Fos induction in the Japanese quail brain after expression of appetitive and consummatory aspects of male sexual behavior

We investigated the expression of Fos, the protein product of the immediate early gene c-fos in the brain of male Japanese quail after they engaged in either appetitive or consummatory sexual behavior (i.e., copulation). For 1 h, castrated males treated with testosterone were either allowed to copul ate with a female or to exhibit a learned social proximity response indicat ive of appetitive sexual behavior. Control birds were either left in their home cage or placed in the experimental chamber but did not exhibit the app etitive sexual behavior because they had never learned it. Fos expression w as studied with an immunocytochemical procedure in two sets of adjacent sec tions through the entire forebrain. These sections were immunolabelled with 2 different antibodies raised against a synthetic fragment corresponding t o the 21 carboxy-terminal residues of the chicken Fos sequence. Contrary to the results of a previous study in which gonadally intact birds were used, Fos induction was observed neither in the medial preoptic nucleus nor in t he nucleus intercollicularis in birds that had interacted for 1 h with a fe male. This may be related to a lower frequency of copulation in the testost erone-implanted birds than in intact birds, or to differences in the time t he brains were collected after the birds engaged in sexual behavior between the two studies (60 min in this study, 120 min in the previous study). The performance of copulation and/or appetitive sexual behavior increased the number of Fos-immunoreactive cells in the ventral hyperstriatum, medial arc histriatum, and nucleus striae terminalis. These increases were observed us ing both antibodies, although each antibody produced minor differences in t he number of Fos-immunoreactive cells observed. Using one of the antibodies , but not the other, increases in Fos immunoreactivity were also observed i n the nucleus accumbens and hyperstriatum after either copulation or appeti tive sexual behavior. These differences illustrate how minor technical vari ations in the Fos immunocytochemical procedure influence the results obtain ed. These differences also show that Fos induction in a number of brain reg ions is observed after performance of consummatory (copulation) as well as appetitive (looking at the female) sexual behavior. This induction is, ther efore, not related solely to the control of copulatory acts but, presumably also to the processing in a variety of telencephalic association areas of stimuli originating from the female. The observation that increased Fos imm unoreactivity is present in birds that had learned the response indicative of appetitive sexual behavior, and not in those that had not learned the be havior, further indicates that it is not simply the sight of the female tha t results in this Fos induction, but the analysis of the relevant stimuli i n a sexually explicit context. Conditioned neural activity resulting from a learned association between the stimulus female and the performance of cop ulatory behavior may also explain some aspects of the brain activation obse rved in birds viewing, but not allowed to interact with, the female. (C) 20 00 Elsevier Science Inc.