Vasopressin (V 1a ) Receptor Binding, mRNA Expression and Transcriptional Regulation by Androgen in the Syrian Hamster Brain

Arginine vasopressin plays an important role in the regulation of social behaviours in rodents. In the Syrian hamster, vasopressin injected directly into the brain stimulates scent marking and aggressive behaviour in a steroid dependent manner and is therefore a useful model for investigating steroid‐peptide–behaviour interactions. In this study, we used in situ hybridization and radioligand binding assays on adjacent sections of hamster brains to compare the relative distribution of vasopressin (V 1a ) receptor mRNA and V 1a receptor binding. V 1a receptor mRNA and binding are abundant in the lateral septum, bed nucleus of the stria terminalis, medial preoptic nucleus, anterodorsal thalamus and suprachiasmatic nucleus. Moderate receptor binding and low levels of receptor mRNA are present in the central nucleus of the amygdala and a lateral zone from the medial preoptic area through the anterior hypothalamus. V 1a receptor mRNA is anatomically more restricted in several areas compared to the ligand binding pattern, which is consistent with significant spread of receptor protein along neuronal processes. Comparison of V 1a receptor ligand binding and mRNA in intact, castrated, and castrated‐testosterone treated animals reveals that V 1a receptors in the medial preoptic nucleus are regulated by androgen, most likely by an upregulation of V 1a receptor gene expression in a cluster of neurones concentrated in the ventromedial part of this nucleus. This study confirms the presence of the V 1a subtype of vasopressin receptors in behaviourally important regions of the hamster brain and suggests that transcriptional regulation by gonadal steroids may play a role in modulating behavioural sensitivity to vasopressin.