Immunoperoxidase staining of Fos protein in the male rat brain after exposure to female pheromones

Abstract

Electrolytic lesion studies and neurotransmitter release studies suggest that sexual behavior in the male rat is regulated by specific brain areas such as the medial preoptic area (MPOA), olfactory bulbs, and the nucleus accumbens. Also, testosterone has long been established as a critical factor in the regulation of sexual behavior. This experiment focuses on the motivational aspects of sexual behavior in the male rat. The effects of exposure of intact and castrated male rats to bedding samples from estrous females were assessed in specific brain areas through immunoperoxidase staining for fos, the protein product of the proto-oncogene c-fos. C-fos has been shown to function in signal transduction in cells. Consequently, fos levels serve as an excellent indicator of neuronal activity. In these experiments, exposure to estrous bedding increased the number of fos stained nuclei in the MPOA, nucleus accumben, diagonal band of broca (DBB), and corpus striatum of intact male rats. Castration blocked the increase in fos in the MPOA, nucleus accumbens and the corpus striatum. Castration did not block the increase in the DBB. The olfactory bulbs showed equal amounts of staining in all groups. These results indicate the MPOA, nucleus accumbens, and corpus striatum, are involved in processing sexually relevant cues from the environment and that testosterone is involved in regulating the process. In contrast, the increase in fos staining in the DBB in response to estrous bedding appears to be independent of testosterone.