Vasopressin-containing Neurons Research Articles

Hypnotic effect of thalidomide is independent of teratogenic ubiquitin/proteasome pathway

Thalidomide exerts its teratogenic and immunomodulatory effects by binding to cereblon (CRBN) and thereby inhibiting/modifying the CRBN-mediated ubiquitination pathway consisting of the Cullin4-DDB1-ROC1 E3 ligase complex. The mechanism of thalidomide's classical hypnotic effect remains largely unexplored, however. Here we examined whether CRBN is involved in the hypnotic effect of thalidomide by generating mice harboring a thalidomide-resistant mutant allele of Crbn (Crbn YW/AA knock-in mice). Thalidomide increased non-REM sleep time in Crbn YW/AA knock-in homozygotes and heterozygotes to a similar degree as seen in wild-type littermates. Thalidomide similarly depressed excitatory synaptic transmission in the cortical slices obtained from wild-type and Crbn YW/AA homozygous knock-in mice without affecting GABAergic inhibition. Thalidomide induced Fos expression in vasopressin-containing neurons of the supraoptic nucleus and reduced Fos expression in the tuberomammillary nuclei. Thus, thalidomide's hypnotic effect seems to share some downstream mechanisms with general anesthetics and GABAA-activating sedatives but does not involve the teratogenic CRBN-mediated ubiquitin/proteasome pathway.

Selective up-regulation of JunD transcript and protein expression in vasopressinergic supraoptic nucleus neurones in water-deprived rats.

The magnocellular neurones (MCN) of the supraoptic nucleus (SON) undergo reversible changes during dehydration. We hypothesise that alterations in steady-state transcript levels might be partially responsible for this plasticity. In turn, regulation of transcript abundance might be mediated by transcription factors. We have previously used microarrays to identify changes in the expression of mRNAs encoding transcription factors in response to water deprivation. We observed down-regulation of 11 and up-regulation of 31 transcription factor transcripts, including members of the activator protein-1 gene family, namely c-fos, c-jun, fosl1 and junD. Because JunD expression and regulation within the SON has not been previously described, we have used in situ hybridisation and the quantitative reverse transcriptase-polymerase chain reaction to confirm the array results, demonstrating a significant increase in JunD mRNA levels following 24 and 72h of water deprivation. Western blot and immunohistochemistry revealed a significant increase in JunD protein expression following dehydration. Double-staining fluorescence immunohistochemistry with a neurone-specific marker (NeuN) demonstrated that JunD staining is predominantly neuronal. Additionally, JunD immunoreactivity is observed primarily in vasopressin-containing neurones with markedly less staining seen in oxytocin-containing MCNs. Furthermore, JunD is highly co-expressed with c-Fos in MCNs of the SON following dehydration. These results suggest that JunD plays a role in the regulation of gene expression within MCNs of the SON in association with other Fos and Jun family members.

Hydration state controls stress responsiveness and social behavior.

Life stress frequently occurs within the context of homeostatic challenge, requiring integration of physiological and psychological need into appropriate hormonal, cardiovascular, and behavioral responses. To test neural mechanisms underlying stress integration within the context of homeostatic adversity, we evaluated the impact of a pronounced physiological (hypernatremia) challenge on hypothalamic-pituitary-adrenal (HPA), cardiovascular, and behavioral responses to an acute psychogenic stress. Relative to normonatremic controls, rats rendered mildly hypernatremic had decreased HPA activation in response to physical restraint, a commonly used rodent model of psychogenic stress. In addition, acute hypernatremia attenuated the cardiovascular response to restraint and promoted faster recovery to prestress levels. Subsequent to restraint, hypernatremic rats had significantly more c-Fos expression in oxytocin- and vasopressin-containing neurons within the supraoptic and paraventricular nuclei of the hypothalamus. Hypernatremia also completely eliminated the increased plasma renin activity that accompanied restraint in controls, but greatly elevated circulating levels of oxytocin. The endocrine and cardiovascular profile of hypernatremic rats was predictive of decreased anxiety-like behavior in the social interaction test. Collectively, the results indicate that acute hypernatremia is a potent inhibitor of the HPA, cardiovascular, and behavioral limbs of the stress response. The implications are that the compensatory responses that promote renal-sodium excretion when faced with hypernatremia also act on the nervous system to decrease reactivity to psychogenic stressors and facilitate social behavior, which may suppress the anxiety associated with approaching a communal water source and support the social interactions that may be encountered when engaging in drinking behavior.

