Regulation of vasopressin V1b receptors in the anterior pituitary gland of the rat

Pituitary corticotroph identity and receptor-mediated signaling: A transcriptomics perspective

Recent single-cell RNA sequencing has offered an unprecedented view of pituitary cell transcriptomic profiles. In this review, these new data are briefly discussed and compared with the classical literature, focusing on pituitary corticotrophs. These cells are introduced by discussing their marker genes, followed by a review of G protein-coupled receptor gene expression, heterotrimeric G protein genes, and genes encoding signaling pathways downstream of G proteins: adenylate cyclases, phosphodiesterases, phospholipases, and protein kinases. The expression patterns of enzyme-linked plasma membrane and nuclear hormone receptor genes was also analyzed. The overview of these selected groups of genes sheds new light on corticotrophic receptors and their signaling pathways and provides guidance for further basic and clinical research by identifying genes that not been studied so far.

AVP-eGFP was significantly upregulated by hypovolemia in the parvocellular division of the paraventricular nucleus in the transgenic rats

Arginine vasopressin (AVP) is produced in the paraventricular (PVN) and supraoptic nuclei (SON). Peripheral AVP, which is secreted from the posterior pituitary, is produced in the magnocellular division of the PVN (mPVN) and SON. In addition, AVP is produced in the parvocellular division of the PVN (pPVN), where corticotrophin-releasing factor (CRF) is synthesized. These peptides synergistically modulate the hypothalamic-pituitary-adrenal (HPA) axis. Previous studies have revealed that the HPA axis was activated by hypovolemia. However, the detailed dynamics of AVP in the pPVN under hypovolemic state has not been elucidated. Here, we evaluated the effects of hypovolemia and hyperosmolality on the hypothalamus, using AVP-enhanced green fluorescent protein (eGFP) transgenic rats. Polyethylene glycol (PEG) or 3% hypertonic saline (HTN) was intraperitoneally administered to develop hypovolemia or hyperosmolality. AVP-eGFP intensity was robustly upregulated at 3 and 6 h after intraperitoneal administration of PEG or HTN in the mPVN. While in the pPVN, eGFP intensity was significantly increased at 6 h after intraperitoneal administration of PEG with significant induction of Fos-immunoreactive (-ir) neurons. Consistently, eGFP mRNA, AVP hnRNA, and CRF mRNA in the pPVN and plasma AVP and corticosterone were significantly increased at 6 h after intraperitoneal administration of PEG. The results suggest that AVP and CRF syntheses in the pPVN were activated by hypovolemia, resulting in the activation of the HPA axis.

Exercise-Induced Adrenocorticotropic Hormone Response Is Cooperatively Regulated by Hypothalamic Arginine Vasopressin and Corticotrophin-Releasing Hormone

INTRODUCTION

Exercise becomes a stress when performed at an intensity above the lactate threshold (LT) because at that point the plasma adrenocorticotropic hormone (ACTH), a marker of stress response, increases. It is possible that the exercise-induced ACTH response is regulated at least by arginine vasopressin (AVP) and possibly by corticotropin-releasing hormone (CRH), but this remains unclear. To clarify the involvement of these factors, it is useful to intervene pharmacologically in the regulatory mechanisms, with a physiologically acceptable exercise model.

METHODS

We used a special stress model of treadmill running (aerobic exercise) for male Wistar rats, which mimic the human physiological response, where plasma ACTH levels increase at just above the LT for 30 min. Animals were administered the AVP V1b receptor antagonist SSR149415 (SSR) and/or the CRH type 1 receptor antagonist CP154526 (CP) intraperitoneally before the exercise, which allowed the monitoring of exercise-induced ACTH response. Immunohistochemical evaluation of activated AVP and CRH neurons with exercise was performed for the animals' hypothalami.

RESULTS

A single injection of either antagonist, SSR or CP, resulted in inhibited ACTH levels after exercise stress. Moreover, the combined injection of SSR and CP strongly suppressed ACTH secretion during treadmill running to a greater extent than each alone. The running-exercise-induced activation of both AVP and CRH neurons in the hypothalamus was also confirmed.

CONCLUSION

These results lead us to hypothesize that AVP and CRH are cooperatively involved in exercise-induced ACTH response just above the LT. This may also reflect the stress response with moderate-intensity exercise in humans.

Complementary Role of Oxytocin and Vasopressin in Cardiovascular Regulation

The neurons secreting oxytocin (OXY) and vasopressin (AVP) are located mainly in the supraoptic, paraventricular, and suprachiasmatic nucleus of the brain. Oxytocinergic and vasopressinergic projections reach several regions of the brain and the spinal cord. Both peptides are released from axons, soma, and dendrites and modulate the excitability of other neuroregulatory pathways. The synthesis and action of OXY and AVP in the peripheral organs (eye, heart, gastrointestinal system) is being investigated. The secretion of OXY and AVP is influenced by changes in body fluid osmolality, blood volume, blood pressure, hypoxia, and stress. Vasopressin interacts with three subtypes of receptors: V1aR, V1bR, and V2R whereas oxytocin activates its own OXTR and V1aR receptors. AVP and OXY receptors are present in several regions of the brain (cortex, hypothalamus, pons, medulla, and cerebellum) and in the peripheral organs (heart, lungs, carotid bodies, kidneys, adrenal glands, pancreas, gastrointestinal tract, ovaries, uterus, thymus). Hypertension, myocardial infarction, and coexisting factors, such as pain and stress, have a significant impact on the secretion of oxytocin and vasopressin and on the expression of their receptors. The inappropriate regulation of oxytocin and vasopressin secretion during ischemia, hypoxia/hypercapnia, inflammation, pain, and stress may play a significant role in the pathogenesis of cardiovascular diseases.

Neurobiological aspects of pain in the context of alcohol use disorder

Alcohol is an effective and widely utilized analgesic. However, the chronic use of alcohol can actually facilitate nociceptive sensitivity over time, a condition known as hyperalgesia. Excessive and uncontrollable alcohol drinking is also a hallmark feature of alcohol use disorder (AUD). Both AUD and chronic pain are typically accompanied by negative affective states that may underlie reinforcement mechanisms contributing to AUD maintenance or progression. Frequent utilization of alcohol to relieve pain in individuals suffering from AUD or other chronic pain conditions may thus represent a powerful negative reinforcement construct. This chapter will describe ties between alcohol-mediated pain relief and potential exacerbation of AUD. We describe neurobiological systems engaged in alcohol analgesia as well as systems recruited in the development and maintenance of AUD and hyperalgesia. Although few effective therapies exist for either chronic pain or AUD, the common interaction of these conditions will likely lead the way for promising new discoveries of more effective and even simultaneous treatment of AUD and co-morbid hyperalgesia. An abundance of neurobiological findings from multiple laboratories has implicated a potentiation of central amygdala (CeA) signaling in both pain and AUD, and these data also suggest that attenuation of stress-related systems (including corticotropin-releasing factor, vasopressin, and glucocorticoid receptor activity) would be particularly effective and comprehensive therapeutic strategies targeting the critical intersection of somatic and motivational mechanisms driving AUD, including alcohol-induced hyperalgesia.

