Vasopressin Neurons Research Articles

Feedback inhibition of action potential discharge by endogenous adenosine enhancement of the medium afterhyperpolarization

Phasic activity in supraoptic nucleus vasopressin neurones is characterized by alternating periods of activity (bursts) and silence. During bursts, activation of a medium afterhyperpolarization induces spike frequency adaptation. Antagonism of A1 adenosine receptors within the supraoptic nucleus decreases spike frequency adaptation and prolongs phasic bursts in vivo, indicating that endogenous adenosine contributes to spike frequency adaptation. Here we used sharp electrode intracellular recordings from supraoptic nucleus neurones in hypothalamic explants to show that endogenous adenosine increases medium afterhyperpolarization amplitude to enhance spike frequency adaptation during phasic bursts. Superfusion of the A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT, 10 microM) increased intraburst firing rate of phasic neurones (by 2.0 +/- 0.7 spikes s(-1), P = 0.03) and burst duration (by 141 +/- 113 s, P = 0.03). The CPT-induced increase in intraburst firing rate developed over the first few seconds of firing and persisted thereafter. In a separate series of experiments, CPT reduced the amplitude of the medium afterhyperpolarization evoked by a 1 s 20 Hz spike train (by 0.8 +/- 0.3 mV, P < 0.001) in supraoptic nucleus neurones; this inhibition was not prevented by 3 mM CsCl (0.8 +/- 0.1 mV decrease, P < 0.01) to block the afterdepolarization (which overlaps temporally with the medium afterhyperpolarization). In the presence of apamin to block the medium afterhyperpolarization, CPT did not alter afterdepolarization amplitude. Taken together, these data show that endogenous adenosine enhances medium afterhyperpolarization amplitude to contribute to spike frequency adaptation in phasic supraoptic nucleus neurones.

Evidence that kisspeptin neurons in the AVPV form part of a bisynaptic pathway connecting suprachiasmatic vasopressin neurons with preoptic GnRH cells

Event Abstract Back to Event Evidence that kisspeptin neurons in the AVPV form part of a bisynaptic pathway connecting suprachiasmatic vasopressin neurons with preoptic GnRH cells Imre Kalló1, 2*, Barbara Vida1, Levente Deli1, Theodosis Kalamatianos3, Erik Hrabovszky1, Alain Caraty4, Zsolt Liposits1, 2 and Coen W. Clive3 1 Institute of Experimental Medicine, Hungary 2 Pázmány Péter Catholic University, Department of Neuroscience, Faculty of Health,Medicine and Life Sciences, Hungary 3 King’s College London, United Kingdom 4 Univ Tours, INRA, France Gonadotropin releasing hormone (GnRH) secretion is under circadian regulation in rodents, but the mechanisms underlying this are poorly understood. Findings of our previous studies suggest that vasopressin (VP) neurons in the suprachiasmatic nucleus (SCN) convey signals to GnRH neurons via the anteroventral periventricular nucleus (AVPV). The AVPV contains kisspeptin (KP) neurons, which have been implicated in oestrogen’s positive feedback on GnRH release. Our studies have used confocal- and electronmicroscopy to test the hypotheses that direct contacts are made by VP-immunoreactive (IR) processes from the SCN on AVPV KP neurons and by KP-IR processes on GnRH neurons. Unlike the VP neurons in the supraoptic and paraventricular nuclei and in the bed nucleus of the stria terminalis and medial amygdala, those in the SCN are characterised by absence of galanin expression. Triple-label immunohistochemistry for VP, galanin and KP was carried out on hypothalamic sections from ovariectomised mice treated with estradiol benzoate. Confocal microscopy analysis indicated that nearly half of the KP-IR neurons in the AVPV show somatic or dendritic appositions from VP-IR varicosities lacking galanin-immunoreactivity; at the ultra-structural level, type II symmetric synapses were observed. KP-IR terminals were seen on GnRH perikarya and dendrites; these were not labelled for Neurokinin-B, markers of the KP fibers with arcuate nucleus origin. At the ultrastructural level KP-GnRH contacts displayed type I asymmetric synapses. The present results provide confocal and ultra-structural evidence which is consistent with the hypothesis that KP-IR neurons in the AVPV act as intermediaries between VP neurons in the SCN and GnRH neurons. Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Homeostatic regulatory mechanisms Citation: Kalló I, Vida B, Deli L, Kalamatianos T, Hrabovszky E, Caraty A, Liposits Z and Clive CW (2009). Evidence that kisspeptin neurons in the AVPV form part of a bisynaptic pathway connecting suprachiasmatic vasopressin neurons with preoptic GnRH cells. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.014 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Feb 2009; Published Online: 25 Feb 2009. * Correspondence: Imre Kalló, Institute of Experimental Medicine, Budapest, Hungary, kallo@koki.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Imre Kalló Barbara Vida Levente Deli Theodosis Kalamatianos Erik Hrabovszky Alain Caraty Zsolt Liposits Coen W Clive Google Imre Kalló Barbara Vida Levente Deli Theodosis Kalamatianos Erik Hrabovszky Alain Caraty Zsolt Liposits Coen W Clive Google Scholar Imre Kalló Barbara Vida Levente Deli Theodosis Kalamatianos Erik Hrabovszky Alain Caraty Zsolt Liposits Coen W Clive PubMed Imre Kalló Barbara Vida Levente Deli Theodosis Kalamatianos Erik Hrabovszky Alain Caraty Zsolt Liposits Coen W Clive Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Vasopressin: more than just an output of the circadian pacemaker? Focus on “Vasopressin receptor V1a regulates circadian rhythms of locomotor activity and expression of clock-controlled genes in the suprachiasmatic nuclei”

