Fos-like immunoreactivity in brain regions of domestic rams following exposure to rams or ewes

Limbic and basal forebrain-hypothalamic regions from male sheep differing i n sexual performance were quantified for fos-like immunoreactivity. Rams cl assified as high-sexually performing (HP), low-sexually performing (LP), an d male-oriented (MO) received noncontact sensory stimulation from either ew es in estrus (HP, n = 5; LP, n = 4; MO, n = 4) or other males (HP, n = 5; L P, n = 4; MO, n = 5) for a 4-h period on each of 3 consecutive days. Follow ing exposure to stimulus animals on the third day, rams were euthanized and their brains were perfused with a 1% paraformaldehyde/1.5% glutaraldehyde solution and sections were analyzed for fos-like immunoreactivity. Brain re gions analyzed were the medial amygdala (meAMY), medial preoptic area (mPOA ), bed nucleus of the stria terminalis (BNST), and ventromedial hypothalami c nucleus (VMH). Fos-like immunoreactivity differed between groups in the m POA and BNST but not in the meAMY or VMH. LP rams exposed to estrous ewes h ad more (P < .05) neurons staining positive for fos and fos-related antigen s (FRA) in the mPOA and BNST than LP rams exposed to other rams or MO rams exposed to either estrous ewes or other rams. Numbers of neurons staining p ositive for FRA in the mPOA and BNST of LP rams exposed to estrous ewes, ho wever, were not different (P < .05) from HP rams exposed to either estrous ewes or other rams. The similar fos-like immunoreactivity in areas importan t for the display of sexual behavior in HP and LP rams may reflect similar sensory input in these two groups of rams; however, LP rams, in contrast to HP rams, do not appear to respond similarly to the same sensory stimulus. (C) 2001 Elsevier Science Inc. All rights reserved.