Peripherally administered cisplatin activates a parvocellular neuronal subtype expressing arginine vasopressin and enhanced green fluorescent protein in the paraventricular nucleus of a transgenic rat

Cisplatin is one of the most potent anti-cancer drugs, though several side effects can induce stress responses such as activation of the hypothalamic-pituitary adrenal (HPA) axis. Arginine vasopressin (AVP) and corticotrophin-releasing hormone (CRH) expressed in the parvocellular division of the paraventricular nucleus (pPVN) play an important role in the stress-induced activation of the HPA axis. We aimed to evaluate whether intraperitoneal (i.p.) administration of cisplatin could activate parvocellular neurons in the pPVN, using a transgenic rat model that expresses the fusion gene of AVP and enhanced green fluorescent protein (eGFP). Along with the induction of FosB, a marker of neuronal activation, i.p. administration of cisplatin significantly increased eGFP fluorescent intensities in the pPVN. In situ hybridization histochemistry revealed that AVP-eGFP and CRH mRNAs in the pPVN were increased significantly in cisplatin-treated rats. These results suggest that cisplatin administration increases neuronal activation and upregulates AVP and CRH expression in the pPVN.

Acute Mono-Arthritis Activates the Neurohypophysial System and Hypothalamo-Pituitary Adrenal Axis in Rats

Various types of acute/chronic nociceptive stimuli cause neuroendocrine responses such as activation of the hypothalamo-neurohypophysial [oxytocin (OXT) and arginine vasopressin (AVP)] system and hypothalamo-pituitary adrenal (HPA) axis. Chronic multiple-arthritis activates the OXT/AVP system, but the effects of acute mono-arthritis on the OXT/AVP system in the same animals has not been simultaneously evaluated. Further, AVP, not corticotropin-releasing hormone (CRH), predominantly activates the HPA axis in chronic multiple-arthritis, but the participation of AVP in HPA axis activation in acute mono-arthritis remains unknown. Therefore, we aimed to simultaneously evaluate the effects of acute mono-arthritis on the activity of the OXT/AVP system and the HPA axis. In the present study, we used an acute mono-arthritic model induced by intra-articular injection of carrageenan in a single knee joint of adult male Wistar rats. Acute mono-arthritis was confirmed by a significant increase in knee diameter in the carrageenan-injected knee and a significant decrease in the mechanical nociceptive threshold in the ipsilateral hind paw. Immunohistochemical analysis revealed that the number of Fos-immunoreactive (ir) cells in the ipsilateral lamina I-II of the dorsal horn was significantly increased, and the percentage of OXT-ir and AVP-ir neurons expressing Fos-ir in both sides of the supraoptic (SON) and paraventricular nuclei (PVN) was increased in acute mono-arthritic rats. in situ hybridization histochemistry revealed that levels of OXT mRNA and AVP hnRNA in the SON and PVN, CRH mRNA in the PVN, and proopiomelanocortin mRNA in the anterior pituitary were also significantly increased in acute mono-arthritic rats. Further, plasma OXT, AVP, and corticosterone levels were significantly increased in acute mono-arthritic rats. These results suggest that acute mono-arthritis activates ipsilateral nociceptive afferent pathways at the spinal level and causes simultaneous and integrative activation of the OXT/AVP system. In addition, the HPA axis is activated by both AVP and CRH in acute mono-arthritis with a distinct pattern compared to that in chronic multiple-arthritis.

Vasopressin Surrogate Marker Copeptin as a Potential Novel Endocrine Biomarker for Antidepressant Treatment Response in Major Depression: A Pilot Study

BACKGROUND

Major depressive disorder (MDD) constitutes the leading cause of disability worldwide. Although efficacious antidepressant pharmacotherapies exist for MDD, only about 40-60% of the patients respond to initial treatment. However, there is still a lack of robustly established and applicable biomarkers for antidepressant response in everyday clinical practice.

OBJECTIVE

This study targets the assessment of the vasopressin (AVP) surrogate marker Copeptin (CoP), as a potential peripheral hypothalamic-level biomarker of antidepressant treatment response in MDD.

METHODS

We measured baseline and dynamic levels of plasma CoP along with plasma ACTH and cortisol (CORT) in drug-naive outpatients with MDD before and after overnight manipulation of the hypothalamic-pituitary-adrenal (HPA) axis [i.e., stimulation (metyrapone) and suppression (dexamethasone)] on three consecutive days and their association with treatment response to 4 weeks of escitalopram treatment.

RESULTS

Our findings suggest significantly higher baseline and post-metyrapone plasma CoP levels in future non-responders, a statistically significant invert association between baseline CoP levels and probability of treatment response and a potential baseline plasma CoP cut-off level of above 2.9 pmol/L for future non-response screening. Baseline and dynamic plasma ACTH and CORT levels showed no association with treatment response.

CONCLUSIONS

This pilot study provide first evidence in humans that CoP may represent a novel, clinically easily applicable, endocrine biomarker of antidepressant response, based on a single-measurement, cut-off level. These findings, underline the role of the vasopressinergic system in the pathophysiology of MDD and may represent a significant new tool in the clinical and biological phenotyping of MDD enhancing individual-tailored therapies.

Reduced vasopressin receptors activation mediates the anti-depressant effects of fluoxetine and venlafaxine in bulbectomy model of depression

RATIONALE

In response to stress, corticotropin releasing hormone (CRH) and vasopressin (AVP) are released from the hypothalamus, activate their receptors (CRHR1, CRHR2 or AVPr1b), and synergistically act to induce adrenocorticotropic hormone (ACTH) release from the anterior pituitary. Overstimulation of this system has been frequently associated with major depression states.

OBJECTIVE

The objective of the study is to assess the role of AVP and CRH receptors in fluoxetine and venlafaxine effects on the expression of depression-related behavior.

METHODS

In an animal model of depression (olfactory bulbectomy in mice, OB), we evaluated the effects of fluoxetine or venlafaxine (both 10 mg/kg/day) chronic administration on depression-related behavior in the tail suspension test. Plasma levels of AVP, CRH, and ACTH were determined as well as participation of their receptors in the expression of depression related-behavior and gene expression of AVP and CRH receptors (AVPr1b, CRHR1, and CRHR2) in the pituitary gland.

