Progesterone regulation of vasopressin-dependent social behavior

Compared to females, little is known about the effect of progesterone in the brain and on the behavior of males. It has been shown that progesterone treatment reduces vasopressin (AVP) in the bed nucleus of the stria terminalis (BST) and medial amygdala (MeA) of adult male rats, which means that progesterone might affect AVP-linked behaviors like social recognition.;We found that progesterone treatment impaired recognition in both the habituation-dishabituation and social discrimination paradigms and that this effect was blocked by pretreatment with the progestin receptor (PR) antagonist RU-486. We have also seen an impairment in social recognition with the synthetic progestin R5020, which only binds to PRs. Furthermore, progesterone appears to interfere with the formation of social recognition memory without interfering with general non-spatial memory or olfactory functioning. We believe that progesterone is influencing social recognition through the AVP system in the BST and MeA, probably via PR that are co-localized with AVP immunoreactive neurons. Additional evidence for the involvement of the AVP system comes from our finding that when AVP was infused into the lateral septum (a projection site of the BST and MeA) of rats treated with progesterone, they exhibited normal social discrimination, suggesting that AVP treatment rescued the impairment in social recognition caused by progesterone. Our results provide a strong link between the previous data from our lab showing that progesterone reduces AVP expression in the bed nucleus of the stria terminalis (BST) and medial amygdala (MeA), and the functional significance of this reduction: an impairment in social recognition behavior in adult male rats.