Androgen and estrogen (alpha) receptor distribution in the periaqueductal gray of the male rat

The midbrain periaqueductal gray (PAG) has been strongly implicated in nume rous behaviors heavily influenced by the gonadal steroids estrogen and test osterone, including reproductive behavior, autonomic regulation, and antino ciception. However, the location of receptors for these steroids within the RAG has not been carefully characterized. Immunocytochemical techniques we re used to map the distribution of neurons immunoreactive for the androgen (AR) and estrogen receptor (alpha subtype; ER alpha) along the rostrocaudal axis of the PAG in the male rat. The results show that the RAG contains a large population of both androgen and estrogen receptor containing neurons. Neurons immunoreactive for either receptor were concentrated within the ca udal two-thirds of the PAG. At midlevels of the PAG, ER alpha and AR immuno reactive neurons were located primarily within the dorsomedial and lateral RAG. In the caudal third of the PAG, immunoreactive cells were distributed primarily within the dorsal half. The distributions of ER alpha and AR were remarkably similar, and it is likely that some PAG neurons contain recepto rs for both gonadal steroids, similar to what has been previously reported for the male rat hypothalamus. The results of this study suggest that the R AG may provide the anatomical substrate for steroid mediated changes in noc iceptive thresholds and reproductive behavior, (C) 1999 Academic Press.