RESULTS

The expression of depressive-like behavior in OB animals was reversed by treatment with both antidepressants. Surprisingly, OB-saline mice exhibited increased AVP and ACTH plasma levels, with no alterations in CRH levels when compared to sham mice. Chronic fluoxetine or venlafaxine reversed these effects. In addition, a significant increase only in AVPr1b gene expression was found in OB-saline.

CONCLUSION

The antidepressant therapy used seems to be more likely related to a reduced activation of AVP rather than CRH receptors, since a positive correlation between AVP levels and depressive-like behavior was observed in OB animals. Furthermore, a full restoration of depressive behavior was observed in OB-fluoxetine- or venlafaxine-treated mice only when AVP was centrally administered but not CRH.

Gestational hypoxia modulates expression of corticotropin-releasing hormone and arginine vasopressin in the paraventricular nucleus in the ovine fetus

Maturation of the fetal hypothalamo-pituitary-adrenocortical (HPA) axis is critical for organ maturation necessary for the fetus to transition to the ex-utero environment. Intrauterine stressors can hasten maturation of the HPA axis leading to fetal growth restriction and in sheep, premature birth. We have previously reported that high-altitude mediated, long-term-moderate gestational hypoxia (LTH) during gestation has a significant impact on the fetal HPA axis. Significant effects were observed at the level of both the anterior pituitary and adrenal cortex resulting in elevated plasma ACTH during late gestation with decreased adrenocortical expression of enzymes rate limiting for cortisol synthesis. As such, these fetuses exhibited the normal ontogenic rise in fetal plasma cortisol but an exaggerated cortisol response to acute stress. This study extended these findings to ACTH secretagogue expression in the PVN using in situ hybridization. We report that the expression of AVP but not CRH was increased in the medial parvocellular PVN (mpPVN) in the LTH fetus. This represented an increase in both AVP mRNA per neuron as well as an increase in AVP hybridizing neurons with no increase in mpPVN CRH neurons. LTH had no effect on PVN volume, area of CRH or AVP hybridization, thus LTH did not have a trophic effect on the size of the nucleus. In conclusion, there appears to be a switch from CRH to AVP as a primary ACTH secretagogue in response to LTH, supporting our previous findings of increased anterior pituitary sensitivity to AVP over CRH in the LTH fetus.

Hypothalamic-pituitary-adrenal axis function during perinatal depression

Abnormal function of the hypothalamic-pituitary-adrenal (HPA) axis is an important pathological finding in pregnant women exhibiting major depressive disorder. They show high levels of cortisol pro-inflammatory cytokines, hypothalamic-pituitary peptide hormones and catecholamines, along with low dehydroepiandrosterone levels in plasma. During pregnancy, the TH2 balance together with the immune system and placental factors play crucial roles in the development of the fetal allograft to full term. These factors, when altered, may generate a persistent dysfunction of the HPA axis that may lead to an overt transfer of cortisol and toxicity to the fetus at the expense of reduced activity of placental 11β-hydroxysteroid dehydrogenase type 2. Epigenetic modifications also may contribute to the dysregulation of the HPA axis. Affective disorders in pregnant women should be taken seriously, and therapies focused on preventing the deleterious effects of stressors should be implemented to promote the welfare of both mother and baby.

Influence of hypothalamic IL-6/gp130 receptor signaling on the HPA axis response to chronic stress

Abnormal basal activity and stress-evoked reactivity of the hypothalamic-pituitary-adrenal (HPA) axis are often seen in depression, implicating HPA axis dysfunction as a potentially causative or exacerbating factor. Chronic stress is also a factor in depression, but it is not known what may underlie the shift from adaptive to maladaptive HPA activity over the course of chronic stress. Interleukin 6 (IL-6), a stress-inducible cytokine that signals through gp130 and IL-6Rα receptors to activate the JAK/STAT3 signaling cascade, is elevated in some subtypes of depression, and may have a modulatory effect on HPA activation, raising the possibility that IL-6 contributes to depression through effects on the HPA axis. In this study, we examined the effects of three different stress modalities, acute footshock, chronic intermittent cold (CIC) stress and chronic unpredictable stress (CUS) on IL-6 signaling in the hypothalamus. We also investigated whether IL-6 modulates the HPA response to chronic stress, by blocking IL-6 signaling in the brain during CIC stress using either a neutralizing antibody or an inhibitor of STAT3 phosphorylation. We show that IL-6 and STAT3 in the hypothalamus are activated in response to footshock and CUS. We also found that basal IL-6 signaling through the JAK/STAT3 pathway is required for the sustained CORT response to chronic, but not acute, cold stress and therefore is a potential determinant of plasticity in the HPA axis specifically during chronic stress exposure.

Effect of arginine vasopressin on the behavioral activity in the behavior despair depression rat model

Arginine vasopressin (AVP), a nonapeptide posterior hormone of the pituitary, is mainly synthesized and secreted in the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON). Large numbers of studies have reported that AVP plays a role in depression. The present study was to investigate by which level, brain or periphery, AVP affects the behavioral activity in the behavior despair depression rat model. The results showed that (1) either forced swimming or tail suspension significantly increased AVP concentration not only in the brain (PVN, SON, frontal of cortex, hippocampus, amygdala, lumber spinal cord) but also in the periphery (posterior pituitary and serum); (2) intraventricular injection (icv) of AVP decreased the animal immobility time, whereas V₁ receptor antagonist d(CH₂)₅Tyr(Me)AVP (icv) increased the animal immobility time in a dose-dependent manner not only in FST but also in TST, but the V₂ receptor antagonist d(CH₂)₅[D-Ile, Ile, Ala-NH₉]AVP did not change the animal immobility time in FST or TST; (3) V₁, not V₂ receptor antagonist could inhibit the animal immobility time decrease induced by AVP (icv); (4) neither AVP nor its receptor antagonist (including V₁ and V₂ receptor antagonist) influenced the animal immobility time in both FST and TST. The data suggested that AVP in the brain rather than the periphery played a role in the behavior despair depression by V₁, not V₂ receptors, which behavior despair might have a positive feedback effect on central AVP and blood AVP might have a negative feedback on central AVP in the depressive process.

