Arginine Vasopressin Neurons Research Articles

Oligodendroglial alpha-synucleinopathy and MSA-like cardiovascular autonomic failure: Experimental evidence

Multiple system atrophy (MSA) is a fatal, rapidly progressive neurodegenerative disease with limited symptomatic treatment options. Discrimination of MSA from other degenerative disorders crucially depends on the presence of early and severe cardiovascular autonomic failure (CAF). We have previously shown that neuropathologic lesions in the central autonomic nuclei similar to the human disease are present in transgenic MSA mice generated by targeted oligodendroglial overexpression of α-syn using the PLP promoter. We here explore whether such lesions result in abnormalities of heart rate variability (HRV) and circadian rhythmicity which are typically impaired in MSA patients.HRV analysis was performed in five month old transgenic PLP-α-syn (tg) MSA mice and age-matched wild type controls. Decreased HRV and alterations in the circadian rhythmicity were detected in the tg MSA group. The number of choline-acetyltransferase-immunoreactive neurons in the nucleus ambiguus was significantly decreased in the tg group, whereas the levels of arginine-vasopressin neurons in the suprachiasmatic and paraventricular nucleus were not affected. Our finding of impaired HRV and circadian rhythmicity in tg MSA mice associated with degeneration of the nucleus ambiguus suggests that a cardinal non-motor feature of human MSA can be reproduced in the mouse model strengthening its role as a valuable testbed for studying selective vulnerability and assessing translational therapies.

Action of glucagon-like peptide 1 and glucose levels on corticotropin-releasing factor and vasopressin gene expression in rat hypothalamic 4B cells

Corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) are the two major regulatory peptides in the hypothalamic–pituitary–adrenal (HPA) axis. Glucagon-like peptide-1 (GLP-1), an important regulator of metabolism or energy homeostasis, is implicated in the regulation of the HPA axis in response to stress and may act directly on CRF and AVP neurons. To elucidate the direct regulation of CRF and AVP genes by GLP-1 in the hypothalamus, we examined the effect of GLP-1 in hypothalamic 4B cells, which show the characteristics of hypothalamic paraventricular nucleus neurons. The mRNA of GLP-1 receptor was detected in 4B cells by RT-PCR. GLP-1 significantly stimulated both CRF and AVP mRNA levels. Cells were transfected with CRF or AVP promoter to examine the activity of each promoter. GLP-1 directly stimulated the activities of both CRF and AVP promoters in hypothalamic 4B cells. Basal promoter activities of both CRF and AVP were increased in higher glucose medium. In addition, CRF and AVP promoter activities were increased by GLP-1 in standard or low glucose medium but not in higher glucose medium. An equimolar concentration of metabolically inactive l-glucose failed to mimic the effect of d-glucose, indicating that the event was caused by changes in glucose levels and not by hyperosmolality. Together, these data suggest that GLP-1 would contribute to stress responses through activation of CRF and AVP genes in the hypothalamic cells. Hyperglycemia may be one of the stressors enhancing the syntheses of CRF and AVP in the hypothalamus.

Expression and distribution of TRPV2 in rat brain

Transient receptor potential (TRP) proteins are non-selective cation channels that mediate sensory transduction. The neuroanatomical localization and the physiological roles of isoform TRPV2 in the rodent brain are largely unknown. We report here the neuroanatomical distribution of TRPV2 in the adult male rat brain focusing on the hypothalamus and hindbrain regions involved in osmoregulation, autonomic function and energy metabolism. For this we utilized immunohistochemistry combined with brightfield microscopy. In the forebrain, the densest immunostaining was seen in both the supraoptic nucleus (SON) and the magnocellular division of the paraventricular nucleus (PVN) of the hypothalamus. TRPV2 immunoreactivity was also seen in the organum vasculosum of the lamina terminalis, the median preoptic nucleus and the subfornical organ, in addition to the arcuate nucleus of the hypothalamus (ARH), the medial forebrain bundle, the cingulate cortex and the globus pallidus to name a few. In the hindbrain, intense staining was seen in the nucleus of the solitary tract, hypoglossal nucleus, nucleus ambiguous, and the rostral division of the ventrolateral medulla (RVLM) and some mild staining in the area prostrema. To ascertain the specificity of the TRPV2 antibody used in this paper, we compared the TRPV2 immunoreactivity of wildtype (WT) and knockout (KO) mouse brain tissue. Double immunostaining with arginine vasopressin (AVP) using confocal microscopy showed a high degree of colocalization of TRPV2 in the magnocellular SON and PVN. Using laser capture microdissection (LCM) we also show that AVP neurons in the SON contain TRPV2 mRNA. TRPV2 was also co-localized with dopamine beta hydroxylase (DBH) in the NTS and the RVLM of the hindbrain. Based on our results, TRPV2 may play an important role in several CNS networks that regulate body fluid homeostasis, autonomic function, and metabolism.

