Dendritic arbor of neurons in the hypothalamic ventromedial nucleus in female prairie voles (Microtus ochrogaster)

Abstract

Female mating behavior in rats is associated with hormone-induced changes in the dendritic arbor of neurons in the ventromedial nucleus of the hypothalamus (VMH), particularly the ventrolateral portion. Regulation of mating behavior in female prairie voles differs substantially from that in rats; therefore, we examined the dendritic morphology of VMH neurons in this species. Sexually naïve adult female prairie voles were housed with a male to activate the females' reproductive endocrine system. Following 48h of cohabitation, females were tested for evidence of reproductive activation by assessing the level of male sexual interest, after which their brains were processed using Golgi impregnation, which allowed ventrolateral VMH neurons to be visualized and analyzed. Dendritic arborization in the female prairie vole VMH neurons was strikingly similar to that of female rats. The key difference was that in the prairie voles the long primary dendrites extended considerably further than those observed in rats. Although most female voles paired with males exhibited sexual activation, some females did not. These two groups displayed specific differences in their VMH dendrites. In particular, the long primary dendrites were longer in the reproductively active females compared with those in the non-activated females. Overall, dendrite lengths were positively correlated with plasma estradiol levels in females exposed to males, but not in unpaired females. Although causal relationships between the neuroendocrine events, dendrite length, and the outward, behavioral manifestation of reproductive activation cannot be determined from this study, these results suggest an association between ventrolateral VMH dendrite morphology and female mating behavior in prairie voles, akin to what has been observed in female rats.