Distribution of preprovasopressin mRNA in the rat central nervous system

Expression of vasopressin and its receptors in migraine-related regions in CNS and the trigeminal system: influence of sex

BACKGROUND

Hypothalamus is a key region in migraine attacks. In addition, women are disproportionately affected by migraine. The calcitonin gene-related peptide (CGRP) system is an important key player in migraine pathophysiology. CGRP signaling could be a target of hormones that influence migraine. Our aim is to identify the expression of vasopressin and its receptors in the brain and in the trigeminovascular system with focus on the migraine-related regions and, furthermore, to examine the role of sex on the expression of neurohormones in the trigeminal ganglion.

METHODS

Rat brain and trigeminal ganglia were carefully harvested, and protein and mRNA levels were analyzed by immunohistochemistry and real-time PCR, respectively.

RESULTS

Vasopressin and its receptors immunoreactivity were found in migraine-related areas within the brain and, in the trigeminal ganglion, predominantly in neuronal cytoplasm. There were no differences in the number of positive immunoreactivity cells expression of CGRP and vasopressin in the trigeminal ganglion between male and female rats. In contrast, the number of RAMP1 (CGRP receptor), oxytocin (molecular relative to vasopressin), oxytocin receptor and vasopressin receptors (V1aR and V1bR) immunoreactive cells were higher in female compared to male rats. Vasopressin and its receptors mRNA were expressed in both hypothalamus and trigeminal ganglion; however, the vasopressin mRNA level was significantly higher in the hypothalamus.

CONCLUSIONS

A better understanding of potential hormonal influences on migraine mechanisms is needed to improve treatment of female migraineurs. It is intriguing that vasopressin is an output of hypothalamic neurons that influences areas associated with migraine. Therefore, vasopressin and the closely related oxytocin might be important hypothalamic components that contribute to migraine pathophysiology.

Multiple Aspects of Inappropriate Action of Renin-Angiotensin, Vasopressin, and Oxytocin Systems in Neuropsychiatric and Neurodegenerative Diseases

The cardiovascular system and the central nervous system (CNS) closely cooperate in the regulation of primary vital functions. The autonomic nervous system and several compounds known as cardiovascular factors, especially those targeting the renin-angiotensin system (RAS), the vasopressin system (VPS), and the oxytocin system (OTS), are also efficient modulators of several other processes in the CNS. The components of the RAS, VPS, and OTS, regulating pain, emotions, learning, memory, and other cognitive processes, are present in the neurons, glial cells, and blood vessels of the CNS. Increasing evidence shows that the combined function of the RAS, VPS, and OTS is altered in neuropsychiatric/neurodegenerative diseases, and in particular in patients with depression, Alzheimer's disease, Parkinson's disease, autism, and schizophrenia. The altered function of the RAS may also contribute to CNS disorders in COVID-19. In this review, we present evidence that there are multiple causes for altered combined function of the RAS, VPS, and OTS in psychiatric and neurodegenerative disorders, such as genetic predispositions and the engagement of the RAS, VAS, and OTS in the processes underlying emotions, memory, and cognition. The neuroactive pharmaceuticals interfering with the synthesis or the action of angiotensins, vasopressin, and oxytocin can improve or worsen the effectiveness of treatment for neuropsychiatric/neurodegenerative diseases. Better knowledge of the multiple actions of the RAS, VPS, and OTS may facilitate programming the most efficient treatment for patients suffering from the comorbidity of neuropsychiatric/neurodegenerative and cardiovascular diseases.

The role of oxytocin, vasopressin, and their receptors at nociceptors in peripheral pain modulation

Oxytocin and vasopressin are neurohypophyseal hormones with sequence similarity and play a central role in bodily homeostatic regulation. Pain is currently understood to be an important phenotype that those two neurohormones strongly downregulate. Nociceptors, the first component of the ascending neural circuit for pain signals, have constantly been shown to be modulated by those peptides. The nociceptor modulation appears to be critical in pain attenuation, which has led to a gradual increase in scientific interest about their physiological processes and also drawn attention to their translational potentials. This review focused on what are recently understood and stay under investigation in the functional modulation of nociceptors by oxytocin and vasopressin. Effort to produce a nociceptor-specific view could help to construct a more systematic picture of the peripheral pain modulation by oxytocin and vasopressin.

Chemoarchitecture of the bed nucleus of the stria terminalis: Neurophenotypic diversity and function

The bed nucleus of the stria terminalis (BNST) is a compact but neurophenotypically complex structure in the ventral forebrain that is structurally and functionally linked to other limbic structures, including the amygdala nuclear complex, hypothalamic nuclei, hippocampus, and related midbrain structures, to participate in a wide range of functions, especially emotion, emotional learning, stress-related responses, and sexual behaviors. From a variety of sensory inputs, the BNST acts as a node for signal integration and coordination for information relay to downstream central neuroendocrine and autonomic centers for appropriate homeostatic physiological and behavioral responses. In contrast to the role of the amygdala in fear, the BNST has gained wide interest from work suggesting that it has main roles in mediating sustained responses to diffuse, unpredictable and/or long-duration threats that are typically associated with anxiety-related responses. Further, some BNST subregions are highly sexually dimorphic which appear contributory to the differential stress and social interactive behaviors, including reproductive responses, between males and females. Notably, maladaptive BNST neuroplasticity and function have been implicated in chronic pain, depression, anxiety-related abnormalities, and other psychopathologies including posttraumatic stress disorders. The BNST circuits are predominantly GABAergic-the glutaminergic neurons represent a minor population-but the complexity of the system results from an overlay of diverse neuropeptide coexpression in these neurons. More than a dozen neuropeptides may be differentially coexpressed in BNST neurons, and from variable G protein-coupled receptor signaling, may inhibit or activate downstream circuit activities. The mechanisms and roles of these peptides in modulating intrinsic BNST neurocircuit signaling and BNST long-distance target cell projections are still not well understood. Nevertheless, an understanding of some of the principal players may allow assembly of the circuit interactions.

