Changes in progesterone receptor isoforms content in the brain of immature, mature and aged male and female chickens.

Progesterone participates in the regulation of several reproductive functions in birds through its interaction with intracellular progesterone receptors (PR) which exhibit two isoforms (PR-A and PR-B) with different function and regulation. We determined the content of PR isoforms in several brain regions of immature (1.5 months-old), mature (12 months-old) and aged (48 months-old) male and female chickens by Western blot analysis. PR isoforms protein content changed in tissue-and age-specific manner in the brain of both male and female chickens. In female animals PR-B content was higher in the hypothalamus of mature animals than in other ages while PR-A content increased in the cerebellum of aged animals. No significant changes were observed in PR isoforms content in the cortex and the tectum of female animals. In contrast, in male animals PR-B content was higher in the hypothalamus of aged animals. The cerebellum, tectum and cortex of male animals did not present significant changes in PR isoforms content. In all studied regions of female animals PR-B was the predominant isoform, whereas, in males a significant predominance of PR-B was only found in the hypothalamus of aged animals. These results demonstrate that PR isoforms content presents a sexual dimorphism in the brain of chickens that changes in tissue- and age-specific manner, and suggest that these variations contribute to the regulation of progesterone actions in brain throughout the lifespan of male and female chickens.