DLK1 Is a Somato-Dendritic Protein Expressed in Hypothalamic Arginine-Vasopressin and Oxytocin Neurons

Delta-Like 1 Homolog, Dlk1, is a paternally imprinted gene encoding a transmembrane protein involved in the differentiation of several cell types. After birth, Dlk1 expression decreases substantially in all tissues except endocrine glands. Dlk1 deletion in mice results in pre-natal and post-natal growth deficiency, mild obesity, facial abnormalities, and abnormal skeletal development, suggesting involvement of Dlk1 in perinatal survival, normal growth and homeostasis of fat deposition. A neuroendocrine function has also been suggested for DLK1 but never characterised. To evaluate the neuroendocrine function of DLK1, we first characterised Dlk1 expression in mouse hypothalamus and then studied post-natal variations of the hypothalamic expression. Western Blot analysis of adult mouse hypothalamus protein extracts showed that Dlk1 was expressed almost exclusively as a soluble protein produced by cleavage of the extracellular domain. Immunohistochemistry showed neuronal DLK1 expression in the suprachiasmatic (SCN), supraoptic (SON), paraventricular (PVN), arcuate (ARC), dorsomedial (DMN) and lateral hypothalamic (LH) nuclei. DLK1 was expressed in the dendrites and perikarya of arginine-vasopressin neurons in PVN, SCN and SON and in oxytocin neurons in PVN and SON. These findings suggest a role for DLK1 in the post-natal development of hypothalamic functions, most notably those regulated by the arginine-vasopressin and oxytocin systems.

Paraventricular Nucleus Neuropeptide Expression in Huntington's Disease Patients

Neuroendocrine, metabolic and autonomic nervous system dysfunctions are prevalent among patients with Huntington's disease (HD) and may underlie symptoms such as depression, weight loss and autonomic failure. Using post-mortem paraffin-embedded tissue, we assessed the integrity of the major neuropeptide populations in the paraventricular nucleus (PVN)-the hypothalamic neuroendocrine and autonomic integration center-in HD patients. The number corticotropin-releasing hormone, cocaine- and amphetamine-regulated transcript, arginine vasopressin and oxytocin immunoreactive (ir) neurons did not differ between HD patients and control subjects. However, the significant positive correlation between arginine vasopressin and oxytocin ir neurons in control subjects (P = 0.036) was absent in patients. Corticotropin-releasing hormone mRNA levels were 68% higher in HD patients (P = 0.046). Thyrotropin-releasing hormone mRNA levels did not differ between HD patients and control subjects, although a negative correlation with disease duration was present in the former (P = 0.036). These findings indicate that the PVN is largely unaffected in HD patients. However, our findings suggest that hypothalamic-pituitary-thyroid axis activity may alter during the course of the disease and that autonomic nervous system dysfunction might partly arise from an imbalance between arginine vasopressin and oxytocin neurons in the PVN.

BiP mRNA expression is upregulated by dehydration in vasopressin neurons in the hypothalamus in mice

The immunoglobulin heavy chain binding protein (BiP) is an endoplasmic reticulum (ER) chaperone that facilitates the proper folding of newly synthesized secretory and transmembrane proteins. Here we report that BiP mRNA was expressed in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus in wild-type mice under basal conditions. Dual in situ hybridization in the SON and PVN demonstrated that BiP mRNA was expressed in almost all the neurons of arginine vasopressin (AVP), an antidiuretic hormone. BiP mRNA expression levels were increased in proportion to AVP mRNA expression in the SON and PVN under dehydration. These data suggest that BiP is involved in the homeostasis of ER function in the AVP neurons in the SON and PVN.