Differential role of specific cardiovascular neuropeptides in pain regulation: Relevance to cardiovascular diseases

In many instances, the perception of pain is disproportionate to the strength of the algesic stimulus. Excessive or inadequate pain sensation is frequently observed in cardiovascular diseases, especially in coronary ischemia. The mechanisms responsible for individual differences in the perception of cardiovascular pain are not well recognized. Cardiovascular disorders may provoke pain in multiple ways engaging molecules released locally in the heart due to tissue ischemia, inflammation or cellular stress, and through neurogenic and endocrine mechanisms brought into action by hemodynamic disturbances. Cardiovascular neuropeptides, namely angiotensin II (Ang II), angiotensin-(1-7) [Ang-(1-7)], vasopressin, oxytocin, and orexins belong to this group. Although participation of these peptides in the regulation of circulation and pain has been firmly established, their mutual interaction in the regulation of pain in cardiovascular diseases has not been profoundly analyzed. In the present review we discuss the regulation of the release, and mechanisms of the central and systemic actions of these peptides on the cardiovascular system in the context of their central and peripheral nociceptive (Ang II) and antinociceptive [Ang-(1-7), vasopressin, oxytocin, orexins] properties. We also consider the possibility that they may play a significant role in the modulation of pain in cardiovascular diseases. The rationale for focusing attention on these very compounds was based on the following premises (1) cardiovascular disturbances influence the release of these peptides (2) they regulate vascular tone and cardiac function and can influence the intensity of ischemia - the factor initiating pain signals in the cardiovascular system, (3) they differentially modulate nociception through peripheral and central mechanisms, and their effect strongly depends on specific receptors and site of action. Accordingly, an altered release of these peptides and/or pharmacological blockade of their receptors may have a significant but different impact on individual sensation of pain and comfort of an individual patient.

VGLUT-VGAT expression delineates functionally specialised populations of vasopressin-containing neurones including a glutamatergic perforant path-projecting cell group to the hippocampus in rat and mouse brain

The origin and functional significance of vasopressin (AVP)-containing fibres in limbic regions has been an ongoing subject of investigation for several years. We have previously identified AVP-magnocellular neurones of rat hypothalamus that provide glutamatergic projections to the hippocampus, amygdala, lateral habenula and locus coeruleus. However, we also reported AVP-immunopositive fibres in those regions that are thin and make Gray type II synapses, which are unlikely to be of magnocellular origin. Therefore, in the present study, we characterised AVP mRNA co-expression with expression of mRNAs marking glutamatergic (vesicular glutamate transporter [VGLUT]) and GABAergic (vesicular GABA transporter [VGAT]) neuronal traits in rat and mouse brain, using high-resolution in situ hybridisation methods, including a radio-ribonucleotide and RNAscope 2.5 HD duplex assay, with Slc17a7, Slc17a6, Slc32a1 and Avp probes corresponding to mRNAs of VGLUT1, VGLUT2, VGAT and AVP, respectively. We located 18 cell groups expressing Avp and identified their molecular signatures for VGLUT and VGAT mRNA expression. Avp cell groups of hypothalamus and midbrain are mainly VGLUT mRNA-expressing, whereas those in regions derived from cerebral nuclei are mainly VGAT mRNA-expressing, suggesting a functional segregation of glutamate/GABA co-transmission with AVP. A newly identified Slc17a7 and Slc17a6 (but not Slc32a1) expressing vasopressinergic cell group was found in layer II-III neurones of the central entorhinal cortex, which projects to the hippocampus. These data support the notion of a complex role for AVP with respect to modulating multiple central circuits controlling behaviour in specific ways depending on co-transmission with glutamate or GABA, potentially giving rise to a functional classification of AVPergic neurones in the central nervous system.

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

Cellular clocks in AVP neurons of the SCN are critical for interneuronal coupling regulating circadian behavior rhythm

The suprachiasmatic nucleus (SCN), the primary circadian pacemaker in mammals, is a network structure composed of multiple types of neurons. Here, we report that mice with a Bmal1 deletion specific to arginine vasopressin (AVP)-producing neurons showed marked lengthening in the free-running period and activity time of behavior rhythms. When exposed to an abrupt 8-hr advance of the light/dark cycle, these mice reentrained faster than control mice did. In these mice, the circadian expression of genes involved in intercellular communications, including Avp, Prokineticin 2, and Rgs16, was drastically reduced in the dorsal SCN, where AVP neurons predominate. In slices, dorsal SCN cells showed attenuated PER2::LUC oscillation with highly variable and lengthened periods. Thus, Bmal1-dependent oscillators of AVP neurons may modulate the coupling of the SCN network, eventually coupling morning and evening behavioral rhythms, by regulating expression of multiple factors important for the network property of these neurons.

