDON, 2002
The Journal of Physiology, 2010
Body fluid balance requires the release of arginine vasopressin (AVP) from the neurohypophysis. T... more Body fluid balance requires the release of arginine vasopressin (AVP) from the neurohypophysis. The hypothalamic supraoptic nucleus (SON) is a major site of AVP synthesis, and AVP release is controlled somatodendritically or at the level of nerve terminals by electrical activities of magnocellular neurosecretory cells (MNCs). Acid-sensing ion channels (ASICs) are neuronal voltage-insensitive cationic channels that are activated by extracellular acidification. Although ASICs are widely expressed in the central nervous system, functional ASICs have not been assessed in AVP neurons. ASICs are modulated by lactate (La − ), which reduces the extracellular calcium ion concentration. We hypothesize that ASICs modify neuronal function through La − that is generated during local hypoxia resulting from osmotic stimulation in the SON. In the present study, we used the whole-cell patch-clamp technique to show that acid-induced ASIC current is enhanced by La − in isolated rat SON MNCs that express an AVP-enhanced green fluorescent protein (eGFP) transgene. Immunohistochemistry and multi-cell reverse transcriptase-polymerase chain reaction experiments revealed that these neurons express the ASIC1a and ASIC2a subunits. In addition, increased La − production was specifically observed in the SON after osmotic stress. These results suggest that interaction between ASICs and La − in the SON plays an important role in the regulatory mechanism of body fluid homeostasis.
The Journal of Physiology, 2002
Effects of adenosine on voltage-gated Ca 2+ channel currents and on arginine vasopressin (AVP) an... more Effects of adenosine on voltage-gated Ca 2+ channel currents and on arginine vasopressin (AVP) and oxytocin (OT) release from isolated neurohypophysial (NH) terminals of the rat were investigated using perforated-patch clamp recordings and hormone-specific radioimmunoassays. Adenosine, but not adenosine 5‚-triphosphate (ATP), dose-dependently and reversibly inhibited the transient component of the whole-terminal Ba 2+ currents, with an IC 50 of 0.875 mM. Adenosine strongly inhibited, in a dose-dependent manner (IC 50 = 2.67 mM), depolarization-triggered AVP and OT release from isolated NH terminals. Adenosine and the N-type Ca 2+ channel blocker v-conotoxin GVIA, but not other Ca 2+ channel-type antagonists, inhibited the same transient component of the Ba 2+ current. Other components such as the L-, Q-and R-type channels, however, were insensitive to adenosine. Similarly, only adenosine and v-conotoxin GVIA were able to inhibit the same component of AVP release. A 1 receptor agonists, but not other purinoceptor-type agonists, inhibited the same transient component of the Ba 2+ current as adenosine. Furthermore, the A 1 receptor antagonist 8-cyclopentyltheophylline (CPT), but not the A 2 receptor antagonist 3, 7-dimethyl-1-propargylxanthine (DMPGX), reversed inhibition of this current component by adenosine. The inhibition of AVP and OT release also appeared to be via the A 1 receptor, since it was reversed by CPT. We therefore conclude that adenosine, acting via A 1 receptors, specifically blocks the terminal N-type Ca 2+ channel thus leading to inhibition of the release of both AVP and OT.
Stress: The International Journal on the Biology of Stress, 2010
Stem Cells and Development, 2013
Human embryonic stem cell-derived neural precursors (hESC NPs) are considered to be a promising t... more Human embryonic stem cell-derived neural precursors (hESC NPs) are considered to be a promising tool for cellbased therapy in central nervous system injuries and neurodegenerative diseases. The Ca 2 + ion is an important intracellular messenger essential for the regulation of various cellular functions. We investigated the role and physiology of Ca 2 + signaling to characterize the functional properties of CCTL14 hESC NPs during long-term maintenance in culture (in vitro). We analyzed changes in cytoplasmic Ca 2 + concentration ([Ca 2 + ] i ) evoked by high K + , adenosine-5¢-triphosphate (ATP), glutamate, g-aminobutyric acid (GABA), and caffeine in correlation with the expression of various neuronal markers in different passages (P6 through P10) during the course of hESC differentiation. We found that only differentiated NPs from P7 exhibited significant and specific [Ca 2 + ] i responses to various stimuli. About 31% of neuronal-like P7 NPs exhibited spontaneous [Ca 2 + ] i oscillations. Pharmacological and immunocytochemical assays revealed that P7 NPs express L-and P/Q-type Ca 2 + channels, P2X 2 , P2X 3 , P2X 7, and P2Y purinoreceptors, glutamate receptors, and ryanodine (RyR1 and RyR3) receptors. The ATP-and glutamate-induced [Ca 2 + ] i responses were concentration-dependent. Higher glutamate concentrations (over 100 mM) caused cell death. Responses to ATP were observed in the presence or in the absence of extracellular Ca 2 + . These results emphasize the notion that with time in culture, these cells attain a transient period of operative Ca 2 + signaling that is predictive of their ability to act as stem elements.
