Seasonal changes in androgen receptor mRNA in the brain of the white-crowned sparrow

Abstract

In songbirds, neurons that regulate learned song behavior undergo extensive seasonal plasticity in their number and size in relation to the bird's reproductive status. Seasonal plasticity of these brain regions is primarily regulated by changes in circulating concentrations of testosterone. Androgen receptors are present in all of the major song nuclei, but it is unknown whether levels of androgen receptor mRNA in the telencephalic song regions HVC, the robust nucleus of the arcopallium, and the lateral magnocellular nucleus of the anterior nidopallium change as a function of season in whitecrowned sparrows. To determine whether seasonal changes in levels of androgen receptor mRNA are specific to the song control system, we also measured levels of androgen receptor mRNA in a limbic nucleus, the the lateral division of the bed nucleus of the stria terminalis (the lateral division of the bed nucleus of the stria terminalis). We found that levels of androgen receptor mRNA were higher in HVC and the lateral division of the bed nucleus of the stria terminalis of birds in the breeding-condition compared with the nonbreeding-condition; however, we observed no seasonal differences in levels of androgen receptor mRNA in either the the robust nucleus of the arcopallium or the lateral magnocellular nucleus of the anterior nidopallium. These results are consistent with previous observations that seasonal plasticity of the song nuclei results fromtestosteronacting directly on HVC, which then exerts transsynaptic trophic effects on its efferent targets. The seasonal change in the expression of androgen receptor in HVC may be one component of the cellular mechanisms underlying androgenic effects on seasonal plasticity of the song control nuclei.

Seasonal changes in the expression of the androgen receptor in the testes of the domestic goose (Anser anser f. domestica)

“…The relation between season and AR protein expression in bird testes still remains explored. Our findings corroborate the results of previous studies focused on central AR seasonal protein expression in songbirds [9,10,21,39]. Moreover, there is growing evidence that photoperiod induces changes in AR protein levels in various organisms and tissues, including the testes of bank vole [4,43] and brushtail possum (Trichosurus vulpecula) [26], the brain of Syrian hamster (Mesocricetus auratus) and electric fish (Brachyhypopomus gauderio) [34,35].…”

“…The seasonal variations in AR gene expression in bird testes have been previously explored only by a single paper reported opposite results [29]. Interestingly, analyses of central AR expression in birds indicated higher AR mRNA level in the breeding than in non-breeding season [5,9,11,44], differentiated AR mRNA level depending on specific brain areas [5] or lack of any seasonal fluctuations in AR gene expression [10]. In view of the above, it seems that the complex regulatory mechanisms, including species-and tissue-dependent manner, are responsible for controlling AR gene expression.…”

Neurogenesis in the Adult Avian Song-Control System

“…Microarray analysis also showed that the expression of proneurogenic genes, including IGF-1 and neuromodulin, is increased in RA of breeding-condition birds (Thompson et al 2012). In HVC, the expression of mRNA for sex steroid receptors, which facilitate the retrograde transport toward the neuronal soma of trophic factors bound to their receptor, also increases during breeding conditions (Fusani et al 2000;Jezierski and Sohrabji 2003;Fraley et al 2010). Once transported back to the soma, trophic factors likely activate signaling cascades that promote the growth and survival of new neurons (Gottschalk et al 1999;Yoshii and Constantine-Paton 2007; EA Brenowitz, K Lent, R Luche, et al, unpubl).…”

Transsynaptic trophic effects of steroid hormones in an avian model of adult brain plasticity

“…Androgen receptor mRNA and protein in HVC are expressed at higher levels in breeding-condition birds [Figure 2 48; 49; 50]. The expression of ER mRNA by cells in HVC is greater in breeding canaries [49].…”