The influence of psychological stress on arginine vasopressin concentration in the human plasma and cerebrospinal fluid

Psychological stress is strain affecting the intangible self, caused by problems in adaptation, perception, and emotions. Previous studies have demonstrated that arginine vasopressin (AVP) plays an important role in psychological stress. The goal of present study was to investigate the interaction between AVP release and cardiovascular functions by measuring AVP concentration and recording blood pressure or heart rate during psychological stress in human. The results showed that (1) psychological stress not only increased the systolic blood pressure, diastolic blood pressure and heart rate, but also elevated the cortisol and AVP concentration in both plasma and CSF in a stress level-dependent manner; (2) there was a positive relationship between plasma AVP concentration and systolic blood pressure, diastolic blood pressure, heart rate or plasma cortisol concentration; (3) there was also a positive relationship between AVP concentrations in plasma and CSF AVP. The data suggested that plasma AVP, which might come from the central nervous system, might influence the cardiovascular functions during psychological stress in human.

Exposure to chronic isolation modulates receptors mRNAs for oxytocin and vasopressin in the hypothalamus and heart

The goal of our study was to explore the effect of social isolation stress of varying durations on the plasma oxytocin (OT), messenger ribonucleic acid (mRNA) for oxytocin receptor (OTR), plasma arginine vasopressin (AVP) and mRNA for V1a receptor of AVP (V1aR) expression in the hypothalamus and heart of socially monogamous female and male prairie voles (Microtus ochrogaster). Continuous isolation for 4 weeks (chronic isolation) increased plasma OT level in females, but not in males. One hour of isolation every day for 4 weeks (repeated isolation) was followed by a significant increase in plasma AVP level. Chronic isolation, but not repeated isolation, significantly decreased OTR mRNA in the hypothalamus and heart in both sexes. Chronic isolation significantly decreased cardiac V1aR mRNA, but no effect on hypothalamic V1aR mRNA expression. We did not find a gender difference within repeated social isolation groups. The results of the present study reveal that although chronic social isolation can down-regulate gene expression for the OTR in both sexes, the release of the OT peptide was increased after chronic isolation only in females, possibly somewhat protecting females from the negative consequences of isolation. In both sexes repeated, but not chronic, isolation increased plasma AVP, which could be permissive for mobilization and thus adaptive in response to a repeated stressor. The differential effects of isolation on OT and AVP systems may help in understanding mechanisms through social interactions can be protective against emotional and cardiovascular disorders.

The vasopressin 1b receptor and the neural regulation of social behavior

To date, much of the work in rodents implicating vasopressin (Avp) in the regulation of social behavior has focused on its action via the Avp 1a receptor (Avpr1a). However, there is mounting evidence that the Avp 1b receptor (Avpr1b) also plays a significant role in Avp's modulation of social behavior. The Avpr1b is heavily expressed on the anterior pituitary cortiocotrophs where it acts as an important modulator of the endocrine stress response. In the brain, the Avpr1b is prominent in the CA2 region of the hippocampus, but can also be found in areas such as the paraventricular nucleus of the hypothalamus and the olfactory bulb. Studies that have employed genetic knockouts or pharmacological manipulation of the Avpr1b point to the importance of central Avpr1b in the modulation of social behavior. However, there continues to be a knowledge gap in our understanding of where in the brain this is occurring, as well as how and if the central actions of Avp acting via the Avpr1b interact with the stress axis. In this review we focus on the genetic and pharmacological studies that have implicated the Avpr1b in the neural regulation of social behaviors, including social forms of aggressive behavior, social memory, and social motivation. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

New potential therapeutic approaches in frontotemporal dementia: oxytocin, vasopressin, and social cognition

Frontotemporal dementias are neurodegenerative disorders marked by mid-life onset and progressive changes in behavior, decision making, and/or language. In several subtypes of frontotemporal dementia (FTD), damage to regions of the frontal and temporal lobes that occurs early in the disease course critically impairs emotional processing, social cognition, and behavior. To date, there are no curative or disease-modifying treatments for FTD, nor any approved treatments for the loss of empathy, impaired social cognition, and behavior of patients with FTD. A growing body of research suggests that the neuropeptides oxytocin and vasopressin are important mediators of social behavior in humans and other animals. Here, we review the effects of oxytocin and vasopressin on social cognition and behavior and discuss the potential implications for these agents as novel treatments in FTD.

Brain vasopressin V(1) receptors contribute to enhanced cardiovascular responses to acute stress in chronically stressed rats and rats with myocardial infarcton

The present study was designed to determine the role of central vasopressin 1 receptors (V(1)R) in the regulation of cardiovascular parameters in chronically stressed infarcted rats and sham-operated rats under resting conditions and during exposure to acute alarming stress. The experiments were performed on four groups of conscious sham-operated and four groups of infarcted rats subjected to intraventricular infusion of either vehicle or a V(1)R antagonist (V(1)RANT). Two groups of infarcted and two groups of sham-operated rats were subjected to mild chronic stressing. Mean arterial blood pressure (MABP) and heart rate (HR) were determined under resting conditions and after exposure to acute stress (air jet). During vehicle infusion, MABP and HR increases in response to acute stress in the infarcted rats not subjected to chronic stress, and in the infarcted and sham-operated chronically stressed rats, were significantly greater than in the sham-operated rats not exposed to chronic stress. However, MABP and HR responses to acute stress in the chronically stressed infarcted rats and chronically stressed sham-operated rats did not differ. V(1)RANT abolished differences in cardiovascular responses to acute stress between the experimental groups. Resting cardiovascular parameters were not affected by any of the experimental treatments. It is concluded that chronic stressing enhances the pressor and tachycardic responses to acute stress in the sham-operated rats but does not further intensify these responses in infarcted rats.The results provide evidence that central V(1)Rs are involved in potentiation of cardiovascular responses to acute stress in chronically stressed rats, infarcted rats, and chronically stressed infarcted rats.