the timing of physiological events is carefully controlled so that incompatible processes do not compete and complementary functions coincide. Given the pivotal role of the hypothalamus in homeostatic regulation, the discovery that a master circadian pacemaker resides in this region was not

Neurotransmitters and peptides: whispered secrets and public announcements

The magnocellular oxytocin and vasopressin neurones of the hypothalamus are now understood in exceptional detail. Extensive quantitative details from many independent sources are available describing the electrical activity of the neurones in diverse circumstances, the subcellular localization of vesicles, and rates of hormone secretion from nerve endings into the blood and from dendrites into the brain. These data enable the relationship of electrical (spike) activity to vesicle exocytosis to be inferred with some precision. Such calculations lead to the conclusion that exocytosis of peptide-containing vesicles is a relatively rare event even in this vesicle-dense system. At any given release site in the neurohypophysis, it seems that several hundred spikes are needed on average to release a single vesicle. Release from compartments within the brain seems also to be very rare, making it implausible that peptides can act in a temporally precise, anatomically specific manner. However, very large amounts of peptide are released by these infrequent events, consistent with their likely role as neurohormonal messengers.

Prolactin Activates Mitogen-Activated Protein Kinase Signaling and Corticotropin Releasing Hormone Transcription in Rat Hypothalamic Neurons

Prolactin (PRL) modulates maternal behavior and mediates hypothalamic pituitary adrenal axis inhibition during lactation via PRL receptors in the brain. To identify mechanisms mediating these effects, we examined the effects of PRL on signaling and CRH transcription in hypothalamic neurons in vivo and in vitro. Western blot of hypothalamic proteins from rats receiving intracerebroventricular PRL injection revealed increases in phosphorylation of the MAPK and ERK. Double-staining immunohistochemistry demonstrated phosphorylated ERK localization in parvocellular CRH neurons as well as magnocellular vasopressin and oxytocin neurons of the hypothalamic paraventricular (PVN) and supraoptic nuclei. PRL also induced ERK phosphorylation in vitro in the hypothalamic cell line, 4B, which expresses PRL receptors, and in primary hypothalamic neuronal cultures. Using reporter gene assays in 4B cells, or quantitative RT-PCR for primary transcript in hypothalamic cell cultures, PRL potentiated forskolin-stimulated CRH transcription through activation of the ERK/MAPK pathway. The effect of PRL in hypothalamic cell cultures was unaffected by tetrodotoxin, suggesting a direct effect on CRH neurons. The data show that PRL activates the ERK/MAPK pathway and facilitates CRH transcription in CRH neurons, suggesting that the inhibitory effect of PRL on hypothalamo-pituitary-adrenal axis activity reported in vivo is indirect and probably mediated through modulation of afferent pathways to the PVN. In addition, the prominent stimulatory action of PRL on the ERK/MAPK pathway in the hypothalamic PVN and supraoptic nucleus is likely to mediate neuroplasticity of the neuroendocrine system during lactation.