Poly(A) Tail Length of Neurohypophysial Hormones Is Shortened Under Endoplasmic Reticulum Stress

Familial neurohypophysial diabetes insipidus (FNDI) is caused by mutations in the gene locus of arginine vasopressin (AVP), an antidiuretic hormone. Although the carriers are normal at birth, polyuria and polydipsia appear several months or years later. Previously, we made mice possessing a mutation causing FNDI and reported that the mice manifested progressive polyuria as do the patients with FNDI. Here, we report that decreases in AVP mRNA expression in the supraoptic nucleus were accompanied by shortening of the AVP mRNA poly(A) tail length in the FNDI mice, a case in which aggregates accumulated in the endoplasmic reticulum (ER) of the hypothalamic AVP neurons. Expression levels of AVP heteronuclear RNA in the supraoptic nucleus, a sensitive indicator for gene transcription, were not significantly different between FNDI and wild-type mice. Incubation of hypothalamic explants of wild-type mice with ER stressors (thapsigargin and tunicamycin) caused shortening of the poly(A) tail length of AVP and oxytocin mRNA, accompanied by decreases in their expression. On the other hand, an ER stress-reducing molecule (tauroursodeoxycholate) increased the poly(A) tail length as well as the expression levels of AVP and oxytocin mRNA. These data reveal a novel mechanism by which ER stress decreases poly(A) tail length of neurohypophysial hormones, probably to reduce the load of unfolded proteins.

Persistent Increase in Hypothalamic Arginine Vasopressin Gene Expression During Protracted Withdrawal from Chronic Escalating-Dose Cocaine in Rodents

Arginine vasopressin (AVP) from the paraventricular nucleus (PVN) of hypothalamus has important roles in regulation of the hypothalamic-pituitary-adrenal (HPA) axis and stress-related behaviors during chronic stress. It is unknown, however, whether AVP in the PVN is involved in the modulation of HPA activity after chronic cocaine exposure. Here, we examined the gene expression alterations of AVP in the hypothalamus, and V1b receptor and pro-opiomelanocortin (POMC) in the anterior pituitary, as well as HPA hormonal changes, in Fischer rats after chronic cocaine and withdrawal, using two different chronic (14-day) 'binge' pattern administration regimens: steady-dose cocaine (SDC, 45 mg/kg/day) and escalating-dose cocaine (EDC, 45 up to 90 mg/kg/day). There was a significant (7-fold) plasma adrenocorticotropic hormone (ACTH) elevation after chronic EDC (but not SDC), coupled with increased V1b and POMC mRNA levels in the anterior pituitary. From acute (1-day) to protracted (14-day) withdrawal from chronic EDC (but not from SDC), we found persistent elevations of both plasma ACTH and corticosterone levels and AVP mRNA levels in the PVN. Selective V1b antagonist SSR149415 (5 mg/kg) attenuated acute withdrawal-induced HPA activation after EDC. To study potential roles of endogenous opioids in modulating the AVP gene, we administered naloxone (1 mg/kg); we found that opioid receptor antagonism increased AVP mRNA levels in cocaine-naive rats, but not in cocaine-withdrawn rats, suggesting less tonic opioid inhibition of PVN AVP neurons after chronic EDC. To assess the effects of cocaine withdrawal on sub-populations of PVN AVP neurons, we utilized AVP-enhanced green fluorescent protein (EGFP) promoter transgenic mice and found that acute withdrawal following chronic EDC increased the number of AVP-EGFP neurons in the parvocellular PVN (pPVN). These results suggest that during protracted withdrawal, enhanced pPVN AVP gene expression is associated with persistent elevations of basal HPA activity; a hyposensitivity of PVN AVP gene expression to naloxone is indicative of reduced opioidergic tone. Our studies indicate that the AVP and its V1b receptor system may be a potential therapeutic target for treating anxiety and depressive symptoms associated with cocaine addiction.