Postnatal expression of V2 vasopressin receptor splice variants in the rat cerebellum

The V(2) vasopressin receptor gene contains an alternative splice site in exon-3, which leads to the generation of two splice variants (V(2a) and V(2b)) first identified in the kidney. The open reading frame of the alternatively spliced V(2b) transcript encodes a truncated receptor, showing the same amino acid sequence as the canonical V(2a) receptor up to the sixth transmembrane segment, but displaying a distinct sequence to the corresponding seventh transmembrane segment and C-terminal domain relative to the V(2a) receptor. Here, we demonstrate the postnatal expression of V(2a) and V(2b) variants in the rat cerebellum. Most importantly, we showed by in situ hybridization and immunocytochemistry that both V(2) splice variants were preferentially expressed in Purkinje cells, from early to late postnatal development. In addition, both variants were transiently expressed in the neuroblastic external granule cells and Bergmann fibers. These results indicate that the cellular distributions of both splice variants are developmentally regulated, and suggest that the transient expression of the V(2) receptor is involved in the mechanisms of cerebellar cytodifferentiation by AVP. Finally, transfected CHO-K1 expressing similar amounts of both V(2) splice variants, as that found in the cerebellum, showed a significant reduction in the surface expression of V(2a) receptors, suggesting that the differential expression of the V(2) splice variants regulates the vasopressin signaling in the cerebellum.

The vasopressin system--from antidiuresis to psychopathology

Vasopressin is a neuropeptide with multiple functions. In addition to its predominantly antidiuretic action after peripheral secretion from the posterior pituitary, it seems to fulfill--together with its receptor subtype--all requirements for a neuropeptide system critically involved in higher brain functions, including cognitive abilities and emotionality. Following somatodendritic and axonal release in distinct brain areas, vasopressin acts as a neuromodulator and neurotransmitter in multiple and varying modes of interneuronal communication. Accordingly, changes in vasopressin expression and release patterns may have wide-spread consequences. As shown in mice, rats, voles, and humans, central vasopressin release along a continuum may be beneficial to the individual, serving to adjust physiology and behavior in stressful scenarios, possibly at the potential expense of increasing susceptibility to disease. Indeed, if over-expressed and over-released, it may contribute to hyper-anxiety and depression-like behaviors. A vasopressin deficit, in turn, may cause signs of both diabetes insipidus and total hypo-anxiety. The identification of genetic polymorphisms underlying these phenomena does not only explain individual variation in social memory and emotionality, but also help to characterize potential targets for therapeutic interventions. The capability of both responding to stressful stimuli and mediating genetic polymorphisms makes the vasopressin system a key mediator for converging (i.e., environmentally and genetically driven) behavioral regulation.

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.

Sodium deprivation and salt intake activate separate neuronal subpopulations in the nucleus of the solitary tract and the parabrachial complex

Salt intake is an established response to sodium deficiency, but the brain circuits that regulate this behavior remain poorly understood. We studied the activation of neurons in the nucleus of the solitary tract (NTS) and their efferent target nuclei in the pontine parabrachial complex (PB) in rats during sodium deprivation and after salt intake. After 8-day dietary sodium deprivation, immunoreactivity for c-Fos (a neuronal activity marker) increased markedly within the aldosterone-sensitive neurons of the NTS, which express the enzyme 11-beta-hydroxysteroid dehydrogenase type 2 (HSD2). In the PB, c-Fos labeling increased specifically within two sites that relay signals from the HSD2 neurons to the forebrain--the pre-locus coeruleus and the innermost region of the external lateral parabrachial nucleus. Then, 1-2 hours after sodium-deprived rats ingested salt (a hypertonic 3% solution of NaCl), c-Fos immunoreactivity within the HSD2 neurons was virtually eliminated, despite a large increase in c-Fos activation in the surrounding NTS (including the A2 noradrenergic neurons) and area postrema. Also after salt intake, c-Fos activation increased within pontine nuclei that relay gustatory (caudal medial PB) and viscerosensory (rostral lateral PB) information from the NTS to the forebrain. Thus, sodium deficiency and salt intake stimulate separate subpopulations of neurons in the NTS, which then transmit this information to the forebrain via largely separate relay nuclei in the PB complex. These findings offer new perspectives on the roles of sensory information from the brainstem in the regulation of sodium appetite.

The vasopressin 1b receptor is prominent in the hippocampal area CA2 where it is unaffected by restraint stress or adrenalectomy

The vasopressin 1b receptor (Avpr1b) is one of two principal receptors mediating the behavioral effects of vasopressin (Avp) in the brain. Avpr1b has recently been shown to strongly influence social forms of aggression in mice and hamsters. This receptor appears to play a role in social recognition and motivation as well as in regulating the hypothalamic-pituitary-adrenal axis. Most of these studies have been performed in knockout mice, a species in which the localization of the Avpr1b has not been described, thus precluding correlations with the behaviors. We performed in situ hybridization histochemistry (ISHH) with specific probes and found especially prominent expression within the CA2 pyramidal neurons of the hippocampus, with much lower expression in the hypothalamic paraventricular nucleus and amygdala. Reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed expression in those as well other areas in which the ISHH was not sensitive enough to detect labeled cells (e.g. piriform cortex, septum, caudate-putamen and lower brainstem areas). Mouse Avpr1b transcript levels were not altered in the CA2 field by restraint stress or adrenalectomy. Finally, ISHH and RT-PCR showed expression of the Avpr1b gene in the rat and human hippocampi as well. We suggest that the CA2 field may form or retrieve associations (memories) between olfactory cues and social encounters.

