Previous work suggests that melatonin mediates a “seasonal switch” from gonadal regulation of aggression during LDs to adrenal regulation of aggression during SDs in Siberian hamsters (reviewed in Munley et al. 2018, Frontiers in Endocrinology). However, each of these studies utilized timed melatonin injections to experimentally manipulate endogenous levels of circulating melatonin. Because this technique systemically alters melatonin levels, it is difficult to distinguish how melatonin acts locally to facilitate this seasonal shift in neuroendocrine regulation. Furthermore, since melatonin receptors are present in several different tissues within the hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-adrenal (HPA) axes, it possible that melatonin modulates seasonal changes in gonadal and adrenal steroid synthesis at one or more tiers of these neuroendocrine pathways.
The goal of this project is to distinguish the central and peripheral actions of melatonin on seasonal aggression in male Siberian hamsters. Specifically, I will examine how melatonin signaling at level of the receptor modulates seasonal aggression by locally infusing melatonin 1a receptor (Mel1aR)-overexpressing lentivirus in either the adrenal glands or the paraventricular hypothalamic nucleus and measuring their effects on aggressive behavior. Unlike most mammals, which possess two subtypes of melatonin receptor (i.e., Mel1aR and the melatonin 1b receptor, Mel1bR), Siberian hamsters only possess one functional melatonin receptor: Mel1aR. Thus, this species is ideal for elucidating the neuroendocrine mechanisms by which melatonin facilitates seasonal changes in aggression, since we can be confident that the actions of melatonin occur solely via the Mel1aR subtype in these animals.
This project is being conducted in collaboration with Aaron Jasnow at Kent State University.