Effects of Gonadal Steroids on the Mesoctocin and Vasotocin System in the Brain of the Domestic Hen

The mammalian nonapeptides oxytocin and vasopressin and their avian homologues mesotocin and vasotocin form part of the neural systems that govern social behaviour. Neurones in the paraventricular nucleus (PVN) and bed nucleus of the stria terminalis (BnST) are particularly sensitive to environmental and hormonal changes. Here we sought to investigate how changes in gonadal steroids effect both the mesotocin and vasotocin system of 2 month old female chickens. Specifically we compared mesotocin and vasotocin mRNA expression following a single injection of one of three sex steroids (testosterone, oestradiol, progesterone or corn oil control; n= 8/group randomly assigned) administered after a period of priming with diethylstilbetrol. Brains were collected, frozen on dry ice and sectioned on a cryostat at 15m. Animal care and use protocols were approved by the Roslin Institute and carried out under the UK Home Office license guidelines and regulations [Animal Scientific Procedures Act (1986)].
Testosterone increased mesotocin mRNA expression in both the PVN and BnST, but neither oestradiol or progesterone had any significant effect on expression. We also quantified mesotocin protein levels using immunohistochemistry, but there was no observable difference between treatments in staining intensity. Mesotocin receptors are primarily located in the lateral septum (LS) in the chicken. In this study we found no significant effect of steroid treatment on mestotocin receptors in the LS using receptor autoradiography. For vasotocin, both testosterone and oestradiol increased mRNA expression in the BnST but not the PVN. Together these findings demonstrate for the first time that gonadal steroid hormones can upregulate the mesotocin and vasotocin systems in the brain of the domestic hen and that the effect of testosterone on mesotocin mRNA expression in the BnST is direct, and not via aromatisation into oestrogen; further studies using aromatase inhibitors could test this hypothesis.

Research supported by the BBSRC and the British Society for Neuroendocrinology.