Afferent Circuitry of the Ventromedial Hypothalamus and Its Activation in Paternal Behavior of the Socially Monogamous Prairie Vole

Paternal behavior is an interesting and important research topic due to its integral contribution to the fitness and well-being of multiple species, including humans. Although paternal behavior is well described in literature, attempts at neurobiological characterization have yielded conflicting results that fail to address brain region interconnectivity. This study was designed to evaluate the relationship between afferent VMH circuitry and the onset of paternal behavior, using the prairie vole (Microtus ochrogaster) model. Sexually naïve male prairie voles received injections of the retrograde neurotracer Fluoro-Gold (FG), into the VMH. Two weeks later, subjects were exposed to either conspecific pups, contained within a tea-ball, or an empty tea-ball (control) for 1 hr. Immunohistochemical labeling was conducted for both FG and the neuronal activity marker Egr-1, in order to evaluate neuronal and afferent pathway activation between the ventromedial hypothalamus (VMH) and the amygdala (AMYG), bed nucleus of the stria terminalis (BNST), lateral septum (LS) and ventral tegmental area (VTA). Similar to the pathway implicated in the onset of maternal behavior, the results of this study showed pup exposure-induced neuronal activation in the AMYG and BNST, particularly in the efferent pathways from these two brain areas to the VMH. This effect was not found in the LS and VTA projection neurons to the VMH. Together, the data suggests a brain region-specific neuronal activation by pup exposure in particular brain circuitry, implicating its possible involvement in paternal behavior.