Aromatase and 5α-reductase type 2 mRNA in the green anole forebrain: An investigation of the effects of sex, season and testosterone manipulation

Abstract

Aromatase and 5α-reductase (5αR) catalyze the synthesis of testosterone (T) metabolites: estradiol and 5α-dihydrotestosterone, respectively. These enzymes are important in controlling sexual behaviors in male and female vertebrates. To investigate factors contributing to their regulation in reptiles, male and female green anole lizards were gonadectomized during the breeding and non-breeding seasons and treated with a T-filled or blank capsule. In situ hybridization was used to examine main effects of and interactions among sex, season, and T on expression of aromatase and one isozyme of 5αR (5αR2) in three brain regions that control reproductive behaviors: the preoptic area, ventromedial nucleus of the amygdala and ventromedial hypothalamus (VMH). Patterns of mRNA generally paralleled previous evaluations of intact animals. Although no main effects of T were detected, interactions were present in the VMH. Specifically, the density of 5αR2 expressing cells was greater in T-treated than control females in this region, regardless of season. Among breeding males, blank-treated males had a denser population of 5αR2 positive cells than T-treated males. Overall, T appears to have less of a role in the regulation of these enzymes than in other vertebrate groups, which is consistent with the primary role of T (rather than its metabolites) in regulation of reproductive behaviors in lizards. However, further investigation of protein and enzyme activity levels are needed before specific conclusions can be drawn.

Relationships among Sex, Season and Testosterone in the Expression of Androgen Receptor mRNA and Protein in the Green Anole Forebrain

“…During this procedure animals were subcutaneously implanted with a Silastic capsule (7 mm long × 0.7 mm inner diameter × 1.65 mm outer diameter) containing either 5 mm of packed TP or left blank, as in previous studies [Holmes and Wade, 2005;Neal and Wade, 2007;Cohen and Wade, 2010]. This hormonal manipulation produces detectable plasma concentrations that average 48.69 ± 4.78 (SEM) ng/ml, with no difference across seasons [Cohen and Wade, 2012]. These androgen levels average about twice that of endogenous androgen in field-collected animals (approx.…”

Hormonal Regulation of Steroid Receptor Coactivator‐1 mRNA in the Male and Female Green Anole Brain

“…Unmanipulated males from the BS and NBS average around 20 ng/ml and 11 ng/ml, respectively, both of which are much higher than female anoles in either the BS or NBS, which average less than 1 ng/ml . Similarly, the difference in circulating testosterone as a result of our implants and the undetectable levels in their castrated controls with empty capsules was somewhat greater on average than the difference between normal males and females .…”

“…This dose has been used in previous studies and reliably activates male sexual behaviour and associated biochemical and morphological changes in the brain (9,13). These capsules produce detectable plasma concentrations with a mean AE SEM of 48.7 AE 4.8 ng/ml of androgen, with no difference across seasons (38). Intact males collected in the wild average approximately 20 ng/ml in the BS and 11 ng/ml in the NBS, although the concentrations produced by our TP capsules overlap with those of breeding individuals (39).…”

Expression of Aromatase and Two Isozymes of 5α‐Reductase in the Developing Green Anole Forebrain

“…Another possible explanation of these results is that testosterone does not regulate aromatase expression in the POA, AMY and VMH. In adults, whole brain aromatase activity is increased by testosterone treatment in breeding season males although the same manipulation does not affect the number or density of aromatase mRNA expressing cells in these regions (38,39). Regardless, the pattern that we observed in the present study was largely consistent with other species.…”

“…Thus, both E 2 and 5α‐DHT have facilitatory roles in anole reproductive behaviours. Additionally, testosterone regulates anole neural aromatase and 5αR such that systemic testosterone treatment in adulthood increases whole brain activities of aromatase and 5αR in males (38), as well as the density of cells expressing 5αR2 mRNA in the female VMH (39). 5αR1 was not detected in the adult hypothalamus, although it is expressed in the brainstem (33).…”