Eating and hypothalamus changes in behavioral‐variant frontotemporal dementia

ObjectiveBehavioral-variant frontotemporal dementia (bvFTD) is a progressive neurodegenerative brain disorder, clinically characterized by changes in cognition, personality, and behavior. Marked disturbances in eating behavior, such as overeating and preference for sweet foods, are also commonly reported. The hypothalamus plays a critical role in feeding regulation, yet the relation between pathology in this region and eating behavior in FTD is unknown. This study aimed to address this issue using 2 complementary approaches.MethodsFirst, 18 early stage bvFTD patients and 16 healthy controls underwent high-resolution structural magnetic resonance imaging and assessment of eating behavior. Hypothalamic volumes were traced manually on coronal images. Second, postmortem analyses of 12 bvFTD cases and 6 matched controls were performed. Fixed hypothalamic tissue sections were stained for a cell marker and for peptides regulating feeding behaviors using immunohistochemistry. Stereological estimates of the hypothalamic volume and the number of neurons and glia were performed.ResultsSignificant atrophy of the hypothalamus in bvFTD was present in both analyses. Patients with high feeding disturbance exhibited significant atrophy of the posterior hypothalamus. Neuronal loss, which was observed only in bvFTD cases with Tar DNA protein-43 deposition, was also predominant posteriorly. In contrast, orexin (hypocretin), neuropeptide Y, cocaine- and amphetamine-regulating transcript, and vasopressin-containing neurons that regulate appetite were spared in posterior nuclei known to participate in feeding regulation.InterpretationDegeneration and consequent dysregulation within the hypothalamus relates to significant feeding disturbance in bvFTD. These findings provide a basis for the development of therapeutic models. Ann Neurol 2011

Daily changes in synaptic innervation of VIP neurons in the rat suprachiasmatic nucleus: contribution of glutamatergic afferents

The daily temporal organization of rhythmic functions in mammals, which requires synchronization of the circadian clock to the 24-h light-dark cycle, is believed to involve adjustments of the mutual phasing of the cellular oscillators that comprise the time-keeper within the suprachiasmatic nucleus of the hypothalamus (SCN). Following from a previous study showing that the SCN undergoes day/night rearrangements of its neuronal-glial network that may be crucial for intercellular phasing, we investigated the contribution of glutamatergic synapses, known to play major roles in SCN functioning, to such rhythmic plastic events. Neither expression levels of the vesicular glutamate transporters nor numbers of glutamatergic terminals showed nycthemeral variations in the SCN. However, using quantitative imaging after combined immunolabelling, the density of synapses on neurons expressing vasoactive intestinal peptide, known as targets of the retinal input, increased during the day and both glutamatergic and non-glutamatergic synapses contributed to the increase (+36%). This was not the case for synapses made on vasopressin-containing neurons, the other major source of SCN efferents in the non-retinorecipient region. Together with electron microscope observations showing no differences in the morphometric features of glutamatergic terminals during the day and night, these data show that the light synchronization process in the SCN involves a selective remodelling of synapses at sites of photic integration. They provide a further illustration of how the adult brain may rapidly and reversibly adapt its synaptic architecture to functional needs.

Non-Peptide Arginine-Vasopressin Antagonists (Vaptans) for the Treatment of Hyponatremia in Neurocritical Care: A New Alternative?