Proceedings of the National Academy of Sciences, 1992
We have investigated the role of endothelin (ET) in the stimulus-secretion coupling mechanism in ... more We have investigated the role of endothelin (ET) in the stimulus-secretion coupling mechanism in the posterior pituitary. We report that isolated nerve endings contain immunoreactive endothelin, the level of which is regulated by homeostatic mechanisms involved in control of water balance. ET-1 and ET-3 potentiate vasopressin release induced by depolarization through interaction with specific receptors of the ETA subtype and this response is antagonized by sarafotoxin S6b. The second messenger for this effect, however, remains unknown since the potentiation of depolarizationinduced vasopressin release occurs in the absence of an increase in cellular calcium.
Proceedings of the National Academy of Sciences, 1987
The free Ca2+ concentration in isolated rat neurohypophysial nerve endings was measured using the... more The free Ca2+ concentration in isolated rat neurohypophysial nerve endings was measured using the Ca2+ indicator fura-2. Depolarization with high K, veratridine, or electrical stimulation induced an increase in intracellular Ca2+ concentration that was abolished by agents known to block voltage-sensitive Ca channels. Electrical stimulation of the isolated nerve endings with a pulse pattern similar to that recorded in vivo from the hypothalamic magnocellular neurons showed that the increase in intracellular Ca2+ concentration was not only a function of the applied frequency but also of the duration of the silent interburst intervals. The relationship between the cytoplasmic free Ca concentration and the release of neuropeptides is discussed.
Ophthalmic Genetics, 2010
Purpose: The regulation of Ca 2+ entry and removal is a fine-tuned process which remains not well... more Purpose: The regulation of Ca 2+ entry and removal is a fine-tuned process which remains not well understood in mouse retinal ganglion cells (RGCs). The latter are known to be sensitive to dysfunctions of mitochondria, organelles playing a pivotal role in Ca 2+ reuptake.
Neuroscience Letters, 1989
The role of Cl- and Mg+ ions has been studied on the secretory mechanism leading to the release o... more The role of Cl- and Mg+ ions has been studied on the secretory mechanism leading to the release of vasopressin from digitonin permeabilized nerve endings isolated from the rat neurohypophysis. Secretion was triggered by challenging the permeabilized nerve endings with 1.1 microM free Ca2+. Magnesium enhances secretion and its maximal effect occurred at a concentration of about 2 mM. Further increase of this divalent cation concentration however led to an inhibition of secretion. Chloride ions are necessary for the final steps in exocytosis and this effect of Cl- was inhibited by the chloride channel antagonist N144. It is concluded that in neurosecretory nerve endings magnesium and chloride ions are crucial components for exocytosis to occur.
Nature, 1987
The hormone relaxin has recently been shown to inhibit not only uterine muscle contraction, but a... more The hormone relaxin has recently been shown to inhibit not only uterine muscle contraction, but also the release of oxytocin into the plasma. Intravenous injection of porcine relaxin in anaesthetized lactating rats inhibits milk ejection and injection of relaxin into the cerebral ventricles disturbs the pattern of the milk ejection reflex. Recent experiments performed in vivo indicate that relaxin might act not only in the uterus, but also in the hypothalamus and possibly in the neurohypophysis. We tested this hypothesis in vitro by studying the effect of relaxin on hormone release from isolated neural lobes of the pituitary and isolated neurosecretory nerve endings of the neurohypophysis from the rat. We report here that relaxin has a dual effect on neurohypophysial hormone secretion. Under basal conditions, vasopressin and oxytocin release was inhibited by relaxin but, when the nerve endings were depolarized, vasopressin and oxytocin secretion was potentiated. We also found that relaxin acts at a stage before the increase in cytoplasmic free Ca2+ that is necessary for inducing hormone release, possibly by gating the calcium channel.
