Abstract
Species differences in neurochemical expression and activity in the brain may play an important role in species-specific patterns of social behavior. In the present study, we used immunoreactive (ir) labeling to compare the regional density of cells containing oxytocin (OT), vasopressin (AVP), tyrosine hydroxylase (TH), or estrogen receptor alpha (ERα) staining in the brains of social Mongolian gerbils (Meriones unguiculatus) and solitary Chinese striped hamsters (Cricetulus barabensis). Multiple region- and neurochemical-specific species differences were found. In the anterior hypothalamus (AH), Mongolian gerbils had higher densities of AVP-ir and ERα-ir cells than Chinese striped hamsters. In the lateral hypothalamus (LH), Mongolian gerbils also had higher densities of AVP-ir and TH-ir cells, but a lower density of OT-ir cells, than Chinese striped hamsters. Furthermore, in the anterior nucleus of the medial preoptic area (MPOAa), Mongolian gerbils had higher densities of OT-ir and AVP-ir cells than Chinese striped hamsters, and an opposite pattern was found in the posterior nucleus of the MPOA (MPOAp). Some sex differences were also observed. Females of both species had higher densities of TH-ir cells in the MPOAa and of OT-ir cells in the intermediate nucleus of the MPOA (MPOAi) than males. Given the role of these neurochemicals in social behaviors, our data provide additional evidence to support the notion that species-specific patterns of neurochemical expression in the brain may be involved in species differences in social behaviors associated with different life strategies.
Highlights
Animals show remarkable differences in their life strategies and social behaviors
We extended our efforts to additional rodent species, Mongolian gerbils (Meriones unguiculatus) and Chinese striped hamsters (Cricetulus barabensis), to further test the hypothesis that differences in neurochemical systems in the brain are related to species differences in life strategies and behaviors
Very intense staining of OT-ir cells was found in the paraventricular nucleus of the hypothalamus (PVN), while moderate clusters of OT-ir cells were present throughout the rostral–caudal extent of the medial preoptic area (MPOA)
Summary
Animals show remarkable differences in their life strategies and social behaviors. Social species, for example, usually display high levels of prosocial behavior towards conspecifics, social affiliation with mates and biparental care of their offspring [1,2]. Solitary species generally display low levels of prosocial behavior and social affiliation, but high levels of aggression to defend their territory [1,3]. Such species differences in life strategy and social behavior may reflect their adaption to the environment, and indicate their potential differences in the central mechanisms that are involved in the regulation of social behavior. The receptor distribution and activity of the neuropeptides oxytocin (OT) and vasopressin (AVP) differ in the brains of social and nonsocial rodent species, and such differences are thought to be involved in the regulation of species-specific social behaviors, such as affiliation, pair bonding, male parental care and territory marking [4,5,6,7]. ERa may affect AVP expression in certain brain areas [20,21] and alters AVP-mediated behaviors, such as aggression and affiliation [22,23]
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