Evidence that vasopressin V1b receptors mediate the transition to excessive drinking in ethanol-dependent rats

Alcoholism is a devastating condition that represents a progression from initial alcohol use to dependence. Although most individuals are capable of consuming alcohol in a limited fashion, the development of alcohol dependence in a subset of individuals is often associated with negative emotional states (including anxiety and depression). Since the alleviation of this negative motivational state via excessive alcohol consumption often becomes a central goal of alcoholics, the transition from initial use to dependence is postulated to be associated with a transition from positive to negative reinforcement mechanisms. Vasopressin is a neuropeptide known to potentiate the effects of CRF on the HPA axis, and emerging evidence also suggests a role for centrally located vasopressin acting on V(1b) receptors in the regulation of stress- and anxiety-like behaviors in rodents. The present study determined state-dependent alterations in vasopressin/V(1b) R signaling in an animal model of ethanol dependence. The V(1b) R antagonist SSR149415 dose-dependently reduced excessive levels of ethanol self-administration observed in dependent animals without affecting the limited levels of ethanol drinking in non-dependent animals. Ethanol self-administration reduced V(1b) receptor levels in the basolateral amygdala of non-dependent animals, a neuroadaptation that could theoretically facilitate the positive reinforcing effects of alcohol. In contrast, V(1b) R levels were seemingly restored in ethanol-dependent rats, a switch that may in part underlie a transition from positive to negative reinforcement mechanisms with dependence. Together, our data suggest a key role for vasopressin/V(1b) R signaling in the transition to ethanol dependence.

Hypothalamic vasopressin response to stress and various physiological stimuli: visualization in transgenic animal models

Arginine vasopressin (AVP) is involved in the homeostatic responses numerous life-threatening conditions, for example, the promotion of water conservation during periods of dehydration, and the activation of the hypothalamo-pituitary adrenal axis by emotional stress. Recently, we generated new transgenic animals that faithfully express an AVP-enhanced green fluorescent protein (eGFP) fusion gene in the paraventricular nucleus (PVN), the supraoptic nucleus (SON) and the suprachiasmatic nucleus (SCN) of the hypothalamus. In these transgenic rats, marked increases in eGFP fluorescence and fusion gene expression were observed in the magnocellular division of the PVN and the SON, but not the SCN, after osmotic challenges, such as dehydration and salt loading, and both acute and chronic nociceptive stimuli. In the parvocellular division of the PVN, eGFP expression was increased after acute and chronic pain, bilateral adrenalectomy, endotoxin shock and restraint stress. In the extra-hypothalamic areas of the brain, eGFP expression was induced in the locus coeruleus after the intracerebroventricular administration of colchicine. Next, we generated another transgenic rat that expresses a fusion gene comprised of c-fos promoter-enhancer sequences driving the expression of monomeric red fluorescent protein 1 (mRFP1). In these transgenic rats, abundant nuclear fluorescence of mRFP1 was observed in the PVN, the SON and other osmosensitive areas after acute osmotic stimulation. Finally, we generated a double transgenic rat that expresses both the AVP-eGFP and c-fos-mRFP1 fusion genes. In this double transgenic rat, we have observed nuclear mRFP1 fluorescence in eGFP-positive neurons after acute osmotic stimulation. These unique transgenic rats provide an exciting new tool to examine neuroendocrine responses to physiological and stressful stimuli in both in vivo and in vitro preparations.

Exaggerated response of a vasopressin-enhanced green fluorescent protein transgene to nociceptive stimulation in the rat

Nociceptive stimulation elicits neuroendocrine responses such as arginine vasopressin (AVP) release as well as activation of the hypothalamo-pituitary-adrenal axis. We have generated novel transgenic rats expressing an AVP-enhanced green fluorescent protein (eGFP) fusion gene, and we examined the effects of nociceptive stimulation on transgene expression in the hypothalamus after subcutaneous injection of saline or formalin into the bilateral hindpaws in these rats. We have assessed (1) AVP levels in plasma and the changes of eGFP mRNA and AVP heteronuclear RNA (hnRNA) in the supraoptic nucleus (SON) and the paraventricular nucleus (PVN) using in situ hybridization histochemistry, (2) gene expression changes in distinct magnocellular and parvocellular divisions of the PVN, (3) eGFP fluorescence in the SON, the PVN, the median eminence (ME), and the posterior pituitary gland (PP). Plasma AVP levels were significantly increased 15 min after formalin injection. In the same time period, the AVP hnRNA levels in the PVN were increased, especially in the parvocellular division of the PVN in formalin-injected rats. In the same region, eGFP mRNA levels after formalin injection were also significantly increased to a much greater extent than those of AVP hnRNA. The eGFP fluorescence in the SON, the PVN, the ME, and the PP was markedly increased in formalin-injected rats and especially increased in the parvocellular divisions of the PVN. Together, our results demonstrate robust and rapid changes in the expression of the AVP-eGFP transgene in the rat hypothalamus after acute nociceptive stimulation.

A complex selection signature at the human AVPR1B gene

BACKGROUND

The vasopressin receptor type 1b (AVPR1B) is mainly expressed by pituitary corticotropes and it mediates the stimulatory effects of AVP on ACTH release; common AVPR1B haplotypes have been involved in mood and anxiety disorders in humans, while rodents lacking a functional receptor gene display behavioral defects and altered stress responses.

RESULTS

Here we have analyzed the two exons of the gene and the data we present suggest that AVPR1B has been subjected to natural selection in humans. In particular, analysis of exon 2 strongly suggests the action of balancing selection in African populations and Europeans: the region displays high nucleotide diversity, an excess of intermediate-frequency alleles, a higher level of within-species diversity compared to interspecific divergence and a genealogy with common haplotypes separated by deep branches. This relatively unambiguous situation coexists with unusual features across exon 1, raising the possibility that a nonsynonymous variant (Gly191Arg) in this region has been subjected to directional selection.

CONCLUSION

Although the underlying selective pressure(s) remains to be identified, we consider this to be among the first documented examples of a gene involved in mood disorders and subjected to natural selection in humans; this observation might add support to the long-debated idea that depression/low mood might have played an adaptive role during human evolution.

Corticosterone- or metapyrone-induced alterations in adrenal function and expression of the arginine vasotocin receptor VT2 in the pituitary gland of domestic fowl, Gallus gallus

The avian neurohypophyseal hormone arginine vasotocin (AVT) is known to be involved in the regulation of adrenocorticotropin (ACTH) release by interacting with the VT2 receptor (VT2R), which is homologous to the mammalian vasopressin V1b receptor (V1bR). To study the role of glucocorticoid in the expression and regulation of the VT2R, corticosterone (1 or 5mg/bird/day) or metapyrone (10 or 50mg/kg body weight/day) were administered daily for 8 days to white leghorn chickens. While low doses were ineffective, a high dose of corticosterone upregulated, while metapyrone downregulated, pituitary VT2R mRNA expression and ir-VT2 in the cephalic lobe of the anterior pituitary. Further, although no change was observed in the expression of POMC mRNA, adrenal activity (as judged by the changes in total cholesterol, 3beta HSD, cortical cord width and cortico-medullary ratio) exhibited suppression or stimulation following treatment with corticosterone or metapyrone, respectively. In view of the classical negative feedback effect of glucocorticoids at the level of hypothalamic CRH neurons and pituitary corticotrophs, high corticosterone level-induced suppression of the CRH-ACTH axis may have been masked by VT2R-mediated stimulation of corticotrophs, and hence the POMC mRNA level did not change. The same argument could be used for metapyrone. It is concluded that expression of the VT2 receptor is regulated by glucocorticoids in chicken. These findings confirm a role for AVT, mediated by the VT2 receptor, in regulating ACTH secretion during stress and suggest that corticotroph VT2 receptor levels may be dynamically regulated depending on the HPA axis activity.