Journal of Veterinary Medical Science, 2010
Adult rat dorsal root ganglion (DRG) neurons cultured in the presence of 100 ng/ml NGF show spont... more Adult rat dorsal root ganglion (DRG) neurons cultured in the presence of 100 ng/ml NGF show spontaneous action potentials and fluctuations in their cytosolic Ca 2+ concentrations ([Ca 2+ ] i ). In the present study, the Ca 2+ sources of the [Ca 2+ ] i fluctuations and the types of neurons whose excitability was affected by NGF were examined. In the subpopulation of NGF-treated neurons, obvious fluctuations of [Ca 2+ ] i were observed. The [Ca 2+ ] i fluctuations were inhibited by Ca 2+ removal or inhibitors of voltage-gated Ca 2+ channels. Regardless of the treatment with NGF, about half of the neurons responded to capsaicin and 10% of the neurons responded to icilin, and almost all icilin-responding neurons also responded to capsaicin. Fluctuations of [Ca 2+ ] i with large amplitudes were observed in 12 out of 131 NGF-treated neurons. Among these 12 neurons, 10 neurons responded to both capsaicin and icilin. The degree of the [Ca 2+ ] i fluctuations in the NGF-treated neurons responding to both capsaicin and icilin was significantly larger than in other neurons. These results suggest that neurons expressing both capsaicin-and icilin-sensitive TRP channels are susceptible to NGF and become hyperexcitable and that Ca 2+ influx through voltage-gated Ca 2+ channels is the major source contributing to the [Ca 2+ ] i fluctuations. Since such DRG neurons could play a physiological role as nociceptors, the NGF-induced spontaneous activity of DRG neurons may be the underlying mechanism of neuropathic pain.
Journal of Neuroendocrinology, 2005
ABSTRACT Oxytocin release from neurophypophysial terminals is particularly sensitive to inhibitio... more ABSTRACT Oxytocin release from neurophypophysial terminals is particularly sensitive to inhibition by the micro-opioid receptor agonist, DAMGO. Because the R-type component of the neurophypophysial terminal Ca2+ current (ICa) mediates exclusively oxytocin release, we hypothesised that micro-opioids could preferentially inhibit oxytocin release by blocking this channel subtype. Whole-terminal recordings showed that DAMGO and the R-type selective blocker SNX-482 inhibit a similar ICa component. Measurements of [Ca2+]i levels and oxytocin release confirmed that the effects of DAMGO and SNX-482 are not additive. Finally, isolation of the R-type component and its associated rise in [Ca2+]i and oxytocin release allowed us to demonstrate the selective inhibition by DAMGO of this channel subtype. Thus, micro-opioid agonists modulate specifically oxytocin release in neurophypophysial terminals by selectively targeting R-type Ca2+ channels. Modulation of Ca2+ channel subtypes could be a general mechanism for drugs of abuse to regulate the release of specific neurotransmitters at central nervous system synapses.
Journal of Neuroendocrinology, 2007
Arginine vasopressin (AVP) plays an important role in stress-induced activation of the hypothalam... more Arginine vasopressin (AVP) plays an important role in stress-induced activation of the hypothalamic-pituitary adrenal axis. In the present study, AVP-enhanced green fluorescent protein (eGFP) transgenic rats were used to investigate changes in AVP-eGFP expression in the hypothalamic paraventricular nucleus (PVN) and the median eminence (ME) upon exposure to stress conditions. The eGFP fluorescence in the parvocellular division of the PVN (pPVN) was markedly increased 5 days after bilateral adrenalectomy (ADX) and it was colocalised with corticotrophin-releasing hormone-like immunoreactivity in the pPVN. Peripheral administration of dexamethasone completely suppressed the increase of eGFP fluorescence in the pPVN and the external layer of the ME (eME) after bilateral ADX. Significant increases of eGFP fluorescence were observed in the pPVN 6, 12, 24 and 48 h after intraperitoneal (i.p.) administration of lipopolysaccharide (LPS). In the eME, eGFP fluorescence was significantly increased 48 h after i.p. administration of LPS. By contrast, eGFP fluorescence changed neither in the magnocellular division of the PVN, nor the internal layer of the ME after i.p. administration of LPS. Our results indicate that AVP-eGFP transgenic rats are useful animal model to study dynamic changes of AVP expression in the hypothalamus under stressful conditions.