Behavioral effects of vasopressin and oxytocin within the medial preoptic area of the golden hamster

Exocrine scent marking: Coordinative role of arginine vasopressin in the systemic regulation of social signaling behaviors

Arginine vasopressin (AVP) is a neurohypophysial hormone that coordinatively regulates central socio-emotional behavior and peripheral control of antidiuretic fluid homeostasis. Most mammals, including rodents, utilize exocrine or urine-contained scent marking as a social signaling tool that facilitates social adaptation. The exocrine scent marking behavior is postulated to fine-tune sensory and cognitive abilities to recognize key social features via exocrine/urinary olfactory cues and subsequently control exocrine deposition or urinary marking through the mediation of osmotic fluid balance. AVP is implicated as a major player in controlling both recognition and signaling responses. This review provides constructive hypotheses on the coordinative processes of the AVP neurohypophysial circuits in the systemic regulations of fluid control and social-communicative behavior, via the expression of exocrine scent marking, and further emphasizes a potential role of AVP in a common mechanism underlying social communication in rodents.

Binding affinities of oxytocin, vasopressin and Manning compound at oxytocin and V1a receptors in male Syrian hamster brains

Oxytocin (OT) and arginine vasopressin (AVP), as well as synthetic ligands targeting their receptors (OTR, V1aR), are used in a wide variety of research contexts, although their pharmacological properties are determined in only a few species. Syrian hamsters (Mesocricetus auratus) have a long history of use as a behavioural and biomedical model for the study of OT and AVP and, more recently, hamsters have been used to investigate behavioural consequences of OT-mediated activation of V1aR. We aimed to determine the binding affinities of OT, AVP and the selective V1aR antagonist, Manning compound, for OTR and V1aR in hamster brains. We performed saturation binding assays to determine the Kd values for the selective OTR and V1aR radioligands, [125 I]ornithine vasotocin analogue and [125 I]linear vasopressin antagonist. We then performed competition binding assays to determine Ki values for OT, AVP and Manning compound at both the OTR and V1aR. We found that OT and AVP each had the highest affinity for their canonical receptors (OT-OTR Ki = 4.28 [95% confidence interval (CI) = 2.9-6.3] nmol L-1 ; AVP-V1ar Ki = 4.70 [95% CI = 1.5-14.1] nmol L-1 ) and had the lowest affinity for their non-canonical ligands (OT-V1aR = 495.2 [95% CI = 198.5-1276] nmol L-1 ; AVP-OTR Ki = 36.1 [95% CI = 12.4-97.0] nmol L-1 ). Manning compound had the highest affinity for the V1aR (MC-V1aR Ki = 6.87 [95% CI = 4.0-11.9] nmol L-1 ; MC-OTR Ki = 213.8 [95% CI = 117.3-392.7] nmol L-1 ), although Manning compound was not as selective for the V1aR in hamsters as has been reported for the receptor in rats. When comparing these data with previously published work, we found that the promiscuity of the V1aR in hamsters with respect to OT and AVP binding is more similar to the promiscuity of the human V1aR than to the rat V1aR receptor. Moreover, the selectivity of OT at hamster receptors is more similar to the selectivity of OT at human receptors than the selectivity of OT at rat receptors. These data highlight the importance of determining the pharmacological properties of behaviourally relevant compounds in diverse model species.

Central distribution of oxytocin and vasopressin 1a receptors in juvenile Richardson's ground squirrels