Copeptin Immunoreactivity and Calcium Mobilisation in Hypothalamic Neurones of the Rat

Copeptin is cleaved from the C-terminus of vasopressin (VP) prohormone. Immunohistochemical studies have revealed intense copeptin-immunoreactivity (irCOPT) in neurones of the rat hypothalamic nuclei, including paraventricular, supraoptic, suprachiasmatic, periventricular, and accessory secretory. Varicose cell processes emanated from irCOPT neurones, some of which projected caudally and traversed the internal layer of the median eminence, and terminated in the posterior pituitary. Double-labelling hypothalamic sections with copeptin antiserum and VP or oxytocin antiserum revealed an extensive overlapping of irCOPT and irVP neurones. The biological activity of human synthetic nonglycosylated copeptin or VP was evaluated in vivo and in vitro. Copeptin (1, 10, and 20 nmol/kg) injected i.v. caused no significant changes in the mean arterial pressure (MAP) and heart rate of urethane-anaesthetised rats. VP (0.1 nmol/kg) increased MAP, which was accompanied by a small decrease of the heart rate. The ratiometric fluorescence method was employed to assess changes in intracellular Ca2+ concentrations [Ca2+](i) which served as an index of the biological activity of peptides. VP (1 microM) markedly increased [Ca2+](i) of rat hypothalamic neurones or vascular smooth muscle cells, whereas copeptin (100 nm to 1 microM) caused a low amplitude, sustained increase of [Ca2+](i) in a population of hypothalamic neurones, but not in any of the vascular smooth muscle cells tested. The results obtained demonstrate that copeptin is expressed in VP neurones and that the peptide in the concentrations tested, although causing little or no detectable changes of blood pressure and heart rate in anaesthetised rats nor changes in [Ca2+](i) of cultured aortic smooth muscle cells, increases [Ca2+](i) in a small population (< 2%) of hypothalamic neurones tested, indicating that copeptin is biologically active in mammalian neurones.

The Effects of Apelin on the Electrical Activity of Hypothalamic Magnocellular Vasopressin and Oxytocin Neurons and Somatodendritic Peptide Release

Apelin, a novel peptide originally isolated from bovine stomach tissue extracts, is widely but selectively distributed throughout the nervous system. Vasopressin and oxytocin are synthesized in the magnocellular neurons of the hypothalamic supraoptic nucleus (SON) and paraventricular nucleus, which are apelin-rich regions in the central nervous system. We made extracellular electrophysiological recordings from the transpharyngeally exposed SON of urethane-anaesthetized rats to assess the role of apelin in the control of the firing activity of identified magnocellular vasopressin and oxytocin neurons in vivo. Apelin-13 administration onto SON neurons via microdialysis revealed cell-specific responses; apelin-13 increased the firing rates of vasopressin cells but had no effect on the firing rate of oxytocin neurons. A direct excitatory effect of apelin-13 on vasopressin cell activity is also supported by our in vitro studies showing depolarization of membrane potential and increase in action potential firing. To assess the effects of apelin-13 on somatodendritic peptide release, we used in vitro release studies from SON explants in combination with highly sensitive and specific RIA. Apelin-13 decreases basal (by 78%; P < 0.05; n = 6) and potassium-stimulated (by 57%; P < 0.05; n = 6) vasopressin release but had no effect on somatodendritic oxytocin release. Taken together, our data suggest a local autocrine feedback action of apelin on magnocellular vasopressin neurons. Furthermore, these data show a marked dissociation between axonal and dendritic vasopressin release with a decrease in somatodendritic release but an increase in electrical activity at the cell bodies, indicating that release from these two compartments can be regulated wholly independently.

Neural circuitry of play fighting in golden hamsters

In hamsters, play fighting matures gradually into adult aggression. As these two behaviors share many similarities in this species, we predicted that a single neural circuitry controls their offensive component. The goal of the present study was to identify neural systems associated with offensive play fighting in male juvenile golden hamsters. The neural circuitry related to this behavior was identified through quantification of c-Fos immunolabeling. We also looked for vasopressin cells possibly associated with play fighting. We found that areas previously associated with offensive aggression in adult hamsters, including the ventrolateral hypothalamus, the medial amygdala, and the bed nucleus of the stria terminalis, also showed enhanced c-Fos expression after play fighting. In addition, vasopressin neurons in the nucleus circularis and the medial division of the supraoptic nucleus expressed enhanced c-Fos immunolabeling in juveniles after play fighting, as previously reported in adult hamsters after aggression. Finally, enhanced c-Fos expression associated with play fighting was also found in areas previously unexplored in adult hamsters, such as the prefrontal cortex. Together, our results support the hypothesis of a single core neural circuitry controlling the offensive components of play fighting and adult aggression throughout puberty in hamsters.