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.

Projections to the preoptic area from the paraventricular nucleus, arcuate nucleus and the bed nucleus of the stria terminalis are unlikely to be involved in stress-induced suppression of GnRH secretion in sheep

Stress compromises reproductive function and the major physiological system activated during stress is the hypothalamo-pituitary-adrenal axis. Corticotrophin-releasing hormone and arginine vasopressin (AVP), which are produced in neurones of the paraventricular nucleus (PVN), drive the hypothalamo-pituitary-adrenal axis and are also implicated in the suppression of the reproductive axis. We used retrograde tracing and Fos labelling to map the projections from the PVN to the preoptic area (POA) where most gonadotrophin releasing hormone (GnRH) neurones are found. Fluorogold (FG) injections were made into the POA of gonadectomised male and female sheep (n = 5/sex), the animals were stressed and the brains recovered for histochemistry. All animals responded to stress with an increase in the number of Fos-labelled nuclei in the PVN. Few retrogradely labelled cells of the PVN were activated by stress. Dual labelling showed that very few FG-labelled cells also stained for corticotrophin-releasing hormone, none for AVP or enkephalin. Dual labelling for FG and Fos in the bed nucleus of the stria terminalis (BNST) and the arcuate nucleus showed that no FG-labelled cells in the BNST and only few in the ARC were activated by stress. No sex differences were observed in the activation of FG-labelled cells in any of the nuclei examined. We conclude that, although cells of the PVN, BNST and/or arcuate nucleus may affect reproduction via the GnRH cells of the POA, this is unlikely to involve direct input to the POA. If cells of these regions are involved in GnRH suppression during stress, this may occur via interneuronal pathways.

Central organization of androgen-sensitive pathways to the hypothalamic-pituitary-adrenal axis: implications for individual differences in responses to homeostatic threat and predisposition to disease

Despite clear evidence of the potency by which sex steroids operate on the hypothalamic-pituitary-adrenal (HPA) axis and genuine sex differences in disorders related to HPA dysfunction, the biological significance of this remains largely ignored. Stress-induced increases in circulating glucocorticoid levels serve to meet the metabolic demands of homeostatic threat head-on. Thus, the nature of the stress-adrenal axis is to protect the organism. As one develops, matures, and ages, still newer and competing physiological and environmental demands are encountered. These changing constraints are also met by shifts in sex steroid release, placing this class of steroids beyond the traditional realm of reproductive function. Here we focus on the dose-related and glucocorticoid-interactive nature by which testosterone operates on stress-induced HPA activation. This provides an overview on how to exploit these characteristics towards developing an anatomical framework of testosterone's actions in the brain, and expands upon the idea that centrally projecting arginine vasopressin circuits in the brain act to register and couple testosterone's effects on neuroendocrine and behavioural responses to stress. More generally, the work presented here underscores how a dual adrenal and gonadal systems approach assist in unmasking the bases by which individuals resist or succumb to stress.

Vasopressin facilitates glycinergic and GABAergic synaptic transmission in developing hypoglossal motoneurons

The hypoglossal nucleus of young rats contains vasopressin binding sites and vasopressin can directly excite hypoglossal motoneurons. In addition, indirect evidence suggests that vasopressin can enhance the synaptic input to motoneurons. We have characterized this latter effect by using brainstem slices and whole-cell recordings. We found that, in the presence of blockers of fast glutamatergic transmission, vasopressin strongly facilitated inhibitory synaptic activity. On average, vasopressin caused a six-fold increase in the frequency and a 1.5-fold increase in the amplitude of GABAergic postsynaptic currents. The effect of vasopressin on glycinergic postsynaptic currents was similar in magnitude. Vasopressin did not affect the frequency of GABAergic or glycinergic miniature postsynaptic currents, indicating that the peptide-induced facilitation of inhibitory transmission was mediated by receptors located on the somatodendritic region rather than on axon terminals of presynaptic neurons. The pharmacological profile of these receptors was determined by using d[Cha4]AVP and dVDAVP, selective agonists of V1b and V2 vasopressin receptors, respectively, and Phaa-D-Tyr-(Et)-Phe-Gln-Pro-Arg-Arg-NH2, a selective antagonist of V1a vasopressin receptors. The two agonists had no effect on the frequency of inhibitory postsynaptic currents. By contrast, the antagonist suppressed the vasopressin-induced facilitation of these currents, indicating that the receptors involved were exclusively of the V1a type. Thus, vasopressin exerts a dual action on hypoglossal motoneurons: a direct excitatory action and an indirect action mediated by GABAergic and glycinergic synapses. By virtue of this dual effect, vasopressin could alter the input-output properties of these motoneurons. Alternatively, it could play a role in generating or modulating specific motor patterns.