The nonapeptide hormone arginine-vasopressin (AVP), also known as antidiuretic hormone (ADH), is the primary regulator of body water content and plasma osmolality. It is synthesized within two hypothalamic nuclei (supraoptic and paraventricular) and stored in the neurohypophysis. Small (parvocellular) vasopressin-containing neurons in the anterior hypothalamus give rise to a complex fiber system that extends throughout the brain. Utilizing immunohistochemical and audioradiographic techniques, extra-hypophyseal vasopressinergic pathways in the brain have been demonstrated that may allow for independent release of central as well as systemic AVP. It has been postulated that these pathways influence water regulation and water permeability in nonneuronal brain cells (glia) [1, 2]. Effects of AVP are mediated through three receptor subtypes, each of which belongs to the rhodopsin-like classA G-protein-coupled receptor family [3]. The V1a receptors are primarily located within the vascular smooth muscle and their stimulation results in vasoconstriction. They are also expressed within the brain where they may play an important role in brain water homeostasis and the evolution of brain edema [4], as well as in the myocardium, platelets, hepatocytes, superior cervical ganglion, the uterus, and cells of the adrenal glands [3, 5]. The V1b (formerly designated V3) receptors are found within the anterior pituitary, adrenal medulla, brain, and pancreas and are implicated in the neurohumoral regulation of centrally and peripherally mediated stress response [3, 5]. V2 receptors are expressed predominantly in basolateral membrane of the renal collecting tubule and to a lesser degree within type 2 pneumocytes and the vascular endothelium [3, 5]. AVP regulates water homeostasis through its interaction with the V2 receptors in the renal collecting tubule [3, 5, 6]. Binding of AVP to the V2 receptor activates adenylate cyclase, increasing intracellular concentration of cyclic adenosine monophosphate (cAMP), leading to stimulation of protein kinase A (PKA). PKA increases water resorption by both immediate and delayed mechanisms, namely: (1) phosphorylation of the aquaporin-2 (AQP 2) channel by PKA results in immediate translocation of AQP 2 to the cell membrane and (2) downstream effects resulting in increased expression of AQP-2 within hours [6]. The release of AVP from the neurohypophysis is exquisitely sensitive to plasma osmolality. AVP is secreted at low levels until plasma osmolality reaches approximately 280 mOsm/kg. Above this threshold, the secretion of AVP increases approximately linearly to a maximum output at a serum osmolality of about 295 mOsm/kg, resulting in maximum antidiuresis (urine osmolality > 800 mOsm/kg) [6]. In addition to plasma osmolality, AVP may be released as a normal physiologic response to decreased blood pressure or effective circulating volume (>10% from baseline), nausea, pain, stress, hypoxia, fear, and anxiety [6, 7]. Finally, inappropriate release of AVP may occur in association with a variety of neoplasms and drugs, as well as with diseases affecting the central nervous system, peripheral nervous system, or lungs [7]. J. D. Fields A. Bhardwaj Neurosciences Critical Care Program, Department of Neurology, Oregon Health & Science University, Portland, OR, USA

P2X receptors are differentially expressed on vasopressin- and oxytocin-containing neurons in the supraoptic and paraventricular nuclei of rat hypothalamus

In the present study, the distribution of P2X receptor protein and colocalization of P2X receptors with vasopressin and oxytocin in the supraoptic and paraventricular nuclei of rat hypothalamus was studied using double-labeling fluorescence immunohistochemistry. The results showed that vasopressin-containing neurons expressed P2X(2), P2X(4), P2X(5) and P2X(6) receptor and oxytocin-containing neurons expressed P2X(2), P2X(4) and P2X(5) receptors in the supraoptic nucleus. In the paraventricular nucleus, vasopressin-containing neurons expressed P2X(4), P2X(5) and P2X(6) receptors, while oxytocin-containing neurons expressed P2X(4) receptors. This study provides the first evidence that P2X receptor subunits are differentially expressed on vasopressin- and oxytocin-containing neurons in the supraoptic and paraventricular nuclei, and hence, provides a substantial neuroanatomical basis for possible functional interactions between the purinergic and vasopressinergic systems, and the purinergic and oxytocinergic systems in the rat hypothalamus.

