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

Sex Differences in the Regulation of Offensive Aggression and Dominance by Arginine-Vasopressin

Arginine-vasopressin (AVP) plays a critical role in the regulation of offensive aggression and social status in mammals. AVP is found in an extensive neural network in the brain. Here, we discuss the role of AVP in the regulation of aggression in the limbic system with an emphasis on the critical role of hypothalamic AVP in the control of aggression. In males, activation of AVP V1a receptors (V1aRs) in the hypothalamus stimulates offensive aggression, while in females activation of V1aRs inhibits aggression. Serotonin (5-HT) also acts within the hypothalamus to modulate the effects of AVP on aggression in a sex-dependent manner. Activation of 5-HT1a receptors (5-HT1aRs) inhibits aggression in males and stimulates aggression in females. There are also striking sex differences in the mechanisms underlying the acquisition of dominance. In males, the acquisition of dominance is associated with the activation of AVP-containing neurons in the hypothalamus. By contrast, in females, the acquisition of dominance is associated with the activation of 5-HT-containing neurons in the dorsal raphe. AVP and 5-HT also play critical roles in the regulation of a form of social communication that is important for the maintenance of dominance relationships. In both male and female hamsters, AVP acts via V1aRs in the hypothalamus, as well as in other limbic structures, to communicate social status through the stimulation of a form of scent marking called flank marking. 5-HT acts on 5-HT1aRs as well as other 5-HT receptors within the hypothalamus to inhibit flank marking induced by AVP in both males and females. Interestingly, while AVP and 5-HT influence the expression of aggression in opposite ways in males and females, there are no sex differences in the effects of AVP and 5-HT on the expression of social communication. Given the profound sex differences in the incidence of many psychiatric disorders and the increasing evidence for a relationship between aggressiveness/dominance and the susceptibility to these disorders, understanding the neural regulation of aggression and social status will have significant import for translational studies.

The regulation of social recognition, social communication and aggression: vasopressin in the social behavior neural network

Neuropeptides in the arginine vasotocin/arginine vasopressin (AVT/AVP) family play a major role in the regulation of social behavior by their actions in the brain. In mammals, AVP is found within a circuit of recriprocally connected limbic structures that form the social behavior neural network. This review examines the role played by AVP within this network in controlling social processes that are critical for the formation and maintenance of social relationships: social recognition, social communication and aggression. Studies in a number of mammalian species indicate that AVP and AVP V1a receptors are ideally suited to regulate the expression of social processes because of their plasticity in response to factors that influence social behavior. The pattern of AVP innervation and V1a receptors across the social behavior neural network may determine the potential range and intensity of social responses that individuals display in different social situations. Although fundamental information on how social behavior is wired in the brain is still lacking, it is clear that different social behaviors can be influenced by the actions of AVP in the same region of the network and that AVP can act within multiple regions of this network to regulate the expression of individual social behaviors. The existing data suggest that AVP can influence social behavior by modulating the interpretation of sensory information, by influencing decision making and by triggering complex motor outputs. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Photoperiodic regulation of vasopressin receptor binding in female Syrian hamsters

During long "summer-like" photoperiods, female Syrian hamsters display a regular 4-day estrous cycle. However, during short "winter-like" photoperiods (<12.5 h of light/day) hamsters become anestrus. Short photoperiod exposure eliminates reproductive behavior but social behaviors such as aggression and scent marking continue to be displayed. In long photoperiods, the types and intensity of social behaviors change as a function of the estrous cycle. For example, aggression and scent marking tend to occur at higher levels on diestrus 1 and diestrus 2 than on proestrus or estrus. Aggression and scent marking may be regulated, at least in part, by changes in the density of arginine vasopressin-V(1a) receptors (V(1a)R). In Experiment 1, it was hypothesized that the density of V(1a)R would change across the estrous cycle in several subcortical regions implicated in the regulation of aggression and scent marking. In Experiment 2, it was hypothesized that exposure to short photoperiod would alter the density of V(1a)R in several regions involved in the regulation of social behavior. Interestingly, there were no dramatic changes in V(1a)R binding across the estrous cycle within any of the neuroanatomical areas measured. However, in hamsters housed in short photoperiod, there were lower levels of V(1a)R binding within the medial preoptic nucleus (MPN), medial preoptic area (MPO), lateral hypothalamus (LH), central nucleus of the amygdala (Ce) and bed nucleus of the stria terminalis (BST) than in hamsters housed in long photoperiod. These data suggest that photoperiodic mechanisms can alter the density of V(1a)R in subset of V(1a) binding sites thought to be involved in the regulation of social behaviors in female hamsters.

Social behavior functions and related anatomical characteristics of vasotocin/vasopressin systems in vertebrates

The neuropeptide arginine vasotocin (AVT; non-mammals) and its mammalian homologue, arginine vasopressin (AVP) influence a variety of sex-typical and species-specific behaviors, and provide an integrational neural substrate for the dynamic modulation of those behaviors by endocrine and sensory stimuli. Although AVT/AVP behavioral functions and related anatomical features are increasingly well-known for individual species, ubiquitous species-specificity presents ever increasing challenges for identifying consistent structure-function patterns that are broadly meaningful. Towards this end, we provide a comprehensive review of the available literature on social behavior functions of AVT/AVP and related anatomical characteristics, inclusive of seasonal plasticity, sexual dimorphism, and steroid sensitivity. Based on this foundation, we then advance three major questions which are fundamental to a broad conceptualization of AVT/AVP social behavior functions: (1) Are there sufficient data to suggest that certain peptide functions or anatomical characteristics (neuron, fiber, and receptor distributions) are conserved across the vertebrate classes? (2) Are independently-evolved but similar behavior patterns (e.g. similar social structures) supported by convergent modifications of neuropeptide mechanisms, and if so, what mechanisms? (3) How does AVT/AVP influence behavior - by modulation of sensorimotor processes, motivational processes, or both? Hypotheses based upon these questions, rather than those based on individual organisms, should generate comparative data that will foster cross-class comparisons which are at present underrepresented in the available literature.

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.

Role of vasopressin and oxytocin in the control of social behavior in Syrian hamsters (Mesocricetus auratus)

Vasopressin (VP) and oxytocin (OT) play an important role in regulating social behavior in a variety of species as a result of their actions in the central nervous system. The following paper reviews the actions of VP and OT in controlling a range of social behaviors involved in communication, aggression and reproduction in the Syrian hamster. These data suggest that social and hormonal stimuli alter the expression of specific social behaviors by altering the release of, or the response to, VP and OT within key elements of the neural circuits controlling these behaviors.

Vasopressin and sex differences in hamster flank marking

Vasopressin (AVP) within the medial preoptic-anterior hypothalamic continuum (MPOA-AH) plays an essential role in the control of flank marking in Syrian hamsters. Sex differences are found in the scent marking of many mammalian species, including hamsters. The first two experiments tested the hypothesis that sex differences in flank marking are the result of sex differences in the availability of AVP for release in several CNS sites. No support for this hypothesis was provided because neither immunohistochemical analysis nor radioimmunoassay of tissue punches revealed sex differences in AVP immunoreactivity in the MPOA-AH or other sites likely to be involved in flank marking. The third experiment, which tested the hypothesis that sex differences in flank marking are the result of sex differences in the sensitivity or response of the MPOA-AH to AVP, found no sex differences in the amount of flank marking stimulated by microinjection of AVP in the MPOA-AH. These data provide no support for the hypothesis that sex differences in vasopressinergic activity are responsible for sex differences in flank marking.