Oxytocin and vasopressin are well-conserved peptides important to the regulation of numerous aspects of social behavior, including sociality. Research exploring the distribution of the receptors for oxytocin (Oxtr) and for vasopressin (Avpr1a) in mammals has revealed associations between receptor distribution, sociality, and species' mating systems. Given that sociality and gregariousness can be tightly linked to reproduction, these nonapeptides unsurprisingly support affiliative behaviors that are important for mating and offspring care. We localized these receptors in juvenile Richardson's ground squirrel brains to determine whether distribution patterns of Oxtr and Avpr1a that are associated with promiscuous mating systems differ in rodents that also exhibit non-reproductive affiliation. These squirrels are social, colonial, and engage in nepotistic alarm calling behavior and affiliation outside of a reproductive context. Juveniles are the most affiliative age-class and are non-reproductive; making them ideal for examining these associations. We found that juveniles had dense Oxtr binding in the dentate gyrus of the hippocampus, amygdala, lateral septum, bed nucleus of the stria terminalis and medial geniculate nucleus. Juveniles had low to modest levels of Avpr1a binding in the medial preoptic area, olfactory bulbs, nucleus accumbens, superior colliculus, and inferior colliculus. We noted Oxtr and Avpr1a binding in the social behavior neural network (SBNN), further supporting a role of these nonapeptides in modulating social behavior across taxa. Oxtr and Avpr1a binding was also present in brain regions important to auditory processing that have known projections to the SBNN. We speculate that these neural substrates may be where these nonapeptides regulate communication.

Species, sex and individual differences in the vasotocin/vasopressin system: relationship to neurochemical signaling in the social behavior neural network

Arginine-vasotocin (AVT)/arginine vasopressin (AVP) are members of the AVP/oxytocin (OT) superfamily of peptides that are involved in the regulation of social behavior, social cognition and emotion. Comparative studies have revealed that AVT/AVP and their receptors are found throughout the "social behavior neural network (SBNN)" and display the properties expected from a signaling system that controls social behavior (i.e., species, sex and individual differences and modulation by gonadal hormones and social factors). Neurochemical signaling within the SBNN likely involves a complex combination of synaptic mechanisms that co-release multiple chemical signals (e.g., classical neurotransmitters and AVT/AVP as well as other peptides) and non-synaptic mechanisms (i.e., volume transmission). Crosstalk between AVP/OT peptides and receptors within the SBNN is likely. A better understanding of the functional properties of neurochemical signaling in the SBNN will allow for a more refined examination of the relationships between this peptide system and species, sex and individual differences in sociality.

Suprachiasmatic vasopressin and the circadian regulation of voluntary locomotor behavior

A role for arginine vasopressin in the circadian regulation of voluntary locomotor behavior (wheel running activity) was investigated in the golden hamster, Mesocricetus auratus. Spontaneous nocturnal running was suppressed in a dose-dependent manner by systemic injections of vasopressin, and also in a concentration-dependent manner by microinjections directly into the hypothalamic suprachiasmatic nucleus. Pre-injections of a vasopressin V1 receptor antagonist into the nucleus reduced the suppression of behavior by vasopressin. Ethogram analyses revealed that peripheral drug injections predominantly increased grooming, flank marking, and sleep-related behaviors. Central injections did not induce sleep, but increased grooming and periods of 'quiet vigilance' (awake but not moving). Nocturnal behavioral profiles following either peripheral or central injections were similar to those shown by untreated animals in the hour prior to the onset of nocturnal wheel running. Site control vasopressin injections into the medial preoptic area or periaqueductal gray increased flank marking and grooming, but had no significant effect on locomotion, suggesting behavioral specificity of a vasopressin target near the suprachiasmatic nucleus. Both peripheral and central administration increased FOS-like immunoreactivity in the retinorecipient core of the suprachiasmatic nucleus. The distribution of FOS-positive cells overlapped the calbindin subregion, but was more extensive, and most calbindin-positive cells did not co-express FOS. We propose a model of temporal behavioral regulation wherein voluntary behavior, such as nocturnal locomotor activity, is inhibited by the activity of neurons in the suprachiasmatic ventrolateral core that project to the posterior hypothalamus and are driven by rhythmic vasopressin input from the dorsomedial shell.