Possible contribution of pannexin channel to ATP-induced currents in vitro in vasopressin neurons isolated from the rat supraoptic nucleus

Release of arginine vasopressin (AVP) from magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus (SON) is controlled by the electrical activity of these neurons. ATP plays a crucial role in the regulation of SON MNCs by activating the purinergic P2X and P2Y receptors. Recent reports of interaction between P2X receptors and pannexin channels have provided new insights into the physiology of the central nervous system; however, the function of pannexin channels has not been assessed in AVP neurons. In the present study, we examined the possible contribution of the pannexin channel in ATP-induced responses in SON AVP neurons. We used the whole-cell patch-clamp technique in isolated rat SON MNCs that express an AVP-enhanced green fluorescent protein transgene. The ATP-induced current was inhibited in a concentration-dependent manner by pannexin channel blockers carbenoxolone and mefloquine, whereas the connexin channel blockers flufenamic acid and lanthanum had no effect. Multi-cell reverse transcriptase-polymerase chain reaction experiments confirmed the existence of pannexin-1 mRNA in AVP neurons. The involvement of the ATP-activated transient receptor potential vanilloid and acid-sensing ion channels was excluded. These results suggest that pannexin channels in SON AVP neurons are involved in the regulatory mechanisms of neuronal activity.

Ghrelin stimulates corticotropin-releasing factor and vasopressin gene expression in rat hypothalamic 4B cells

Corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) play a central role in regulating the stress response. In response to stress, CRF and AVP neurons in the hypothalamic paraventricular nucleus secrete the peptides to stimulate the release of adrenocorticotropic hormone from the anterior pituitary. Ghrelin, an endogenous ligand of the growth hormone-releasing peptide receptors (GHSR), has been shown to stimulate the release of CRF and AVP by rat hypothalamic explants. However, little is known about the ability of the ghrelin signaling pathways to activate the CRF and AVP genes in the hypothalamus. In the present study, we examined the direct effect of ghrelin on CRF and AVP gene expression in hypothalamic 4B cells, which show the characteristics of the hypothalamic parvocellular paraventricular nucleus neurons. Cells were transfected with CRF or AVP promoter to examine the activity of each promoter. Ghrelin stimulated the promoter activities and mRNA levels for both CRF and AVP. The involvement of a protein kinase pathway was examined using inhibitors. Protein kinase A and phospholipase C pathways were shown to be involved in ghrelin-induced increases in both CRF and AVP promoter activities. GHSR type 1a (GHSR1a) mRNA levels were also increased by ghrelin, and these ghrelin-induced levels were suppressed by a GHSR1a antagonist. Thus, ghrelin-dependent pathways are involved in the regulation of CRF and AVP gene expression in the hypothalamus: ghrelin, an orexigenic hormone, stimulates CRF, an anorexigenic/anxiogenic factor in the hypothalamus, resulting in hypothalamic–pituitary–adrenal axis activation to stimulate the release of glucocorticoids.

The Notch effector gene Hes1 regulates migration of hypothalamic neurons, neuropeptide content and axon targeting to the pituitary

Proper development of the hypothalamic-pituitary axis requires precise neuronal signaling to establish a network that regulates homeostasis. The developing hypothalamus and pituitary utilize similar signaling pathways for differentiation in embryonic development. The Notch signaling effector gene Hes1 is present in the developing hypothalamus and pituitary and is required for proper formation of the pituitary, which contains axons of arginine vasopressin (AVP) neurons from the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON). We hypothesized that Hes1 is necessary for the generation, placement and projection of AVP neurons. We found that Hes1 null mice show no significant difference in cell proliferation or death in the developing diencephalon at embryonic day 10.5 (e10.5) or e11.5. By e16.5, AVP cell bodies are formed in the SON and PVN, but are abnormally placed, suggesting that Hes1 may be necessary for the migration of AVP neurons. GAD67 immunoreactivity is ectopically expressed in Hes1 null mice, which may contribute to cell body misplacement. Additionally, at e18.5 Hes1 null mice show continued misplacement of AVP cell bodies in the PVN and SON and additionally exhibit abnormal axonal projection. Using mass spectrometry to characterize peptide content, we found that Hes1 null pituitaries have aberrant somatostatin (SS) peptide, which correlates with abnormal SS cells in the pituitary and misplaced SS axon tracts at e18.5. Our results indicate that Notch signaling facilitates the migration and guidance of hypothalamic neurons, as well as neuropeptide content.

