My manuscript on how melatonin regulates seasonal variation in neurosteroids and aggressive behavior was recently published in the Journal of Neuroendocrinology! For this study, I developed a protocol to measure the concentrations of five steroid hormones in circulation and in brain regions associated with aggressive behavior using liquid chromatography-tandem mass spectrometry (LC-MS/MS). I found that male hamsters given a long-term, short day (SD)-like melatonin signal, either via timed melatonin injections or exposure to SD photoperiods (LD-M and SD hamsters, respectively), displayed increased aggression and showed region-specific reductions in neural dehydroepiandrosterone (DHEA), testosterone (T), and estradiol (E₂) levels. I also showed that LD-M and SD hamsters exhibited similar associations between aggression and neurosteroid levels, in which neural T, E₂, and cortisol were negatively correlated with aggression, whereas neural progesterone and DHEA were positively correlated with aggression. Together, my findings suggest that seasonal changes in neurosteroid levels and aggression in mammals are mediated, at least in part, by melatonin.

A link for the manuscript can be found under the “Publications” page and can also be accessed here.

Image: coronal section of Siberian hamster brain (Nissl stained) illustrating the location at which micropunches from the periaqueductal gray (PAG), one of the brain regions of interest for this study, were acquired for LC-MS/MS analysis.