The medial preoptic area is necessary for sexual odor preference, but not sexual solicitation, in female Syrian hamsters

Precopulatory behaviors that are preferentially directed towards opposite-sex conspecifics are critical for successful reproduction, particularly in species wherein the sexes live in isolation, such as Syrian hamsters (Mesocricetus auratus). In females, these behaviors include sexual odor preference and vaginal scent marking. The neural regulation of precopulatory behaviors is thought to involve a network of forebrain areas that includes the medial amygdala (MA), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA). Although MA and BNST are necessary for sexual odor preference and preferential vaginal marking to male odors, respectively, the role of MPOA in odor-guided female precopulatory behaviors is not well understood. To address this issue, female Syrian hamsters with bilateral, excitotoxic lesions of MPOA (MPOA-X) or sham lesions (SHAM) were tested for sexual odor investigation, scent marking, and lordosis. MPOA-X females did not investigate male odors more than female odors in an odor preference test, indicating that MPOA may be necessary for normal sexual odor preference in female hamsters. This loss of preference cannot be attributed to a sensory deficit, since MPOA-X females successfully discriminated male odors from female odors during an odor discrimination test. Surprisingly, no deficits in vaginal scent marking were observed in MPOA-X females, although these females did exhibit decreased overall levels of flank marking compared to SHAM females. Finally, all MPOA-X females exhibited lordosis appropriately. These results suggest that MPOA plays a critical role in the neural regulation of certain aspects of odor-guided precopulatory behaviors in female Syrian hamsters.

Photoperiodic mechanisms controlling scent marking: interactions of vasopressin and gonadal steroids

Microinjection of arginine vasopressin (Avp) into the rostral hypothalamus of Syrian hamsters induces a form of scent marking known as flank marking. The ability of Avp to stimulate flank marking is mediated by the vasopressin 1a receptor (Avpr1a). In hamsters housed in long 'summer-like' photoperiods, the amount of flank marking and the number of Avpr1a receptors in the rostral hypothalamus are regulated by testosterone. However, hamsters housed in short 'winter-like' photoperiods for 6-8 weeks continue to flank mark at high levels despite significant reductions in the circulating levels of testosterone. In the present study, we compared the effects of gonadal steroids on Avp-induced flank marking and Avpr1a binding and affinity in hamsters housed in short photoperiods and those housed in long photoperiods. In long-photoperiod-housed hamsters, castration significantly reduced the amount of Avp-induced flank marking; however, in short-photoperiod-housed hamsters there were no significant differences between gonadally regressed and castrated hamsters. Surprisingly, Avpr1a receptor binding, but not affinity, in the medial preoptic area and the medial preoptic nucleus was significantly reduced in long-photoperiod-housed castrates as well as short-photoperiod-housed gonadally regressed and castrated hamsters, compared with long-photoperiod-housed gonadally intact hamsters. These data demonstrate that in short photoperiods Avp-induced flank marking is independent of gonadal hormones, despite gonadal steroid-dependent reductions in Avpr1a binding.

Ibotenic acid lesions of the medial preoptic area disrupt the expression of partner preference in sexually receptive female rats

The present study evaluated the effects of ibotenic acid lesions of the medial preoptic area (mPOA) on the display of partner preference in ovariectomized, estrogen- and progesterone-primed rats. Preference for a sexually vigorous male or an estrous female rat was determined in one of two conditions: unlimited physical access to the stimulus rats (Contact condition) or access that was limited to olfactory, auditory and visual cues (No-contact condition). Lesions of the mPOA reduced the male preference, social preference, and arena crossings, independent of test condition. However, the reduction in male preference following mPOA lesions was most pronounced during tests with unlimited physical access. These results suggest that the mPOA may be involved in integrating somatosensory signals from coital stimulation with the motor responses associated with the appetitive aspects of female sexual behavior.

New developments in tracing neural circuits with herpesviruses

Certain neurotropic viruses can invade the nervous system of their hosts and spread in chains of synaptically connected neurons. Consequently, it is possible to identify entire hierarchically connected circuits within an animal. In this review, we discuss the use of neurotropic herpesviruses as neuronal tract tracers. Although a variety of tract tracing viruses are available, each with its own unique infection characteristics, we focus on the widespread use of attenuated strains of pseudorabies virus (PRV), a swine herpesvirus with a broad host range. In particular, we focus on new applications of PRV for tract tracing including use of multiple infections by PRV reporter viruses to test for circuit convergence/divergence within the same animal. We provide examples of these combined application techniques within the context of an animal model to study the naturally occurring reversal of seasonal obesity in Siberian hamsters.