A role for the paraventricular nucleus of the hypothalamus in the autonomic control of heart and kidney

It is now well accepted that the sympathetic nervous system responds to specific afferent stimuli in a unique non-uniform fashion. The means by which the brain transforms the signals from a single type of receptor into an appropriate differential sympathetic output is discussed in this brief review. The detection of and response to venous filling are used for illustration. An expansion of blood volume has been shown in a number of species to increase heart rate reflexly via sympathetic nerves and this effect is primarily an action of volume receptors at the venous-atrial junctions of the heart. Stimulation of these volume receptors also leads to an inhibition of renal sympathetic nerve activity. Thus the reflex response to an increase in plasma volume consists of a distinctive unique pattern of sympathetic activity to maintain fluid balance. This reflex is dependent on neurones in the paraventricular nucleus (PVN). Neurones in the PVN show early gene activation on stimulation of atrial receptors, and a similar differential pattern of cardiac sympathetic excitation and renal inhibition can be evoked by activating PVN neurones. Cardiac atrial afferents selectively cause a PVN GABA neurone-induced inhibition within the PVN of PVN spinally projecting vasopressin-containing neurones that project to renal sympathetic neurones. A lesion of these spinally projecting neurones abolishes the reflex. With regard to the cardiac sympathetics, there is a population of PVN spinally projecting neurones that selectively increase heart rate by the release of oxytocin, a peptide pathway that has no action on renal sympathetic outflow. In heart failure the atrial reflex becomes blunted, and evidence is emerging that there is a downregulation of nitric oxide synthesis and reduced GABA activity in the PVN. How this might give rise to increased sympathetic activity associated with heart failure is briefly discussed.

Nicotinic receptor alpha subunits in magnocellular neurons of rat hypothalamus

Mab35 is a monoclonal antibody against one specific immunogenic region in alpha1, alpha3, alpha5 subunits of nicotinic acetylcholine receptors (N-AChR) of a variety of species. It has previously been claimed that N-AChR-like immunoreactivity (-LI) identified by mab35 is present in vasopressin-containing magnocellular neurons. However, we show here by double immunofluorescence labelling that mab35 immunoreactivity is predominantly localized to oxytocinergic rather than vasopressinergic magnocellular neurons. We further infer that mab35 predominantly stained the alpha3 and/or alpha5 subunits in rat oxytocinergic neurons, and suggest that the unbalanced distribution of these subunits may contribute to some specific physiological properties of oxytocinergic neurons.

Circasemiannual chronomics: half-yearly biospheric changes in their own right and as a circannual waveform

Geomagnetic activity has a strong half-yearly but no precise yearly component in its spectrum, as Armin Grafe suggested nearly half a century ago. We have postulated elsewhere that non-photic cycles such as those in geomagnetics may have signatures in the biosphere and vice versa that biological rhythms have likely counterparts in the physical environment. Accordingly, we document phenomena characterized by a prominent about half-yearly variation, re-analyzed to constitute the start of a transdisciplinary chronomic (time structural) map, aligning these conditions with a half-yearly cycle in the geomagnetic index K p. At least some biospheric phenomena fitted concomitantly with 1– and 0.5–year cosine curves exhibit an amplitude ( A) ratio of A 0.5–year/ A 1–year larger than unity. Methodologically, it is pertinent that even if data were read off published graphs, the resulting analyses were practically the same as those in the original data received subsequently. The main point is a circasemiannual pattern in status epilepticus, in several morbid oral conditions, in the cell density of vasopressin-containing neurons in the human suprachiasmatic nuclei (SCN), in circulating melatonin at middle latitudes at night during years of minimal solar activity or around noon at high latitudes, and in an unusual circasemiannual aspect of a birth-month-dependence of human longevity. Others have asked whether annual rhythms in human reproduction are biological, sociological or both. We show some other possibilities herein, involving the physical environment, hardly to be neglected in the case of open systems. As to almost certainly multifactorial circasemiannual rhythms, geomagnetics may also be a signal, a proxy or a putative, at least partial mechanism. Geomagnetic activity is related in its turn to solar and galactic activity, and may be a marker for other cyclic events that affect the biosphere. The similarity of cycle lengths in itself can only be a hint prompting the search for causal relations.

Regulation of rat APJ receptor messenger ribonucleic acid expression in magnocellular neurones of the paraventricular and supraopric nuclei by osmotic stimuli.