Vasopressin: behavioral roles of an "original" neuropeptide

Vasopressin (Avp) is mainly synthesized in the magnocellular cells of the hypothalamic supraoptic (SON) and paraventricular nuclei (PVN) whose axons project to the posterior pituitary. Avp is then released into the blood stream upon appropriate stimulation (e.g., hemorrhage or dehydration) to act at the kidneys and blood vessels. The brain also contains several populations of smaller, parvocellular neurons whose projections remain within the brain. These populations are located within the PVN, bed nucleus of the stria terminalis (BNST), medial amygdala (MeA) and suprachiasmatic nucleus (SCN). Since the 1950s, research examining the roles of Avp in the brain and periphery has intensified. The development of specific agonists and antagonists for Avp receptors has allowed for a better elucidation of its contributions to physiology and behavior. Anatomical, pharmacological and transgenic, including "knockout," animal studies have implicated Avp in the regulation of various social behaviors across species. Avp plays a prominent role in the regulation of aggression, generally of facilitating or promoting it. Affiliation and certain aspects of pair-bonding are also influenced by Avp. Memory, one of the first brain functions of Avp that was investigated, has been implicated especially strongly in social recognition. The roles of Avp in stress, anxiety, and depressive states are areas of active exploration. In this review, we concentrate on the scientific progress that has been made in understanding the role of Avp in regulating these and other behaviors across species. We also discuss the implications for human behavior.

Decreased ACTH secretion during prolonged transportation stress is associated with reduced pituitary responsiveness to tropic hormone stimulation in cattle

The present study examined the effect of transportation stress on hypothalamic-pituitary-adrenal axis responsiveness to tropic hormone stimulation and on abundance of corticotropin releasing factor (CRF) receptor R1 (CRFR1) and arginine vasopressin (AVP) receptor V3 (V3) mRNAs in the anterior pituitary (AP) of cattle. Holstein steers were transported for 10 h or used as non-transported controls (NTC). Blood samples were collected at start of transportation and every 1-2h thereafter. To test AP responsiveness to tropic hormones, animals were challenged (i.v.) with CRF (0.5 microg/kg), AVP (1 microg/kg) or CRF plus AVP immediately after end of transportation and blood samples collected every 30 min for 3h. The AP of animals transported for 0, 4 or 10 h were harvested for mRNA analyses. Plasma ACTH in transported animals increased within 1h and remained elevated for 6 and 8h versus NTC and 0 h values, respectively. Plasma concentrations of cortisol increased in response to transportation and remained elevated throughout the transport period. Injection of CRF or AVP to NTC animals increased plasma ACTH, but ACTH secretion in response to CRF or AVP was dramatically reduced in transported animals. ACTH secretion following co-injection of CRF and AVP tended to be less in transported animals, but was almost 100% greater than when secretagogues were administered separately. Despite decreased AP responsiveness to CRF and AVP, AP CRFR1 and V3 mRNAs were increased after 10 h transportation. Results indicate decreased AP responsiveness to CRF and AVP may regulate duration of ACTH secretion in response to transportation stress in cattle.

Physiological studies of stress responses in the hypothalamus of vasopressin-enhanced green fluorescent protein transgenic rat

Arginine vasopressin (AVP) plays an important role in stress-induced activation of the hypothalamic-pituitary adrenal axis. In the present study, AVP-enhanced green fluorescent protein (eGFP) transgenic rats were used to investigate changes in AVP-eGFP expression in the hypothalamic paraventricular nucleus (PVN) and the median eminence (ME) upon exposure to stress conditions. The eGFP fluorescence in the parvocellular division of the PVN (pPVN) was markedly increased 5 days after bilateral adrenalectomy (ADX) and it was colocalised with corticotrophin-releasing hormone-like immunoreactivity in the pPVN. Peripheral administration of dexamethasone completely suppressed the increase of eGFP fluorescence in the pPVN and the external layer of the ME (eME) after bilateral ADX. Significant increases of eGFP fluorescence were observed in the pPVN 6, 12, 24 and 48 h after intraperitoneal (i.p.) administration of lipopolysaccharide (LPS). In the eME, eGFP fluorescence was significantly increased 48 h after i.p. administration of LPS. By contrast, eGFP fluorescence changed neither in the magnocellular division of the PVN, nor the internal layer of the ME after i.p. administration of LPS. Our results indicate that AVP-eGFP transgenic rats are useful animal model to study dynamic changes of AVP expression in the hypothalamus under stressful conditions.

The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine responses to stress

Animals respond to stress by activating a wide array of behavioral and physiological responses that are collectively referred to as the stress response. Corticotropin-releasing factor (CRF) plays a central role in the stress response by regulating the hypothalamic-pituitary-adrenal (HPA) axis. In response to stress, CRF initiates a cascade of events that culminate in the release of glucocorticoids from the adrenal cortex. As a result of the great number of physiological and behavioral effects exerted by glucocorticoids, several mechanisms have evolved to control HPA axis activation and integrate the stress response. Glucocorticoid feedback inhibition plays a prominent role in regulating the magnitude and duration of glucocorticoid release. In addition to glucocorticoid feedback, the HPA axis is regulated at the level of the hypothalamus by a diverse group of afferent projections from limbic, mid-brain, and brain stem nuclei. The stress response is also mediated in part by brain stem noradrenergic neurons, sympathetic andrenornedullary circuits, and parasympathetic systems. In summary, the aim of this review is to discuss the role of the HPA axis in the integration of adaptive responses to stress. We also identify and briefly describe the major neuronal and endocrine systems that contribute to the regulation of the HPA axis and the maintenance of homeostasis in the face of aversive stimuli.

