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.