Differential regulation of central vasopressin receptors in transgenic rats with low brain angiotensinogen

The consequences of permanent alteration to the brain renin-angiotensin system (RAS) on central vasopressinergic system was studied in transgenic rats with low brain angiotensinogen [TGR(ASrAOGEN)]. Levels of vasopressin (AVP) and V1a receptor mRNAs were measured by ribonuclease protection assay (RPA) and AVP by radioimmunoassay (RIA). AVP (100 pmol/50 nl) was microinjected into the nucleus tractus solitarii (NTS) of urethane-anesthetized TGR(ASrAOGEN) and Sprague-Dawley (SD) rats and the mean arterial pressure (MAP) and heart rate (HR) baroreflex induced by phenylephrine were evaluated. AVP but not its mRNA levels were significantly lower in the hypothalamus and hypophysis of TGR(ASrAOGEN) rats. Brainstem V1a mRNA levels were significantly higher in TGR(ASrAOGEN) in comparison to SD rats (5.2+/-0.4% vs. 3.3+/-0.2% of beta-actin mRNA, P<0.05). In contrast, the hypothalamic V1a mRNA levels in TGR(ASrAOGEN) were not different from those found in SD rats. AVP microinjections induced a greater decrease in MAP in TGR(ASrAOGEN) in comparison with SD rats (-19.9+/-5.2 vs. -7.5+/-0.7 mm Hg, P<0.01). The significantly higher baroreflex sensitivity observed in TGR compared to that of SD rats was normalized after AVP microinjection. The increased brainstem V1a mRNA levels and sensitivity to AVP in TGR(ASrAOGEN) rats indicates a functional upregulation of AVP receptors in the NTS. The fact that the hypothalamic V1a mRNA levels are not altered indicates that these receptors are differentially regulated in different brain regions. This study demonstrates that a permanent deficit in brain angiotensinogen synthesis can alter the functionality of central vasopressinergic system.

Identification and characterization of two functionally distinct groups of spinal cord-projecting paraventricular nucleus neurons with sympathetic-related activity

Activation of spinal cord-projecting neurons of the hypothalamic paraventricular nucleus (PVN) has been implicated in a host of sympathetic nervous system functions. Here, we report two distinct activity patterns among electrophysiologically identified PVN spinal neurons that may contribute to the varied functional responses elicited by PVN activation. Extracellular single-unit recording was performed in anesthetized rats, and PVN neurons were antidromically identified by electrical stimulation of the spinal cord (T1-3 or T10-12). Axonal conduction velocity was determined for each identified neuron and revealed two distinct groups of cells, designated Group I (n=19) and Group II (n=34). Conduction velocity was significantly (P<0.01) different between Group I (3.67+/-0.29 m/s) and Group II (0.45+/-0.01 m/s) cells and indicates that axons of Group I cells are larger and/or more heavily myelinated than those of Group II, which appear to be unmyelinated. The majority of Group I (15/19: 79%) and Group II (23/34: 68%) cells discharged spontaneously. Basal firing rates were significantly different between groups (Group I: 2.7+/-0.85 versus Group II: 1.8+/-0.64 spikes s(-1); P<0.05). Spike-triggered averaging of renal sympathetic nerve activity revealed sympathetic-related discharge among a majority of Group I (11/15:73%) and Group II (17/23: 74%) neurons. In addition, seven of 11 Group I cells showed cardiac-related discharge. Pulse-rhythmic discharge was not detectable in any Group II cells tested (n=17). Among 11 Group I cells tested for barosensitivity, discharge in eight (73%) was graded by changes in mean arterial pressure. None of the 16 Group II cells tested for arterial pressure sensitivity responded.We conclude that the PVN spinal pathway is comprised of at least two functionally distinct cell types. The response profile and activity patterns of Group I cells suggest involvement in regulating vasomotor components of sympathetic outflow. By comparison, the activity of Groups II cells suggests a possible role in non-vasomotor sympathetic control.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Presence of functional vasopressin receptors in spinal ventral horn neurons of young rats: a morphological and electrophysiological study

The objective of the present work was double. (i) Light microscopic autoradiography was used to determine the distribution of vasopressin and oxytocin binding sites in the spinal cord of rats. (ii) Whole-cell recordings were performed in lumbar spinal cord slices in order to assess whether these receptors are functional, whether they are located pre- or postsynaptically and whether they are present in motoneurons. In newborns, vasopressin binding sites of the V1a type were present in all laminae of the central gray at all segmental levels, whereas oxytocin binding sites were found only in the superficial layers of the dorsal horn. In adults, binding sites for both neuropeptides were also present, but were less dense. The dissociation constants for vasopressin were similar in newborns and adults. Whole-cell recordings showed that in identified motoneurons vasopressin exerted a direct effect, by inducing a membrane depolarization or by generating a sustained inward current, and an indirect effect, by enhancing glycinergic and GABAergic inhibitory transmission. Vasopressin-induced facilitation of inhibitory transmission could also be demonstrated in unidentified ventral horn neurons. All these effects were mediated by V1a but not V1b receptors. In some neurons, glycinergic transmission was also facilitated by a selective oxytocin receptor agonist. Our data, together with data obtained previously in brainstem motor nuclei, suggest that vasopressin of hypothalamic origin could play a role in motricity. The neuropeptide could act as a neuromodulator, because it would not directly activate motoneurons, but rather render them more responsive to incoming excitatory inputs. Vasopressin may thus act as a regulator of muscular force.