The single-prolonged stress paradigm alters both the morphology and stress response of magnocellular vasopressin neurons

Vasopressin (AVP) plays an important role in anxiety-related and social behaviors. Single-prolonged stress (SPS) has been established as an animal acute severe stress model and has been shown to induce a lower adrenocorticotropic hormone (ACTH) response upon cortisol challenge. Here, we show results from immunoassays for AVP, ACTH, and corticosterone (CORT), and in situ hybridizations for AVP mRNA performed 7 days after SPS exposure. Immunofluorescence for AVP was also performed during the 7-day period following SPS exposure and after an additional forced swimming stress paradigm. We observed that the plasma concentrations of AVP, ACTH, and CORT were not altered by SPS; ACTH content in the pituitary and AVP mRNA expression in the supraoptic nucleus (SON) were significantly reduced by SPS. During the 7-day period following SPS, the intensity of immunoreactivity, the size of the soma, and the immunoreactive optical density of the dendrites of AVP neurons in the SON all increased. An apparent reduction in the intensity of AVP immunoreactivity was observed in the SON at 4 h after additional stress. Additional forced swimming led to a rapid increase in the dendritic AVP content only in the controls and not in the SPS-treated rats. These findings suggest that AVP is a potential biomarker for past exposure to severe stress and that alterations in AVP may affect the development of pathogenesis in stress-related disorders.

Blockade of NK3R signaling in the PVN decreases vasopressin and oxytocin release and c-Fos expression in the magnocellular neurons in response to hypotension

Tachykinin neurokinin 3 receptor (NK3R) signaling has a broad role in vasopressin (VP) and oxytocin (OT) release. Hydralazine (HDZ)-induced hypotension activates NK3R expressed by magnocellular neurons, increases plasma VP and OT levels, and induces c-Fos expression in VP and OT neurons. Intraventricular pretreatment with the specific NK3R antagonist, SB-222200, eliminates the HDZ-stimulated VP and OT release. NK3R are distributed in the central pathways conveying hypotension information to the magnocellular neurons, and the NK3R antagonist could act anywhere in the pathways. Alternatively, the antagonist could act at the NK3R expressed by the magnocellular neurons. To determine whether blockade of NK3R on magnocellular neurons impairs VP and OT release to HDZ, rats were pretreated with a unilateral PVN injection of 0.15 M NaCl or SB-222200 prior to an intravenous injection of 0.15 M NaCl or HDZ. Blood samples were taken, and brains were processed for VP/c-Fos and OT/c-Fos immunohistochemistry. Intravenous injection of 0.15 M NaCl did not alter plasma hormone levels, and little c-Fos immunoreactivity was present in the PVN. Conversely, intravenous injection of HDZ increased plasma VP and OT levels and c-Fos expression in VP and OT magnocellular neurons. Intra-PVN injection of SB-222200 prior to an intravenous injection of HDZ significantly decreased c-Fos expression in both VP and OT neurons by approximately 70% and attenuated plasma VP and OT levels by 33% and 35%, respectively. Therefore, NK3R signaling in magnocellular neurons has a critical role for the release of VP and OT in response to hypotension.

Immunoreactive vasoactive intestinal polypeptide and vasopressin cells after a protein malnutrition diet in the suprachiasmatic nucleus of the rat

The aim of the present study was to evaluate the effects of prenatal and postnatal protein deprivation on the morphology and density of vasopressin (VP) and vasoactive intestinal polypeptide (VIP) immunoreactive neurons in the suprachiasmatic nucleus (SCN) of young rats. Female Wistar rats were fed either 6% (malnourished group) or 25% (control group) casein diet five weeks before conception, during gestation and lactation. After weaning, the pups were maintained on the same diet until sacrificed at 30 days of age. The major and minor axes, somatic area and the density of VP- and VIP-immunoreactive neurons were evaluated in the middle sections of the SCN. The present study shows that chronic protein malnutrition (ChPM) in VP neurons induces a significant decrease in number of cells (-31%,) and a significant increase in major and minor axes and somatic area (+12.2%, +21.1% and +15.0%, respectively). The VIP cells showed a significant decrease in cellular density (-41.5%) and a significant increase in minor axis (+13.5%) and somatic area (+10.1%). Our findings suggest that ChPM induces abnormalities in the density and morphology of the soma of VP and VIP neurons. These alterations may be a morphological substrate underlying circadian alterations previously observed in malnourished rats.

