Meeting Abstract
Numerous studies have reported seasonal variations in regional morphology in the brains of seasonally breeding vertebrates. In many cases, this neural plasticity has been found to be in response to changes in circulating sex steroid hormone levels and occur within pathways essential for the control of reproductive behaviors. Male red-sided garter snakes (Thamnophis sirtalis parietalis) exhibit a dissociated reproductive pattern where mating is initiated at a time when the gonads and steroidogenesis are inactive. The current study examined seasonal and hormonal influences on the density and morphology of dendritic spines within regions shown to be critical for the regulation of reproductive behaviors. In many seasonally breeding species, alteration of dendritic spine density and/or morphology appears to be an active process within neural regions regulating reproductive behaviors. In male red-sided garter snakes, dendritic spines on neurons within pathways controlling reproductive behaviors are dramatically denser during spring mating than in fall collected non-mating individuals. In addition, animals maintained under conditions of low temperature dormancy (LTD) exhibited increasing spine density the longer animals were maintained in LTD. Animals receiving either testosterone or estradiol exhibited greater density of dendritic spines than control animals. These results add to the increasing amount of evidence suggesting that testosterone may play a critical, although indirect, role in the regulation of reproductive activity in an animal exhibiting a dissociated reproductive pattern.