Integration Between Different Hypothalamic Nuclei Involved in Stress and GnRH Secretion in the Ewe

This study investigated possible integrated links in the neuroanatomical pathways through which the activity of neurones in the paraventricular nucleus and arcuate nucleus may modulate suppression of gonadotrophin-releasing hormone (GnRH) secretion during stressful situations. Double-label immunofluorescence and laser scanning confocal microscopy were used to examine the hypothalamic sections from the follicular phase ewes. Noradrenergic terminals were in close contact with 65.7 ± 6.1% corticotrophin-releasing hormone (CRH) and 84.6 ± 3.2% arginine vasopressin (AVP) cell bodies in the paraventricular nucleus but not with β-endorphin cell bodies in the arcuate nucleus. Furthermore, γ-amino butyric acid (GABA) terminals were close to 80.9 ± 3.5% CRH but no AVP cell bodies in the paraventricular nucleus, as well as 60.8 ± 4.1%β-endorphin cell bodies in the arcuate nucleus. Although CRH, AVP and β-endorphin cell terminals were identified in the medial pre-optic area, no direct contacts with GnRH cell bodies were observed. Within the median eminence, abundant CRH but not AVP terminals were close to GnRH cell terminals in the external zone; whereas, β-endorphin cells and terminals were in the internal zone. In conclusion, neuroanatomical evidence is provided for the ewe supporting the hypothesis that brainstem noradrenergic and hypothalamic GABA neurones are important in modulating the activity of CRH and AVP neurones in the paraventricular nucleus, as well as β-endorphin neurones in the arcuate nucleus. These paraventricular and arcuate neurones may also involve interneurones to influence GnRH cell bodies in medial pre-optic area, whereas the median eminence may provide a major site for direct modulation of GnRH release by CRH terminals.

(Re-)activation of neurons in aging and dementia: Lessons from the hypothalamus

Our hypothesis is that there is ‘wear and tear’ in the brain, which is the basis of the process of aging, but that stimulation of brain function may slow down brain aging and diminish the risk for neurodegenerative diseases such as Alzheimer's disease (AD), possibly by activating repair mechanisms. Evidence supporting this hypothesis is presented in this review. During normal aging and in AD, cell loss is not as prominent a phenomenon as is often presumed. In fact, unaltered neuronal numbers have been reported in many brain areas in AD, e.g. in the nucleus basalis of Meynert (NBM) where the number of large neurons decreases while that of small neurons increases. Decreased neuronal activity is an essential characteristic of AD, and a substantial decrease of cerebral glucose metabolism may even precede cognitive impairments. Some hypothalamic neurons remain intact and active during the process of aging, others become even hyperactive, which may lead to disorders. Arginine vasopressin (AVP) levels were found to be higher in the elderly than in young subjects. There is an age-related, sex-dependent activation of the AVP neurons in the supraoptic nucleus (SON) and in the paraventricular nucleus (PVN), which may be the basis of analogous changes in the prevalence of hypertension and hyponatraemia in the elderly. No significant functional loss of magnocellular hypothalamic neurosecretory neurons were found in the SON or PVN in AD. The activity of the corticotrophin releasing hormone (CRH) neurons in the hypothalamic PVN is the basis for the activity of the hypothalamo-pituitary-adrenal (HPA) axis, which is activated during aging in a sex-dependent way, and even more activated in AD. The activated HPA axis is a risk for depression. Environmental stimulation increases brain reserve. An increase in time spent on intellectual activities was associated with a significant decrease in probability to get AD, and occupation has even a stronger indication of diminished risk for dementia. A series of observations showed that a dysfunctional clock may underlie the disordered rhythms in AD. Additional bright light improved the rest–activity rhythms, while giving bright light and/or melatonin to AD patients ameliorated the progression of cognitive and noncognitive symptoms. This implies that neurons affected by AD can still be reactivated if the right stimuli are applied. Unknown diffusible factors from the neural stem cells improve the survival of aged and degenerating neurons in postmortem human brain slice cultures. Gene therapy with nerve growth factor aimed at the NBM showed metabolic activation of various brain regions. A microarray study of the prefrontal cortex in the course of AD revealed an increased expression of genes related to synaptic activity and changes in plasticity during the very early pre-symptomatic stages, which is proposed to represent a coping mechanism against increased soluble β-amyloid levels. In brief, these examples of the ‘use it or lose it’ principle during the course of aging or AD now provide novel targets for the development of therapeutic strategies aiming at the prevention and treatment of AD.