Apoptosis of supraoptic AVP neurons is involved in the development of central diabetes insipidus after hypophysectomy in rats

BackgroundIt has been reported that various types of axonal injury of hypothalamo-neurohypophyseal tract can result in degeneration of the magnocellular neurons (MCNs) in hypothalamus and development of central diabetes insipidus (CDI). However, the mechanism of the degeneration and death of MCNs after hypophysectomy in vivo is still unclear. This present study was aimed to disclose it and to figure out the dynamic change of central diabetes insipidus after hypophysectomy.ResultsThe analysis on the dynamic change of daily water consumption (DWC), daily urine volume(DUV), specific gravity of urine(USG) and plasma vasopressin concentration showed that the change pattern of them was triphasic and neuron counting showed that the degeneration of vasopressin neurons began at 10 d, aggravated at 20 d and then stabilized at 30 d after hypophysectomy. There was marked upregulation of cleaved Caspase-3 expression of vasopressin neurons in hypophysectomy rats. A "ladder" pattern of migration of DNA internucleosomal fragments was detected and apoptotic ultrastructure was found in these neurons. There was time correlation among the occurrence of diabetes insipidus, the changes of plasma vasopressin concentration and the degeneration of vasopressin neurons after hypophysectomy.ConclusionThis study firstly demonstrated that apoptosis was involved in degeneration of supraoptic vasopressin neurons after hypophysectomy in vivo and development of CDI. Our study on time course and correlations among water metabolism, degeneration and apoptosis of vasopressin neurons suggested that there should be an efficient therapeutic window in which irreversible CDI might be prevented by anti-apoptosis.

TRPV1 Gene Required for Thermosensory Transduction and Anticipatory Secretion from Vasopressin Neurons during Hyperthermia

Increases in core body temperature promote thermoregulatory cooling by stimulating sweat production and preemptive renal water reabsorption through the release of vasopressin (VP, antidiuretic hormone). The mechanism by which the hypothalamus orchestrates this anticipatory VP release during hyperthermia is unknown but has been linked to a central thermosensory mechanism. Here, we report that thermal stimuli spanning core body temperatures activate a calcium-permeable, ruthenium red- and SB366791-sensitive nonselective cation conductance in hypothalamic VP neurons. This response is associated with a depolarizing receptor potential and an increase in action potential firing rate, indicating that these neurons are intrinsically thermosensitive. The thermosensitivity of VP neurons isolated from trpv1 knockout (Trpv1(-/-)) mice was significantly lower than that of wild-type counterparts. Moreover, Trpv1(-/-) mice showed an impaired VP response to hyperthermia in vivo. Channels encoded by the trpv1 gene thus confer thermosensitivity in central VP neurons and contribute to the thermal control of VP release in vivo.

Oxytocin reduces anxiety via ERK1/2 activation: local effect within the rat hypothalamic paraventricular nucleus

The neuropeptide oxytocin (OT) modulates social behaviours and is an important anxiolytic substance of the brain. However, sites of action and the intracellular signalling pathways downstream of OT receptors (OTR) within the brain remain largely unknown. In the present studies, we localized the anxiolytic effect of OT by bilateral microinfusion of OT (0.01 nmol/0.5 microL) into the hypothalamic paraventricular nucleus (PVN) in male rats using both the elevated plus-maze and the light-dark box. Moreover, intracerebroventricular administration of OT, but not of the related neuropeptide vasopressin (VP), dose-dependently activated the extracellular signal-regulated kinase 1/2 (ERK1/2) cascade. Specifically, OT induced the phosphorylation of Raf-1, MEK1/2 and ERK1/2 in the hypothalamus in vivo and in hypothalamic H32 neurons via EGF receptors. OT-induced ERK1/2 phosphorylation was immunohistochemically localized within VP neurons of the PVN and the supraoptic nucleus. Importantly, the anxiolytic effect of OT within the PVN was prevented by local inhibition of the MAP kinase cascade with a MEK1/2 inhibitor (U0126, 0.5 nmol/0.5 microL) locally infused prior to OT, indicating the causal involvement of this intracellular signalling cascade in the behavioural effect of OT. OT effects within the hypothalamus may have far-reaching implications for the regulation of emotionality and social behaviours and, consequently, for the development of possible therapeutic strategies to treat affective disorders. Thus, OTR agonism or activation of the ERK1/2 cascade, specifically within the hypothalamus, may provide therapeutically relevant mechanisms.