Short-photoperiod exposure reduces vasopressin (V1a) receptor binding but not arginine-vasopressin-induced flank marking in male Syrian hamsters

In Syrian hamsters, socially relevant information is communicated with a form of scent marking known as flank marking. There is substantial evidence that arginine-vasopressin acting on V1a vasopressin receptors (V1aR) in the medial preoptic-anterior hypothalamic continuum (MPOA-AH) regulates the expression of flank marking. Previous studies have shown that the expression of flank marking is also influenced by the circulating concentrations of gonadal hormones. In hamsters housed in long 'summer-like' photoperiods (i.e. >12.5 h of light/day), castration reduces flank marking and administration of testosterone restores precastration levels of flank marking. When exposed to short 'winter-like' photoperiods (i.e. <12.5 h of light/day), hamsters undergo gonadal regression and the circulating levels of testosterone decline. Surprisingly, flank marking induced during social encounters is not reduced in hamsters exposed to short photoperiods despite the low circulating concentrations of testosterone. In the present study, it was hypothesized that reductions in testosterone, caused by exposure to short photoperiod, would not reduce the ability of vasopressin to stimulate flank marking by its actions in the MPOA-AH. The amount of flank marking induced by vasopressin injected into the MPOA-AH did not significantly differ between hamsters housed in long and short photoperiods; however, short photoperiod-exposed males had significantly less V1aR binding in the MPOA than long photoperiod-exposed males. These results support the hypothesis that the sensitivity of the MPOA-AH to vasopressin is not reduced in short photoperiod-exposed males, despite decreases in serum testosterone. However, by contrast to our predictions, short photoperiod-exposed males have significantly reduced V1aR binding in the MPOA-AH compared to long photoperiod-exposed males.

Representations of motivational drives in mesial cortex, medial thalamus, hypothalamus and midbrain

We propose that neural representations of motivational drives, including sexual desire, hunger, thirst, fear, power-dominance, the motivational aspect of pain, the need for sleep, and nurturance, are represented in four areas in the brain. These are located in the medial hypothalamic/preoptic area, the periaqueductal gray matter (PAG) in the midbrain/pons, the midline and intralaminar thalamic nuclei, and in the anterior part of the mesial cortex, including the medial prefrontal and anterior cingulate areas. We attempt to determine the locations of each of these representations within the hypothalamus/preoptic area, periaqueductal gray and cortex, based on the available literature on activation of brain structures by stimuli that evoke these forms of motivation, on the effects of electrical and chemical stimulation and lesions of candidate structures, and on hodological data. We discuss the hierarchical organization of the representations for a given drive, outputs from these representations to premotor structures in the medulla, caudate-putamen, and cortex, and their contributions to involuntary, learned-sequential (operant) and voluntary behaviors.

Fear and power-dominance motivation: proposed contributions of peptide hormones present in cerebrospinal fluid and plasma

We propose that fear and power-dominance drive motivation are generated by the presence of elevated plasma and cerebrospinal fluid (CSF) levels of certain peptide hormones. For the fear drive, the controlling hormone is corticotropin releasing factor, and we argue that elevated CSF and plasma levels of this peptide which occur as a result of fear-evoking and other stressful experiences in the recent past are detected and transduced into neuronal activities by neurons in the vicinity of the third ventricle, primarily in the periventricular and arcuate hypothalamic nuclei. For the power-dominance drive, we propose that the primary signal is the CSF concentration of vasopressin, which is detected in two circumventricular organs, the subfornical organ and organum vasculosum of the lamina terminalis. We suggest that the peptide-generated signals detected in periventricular structures are transmitted to four areas in which neuronal activities represent fear and power-dominance: one in the medial hypothalamus, one in the dorsolateral quadrant of the periaqueductal gray matter, a third in the midline thalamic nuclei, and the fourth within medial prefrontal cortex. The probable purpose of this system is to maintain a state of fear or anger and consequent vigilant or aggressive behavior after the initial fear- or anger-inducing stimulus is no longer perceptible. We further propose that all the motivational drives, including thirst, hunger and sexual desire are generated in part by non-steroidal hormonal signals, and that the unstimulated motivational status of an individual is determined by the relative CSF and plasma levels of several peptide hormones.

