Distribution of Androgen Receptor mRNA Expression and Immunoreactivity in the Brain of the Green Anole Lizard

Abstract

Male courtship and copulation are androgen dependent in the green anole lizard, and female receptivity can be facilitated by testosterone. However, only a few, and relatively large, regions in the brain have been implicated in the control of these behaviours. In situ hybridization and immunohistochemistry were therefore used to determine in detail where androgens are likely to act in the brains of breeding males and females. A 697-bp fragment of the anole androgen receptor (AR) was cloned from total RNA isolated from the kidney, which contains the highly androgen-sensitive renal sex segment. The cloned fragment spanned part of the C, the entire D, and part of the E domains, and shared a high degree of similarity with the AR of various species. 35S-labelled antisense and sense probes were generated from the 697-bp fragment for use in in situ hybridization, and the AR antibody PG-21 was used for immunohistochemistry. Both sexes consistently had AR mRNA expression and immunoreactivity in areas associated with vertebrate reproductive behaviours and in motor areas of the brainstem. Interestingly, the PG-21 antibody produced labelling in both the nucleus and cytoplasm, including neuronal processes. The distribution of mRNA and immunoreactivity were comparable in males and females, and the amount of labelling was generally similar, although slightly greater in females. The expression pattern of AR in this species supports the idea that distribution is highly conserved among vertebrates, but that it probably does not dictate behavioural differences between the sexes in anoles.

Courtship and copulation in the adult male green anole: Effects of season, hormone and female contact on reproductive behavior and morphology

“…ARs are expressed in the anole POA and AMY during the BS [72], but further work is needed to determine whether AR expression in these areas is modified by either T or environmental conditions. We do have information about neuromuscular structures, however.…”

“…ARs are located throughout the copulatory system, and exogenous T increases their expression in the hemipenes and RPM, although it does not increase the percent of AR-positive T17-S1 motoneurons [42]. ARs are also expressed in ceratohyoid muscles and 45% of AmbX motoneurons, but apparently not in AmbIX/VIImv motoneurons in intact males [42,72]. Unlike the copulatory system, but consistent with the relative lack of plasticity, T does not seem to alter AR expression in dewlap structures [42].…”

Effects of season, testosterone and female exposure on c-fos expression in the preoptic area and amygdala of male green anoles

“…T enhances both the behaviors and soma size in these areas, and the effects are greater in the BS than NBS on both courtship and copulatory behavior and AMY soma size (Neal and Wade, 2007;O'Bryant and Wade, 1999). As cells in the POA and AMY express AR (Rosen et al, 2002), T could act directly in these forebrain areas to facilitate both behavioral and morphological change, but this idea has not yet been tested. In the present study, with the exception of males in the BS that were not exposed to females, the pattern of T effects in the POA and AMY were the same.…”

“…Soma size of POA and AMY neurons is increased by T, and an interaction exists in the AMY, such that the hormone enhances soma size more in the BS than NBS (Neal and Wade, 2007;O'Bryant and Wade, 2002). Androgen receptors are present in the POA and AMY (Rosen et al, 2002), suggesting that T may act directly in these regions, although it is currently unknown whether that is in fact the case. While at least visual exposure to females is required for males to display courtship behaviors, neither visual nor direct female contact affects POA or AMY morphology (Neal and Wade, 2007).…”

Genetic regulation of sex differences in songbirds and lizards

“…AR are expressed in the forebrain (POA, AMY and VMH), as well as in the muscles and motoneurons of both the dewlap and copulatory neuromuscular systems [84][85][86]. However, patterns of expression are generally not consistent with the idea that differences in AR availability regulate seasonal changes in responsiveness to T. For example, among gonadectomized animals in which some were treated with T, greater levels of AR protein in POA/hypothalamic dissections were detected in males compared with females, specifically within the breeding season.…”