Nuclei and subnuclei gene expression profiling in mammalian brain

Information on the neuroanatomical expression of a given gene is critical to understanding its function in the central nervous system. The integration of laser capture microdissection (LCM), T7-based RNA amplification and cDNA microarrays allows for this information to be simultaneously generated for thousands of genes. To validate this integrative approach, we catalogued the gene expression profiles of seven rat brain nuclei or subnuclei. A hundred cells from the following seven brain nuclei were analyzed: locus coeruleus (LC), dorsal raphe nucleus (DR), parvocellular division (PA) and magnocellular division (MG) of the hypothalamic paraventricular nucleus (PVN) and CA1, CA3 and dentate gyrus (DG) divisions of the hippocampal formation. Of the 2145 genes investigated, 1402 genes (65%) gave a hybridization signal statistically different from the background level that was defined by non-specific hybridizations to 15 different plant genes. Validation of our microarray data on four arbitrarily selected genes was confirmed by Real-Time PCR. Previous research showing expression patterns of 'signature' genes (n=17) for specific brain nuclei are consistent with our findings. For example, as previously shown, enriched mRNA expression encoding the serotonin transporter or tyrosine hydroxylase was found in DR and LC cells, respectively. Interestingly, expression of the serotonin 5-HT(2B) receptor mRNA was also found in DR cells. We confirmed this new finding by in-situ hybridization. The hierarchical clustering analysis of gene expression shows that the two divisions of the PVN (PA and MG) are closely related to each other, as well as the three regions of the hippocampal formation (CA1, CA3 and DG), which also showed similar gene expression profiles. This study demonstrates the importance, feasibility and utility of cellular brain nuclei profiling.

Descending control of pain

Upon receipt in the dorsal horn (DH) of the spinal cord, nociceptive (pain-signalling) information from the viscera, skin and other organs is subject to extensive processing by a diversity of mechanisms, certain of which enhance, and certain of which inhibit, its transfer to higher centres. In this regard, a network of descending pathways projecting from cerebral structures to the DH plays a complex and crucial role. Specific centrifugal pathways either suppress (descending inhibition) or potentiate (descending facilitation) passage of nociceptive messages to the brain. Engagement of descending inhibition by the opioid analgesic, morphine, fulfils an important role in its pain-relieving properties, while induction of analgesia by the adrenergic agonist, clonidine, reflects actions at alpha(2)-adrenoceptors (alpha(2)-ARs) in the DH normally recruited by descending pathways. However, opioids and adrenergic agents exploit but a tiny fraction of the vast panoply of mechanisms now known to be involved in the induction and/or expression of descending controls. For example, no drug interfering with descending facilitation is currently available for clinical use. The present review focuses on: (1) the organisation of descending pathways and their pathophysiological significance; (2) the role of individual transmitters and specific receptor types in the modulation and expression of mechanisms of descending inhibition and facilitation and (3) the advantages and limitations of established and innovative analgesic strategies which act by manipulation of descending controls. Knowledge of descending pathways has increased exponentially in recent years, so this is an opportune moment to survey their operation and therapeutic relevance to the improved management of pain.

Electrophysiological evidence for vasopressin V(1) receptors on neonatal motoneurons, premotor and other ventral horn neurons

Prominent arginine-vasopressin (AVP) binding and AVP V(1) type receptors are expressed early in the developing rat spinal cord. We sought to characterize their influence on neural excitability by using patch-clamp techniques to record AVP-induced responses from a population of motoneurons and interneurons in neonatal (5-18 days) rat spinal cord slices. Data were obtained from 58 thoracolumbar (T(7)-L(5)) motoneurons and 166 local interneurons. A majority (>90%) of neurons responded to bath applied AVP (10 nM to 3 microM) and (Phe(2), Orn(8))-vasotocin, a V(1) receptor agonist, but not V(2) or oxytocin receptor agonists. In voltage-clamp, postsynaptic responses in motoneurons were characterized by slowly rising, prolonged (7-10 min) and tetrodotoxin-resistant inward currents associated with a 25% reduction in a membrane potassium conductance that reversed near -100 mV. In interneurons, net AVP-induced inward currents displayed three patterns: decreasing membrane conductance with reversal near -100 mV, i.e., similar to that in motoneurons (24 cells); increasing conductance with reversal near -40 mV (21 cells); small reduction in conductance with no reversal within the current range tested (41 cells). A presynaptic component recorded in most neurons was evident as an increase in the frequency but not amplitude (in motoneurons) of inhibitory and excitatory postsynaptic currents (IPSCs and EPSCs), in large part due to AVP-induced firing in inhibitory (mainly glycinergic) and excitatory (glutamatergic) neurons synapsing on the recorded cells. An increase in frequency but not amplitude of miniature IPSCs and EPSCs also indicated an AVP enhancement of neurotransmitter release from axon terminals of inhibitory and excitatory interneurons. These observations provide support for a broad presynaptic and postsynaptic distribution of AVP V(1) type receptors and indicate that their activation can enhance the excitability of a majority of neurons in neonatal ventral spinal cord.

Effect of vasopressin on the input-output properties of rat facial motoneurons

Vasopressin can directly excite facial motoneurons in young rats and mice. It acts by generating a persistent inward current, which is Na(+)-dependent, tetrodotoxin-insensitive and voltage-gated. This peptide-evoked current is unaffected by Ca(++) or K(+) channel blockade and is modulated by extracellular divalent cations. In the present work, we determined how vasopressin alters the input-output properties of facial motoneurons. Whole-cell recordings were obtained from these neurons in the current clamp mode, in brainstem slices of young rats. Repetitive firing was evoked by injecting depolarizing current pulses. Steady-state frequency-current (f-I) relationships were constructed and the effect of vasopressin on these relationships was studied. We found that vasopressin caused a parallel shift to the left of the cell steady-state f-I relationship. This effect persisted in the presence of blockers of K(+) or Ca(++) channels. The peptide effect was distinct from that brought about by Ca(++) channel suppression or by apamin, a blocker of the mAHP. These latter manipulations resulted in an increase in the slope of the steady-state f-I relationship. We conclude that the vasopressin-induced modification of the input-output properties of facial motoneurons is probably exclusively caused by the sodium-dependent, voltage-modulated inward current elicited by the peptide, rather than being due to indirect effects of the peptide on Ca(++) channels, K(+) channels or Ca(++)-dependent K(+) channels. Computer simulation, based on a simple model of facial motoneurons, indicates that the introduction of a conductance having the properties of the vasopressin-dependent conductance can entirely account for the observed peptide-induced shift of the f-I relationship.

