Androgen Metabolism in the Brain of the Green Anole Lizard (Anolis carolinensis): Effects of Sex and Season

Abstract

Courtship behavior in male green anoles is partly mediated by the 5α-reductase enzyme, which converts testosterone (T) to 5α-dihydrotestosterone. This study aimed to determine whether the activity of 5α-reductase is enhanced in breeding males compared to females and nonbreeding males who do not normally display masculine behaviors. In some cases, aromatase, which converts T to 17β-estradiol, also was assessed to determine whether the pattern of its activity in anoles is similar to that in other vertebrates. 5α-Reductase is greatest in the brainstem, so its activity was determined separately in homogenates of whole brain and brainstems. The following comparisons were done in different assays: (1) breeding males with breeding females, (2) nonbreeding males with nonbreeding females, and (3) breeding males with nonbreeding males. Aromatase activity was greater in breeding males (mean ± SE, 0.61 ± 0.06 fmol/min/mg protein) than in breeding females (0.41 ± 0.08 fmol/min/mg protein). It was also greater in breeding males (0.84 ± 0.16 fmol/min/mg protein) than in nonbreeding males (0.33 ± 0.07 fmol/min/mg protein). In contrast, sex or seasonal differences did not exist in 5α-reductase activity. The results are consistent with those of other vertebrate species in which male-biased sex dimorphisms and seasonal differences occur in aromatase, but not in 5α-reductase activity. The greater levels of aromatase activity in breeding male anoles suggest that this enzyme might mediate male-specific functions. The equivalently high levels of 5α-reductase activity in both sexes suggests that, in addition to facilitating male courtship behavior, the enzyme has a basic function common to both sexes.