Comparison of arginine vasotocin immunoreactivity differences in dominant and subordinate green anole lizards.

ABSTRACT

The neuropeptide arginine vasotocin (AVT) and its mammalian homologue arginine vasopressin (AVP) are believed to be involved in many social behaviors including territorial aggression. Testosterone (T) is also important for controlling territorial aggression, and it is believed to be involved in modulating AVT/AVP levels in the brain. In this study, male Anolis carolinensis were paired (n=11 pairs) in a neutral cage and were allowed to establish a dominant-subordinate relationship for 10 days (experimental groups) or housed in a neutral cage with or without a female (control groups; each n=4). On 10th day animals were sacrificed and their brain sections were processed for AVT immunohistochemistry and their serum was analyzed for testosterone levels. AVT immunoreactive (AVT-ir) cell numbers were counted in the anterior hypothalamus (AH), paraventricular nucleus (PN), posterior hypothalamus (PH), preoptic area (POA), and supra optic nuclei (SON). 2-way randomized block design was conducted to assess AVT-ir cell number differences between dominant and subordinate animals and Pearson's correlations were used to determine if a relationship existed between T levels and AVT-ir cell numbers. Dominant animals had more AVT-ir cells in the POA compared to subordinate animals, and subordinate animals had fewer AVT-ir cells in the POA compared to males housed either singly or with a female. There were no differences in AVT-ir cell numbers between dominant and subordinate animals in other areas. T levels were not correlated with the AVT-ir cell numbers in any area. Thus dominant animals have increased AVT-ir cell numbers compared to subordinate animals in a brain region known to be important in male sexual behavior. However, this difference is not related to differences in T.