Vasopressin- and oxytocin-induced activity in the central nervous system: electrophysiological studies using in-vitro systems

During the last two decades, it has become apparent that vasopressin and oxytocin, in addition to playing a role as peptide hormones, also act as neurotransmitters/neuromodulators. A number of arguments support this notion: (i) vasopressin and oxytocin are synthesized not only in hypothalamo-neurohypophysial cells, but also in other hypothalamic and extrahypothalamic cell bodies, whose axon projects to the limbic system, the brainstem and the spinal cord. (ii) Vasopressin and oxytocin can be shed from central axons as are classical neurotransmitters. (iii) Specific binding sites, i.e. membrane receptors having high affinity for vasopressin and oxytocin are present in the central nervous system. (iv) Vasopressin and oxytocin can alter the firing rate of selected neuronal populations. (v) In-situ injection of vasopressin and oxytocin receptor agonists and antagonists can interfere with behavior or physiological regulations. Morphological studies and electrophysiological recordings have evidenced a close anatomical correlation between the presence of vasopressin and oxytocin receptors in the brain and the neuronal responsiveness to vasopressin or oxytocin. These compounds have been found to affect membrane excitability in neurons located in the limbic system, hypothalamus, circumventricular organs, brainstem, and spinal cord. Sharp electrode intracellular recordings and whole-cell recordings, done in brainstem motoneurons or in spinal cord neurons, have revealed that vasopressin and oxytocin can directly affect neuronal excitability by opening non-specific cationic channels or by closing K(+) channels. These neuropeptides can also influence synaptic transmission, by acting either postsynaptically or upon presynaptic target neurons or axon terminals. Whereas, in cultured neurons, vasopressin and oxytocin appear to mobilize intracellular Ca(++), in brainstem slices, the action of oxytocin is mediated by a second messenger that is distinct from the second messenger activated in peripheral target cells. In this review, we will summarize studies carried out at the cellular level, i.e. we will concentrate on in-vitro approaches. Vasopressin and oxytocin will be treated together. Though acting via distinct receptors in distinct brain areas, these two neuropeptides appear to exert similar effects upon neuronal excitability.

Neuropeptide expression in rat paraventricular hypothalamic neurons that project to the spinal cord

The paraventricular hypothalamic nucleus (PVH) exerts many of its regulatory functions through projections to spinal cord neurons that control autonomic and sensory functions. By using in situ hybridization histochemistry in combination with retrograde tract tracing, we analyzed the peptide expression among neurons in the rat PVH that send axons to the spinal cord. Projection neurons were labeled by immunohistochemical detection of retrogradely transported cholera toxin subunit B, and radiolabeled long riboprobes were used to identify neurons containing dynorphin, enkephalin, or oxytocin mRNA. Of the spinally projecting neurons in the PVH, approximately 40% expressed dynorphin mRNA, 40% expressed oxytocin mRNA, and 20% expressed enkephalin mRNA. Taken together with our previous findings on the distribution of vasopressin-expressing neurons in the PVH (Hallbeck and Blomqvist [1999] J. Comp. Neurol. 411:201-211), the results demonstrated that the different PVH subdivisions display distinct peptide expression patterns among the spinal cord-projecting neurons. Thus, the lateral parvocellular subdivision contained large numbers of spinal cord-projecting neurons that express any of the four investigated peptides, whereas the ventral part of the medial parvocellular subdivision displayed a strong preponderance for dynorphin- and vasopressin-expressing cells. The dorsal parvocellular subdivision almost exclusively contained dynorphin- and oxytocin-expressing spinal cord-projecting neurons. This parcellation of the peptide-expressing neurons suggested a functional diversity among the spinal cord-projecting subdivisions of the PVH that provide an anatomic basis for its various and distinct influences on autonomic and sensory processing at the spinal level.

Anatomy and function of extrahypothalamic vasopressin systems in the brain

The most prominent sites of vasopressin (VP) production in the rat brain are the paraventricular nucleus, the supraoptic nucleus, the suprachiasmatic nucleus, the bed nucleus of the stria terminalis (BST), and the medial amygdaloid nucleus (MA). Recently a number of new sites have been suggested, including the hippocampus, the diagonal band of Broca, and the choroid plexus. This chapter shows how differential regulation of these VP systems can be exploited to identify the contributions of individual VP systems to the various central functions in which VP has been implicated. It will focus on the development, anatomy, and function of the sexually dimorphic VP projections of the BST and MA. This system contains more cells and has denser projections in males than in females. This system is also extremely responsive to gonadal steroids as it only produces VP in the presence of gonadal steroids. It has been implicated in sexually dimorphic functions such as aggressive behavior as well as in non-sexually dimorphic functions such as social recognition memory. Using comparative studies done in prairie voles as an example, this chapter makes the case that the VP projections of the BST and MA may simultaneously generate sex differences in some brain functions and behaviors and prevent them in others.