The novel apelin receptor (APJ receptor, APJR) has a restricted expression in the central nervous system suggestive of an involvement in the regulation of body fluid homeostasis. The endogenous ligand for APJR, apelin, is also highly concentrated in regions that are involved in the control of drinking behaviour. While the physiological roles of APJR and apelin are not fully known, apelin has been shown to stimulate drinking behaviour in rats and to have a regulatory effect on vasopressin release from magnocellular neurones of the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. To determine the role of APJR in the regulation of water balance, this study examined the effects of osmotic stimulation on the expression of APJR mRNA in the magnocellular PVN (mPVN) and SON of salt-loaded and water-deprived rats. Intake of 2% NaCl and water deprivation for 48 h induced expression of APJR mRNA in the mPVN and SON. Using dual-label in situ hybridization histochemistry, we also investigated whether APJR is colocalized within vasopressin neurones in control, salt-loaded and water-deprived rats. APJR mRNA was found to colocalize with a small population of vasopressin-containing magnocellular neurones in control and water-deprived rats. Salt-loading resulted in an increased colocalization of APJR and vasopressin mRNAs in the SON. These data verify a role for APJ receptors in body fluid regulation and suggest a role for apelin in the regulation of vasopressin-containing neurones via a local autocrine/paracrine action of the peptide.

Paraventricular vasopressin-containing neurons project to brain stem and spinal cord respiratory-related sites.

We studied in the rat projections of vasopressin-containing neurons of the paraventricular nucleus (PVN) to phrenic nuclei and to the pre-Botzinger complex (pre-BotC). In addition, we determined vasopressin receptor expression within the pre-BotC and the physiological effects of vasopressin on respiratory drive and arterial blood pressure when injected into the pre-BotC. Retrograde tracing with cholera toxin B subunit (CT-b) showed that a subpopulation of vasopressin-containing PVN neurons project to phrenic nuclei and the pre-BotC. The latter region, identified by expression of neurokinin-1 receptors, contained a subpopulation of neurons that were immunoreactive for the vasopressin type 1 receptor (V(1)R). Microinjection of vasopressin in the pre-BotC (0.2 nmol/200 nl) significantly increased diaphragm electromyographic activity and frequency discharge (P<0.05). In addition, vasopressin increased blood pressure and heart rate (P<0.05). These data indicate that PVN vasopressin-containing neurons innervate respiratory-related regions of the medulla oblongata and spinal cord and when vasopressin is released at these sites, it may increase respiratory drive via activation of the distinct V(1)R.

Gradual reappearance of post-hibernation circadian rhythmicity correlates with numbers of vasopressin-containing neurons in the suprachiasmatic nuclei of European ground squirrels.

European ground squirrels (Spermophilus citellus) in outside enclosures show suppressed circadian rhythmicity in body temperature patterns during the first days of euthermia after hibernation. This may reflect either gradual reappearance of circadian rhythmicity following suppressed functioning of the circadian system during hibernation, or it may reflect transient days during re-entrainment of the circadian system which, during hibernation, has drifted out of phase with the environmental light-dark cycle. Here we report that animals kept under continuous dim light conditions also showed absence of circadian rhythmicity in activity and body temperature in the first 5-15 days after hibernation. After post-hibernation arrhythmicity, spontaneous circadian rhythms re-appeared gradually and increased daily body temperature range. Numbers of arginine-vasopressin immunoreactive neurons in the suprachiasmatic nuclei correlated positively with individual circadian rhythmicity and increased gradually over time after hibernation. Furthermore, circadian rhythmicity was enhanced rather than suppressed after exposure to a light-dark cycle but not after a single 1-h light pulse (1,700 lux). The results support the view that the functioning of the circadian system in the European ground squirrel is suppressed during hibernation at low temperatures and that it requires several days of euthermia to resume its summer function.