Fear and power-dominance drive motivation: neural representations and pathways mediating sensory and mnemonic inputs, and outputs to premotor structures

Based on the available literature on activation of brain structures by fear- and anger-inducing stimuli, on the effects of electrical and chemical stimulation and lesions of candidate structures, and on connectional data, we propose that both the fear and power-dominance drives are represented in four distinct locations: the medial hypothalamus, lateral/dorsolateral periaqueductal gray, midline thalamic nuclei, and medial prefrontal cortex. The hypothalamic fear representation is located in the dorsomedial and posterior hypothalamic nuclei, the midbrain representation in the caudal part of the lateral/dorsolateral periaqueductal gray, the thalamic representation primarily in parts of the paraventricular and reuniens thalamic nuclei, and the cortical representation in prelimbic cortex. The hypothalamic power-dominance representation is located in the anterior hypothalamic nucleus, dorsomedial aspect of the ventromedial nucleus, and in adjacent parts of the medial preoptic area. The corresponding midbrain representation occurs in rostral part of the lateral/dorsolateral periaqueductal gray, and the thalamic representation in parts of the paraventricular, parataenial, and reuniens thalamic nuclei. We discuss sensory/mnemonic inputs to these representations, and outputs to premotor structures in the medulla, caudate-putamen, and cortex, and their differential contributions to involuntary, learned sequential, and voluntary motor acts. We examine potential contributions of neuronal activities in these representations to the subjective awareness of fear and anger.

Social experience and social context alter the behavioral response to centrally administered oxytocin in female Syrian hamsters

The type of social behavior displayed by an individual is profoundly influenced by its immediate social environment or context and its prior social experience. Although oxytocin is important in the expression of social behavior in several species, it is not known if social factors alter the ability of oxytocin to influence behavior. The purpose of the present study was to test the hypothesis that social experience and social context alter the ability of oxytocin to regulate flank marking (a form of scent marking) in female Syrian hamsters. Oxytocin was microinjected into the medial preoptic anterior hypothalamic continuum (MPOA-AH) of socially experienced, dominant female hamsters which were then tested with either a subordinate partner, with a novel partner, or alone. Oxytocin induced flank marking in a dose-dependent manner but only when the experienced dominant hamsters were tested with their familiar, subordinate partners. Oxytocin did not induce flank marking when injected into socially naive female hamsters that were tested with an opponent or alone. In males, by contrast, oxytocin induced flank marking in dominant hamsters when they were tested with their subordinate partner or alone. These data support the hypothesis that social experience and social context interact to regulate the ability of oxytocin to stimulate flank marking by its actions in the MPOA-AH in female hamsters.

The neuroendocrine basis of social recognition

All social relationships are dependent on an organism's ability to remember conspecifics. Social memory may be a unique form of memory, critical for reproduction, territorial defense, and the establishment of dominance hierarchies in a natural context. In the laboratory, social memory can be assessed reliably by measuring the reduction in investigation of a familiar partner relative to novel conspecifics. The neurohypophyseal neuropeptides oxytocin and vasopressin have been shown to influence a number of forms of social behavior, including affiliation, aggression, and reproduction. This article reviews vasopressin and oxytocin effects on social cognition, particularly the acquisition and retention of social recognition in rats and mice. Studies in rats have demonstrated that vasopressin in specific neural pathways, such as the lateral septum, is necessary for social recognition. As vasopressin facilitates recall when given after an initial encounter, the peptide appears important for the consolidation not the acquisition of a social memory. Although oxytocin has complex effects on social memory in rats, mice with a null mutation of the oxytocin gene are completely socially amnestic without other cognitive deficits evident. As oxytocin given centrally before but not after the initial encounter restores social recognition in these mutant mice, the neuropeptide appears critical for the acquisition rather than the consolidation phase of memory. Oxytocin's effects on social memory are mediated via a discrete cell population in the medial amygdala. These findings support the hypothesis that vasopressin and oxytocin are essential for social memory, although they appear to influence different cognitive processes and may modulate different neural systems. (c) Elsevier Science.