Minireview: rapid glucocorticoid signaling via membrane-associated receptors

Glucocorticoids are secreted into the systemic circulation from the adrenal cortex and initiate a broad range of actions throughout the organism that regulate the function of multiple organ systems, including the liver, muscle, the immune system, the pancreas, fat tissue, and the brain. Delayed glucocorticoid effects are mediated by classical steroid mechanisms involving transcriptional regulation. Relatively rapid effects of glucocorticoids also occur that are incompatible with genomic regulation and invoke a noncanonical mode of steroid action. Studies conducted in several labs and on different species suggest that the rapid effects of glucocorticoids are mediated by the activation of one or more membrane-associated receptors. Here, we provide a brief review focused on multiple lines of evidence suggesting that rapid glucocorticoid actions are triggered by, or at least dependent on, membrane-associated G protein-coupled receptors and activation of downstream signaling cascades. We also discuss the possibility that membrane-initiated actions of glucocorticoids may provide an additional mechanism for the regulation of gene transcription.

Insidious adrenocortical insufficiency underlies neuroendocrine dysregulation in TIF-2 deficient mice

The transcription-intermediary-factor-2 (TIF-2) is a coactivator of the glucocorticoid receptor (GR), and its disruption would be expected to influence glucocorticoid-mediated control of the hypothalamo-pituitary-adrenal (HPA) axis. Here, we show that its targeted deletion in mice is associated with altered expression of several glucocorticoid-dependent components of HPA regulation (e.g., corticotropin-releasing hormone, vasopressin, ACTH, glucocorticoid receptors), suggestive of hyperactivity under basal conditions. At the same time, TIF-2(-/-) mice display significantly lower basal corticosterone levels and a sluggish and blunted initial secretory response to brief emotional and prolonged physical stress. Subsequent analysis revealed this discrepancy to result from pronounced aberrations in the structure and function of the adrenal gland, including the cytoarchitectural organization of the zona fasciculata and basal and stress-induced expression of key elements of steroid hormone synthesis, such as the steroidogenic acute regulatory (StAR) protein and 3beta-hydroxysteroid dehydrogenase (3beta-HSD). In addition, altered expression levels of two nuclear receptors, DAX-1 and steroidogenic factor 1 (SF-1), in the adrenal cortex strengthen the view that TIF-2 deletion disrupts adrenocortical development and steroid biosynthesis. Thus, hyperactivity of the hypothalamo-pituitary unit is ascribed to insidious adrenal insufficiency and impaired glucocorticoid feedback.

The role of central vasopressin receptors in the modulation of autonomic cardiovascular controls: a spectral analysis study

Although it has been suggested that vasopressin (VP) acts within the central nervous system to modulate autonomic cardiovascular controls, the mechanisms involved are not understood. Using nonpeptide, selective V(1a), V(1b), and V(2) antagonists, in conscious rats, we assessed the roles of central VP receptors, under basal conditions, after the central application of exogenous VP, and after immobilization, on cardiovascular short-term variability. Equidistant sampling of blood pressure (BP) and heart rate (HR) at 20 Hz allowed direct spectral analysis in very-low frequency (VLF-BP), low-frequency (LF-BP), and high-frequency (HF-BP) blood pressure domains. The effect of VP antagonists and of exogenous VP on body temperature (T(b)) was also investigated. Under basal conditions, V(1a) antagonist increased HF-BP and T(b), and this was prevented by metamizol. V(1b) antagonist enhanced HF-BP without affecting T(b), and V(2) antagonist increased VLF-BP variability which could be prevented by quinapril. Immobilization increased BP, LF-BP, HF-BP, and HF-HR variability. V(1a) antagonist prevented BP and HR variability changes induced by immobilization and potentiated tachycardia. V(1b) antagonist prevented BP but not HR variability changes, whereas V(2) antagonist had no effect. Exogenous VP increased systolic arterial pressure (SAP) and HF-SAP variability, and this was prevented by V(1a) and V(1b) but not V(2) antagonist pretreatment. Our results suggest that, under basal conditions, VP, by stimulation of V(1a), V(1b), and cognate V(2) receptors, buffers BP variability, mostly due to thermoregulation. Immobilization and exogenous VP, by stimulation of V(1a) or V(1b), but not V(2) receptors, increases BP variability, revealing cardiorespiratory adjustment to stress and respiratory stimulation, respectively.

Altered hypothalamo-pituitary-adrenal and sympatho-adrenomedullary activities in rats bred for high anxiety: central and peripheral correlates

Wistar rats have been selectively bred for high (HABs) or low (LABs) anxiety-related behavior based on results obtained in the elevated-plus maze. They also display robust behavioral differences in a variety of additional anxiety tests. The present study was undertaken to further characterize physiological substrates that contribute to the expression of this anxious trait. We report changes in brain and peripheral structures involved in the regulation of both the hypothalamo-pituitary-adrenal (HPA) and sympatho-adrenal systems. Following exposure to a mild stressor, HABs displayed a hyper-reactivity of the HPA axis associated with a hypo-reactivity of the sympatho-adrenal system and a lower serotonin turnover in the lateral septum and amygdala. At rest, HABs showed a higher adrenal weight and lower tyrosine hydroxylase and phenylethanolamine-N-methyltransferase mRNAs expression in their adrenals than LABs. In the anterior pituitary, HABs also exhibited increased proopiomelanocortin and decreased vasopressin V1b receptor mRNAs expression, whereas glucocorticoid receptor mRNA levels remained unchanged. These results indicate that the behavioral phenotype of HABs is associated with peripheral and central alterations of endocrine mechanisms involved in stress response regulation. Data are discussed in relation to coping strategies adopted to manage stressful situations. In conclusion, HABs can be considered as an useful model to study the etiology and pathophysiology of stress-related disorders and their neuroendocrine substrates.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Reduced hypothalamic vasopressin secretion underlies attenuated adrenocorticotropin stress responses in pregnant rats

We sought to explain decreased ACTH secretory responses to stress in pregnant rats by investigating hypothalamic CRH and vasopressin secretion and actions on anterior pituitary corticotrophs. In late pregnancy median eminence, CRH content was reduced (by 12%). Anterior pituitary proopiomelanocortin mRNA expression, measured by in situ hybridization but not radioimmunoassayed ACTH content, was also reduced (by 45% on d 21); CRH receptor (CRHR)1 mRNA expression was unaltered in pregnancy, but V1b receptor mRNA expression was reduced (by 19%). ACTH secretory responses, measured in jugular blood, to CRH (200 ng/kg iv) or vasopressin (1.7 microg/kg, iv) were reduced on d 21 vs. virgins (49% and 44%), but the response to combined CRH and vasopressin injection was intact. Either antalarmin (CRHR1 antagonist; 20 mg/kg ip) or dP(Tyr(Me)2),Arg-NH2(9))AVP (V1a/b antagonist; 10 microg/kg, iv) pretreatment reduced the ACTH secretory response to forced swimming (90 sec) in virgin rats (by 57% and 40%), but only antalarmin was effective in pregnant rats (53% decrease). In vitro, measuring ACTH secretion from acutely dispersed anterior pituitary cells showed increased corticotroph sensitivity in pregnancy to CRH and to CRH augmentation by vasopressin, attributable to increased intracellular cAMP action. Hence, in late pregnancy, reduced anterior pituitary CRHR1 or V1b receptor expression did not impair corticotroph responses to CRH or vasopressin. Rather, diminished secretagogue secretion in vivo accounts for reduced action of stress levels of exogenous CRH or vasopressin alone; the late pregnancy attenuated ACTH secretory response to swim stress is deduced to be due to reduced vasopressin release by parvocellular paraventricular nuclei neurones.