5-HT2AReceptors Stimulate ACTH, Corticosterone, Oxytocin, Renin, and Prolactin Release and Activate Hypothalamic CRF and Oxytocin-Expressing Cells

The 5-HT(2A/2C) agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI) stimulates hypothalamic neurons to increase the secretion of several hormones. This study addressed two questions: 1) are the neuroendocrine effects of DOI mediated via activation of 5-HT(2A) receptors; and 2) which neurons are activated by 5-HT(2A) receptors. The 5-HT(2A) antagonist (+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidinemethanol (MDL 100,907; 0.001, 0.01, or 0.1 mg/kg, s.c.) was administered before rats were challenged with DOI (2.5 mg/kg, i.p.). MDL 100,907 produced a dose-dependent inhibition (ED(50) congruent with 0.001 mg/kg) of the effect of DOI on plasma levels of ACTH, corticosterone, oxytocin, prolactin, and renin without altering basal hormone levels. Complete blockade of the effect of DOI was achieved for all hormones at MDL 100,907 doses of 0.01-0.1 mg/kg. In a parallel experiment, DOI was injected 2 hr before killing to determine its effects on the expression of Fos, the product of the immediate early gene c-fos. DOI induced an increase in Fos immunoreactivity in corticotropin-releasing factor (CRF) and in oxytocin-expressing neurons but not in vasopressin-containing neurons in the hypothalamic paraventricular nucleus or CRF cells in the amygdala. Pretreatment with MDL 100,907 (0.1 mg/kg, s.c.) blocked the DOI-induced increase in Fos expression in all regions including the hypothalamus, amygdala (central and corticomedial), bed nucleus of the stria terminalis, and prefrontal cortical regions. The combined neuroanatomical and pharmacological observations suggest that the neuroendocrine responses to DOI are mediated by activation of neurons in the hypothalamic paraventricular nucleus and associated circuitry. Furthermore, selective activation of 5-HT(2A) receptors mediates the hormonal and Fos-inducing effects of DOI.

Intracerebroventricular injection of senktide-induced Fos expression in vasopressin-containing hypothalamic neurons in the rat

Intracerebroventricular injection of senktide, a selective agonist for neurokinin B receptor (NK3), induced Fos expression in many neurons of the rat hypothalamus. Fos-positive neurons were predominantly present in the supraoptic and paraventricular hypothalamic nuclei, and some of them were seen in the lateral preoptic area, lateral hypothalamic area, arcuate nucleus, perifornical region, posterior hypothalamic area, circular nucleus, and along relatively large blood vessels (lateral hypothalamic perivascular nucleus) in the anterior hypothalamus. A double labeling study was performed to examine if vasopressin-containing neurons in the hypothalamus could be activated by the treatment. Neurons with both Fos-like immunoreactivity (-LI) and vasopressin-LI were found in the paraventricular nucleus, supraoptic nucleus, circular nucleus and lateral hypothalamic perivascular nucleus. In the supraoptic nucleus, about 87% of vasopressin-containing neurons exhibited Fos-LI, which corresponded to about 64% of Fos-positive neurons in the nucleus. In the paraventricular nucleus, about 80% of vasopressin-like immunoreactive neurons exhibited Fos-LI, which constituted about 51% of the total population of Fos-positive neurons in the region. The results suggest that NK3 receptor may be involved in the modulation of release of vasopressin from the hypothalamus in the rat.

Activation of an Inwardly Rectifying K+ Conductance by Orphanin-FQ/Nociceptin in Vasopressin-Containing Neurons