Vasopressin-dependent flank marking in golden hamsters is suppressed by drugs used in the treatment of obsessive-compulsive disorder

BACKGROUND

Alterations in arginine vasopressin regulation and secretion have been proposed as one possible biochemical abnormality in patients with obsessive-compulsive disorder. In golden hamsters, arginine vasopressin microinjections into the anterior hypothalamus trigger robust grooming and flank marking, a stereotyped scent marking behaviors. The intensity and repetition of the behaviors induced by arginine vasopressin is somewhat reminiscent of Obsessive Compulsive Disorder in humans. The present experiments were carried out to test whether pharmacological agents used to alleviate obsessive compulsive disorder could inhibit arginine vasopressin-induced flank marking and grooming.

RESULTS

Male golden hamsters were treated daily for two weeks with either vehicle, fluoxetine, clomipramine, or desipramine (an ineffective drug), before being tested for arginine vasopressin-induced flank marking and grooming. Flank marking was significantly inhibited in animals treated with fluoxetine or clomipramine but unaffected by treatment with desipramine. Grooming behavior was not affected by any treatment.

CONCLUSION

These data suggest that arginine vasopressin-induced flank marking may serve as an animal model for screening drugs used in the control of Obsessive Compulsive Disorder.

Vasopressin into the preoptic area increases grooming behavior in mice

In mice, the neuropeptide arginine-8-vasopressin (AVP) induces excessive grooming, scratching, and hyperactivity when administered intracerebroventricularly. In hamsters, AVP infusion into the medial preoptic area/anterior hypothalamus (MPOA/AH) increases flank marking and flank mark grooming. We measured the behavioral effects of administration of AVP (0, 1, and 10 ng/250 nl) into the preoptic area (POA) of male C57BL/6 mice. Administration of AVP into the POA induced robust effects on grooming, including increased hindleg scratching and face washing. Rearing and olfactory investigation were inhibited by AVP into the POA. These findings indicate that the POA is one site in which AVP induces grooming behavior in mice.

Repeated cocaine treatment activates flank marking in adolescent female hamsters

Cocaine abuse during adolescence represents a significant health risk due to the potential for both acute and long-term negative physical and psychological sequelae, including increased aggressive behavior. This study examined the effect of adolescent cocaine treatment on flank marking (i.e., a stereotypic motor behavior that is part of the response pattern of offensive aggression) in female and male Syrian hamsters (Mesocricetus auratus). Adolescent cocaine treatment activated flank marking in female hamsters when animals were measured upon return to their home cage immediately following drug treatment. Sex differences were observed in cocaine-induced flank marking, as males failed to flank mark when returned to the home cage. In females, the behavioral response was most marked on Day 11 of cocaine treatment in all doses tested. Yet, animals treated with low-dose cocaine (0.5 mg/kg/day) showed the most significant increase in flank marking on and from Day 11 forward as compared to medium- and high-dose cocaine-treated animals and controls. In addition, the response of cocaine-treated animals was vigorous and nearly immediate, as >75% of the flank marks scored were performed within the first 2 min of the behavioral test in >85% of animals examined. Measures of locomotion showed that cocaine had stimulatory effects on motor activity in adolescent female hamsters at all doses tested. Cocaine-treated animals did not differ in body weight gain from controls, suggesting no dramatic physiological effects of adolescent cocaine exposure on body growth at the doses tested.

Injection of oxytocin into the medial preoptic-anterior hypothalamus increases ultrasound production by female hamsters

Recent studies of hamsters have documented the facilitation of lordosis and other sociosexual responses by injections of oxytocin (OXT) into the medial preoptic area-anterior hypothalamus (MPOA-AH). These data suggest the regulation of social interaction and bonds by OXT. In turn, this suggests that OXT could act in the MPOA-AH to control other behaviors involved in the initiation or maintenance of social contact, including the ultrasonic vocalizations that female hamsters use to alert and attract potential mates. To test this possibility, we compared the ultrasound rates of 11 naturally estrous hamsters before and after injections of OXT (200 ng/200 nl of saline) or saline (200 nl) into the MPOA-AH. The data revealed a clear facilitation of ultrasound rate 30 min after OXT treatment. This result suggests the modulation of ultrasound rate by endogenous OXT acting within the MPOA-AH. It extends the range of social behaviors sensitive to control by OXT and supports the possibility that OXT acts within the MPOA-AH to facilitate a variety of behaviors involved in the establishment or maintenance of the social interactions required for successful reproduction. At the same time, these data extend earlier observations linking ultrasound production to the MPOA-AH, and begin to describe the peptidergic mechanisms controlling this form of reproductive behavior.