Regulation of vasopressin V1b receptors and stress adaptation

Vasopressin (VP) regulates pituitary corticotroph function by acting upon plasma membrane G-protein receptors of the V1b subtype (V1bR), coupled to calcium-phospholipid signaling. The number of these receptors in the anterior pituitary varies during stress in direct correlation with corticotroph responsiveness, suggesting that the V1bR plays an important role during adaptation of the hypothalamic-pituitary-adrenal (HPA) axis to stress. The molecular regulation of pituitary V1bR involves transcriptional and translational mechanisms. V1bR gene transcription, which is necessary to maintain V1bR mRNA levels, depends on a number of responsive elements in the promoter region, of which the stretch of GA repeats near the transcription start point (GAGA box) is essential. Although transcriptional activation is necessary to maintain V1bR mRNA levels, the lack of correlation between VP binding and V1bR mRNA suggests that V1bR content is mainly regulated at the translational level. Two potential mechanisms by which the 5' untranslated region (5'UTR) of the V1bR mediates negative and positive regulation of V1bR translation were identified. This includes the repressor effect of small open reading frames (ORF) present upstream of the main V1bR ORF, and an internal ribosome entry site (IRES), which activates V1bR translation. The existence of multiple loci of regulation for the V1bR at transcriptional and translational levels provides a mechanism to facilitate plasticity of regulation of the number of pituitary vasopressin receptors according to physiological demand.

The Role of Vasopressin in Hypothalamo-Pituitary-Adrenal Axis Activation during Stress: An Assessment of the Evidence

The hypothalamo-pituitary-adrenal (HPA) axis is a key component of the stress reaction. Most contemporary reviews mention the corticotropin-releasing hormone and arginine vasopressin (AVP)-containing parvocellular neurons of the hypothalamic paraventricular nucleus as the endocrinomotor component of the system. Although there are many studies about the role of AVP in the stress activation, there is evidence consistent and inconsistent with the general view on the importance of AVP. We propose a list of experiments that may provide critical evidence for or against the widely held opinion. The naturally AVP-deficient Brattleboro rat seems to be a good tool for studying the role of AVP. Our experiments on Brattleboro rats with restraint and ip hypertonic saline injection did not support the prominent role of AVP in acute stress, although in forced swim the lack of AVP influenced the HPA axis activation. Among different chronic stress situations (14 days' restraint, chronic morphine or ip hypertonic saline treatment, streptozotocin-induced diabetes mellitus), the role of AVP was not confirmed by changes in somatic parameter (i.e., body, thymus, and adrenal weight changes).

Single administration of interleukin-1 increased corticotropin releasing hormone and corticotropin releasing hormone-receptor mRNA in the hypothalamic paraventricular nucleus which paralleled long-lasting (weeks) sensitization to emotional stressors

Single exposure to the proinflammatory cytokine interleukin-1 induces sensitization of the adrenocorticotropin hormone and corticosterone responses to stressors weeks later (hypothalamus-pituitary-adrenal sensitization). Hypothalamus-pituitary-adrenal responses are controlled by corticotropin-releasing hormone and arginine-vasopressin secreted from parvocellular corticotropin-releasing hormone neurons of the hypothalamic paraventricular nucleus and may involve autoexcitatory feedback mechanisms. Therefore, we studied the temporal relationship between resting levels of corticotropin-releasing hormone, corticotropin-releasing hormone-R1 and arginine-vasopressin receptor (V1a, V1b) mRNAs in the paraventricular nucleus and the development of hypothalamus-pituitary-adrenal sensitization to an emotional stressor (novelty). The adrenocorticotropin hormone precursor molecule proopiomelanocortin hnRNA in the pituitary gland served as an index for acute activation. Single administration of interleukin-1 induced sensitization of the hypothalamus-pituitary-adrenal to novelty from 3 to 22 days later, but not after 42 days. Single administration of interleukin-1 induced biphasic increases in corticotropin-releasing hormone and corticotropin-releasing hormone-R1 mRNAs in the paraventricular nucleus: an early peak within 24 h, followed by a delayed (>7 days) increase that peaked after 22 days. Hypothalamic V1a and V1b mRNA levels were unaffected. In contrast, in the pituitary gland, there was an early decrease in corticotropin-releasing hormone-R1 mRNA (from 10.5 to 3 h after interleukin-1) and V1b receptor mRNA (3 to 6 h), which returned to control levels from 24 h onwards. Thus, interleukin-1-induced long-lasting hypothalamus-pituitary-adrenal sensitizations associated with prolonged activation of corticotropin-releasing hormone and corticotropin-releasing hormone-R1 mRNA expression in the paraventricular nucleus, but not with changes in the expression of proopiomelanocortin hnRNA or V1b receptor or corticotropin-releasing hormone R1 mRNAs in the pituitary gland. We propose that transient exposure to immune events can induce long-lasting hypothalamus-pituitary-adrenal sensitization, which at least in part involves long-term hypothalamic adaptations that enhance central corticotropin-releasing hormone signaling.