Diurnal changes of arginine vasopressin-enhanced green fluorescent protein fusion transgene expression in the rat suprachiasmatic nucleus

We have recently developed a new transgenic rat line expressing an arginine vasopressin (AVP)-enhanced green fluorescent protein (eGFP) fusion gene. The AVP-eGFP transgene is expressed in the paraventricular (PVN) and supraoptic (SON) nuclei and the suprachiasmatic nucleus (SCN) of the hypothalamus. Transgene expression in the PVN and SON showed an exaggerated response to salt loading and nociceptive stimulation. However, the expression of the AVP-eGFP transgene in the SCN did not change under these stressful conditions. Here, we examined daily profiles of the expression of the AVP-eGFP transgene in the SCN in comparison with the endogenous AVP and Period (Per1 and Per2) genes. While all of these genes elicited diurnal patterns of expression in the SCN, the rate of rhythmic change of transgene expression was significantly greater than that of the endogenous AVP gene. We also examined the effect of a light stimulus on the expression of the AVP-eGFP, AVP, Per1 and Per2 genes in the SCN of transgenic rats. Ninety minutes after a light stimulus, AVP-eGFP mRNA and AVP hnRNA levels in the SCN were significantly decreased, while Per2 mRNA levels were significantly increased. In addition, we observed the eGFP fluorescence in the SCN and recorded the electrophysiological properties of a dissociated SCN eGFP-positive neuron. The AVP-eGFP transgenic rat is a useful animal model to study the diurnal change and dynamics of the AVP system, and enables the facile identification of SCN AVP neurons both in vivo and in vitro.

Modulators of BK and SK channels alter electrical activity in vitro in single vasopressin neurons isolated from the rat supraoptic nucleus

Release of arginine vasopressin (AVP) from magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus (SON) is controlled by the electrical activities of the MNCs. Ca 2+-activated K + channels, such as the BK and SK channels, are K +-selective ion channels that are activated in response to increased intracellular calcium concentrations. Intrinsic affinities for Ca 2+ permit these channels to exert a negative feedback effect on cellular excitability. In the present study, we used the whole-cell patch-clamp technique to examine the effects of BK or SK channel modulators on neuronal activity in single isolated rat SON MNCs that express an AVP-enhanced green fluorescent protein (eGFP) transgene. Application of BK or SK channel activators abolished the action potentials and induced hyperpolarization. In contrast, the number of action potentials was significantly increased after application of BK or SK channel blockers. Our results suggest that BK and SK channels in AVP neurons may play a role in the regulatory mechanisms of neural activity.

Acid‐sensing ion channels in rat hypothalamic vasopressin neurons of the supraoptic nucleus

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.

Differential immunoreactivity of glucocorticoid receptors and vasopressin in neurons of the anterior and medial parvocellular subdvisions of the hypothalamic paraventricular nucleus

arginine-vasopressin in the parvocellular neurons of the hypothalamic paraventricular nucleus is known to play an important role in the control of the hypothalamo-pituitary–adrenal axis. In the present study, we verify plasma corticosterone levels, the distribution of glucocorticoid receptor- and arginine-vasopressin-positive neurons, and the co-localization of both glucocorticoid receptors and arginine-vasopressin in neurons in the anterior and medial parvocellular subdivisions of the paraventricular nucleus after manipulations of the hypothalamus–pituitary–adrenal axis. Normal, sham surgery, and adrenalectomized male rats were subjected to intraperitoneal injections of saline or dexamethasone to measure plasma corticosterone levels by a radioimmunoassay. We also examined arginine-vasopressin and glucocorticoid receptor immunofluorescence in sections from the paraventricular nucleus. Our results showed that the immunoreactivity of arginine-vasopressin neurons increased in the anterior parvocellular subdivision and decreased in the medial parvocellular subdivision from adrenalectomized rats treated with dexamethasone. On the other hand, we showed that the immunoreactivity of glucocorticoid receptors increased in the anterior and medial parvocellular subdivisions of these same animals. However, the immunoreactivity of glucocorticoid receptors is higher in the medial parvocellular than anterior parvocellular subdivision. The co-localization of arginine-vasopressin and glucocorticoid receptors was found only in the medial parvocellular subdivision. These findings indicate that glucocorticoids have direct actions on arginine-vasopressin-positive neurons in the medial parvocellular but not anterior parvocellular subdivision. There is a differentiated pattern of arginine-vasopressin-positive neuron expression between the anterior and medial parvocellular subdivisions.