Behavioral consequences of intracerebral vasopressin and oxytocin: focus on learning and memory

Since the pioneering work of David de Wied and his colleagues, the neuropeptides arginine vasopressin and oxytocin have been thought to play a pivotal role in behavioral regulation in general, and in learning and memory in particular. The present review focuses on the behavioral effects of intracerebral arginine vasopressin and oxytocin, with particular emphasis on the role of these neuropeptides as signals in interneuronal communication. We also discuss several methodological approaches that have been used to reveal the importance of these intracerebral neuropeptides as signals within signaling cascades. The literature suggests that arginine vasopressin improves, and oxytocin impairs, learning and memory. However, a critical analysis of the subject indicates the necessity for a revision of this generalized concept. We suggest that, depending on the behavioral test and the brain area under study, these endogenous neuropeptides are differentially involved in behavioral regulation; thus, generalizations derived from a single behavioral task should be avoided. In particular, recent studies on rodents indicate that socially relevant behaviors triggered by olfactory stimuli and paradigms in which the animals have to cope with an intense stressor (e.g., foot-shock motivated active or passive avoidance) are controlled by both arginine vasopressin and oxytocin released intracerebrally.

Norepinephrine inhibits vasopressin-stimulated flank marking in the Syrian hamster by acting within the medial preoptic-anterior hypothalamus

Syrian hamsters exhibit a form of scent marking behavior called flank marking. Flank marking, which is elicited during social contact with other hamsters and by the odors of other hamsters, communicates socially important information such as mate choice and dominance status. Vasopressinergic activity within the medial preoptic-anterior hypothalamic continuum (MPOA-AH) is essential for the expression of flank marking. In female hamsters, an inverse relationship exists between the expression of flank marking and sexual receptivity during the 4-day estrous cycle. Since norepinephrine (NE) appears to facilitate sexual receptivity, the present study investigated whether NE might have an inhibitory effect on flank marking by acting on Vasopressinergic activity within the MPOA-AH. Microinjection of 9.0 μM arginine vasopressin (AVP) into the MPOA-AH stimulated high levels of flank marking. Microinjection of 9.0 μM AVP combined with NE in concentrations of 4.0, 0.4 or 0.2 nM, drastically reduced or eliminated flank marking. In contrast, AVP in combination with 0.09, 0.04 or 0.004 nM NE produced no significant reductions in flank marking. In addition, microinjection of 9.0 μM AVP, in combination with epinephrine (4.0 nM), but not dopamine (4.0 nM), serotonin (4.0 nM) or neuropeptide Y (900 μM), significantly reduced AVP-induced flank marking. In male hamsters, microinjection of NE (4.0 nM) combined with AVP (9.0 μM) into the MPOA-AH was not found to inhibit AVP-stimulated flank marking. These results suggest that NE is involved in regulating the expression of flank marking during the estrous cycle by acting on Vasopressinergic activity within the MPOA-AH.

Vasopressin innervation of sexually dimorphic structures of the gerbil forebrain under various hormonal conditions

