Distribution of androgen receptor mRNA expression and immunoreactivity in the brain of the green anole lizard

Sexually dimorphic neurocalcin expression in the developing zebra finch telencephalon

Differential display RT-PCR was used on RNA isolated from the zebra finch telencephalon to identify gene products potentially involved in its development, including the sexually dimorphic nuclei responsible for song learning and production. A cDNA identified only in juvenile females was cloned and sequenced. It shares homology with neurocalcin, a calcium binding protein. Northern blots indicated three neurocalcin species. A 10.6 kb transcript was present in males and most females throughout development and in adulthood. Smaller 6.2 and 3.3 kb species were detected almost exclusively in females and primarily between posthatching days 18-25. In situ hybridization, using a probe that identified all three mRNA species, indicated a broad distribution in the telencephalon of both sexes, with particularly high levels in the song nucleus RA. Across regions examined, neurocalcin expression was enhanced in females compared to males, probably reflecting the presence of the two smaller transcripts. However, within RA, neurocalcin expression was statistically equivalent between the sexes. These data indicate that calcium signaling via neurocalcin may be involved in telencephalic development, but suggest that sexually dimorphic expression of this gene exists on a level too general to specifically regulate masculine or feminine development of song control regions. Neurocalcin might: broadly influence functional differentiation, including areas that are not morphologically distinct between the sexes; be a benign consequence of general dimorphisms, such as those due to sex chromosomes; or involve a compensatory mechanism, which allows function of the juvenile female telencephalon to equal that of males, despite fundamental physiological differences.

Relationships between hormones and aggressive behavior in green anole lizards: an analysis using structural equation modeling

We investigated the relationship between aggressive behavior and circulating androgens in the context of agonistic social interaction and examined the effect of this interaction on the androgen-aggression relationship in response to a subsequent social challenge in male Anolis carolinensis lizards. Individuals comprising an aggressive encounter group were exposed to an aggressive conspecific male for 10 min per day during a 5-day encounter period, while controls were exposed to a neutral stimulus for the same period. On the sixth day, their responses to an intruder test were observed. At intervals, individuals were sacrificed to monitor plasma androgen levels. Structural equation modeling (SEM) was used to test three a priori interaction models of the relationship between social stimulus, aggressive behavior, and androgen. Model 1 posits that exposure to a social stimulus influences androgen and aggressive behavior independently. In Model 2, a social stimulus triggers aggressive behavior, which in turn increases circulating levels of androgen. In Model 3, exposure to a social stimulus influences circulating androgen levels, which in turn triggers aggressive behavior. During the 5 days of the encounter period, circulating testosterone (T) levels of the aggressive encounter group followed the same pattern as their aggressive behavioral responses, while the control group did not show significant changes in their aggressive behavior or T level. Our SEM results supported Model 2. A means analysis showed that during the intruder test, animals with 5 days of aggressive encounters showed more aggressive responses than did control animals, while their circulating androgen levels did not differ. This further supports Model 2, suggesting that an animal's own aggressive behavior may trigger increases in levels of plasma androgen.

Seasonal and sexual dimorphisms in the green anole forebrain

During the breeding season, male green anole lizards extend a throat fan (dewlap) in courtship. This behavior is facilitated by testosterone (T). Females extend a much smaller dewlap less often, even with the same dose of T. During the nonbreeding season when T is low, dewlap extension is reduced. To determine if parallels exist between structure and function, we investigated neuron soma size and density in the preoptic area (POA) and ventromedial nucleus of the amygdala (AMY), which are involved in the display behavior, in breeding and nonbreeding males and females. Cells from breeding animals were larger than cells from nonbreeding animals, but they were not sexually dimorphic. No significant effects existed in neuron density. This experiment indicates that portions of the anole forebrain important for sexual behavior are plastic and might be influenced by seasonal changes in steroid hormones. To investigate whether T can reverse the seasonal difference in soma size in both sexes, gonadectomized nonbreeding anoles were implanted with an empty or T propionate-filled capsule; animals were also tested for male-typical courtship behavior. Males and females treated with T had higher rates of dewlap extension, but across treatment groups these rates were greater in males. Neuron soma size in the POA and AMY was larger in males than females, but no effects of treatment were detected. Taken together, the results indicate that T can stimulate behavior in the nonbreeding season and suggest that a dissociation exists between the regulation of the courtship display and soma size of relevant brain regions.