The orphanin-FQ/nociceptin (OFQ/N) receptor (previously, ORL₁, LC132) has been shown to be coupled to an inwardly rectifying K⁺ conductance in several neuronal populations. Although OFQ/N receptor mRNA is densely expressed in the supraoptic nucleus (SON), little is known about its coupling to effector system(s). The present study examined the effects of OFQ/N on guinea pig magnocellular neurons within the SON using intracellular recording from hypothalamic slices. In the presence of tetrodotoxin, OFQ/N hyperpolarized 48 of 48 SON magnocellular neurons, 24 of which were subsequently identified by immunocytochemistry as arginine vasopressin positive (AVP⁺). Nineteen of the 48 SON neurons, including 7 which were AVP⁺, responded to OFQ/N with an outward current that reversed at the K⁺ equilibrium potential (E_K+) and a decrease in slope resistance consistent with the activation of an inwardly rectifying K⁺ channel. In 4 of these neurons, BaCl₂ significantly attenuated both the hyperpolarization and the decrease in slope resistance induced by OFQ/N. Twenty-one SON neurons, 13 of which were AVP⁺, responded to OFQ/N with an increase in slope resistance which did not reverse at E_K+. An additional 5 neurons (2 were AVP⁺) were treated with the gap junction blocking agent carbenoxolone (CARB). CARB induced a small hyperpolarization, increased slope resistance and significantly reduced the subsequent OFQ/N-induced hyperpolarization. However, when the CARB and CARB plus OFQ/N hyperpolarizations were summed in these 5 cells, they were no different than the OFQ/N hyperpolarization alone. The effect of two putative OFQ/N receptor antagonists was also evaluated. The ĸ₃-opioid antagonist naloxone benzoylhydrazone was without effect (n = 3), and the 13-amino-acid [Phe¹Ψ(CH₂-NH)Gly²]OFQ/N(1–13)NH₂ OFQ/N analog produced a small hyperpolarization on its own in addition to partially antagonizing the effects of OFQ/N (n = 3). Taken together, these results suggest that OFQ/N acts upon SON neurons through two mechanisms, one which hyperpolarizes the neuron by activating an inwardly rectifying K⁺ conductance, and another which may increase membrane resistance by closing the low-resistance gap junctions.

Co-localization of interleukin-1 receptor type I and interleukin-1 receptor antagonist with vasopressin in magnocellular neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus

Interleukin-1 receptor type I and interleukin-I receptor antagonist were found in magnocellular neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus by immunohistochemical detection. Double-labelling experiments revealed that both proteins occurred in vasopressin-containing neurons. A similar distribution pattern was observed in a group of vasopressin-positive accessory magnocellular neurons. Axons emanating from the interleukin-1 receptor type I- and interleukin-1 receptor antagonist-immunoreactive neuronal cell bodies could be seen within the hypothalamic nuclei, and varicosities expressing interleukin-1 receptor antagonist immunoreactivity were observed in the internal zone of the median eminence, as well as in the hypothalamo-pituitary projection. The co-localization of interleukin-1 receptor type I with vasopressin is in agreement with findings that interleukin-1 has a stimulatory effect on vasopressin synthesis and release. The hypothalamic neurons may serve as a source of interleukin-1 receptor antagonist to balance the effects of interleukin-1.

Pituitary adenylate cyclase-activating polypeptide (PACAP): a novel regulator of vasopressin-containing neurons

Pituitary adenylate cyclase-activating polypeptide (PACAP) was localized in nerve terminals that innervate arginine-vasopressin (AVP)-containing neurons in the rat hypothalamic supraoptic nucleus (SON). PACAP receptor (PACAPR) mRNA was expressed at high-levels in AVP-containing neurons in the SON, but at very low-levels in oxytocin-containing neurons. PACAPR-like immunoreactivity was found in SON and it was observed in the post-synaptic membranes as well as on the rough endoplasmic reticulum and cytoplasmic matrices in the magnocellular neurons. Doses of PACAP in the nanomolar range increased cytoplasmic Ca 2+ concentrations ([Ca 2+] i) in AVP-containing neurons; the increase in [Ca 2+] i was inhibited by a protein kinase A blocker. These findings suggest that PACAP serves as a transmitter and/or modulator and the activation of PACAPR stimulates a cAMP-protein kinase A pathway which in turn evokes the Ca 2+ signaling system. It is hypothesized that PACAP regulates the functions of AVP-containing neurons which participate in the control of plasma osmolarity and blood pressure.

2320 Calcium-binding proteins are differentially localized in oxytocin- and vasopressin-containing neurons

2320 Calcium-binding proteins are differentially localized in oxytocin- and vasopressin-containing neurons

Calcium-binding proteins are differentially localized in oxytocin-and vasopressin-containing neurons

Calcium-binding proteins are differentially localized in oxytocin-and vasopressin-containing neurons