Our 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). Most of our studies, however, 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 behavior via one or more tiers of these neuroendocrine pathways.
The goal of this project is to assess the role of adrenal MT1 melatonin receptor signaling in regulating seasonal aggression in male Siberian hamsters. For this study, I will infuse MT1 melatonin receptor (MT1)-overexpressing lentivirus bilaterally into the adrenal glands to measure the effects of adrenal mt1 overexpression on aggressive and non-aggressive social behaviors. Unlike most mammals, which possess two subtypes of melatonin receptor (i.e., the MT1 and MT2 melatonin receptors), Siberian hamsters only possess one functional melatonin receptor: the MT1 receptor. 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 MT1 receptor subtype in these animals.
This project is being conducted in collaboration with Aaron Jasnow at Kent State University.