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 be haviours in rodents. In the Syrian hamster, vasopressin injected directly i nto the brain stimulates scent marking and aggressive behaviour in a steroi d dependent manner and is therefore a useful model for investigating steroi d-peptide-behaviour interactions. In this study, we used in situ hybridizat ion and radioligand binding assays on adjacent sections of hamster brains t o 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 terminatis, medial preoptic nucleu s, anterodorsal thalamus and suprachiasmatic nucleus. Moderate receptor bin ding 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 a nterior 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. Compa rison of V-1a receptor ligand binding and mRNA in intact, castrated, and ca strated-testosterone treated animals reveals that V-1a receptors in the med ial preoptic nucleus are regulated by androgen, most likely by an upregulat ion 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 reg ions of the hamster brain and suggests that transcriptional regulation by g onadal steroids may play a role in modulating behavioural sensitivity to va sopressin.