Effects of selective Bcl-2 inhibitor HA14-1 treatments on functional activity of magnocellular vasopressinergic neurons of rat hypothalamus

In this study we examined whether in vivo treatments with Bcl-2 inhibitor HA14-1 can affect the function of vasopressinergic system of rat. HA14-1 is a novel organic compound that has micromolar affinity for Bcl-2 and Bcl-xL and acts as a mimetic of BH3-only proteins by antagonizing the anti-apoptotic Bcl-2 proteins and triggering Bax-dependent apoptosis. We found that intrahypothalamic injections of HA14-1 did not induce apoptosis of vasopressin (VP) cells of supraoptic nucleus, but led to activation of VP synthesis and release, resulting in decreased diuresis. Our data has also demonstrated that injections of HA14-1 increased phospho-MEK1/2, phospho-CREB and phospho-Elk-1 levels in magnocellular neurons. Thus we propose that injections of HA14-1 into the hypothalamus do not lead to neuronal death, but change the functional activity of VP neurons of hypothalamus centres.

Role of FosB in the supraoptic nucleus of rats with hepatic cirrhosis

Bile duct ligation (BDL), a model of hepatic cirrhosis, is associated with inappropriate vasopressin release and increased FosB expression in vasopressin neurons in the supraoptic nucleus (SON). BDL rats were injected bilaterally in the SON (n = 5) with 400 nl of an adeno‐associated virus (AAV) vector expressing a dominant negative construct for FosB (AAV‐ΔJunD) plus GFP. AAV injected BDL rats, control BDL rats, and sham ligated rats were instrumented with radio telemetry transmitters for measuring blood pressure and heart rate. Three weeks after BDL surgery, rats were individually housed in metabolism cages for 1 week. Daily average mean arterial pressures and heart rates were not different among the groups. Average daily water intake was significantly greater in AAV‐BDL rats (55 ± 7 ml) and BDL rats (47 ±4) compared to sham ligated controls (35 ± 1). Urine output was significantly greater in AAV‐treated BDL rats (38 ± 5 ml) than control BDL rats (21 ± 2) or sham controls (23 ± 1). Urine sodium was significantly lower in AAV‐treated BDL rats (47 ± 13 mmol/L) than the other groups (BDL 89 ± 12; Sham 136 ± 22) although average daily Na excretion was not different among the groups. SON injections of the FosB dominant null produced a diuresis in BDL rats that may be related to decreased circulating levels of vasopressin. FosB expression in vasopressin SON neurons may contribute to inappropriate vasopressin release in BDL rats. (HL62579)

Non‐desensitizing purinergic receptors (P2R) are responsible for sustained stimulation of vasopressin (VP) release by ATP and phenylephrine (PE)

ATP and norepinephrine (NE) are neurotransmitters carrying cardiovascular information to vasopressin (VP) neurons. Simultaneous exposure of hypothalamo‐neurohypophyseal system explants to ATP and PE (α1‐adrenergic receptor agonist) results in potentiation of VP release characterized by both an increase in the peak response and conversion of a transient response to a response that is sustained for hours. (J. Neurosci. 20:8868, 2000). Since the P2X2/3 and P2X7 subtypes of P2XRs do not desensitize, we hypothesized that these receptors are responsible for the sustained response to ATP. A317491 (300nM, P2X3 and P2X2/3R antag.), or 1uM BBG (P2X7R antag.) added during sustained response to ATP+PE attenuated VP release. These data supported the hypothesis that activation of the non‐desensitizing P2X2/3 and P2X7Rs is required for the sustained elevation of VP release characteristic of ATP+PE synergism. A more rapid effect of BBG suggests a prominent role for P2X7Rs. To determine if continued exposure to ATP or PE is required to sustain elevated hormone release, either ATP or PE was removed after 2hrs exposure to ATP+PE. Continued perifusion with PE alone but not ATP is required to maintain VP release. Since NE has been shown to stimulate ATP release from glia (Gorden et al Nat Neurosci 8:1078, 2005), these findings in conjunction with the ability of the P2X2/3 and P2X7R antagonists to attenuate sustained VP release support the interpretation that continuous exposure to PE is required to maintain P2X2/3 and/or P2X7R function. Supported by NIH RO1‐NS27975.