Mechanisms Underlying Progressive Polyuria in Familial Neurohypophysial Diabetes Insipidus

Familial neurohypophysial diabetes insipidus (FNDI), an autosomal dominant disorder, is mostly caused by mutations in the gene of neurophysin II (NPII), the carrier protein of arginine vasopressin (AVP). The analyses of knock-in mice expressing a mutant NPII that causes FNDI in humans demonstrated that polyuria progressed substantially in the absence of loss of AVP neurones. Morphological analyses revealed that inclusion bodies were present in the AVP neurones in the supraoptic nucleus and that the size and numbers of inclusion bodies gradually increased in parallel with the increases in urine volume. Electron microscopic analyses showed that aggregates existed in the endoplasmic reticulum (ER) of AVP neurones. These data suggest that cell death is not the primary cause of polyuria in FNDI, and that the aggregate formation in the ER is likely to be related to the pathogenesis of the progressive polyuria.

Central angiotensin I increases fetal AVP neuron activity and pressor responses

Angiotensin (Ang) II plays a critical role in cardiovascular homeostasis and neuroendocrine regulation. Little is known about whether central angiotensin-converting enzyme (ACE) is functional in the fetal brain. We investigated cardiovascular and neuroendocrinological responses to intracerebroventricular (icv) application of Ang I in the chronically prepared near-term ovine fetus in utero and examined the action sites marked by c-fos expression in the fetal hypothalamus. ACE mRNA was detected in the specific central areas. Intracerebroventricular Ang I significantly increased fetal blood pressure and c-fos expression in the supraoptic nuclei (SON) and the paraventricular nuclei (PVN) in the hypothalamus, accompanied by an increase of fetal plasma arginine vasopressin (AVP). Double labeling demonstrated that AVP neurons in the fetal SON and PVN were expressing c-fos. Captopril, an inhibitor of ACE, significantly suppressed fetal pressor responses and plasma AVP. Double labeling experiments showed colocalization of AT(1) receptor (AT(1)R) and c-fos expression in both SON and PVN following icv Ang I. The results indicate that central endogenous ACE has been functional at least at the last third of gestation and the endogenous brain renin-angiotensin system-mediated pressor responses and AVP release via AT(1)Rs by acting at the sites consistent with the cardiovascular network in the hypothalamus.

Gender-Dependent Effects of Early Maternal Separation and Variable Chronic Stress on Vasopressinergic Activity and Glucocorticoid Receptor Expression in Adult Rats

The aim of the present study was to investigate the influence of early maternal separation on Fos, arginine vasopressin (AVP) and glucocorticoid receptor (GR) expression in the medial parvocellular portion of the paraventricular hypothalamic nucleus (PaMP), and GR expression in the hippocampus of adult male and female rats subjected to variable chronic stress (VCS). Male and female Wistar rats were isolated 4.5 h daily, during the first 3 weeks of life. At 48 days of age, the rats were exposed to VCS. Nonmaternally separated (NMS) females had a higher number of activated AVP neurons than NMS male rats. Maternally separated (MS) females subjected to VCS also showed a higher number of Fos/AVP double-labeled neurons than males with the same treatment. Males and females subjected to early maternal separation and VCS, compared with the MS animals, showed a decrease in the expression of GR in the PaMP. As regards GR expression in the hippocampus, MS animals subjected to VCS as adults, both males and females, showed an increase in GR expression in the subfields CA1, CA2 and CA3. The increase in AVP-immunoreactive neurons coexpressing Fos in response to stress in females exposed to early maternal separation suggests that perhaps early life stress results in a more reactive neuroendocrine stress response in females. Furthermore, our results demonstrate that the different anatomical levels of the hypothalamic-pituitary-adrenal axis have different roles related to its stress response and support the evidence of regional specificity in GR regulation.