Distribution of sex steroid hormone receptors in the avian brain: Functional implications for neural sex differences and sexual behaviors

Abstract

Developmental and seasonal changes in the production of androgens, estrogens, and progestins seem to control sex-specific differentiation and seasonal changes in appetitive and consummatory sexual behaviors of birds. This results in profound sex differences in the quality (sex-specific) or quantity (sex-typical) of behaviors such as courtship, territoriality, or copulation. Steroids affect the brain by binding to intracellularly located receptors. The same brain areas express androgen, estrogen, and progesterone receptors in male and female brains. Sex differences in these genetically determined patterns occur in the size of neuron populations that intrinsically express sex steroid receptors. Further permanent sex differences are subsequent to degenerative fates of receptor expressing neuron populations during ontogeny. Transient sex differences in receptor expression appear to be due to area-specific up- and down-regulation of receptor levels, reflecting transient changes in the level of circulating steroids, changes in environmental conditions, or in the physiological status of the individuals. In particular, intrinsic sex differences in the expression pattern of sex steroid receptors and steroid-independent regulation of the expression level of these receptors in the brain are limiting mechanisms for gonad-dependent sexual development and activities.

Low sex steroids, high steroid receptors: Increasing the sensitivity of the nonreproductive brain

“…The lack of ER expression in nT is surprising and differs from what has been observed in other avian species (Bernard et al, 1999;Gahr, 2001). Despite the lack of ER mRNA in nT, we found a strong tendency for increased AROM expression in nT during the nonbreeding season (p ¼ 0.058).…”

“…Hybridization specificity was confirmed for each probe in initial experiments by the absence of label over brain sections hybridized with sense probes. In addition, the overall neural patterns of hybridization with antisense probes closely matched patterns predicted from studies of the corresponding mRNA or protein in other suboscine and oscine species Foidart et al, 1998;Metzdorf et al, 1999;Fusani et al, 2000;Gahr, 2001). …”

Organohalogen contaminants and metabolites in cerebrospinal fluid and cerebellum gray matter in short-beaked common dolphins and Atlantic white-sided dolphins from the western North Atlantic

“…Environmental exposure of p,p'-DDE has been associated with alterations in the brains of American robins (Turdus migratorius), including a decrease in the size of two song control nuclei -the robust nucleus of the arcopallium (RA) and the HVC -and a reduction in the volume of the nucleus intercollicularis (IC o ), a brain structure critical for normal sexual behavior (Iwaniuk et al, 2006). Both RA and HVC contain a high prevalence of androgen receptors (Gahr, 2001;Metzdorf et al, 1999), and testosterone has been shown to increase the size of these brain structures (Alvarez-Borda and Nottebohm, 2002;Ball et al, 2002). Thus, the ability of p,p'-DDE to act as potent androgen receptor antagonist (Kelce et al, 1995) may explain the effects of p,p'-DDE on brain structure size (Iwaniuk et al, 2006).…”

Examining a pathway for hormone mediated maternal effects – Yolk testosterone affects androgen receptor expression and endogenous testosterone production in young chicks (Gallus gallus domesticus)

“…The domestic chicken is an excellent study species for this research because their endocrine system has been extensively studied, enabling reliable measurements of plasma testosterone and AR mRNA expression in the brain [15,20,32].…”

“…We quantitatively studied AR mRNA expression in the preoptic area (including different nuclei in the medial and lateral preoptic area), the BnST (bed nuclei of stria terminalis), the ventral pallidum, and the lateral septum. Previous research has shown that these nuclei contain androgen receptors and are involved in social, aggressive and copulatory behaviors [4,10,15,19,46,47] and might therefore represent nuclei that are possibly involved in early chick behavior.…”