Green anole lizards breed seasonally, with an annual rise in testosterone (T) regulating male sexual behavior.  T, acting at androgen receptors (AR), has dramatic effects on these behaviors, as well as on related morphological and biochemical functions in the brain, during the breeding season (BS).  In many cases, these effects of T are diminished or non-existent in the non-breeding season (NBS).  While changes in AR across season could confer this differential responsiveness, an alternate possibility involves changes in AR coactivators.  We hypothesized that increased expression of steroid receptor coactivator-1 (SRC-1) in the BS facilitates responsiveness to T in the male brain.  In situ hybridization was performed on the brains of gonadally intact male and female anoles from the BS and NBS.  In the preoptic area, males had more cells expressing SRC-1 mRNA and the volume defined by this labeling was greater than in than females (F≥4.60, p≤0.040).  Main effects of sex, season, and a significant sex x season interaction existed in the ventromedial hypothalamus for both total SRC-1+ cell number and brain region volume (all F≥4.42, p≤0.045).  The interaction was driven by BS males, which had more cells and larger volumes than females from both seasons and NBS males (all t≥2.85, p≤0.014).  A significant sex x season interaction was also found in the density of SRC-1 cells in this region (F=7.74, p=0.010).  Among females, it was greater in the NBS than BS (t=2.69, p=0.017), and within the BS a trend existed for males to have a higher density than females (t=2.49, p=0.027).  No significant effects were observed in the amygdala (F≤3.30, p≥0.080). Collectively, the results are consistent with the idea that SRC-1 facilitates some regionally specific sex and seasonal differences in responsiveness to T.

This work was supported by NSF Grant IOS-0742833.