Neuroendocrine pharmacology of stress

Exposure to hostile conditions initiates responses organized to enhance the probability of survival. These coordinated responses, known as stress responses, are composed of alterations in behavior, autonomic function and the secretion of multiple hormones. The activation of the renin-angiotensin system and the hypothalamic-pituitary-adrenocortical axis plays a pivotal role in the stress response. Neuroendocrine components activated by stressors include the increased secretion of epinephrine and norepinephrine from the sympathetic nervous system and adrenal medulla, the release of corticotropin-releasing factor (CRF) and vasopressin from parvicellular neurons into the portal circulation, and seconds later, the secretion of pituitary adrenocorticotropin (ACTH), leading to secretion of glucocorticoids by the adrenal gland. Corticotropin-releasing factor coordinates the endocrine, autonomic, behavioral and immune responses to stress and also acts as a neurotransmitter or neuromodulator in the amygdala, dorsal raphe nucleus, hippocampus and locus coeruleus, to integrate brain multi-system responses to stress. This review discussed the role of classical mediators of the stress response, such as corticotropin-releasing factor, vasopressin, serotonin (5-hydroxytryptamine or 5-HT) and catecholamines. Also discussed are the roles of other neuropeptides/neuromodulators involved in the stress response that have previously received little attention, such as substance P, vasoactive intestinal polypeptide, neuropeptide Y and cholecystokinin. Anxiolytic drugs of the benzodiazepine class and other drugs that affect catecholamine, GABA(A), histamine and serotonin receptors have been used to attenuate the neuroendocrine response to stressors. The neuroendocrine information for these drugs is still incomplete; however, they are a new class of potential antidepressant and anxiolytic drugs that offer new therapeutic approaches to treating anxiety disorders. The studies described in this review suggest that multiple brain mechanisms are responsible for the regulation of each hormone and that not all hormones are regulated by the same neural circuits. In particular, the renin-angiotensin system seems to be regulated by different brain mechanisms than the hypothalamic-pituitary-adrenal system. This could be an important survival mechanism to ensure that dysfunction of one neurotransmitter system will not endanger the appropriate secretion of hormones during exposure to adverse conditions. The measurement of several hormones to examine the mechanisms underlying the stress response and the effects of drugs and lesions on these responses can provide insight into the nature and location of brain circuits and neurotransmitter receptors involved in anxiety and stress.

Transcriptional regulation of the pituitary vasopressin V1b receptor involves a GAGA-binding protein

The role of CT repeats (inverted GAGA box) in the rat vasopressin V1b receptor (V1bR) promoter in the transcriptional regulation of this gene was studied in H32 hypothalamic cells, which express endogenous V1bR. Transfection of a 2.5-kb V1bR fragment (2161 bp upstream and 377 bp downstream of the proximal transcriptional start point) into a luciferase vector (V1bRp2.5-Luc) results in promoter activity in these cells. The 670-bp proximal promoter fragment containing the GAGA box showed maximal promoter activity, whereas deletion of the GAGA box abolished transcription. Drosophila GAGA-binding protein increased V1bR promoter activity by 11-fold when cotransfected with V1bRp2.5-Luc and increased endogenous V1bR expression. Electrophoretic mobility shift assay showed specific binding of pituitary nuclear extracts to radiolabeled GAGA oligonucleotides, which increased following restraint stress in rats, a condition associated with V1bR up-regulation. DNA-binding activity involved a protein complex because it was abolished by deoxycholate. Size-exclusion column chromatography showed a complex of 127 kDa, which dissociated into approximately 70-kDa components after deoxycholate/Nonidet P-40 treatment. This study demonstrates that interactions of GAGA-binding proteins with the GAGA box of the V1bR promoter activate V1bR gene expression and provides a potential mechanism for physiological regulation of V1bR transcription.

Bacterial lipopolysaccharide-induced coordinate downregulation of arginine vasopressin receptor V3 and corticotropin-releasing factor receptor 1 messenger ribonucleic acids in the anterior pituitary of endotoxemic steers

AVP and CRF are potent stimulators of pituitary ACTH secretion in cattle. Actions of AVP and CRF at the anterior pituitary are mediated by AVP receptor V3 (V3) and CRF receptor 1 (CRFR1). The primary objective of these studies was to determine the effect of systemic inflammatory stress on V3 and CRFR1 mRNAs in the bovine anterior pituitary. Holstein steers (n = 20) were injected with 200 ng/kg bacterial lipopolysaccharide (LPS) and tissues collected 0, 2, 4, 12, and 24 h later. All animals responded to LPS administration with an increase in body temperature, plasma ACTH, and cortisol (p < 0.05). Abundance of anterior pituitary V3 mRNA was decreased at 2, 4, and 12 h following LPS administration (p < 0.05) and returned to basal by 24 h. A similar temporal regulation of pituitary CRFR1 mRNA (p < 0.05), but not pituitary pro-opiomelanocortin (POMC) mRNA, was observed following LPS administration. Similar downregulation of CRFR1 mRNA was not observed in other brain regions following LPS administration (cerebellum, hypothalamus). Our results indicate that V3 and CRFR1 mRNAs are coordinately downregulated in the anterior pituitary during systemic inflammatory stress. Decreased AVP and CRF receptor expression may help regulate the pituitary-adrenal response to stress.

Decreased corticotropin-releasing factor receptor expression and adrenocorticotropic hormone responsiveness in anterior pituitary cells of Wistar-Kyoto rats

The Wistar-Kyoto (WKY) rat shows signs of persistent activation of the hypothalamic-pituitary-adrenal axis, but the cause and site of this activation is not yet known. Chronically activated corticotrophs generally show blunted adrenocorticotropic hormone (ACTH) response to corticotropin releasing factor (CRF); therefore, the anterior pituitary responsiveness to ACTH secretagogues, CRF and vasopressin, was compared in male WKY and Wistar rats. Anterior pituitary CRF binding and CRF receptor mRNA expression was significantly decreased in WKY rats. ACTH response to CRF or vasopressin was markedly impaired, and vasopressin failed to potentiate the CRF-stimulated ACTH release in cultured WKY anterior pituitary cells. In contrast, CRF and vasopressin alone and in combination stimulated large, concentration-dependent increases in ACTH release in Wistar anterior pituitary cells. By contrast to the decreased ACTH secretory responses, steady-state anterior pituitary pro-opiomelanocortin mRNA levels were approximately 12-fold greater in WKY rats compared to Wistar rats, and they further increased in response to CRF stimulation. These findings suggest that, although the WKY rat corticotroph is under a chronic state of activation or disinhibition, the in vitro secretory responses to classic ACTH secretagogues are impaired.

Salt-loading increases vasopressin and vasopressin 1b receptor mRNA in the hypothalamus and choroid plexus

The choroid plexus plays a pivotal role in the production of cerebrospinal fluid (CSF). Messenger RNA (mRNA) transcripts encoding arginine vasopressin (AVP) and the vasopressin 1b receptor (V(1b)R) are found in various structures of the central nervous system, including the choroid plexus. The present study measured AVP and V(1b)R mRNA production in response to plasma hyperosmolality. Compared to rats maintained on water, 2% salt-drinking rats had increased levels of AVP and V(1b)R mRNAs in the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus and in the choroid plexus. The increase in V(1b)R mRNA in the SON and PVN as a result of plasma hyperosmolality may reflect changes in receptor production that, in turn, have a role in AVP autoregulation of hypothalamic magnocellular neurons. The increase of AVP and V(1b)R mRNAs in the choroid plexus further shows the involvement of AVP in the regulation of brain water content and cerebral edema.