Microinjection of a selective kappa opioid agonist into the supraoptic nucleus (SON) increases inducible cAMP element repressor (ICER) expression

Administration of kappa opioid (κ) agonists in conscious rats produce diuresis via central inhibition of vasopressin (AVP) neurons in the SON and paraventricular nucleus of the hypothalamus, but the molecular mechanism is unknown. Activation of κ receptors produces an inhibition of cAMP accumulation via Gi/o proteins. However, pre‐treatment with pertussis toxin (an inhibitor of Gi/o) fails to block the κ effects in the SON. This suggests that activation of other transcriptions factors may participate in cAMP inhibition (i.e., ICER). This study examined changes in ICER staining following direct microinjection of a selective κ opioid agonist, U50‐488H (U50), into the SON of conscious rats. The forebrain was processed for ICER using polyclonal anti‐ICER antibody raised in rabbit. Microinjection of U50 elicited significant increases in ICER staining in the SON (C, 35 ± 4; U50, 64 ± 5; P &lt; .05). In addition, double labeling shows significant increase in AVP/ICER staining as compared to control (C, 11 ± 1; U50, 22 ± 2; P&lt;.05). This is the first study to show direct activation of ICER by κ. In addition, U50 preferentially increased ICER expression in AVP neurons and not in oxytocin neurons. These results suggest a novel pathway for κ opioid‐mediated suppression of cAMP accumulation, AVP neurons inhibition, and suppression of AVP secretion that is independent of Gi/o. Supported by NIH HL62579 &amp; DK57822.

Galanin immunoreactivity increased in chicken supraoptic neurons after activation of the vasotocin system at oviposition

The avian arginine vasotocin (AVT) synthesized in the hypothalamic magnocellular neurons and released from the posterior pituitary is known to be involved in the regulation of uterine contractions for oviposition in chickens. However, regulation of AVT synthesis and release within the magnocellular hypothalamus has not been elucidated. Galanin, the oviposition inducing factor in the oviduct of the hen, has been demonstrated to have sexually dimorphic stimulatory action in oxytocin- and vasopressin neurons in the mammalian hypothalamus. In this study, galanin and AVT immunoreactivity was investigated around the time of oviposition in the supraoptic nucleus (SON) to determine if galanin modulates AVT synthesis and/or release. Within SON neurons increased AVT immunoreactivity before oviposition and the decreased AVT immunoreactivity after oviposition implied function-related peptide release. The significantly increased number of galanin neurons co-localizing with AVT immediately after oviposition suggests that galanin is involved in the negative feedback to limit AVT release in the SON. Thus, these data support the idea that AVT in the SON is involved in central regulation of oviposition and that AVT release could be modulated by the neuropeptide galanin.

Dorsomedial SCN neuronal subpopulations subserve different functions in human dementia

The suprachiasmatic nuclei (SCN) are necessary and sufficient for the maintenance of circadian rhythms in primate and other mammalian species. The human dorsomedial SCN contains populations of non-species-specific vasopressin and species-specific neurotensin neurons. We made time-series recordings of core body temperature and locomotor activity in 19 elderly, male, end-stage dementia patients and 8 normal elderly controls. Following the death of the dementia patients, neuropathological diagnostic information and tissue samples from the hypothalamus were obtained. Hypothalamic tissue was also obtained from eight normal control cases that had not had activity or core temperature recordings previously. Core temperature was analysed for parametric, circadian features, and activity was analysed for non-parametric and parametric circadian features. These indices were then correlated with the degree of degeneration seen in the SCN (glia/neuron ratio) and neuronal counts from the dorsomedial SCN (vasopressin, neurotensin). Specific loss of SCN neurotensin neurons was associated with loss of activity and temperature amplitude without increase in activity fragmentation. Loss of SCN vasopressin neurons was associated with increased activity fragmentation but not loss of amplitude. Evidence for a circadian rhythm of vasopressinergic activity was seen in the dementia cases but no evidence was seen for a circadian rhythm in neurotensinergic activity. These results provide evidence that the SCN is necessary for the maintenance of the circadian rhythm in humans, information on the role of neuronal subpopulations in subserving this function and the utility of dementia in elaborating brain-behaviour relationships in the human.