The distribution of vasopressin-immunoreactive fibers in the forebrain of male and female gerbils was studied, focusing on the lateral septum and the sexually dimorphic area (SDA) found at the border between the medial preoptic area and the anterior hypothalamus. To study hormonal influences on the densities of these fibers, some animals of each sex were gonadectomized or gonadectomized and given testosterone. Others were given sham operations. High densities of vasopressin-immunoreactive fibers were found in the lateral septum. In the SDA, the densities of these fibers varied considerably. Many were found in the medial half of the medial SDA, but few in the lateral SDA. Vasopressin-immunoreactive fibers were also sparse in the lateral half of the medial SDA, except for a dense cluster in the SDA pars compacta of males. Similar but smaller clusters were seen in the same location in females although the SDA pars compacta could not be detected in Nissl-stained sections from the female brains. Fiber densities in two areas, the lateral septum and the lateral SDA, were sensitive to gonadal steroids. In both cases, castration reduced fiber density and testosterone enhanced it. In addition, fiber densities in two areas, the lateral septum and the medial SDA, were sexually dimorphic. In each case, fiber density was greater in males. There was no hormonal effect, however, on the fiber densities in the medial SDA. The fact that the fiber plexuses in the lateral septum and the medial SDA respond differently to gonadal steroids suggests that they arise from different cells and possibly from different areas of the brain. The vasopressin-immunoreactive fibers in the lateral septum probably come from steroid-sensitive vasopressin neurons in the bed nucleus of the stria terminalis. Those in the medial SDA may originate in the dorsal aspect of the suprachiasmatic nucleus where vasopressin-immunoreactive cell bodies were seen.

Microinjection of arginine-vasopressin into the periaqueductal gray stimulates flank marking in Syrian hamsters (Mesocricetus auratus)

Syrian hamsters can communicate using a distinctive form of scent marking called flank marking. Vasopressin-sensitive neurons within the medial preoptic-anterior hypothalamic continuum (MPOA-AH) play a critical role in the control of this form of olfactory communication. Extrahypothalamic regions may also mediate hamster flank marking. Since the MPOA-AH and the periaqueductal gray (PAG) are reciprocally connected, the present study investigated whether PAG neurons are involved in the control of flank marking. The first study found that microinjection of vasopressin, but not oxytocin or saline, into the PAG induced high levels of flank marking in male (n = 8) and female (n = 5) hamsters (P less than 0.01). The second study demonstrated that microinjection of vasopressin into the PAG stimulated flank marking in a dose-dependent manner in both male (n = 7) and female (n = 11) hamsters (P less than 0.01). These data suggest that vasopressin-responsive neurons within the periaqueductal gray participate in the control of hamster flank marking.

Role of the flank gland in vasopressin induced scent marking behavior in the hamster

The present study examined whether the induction of scent marking behavior and grooming of the flank gland region by injection of arginine-vasopressin (AVP) or oxytocin (OXY) into the anterior hypothalamus-medial preoptic area (AH-MPOA) required the presence of the flank glands. The flank glands were surgically removed (GLDX) in ten hamsters or patches of skin just dorsal to the flank glands were removed (SHAM) in the control group (N = 7). No statistically significant differences were observed in flank marking or flank grooming between the GLDX and SHAM groups during a 10 min test period immediately following injection of AVP or OXY. AVP and OXY injection produced similar amounts of flank grooming, but AVP resulted in significantly (p less than 0.01) more flank marking than OXY. These data indicate that scent marking induced by AVP injected into the AH-MPOA is similar to environmentally induced scent marking in not requiring the presence of an intact scent gland.

A vasopressin antagonist can reverse dominant/subordinate behavior in hamsters

Golden hamsters communicate dominance status by flank marking, a behavior that is dependent upon vasopressin-sensitive neurons in the anterior hypothalamus-medial preoptic area (AH-MPOA). The purpose of the present study was to investigate whether arginine vasopressin (AVP) and an antagonist of AVP could alter or reverse dominant/subordinate relationships in pairs of hamsters. Microinjection of AVP into the AH-MPOA of subordinate hamsters dramatically increased their flank marking despite the presence of their dominant partners. Conversely, microinjection of the AVP antagonist into the AH-MPOA of dominant hamsters blocked flank marking in the presence of their subordinate partners. Surprisingly, the untreated subordinate hamsters significantly increased their own flank marking when tested with their dominant partners treated with the AVP antagonist, thereby reversing the pattern of flank marking normally seen in dominant/subordinate relationships. However, the effect of AVP and the AVP antagonist were limited to the day of treatment. When flank marking behavior was reversed in a pair of hamsters by treatments for three consecutive days, the pair immediately displayed the original dominant/subordinate behavior when treatment was stopped.