Sexual behavior, endocrinology, neural development, andc-fos activation of specific brain structures in low-performing, high-performing, and male-oriented domestic rams

Rams classified as high-performing (HP), low-performing (LP), and male-oriented (MO) had visual and olfactory contact with either estrous ewes or rams for 4 h on three consecutive days. During exposure to stimulus animals, blood samples were collected and investigatory behaviors recorded. Following exposure on d 3 rams were euthanized and brains perfused. Sections containing regions of interest were stained using cresyl violet. To gauge neural activity involving gene transcription in rams, identified regions were analyzed for fos immunoreactivity. Neural development was assessed by quantifying numbers of neurons and soma size in regions of known importance for sexual behavior.;High-performing rams exhibited more investigatory behaviors toward stimulus animals than LP or MO rams. Plasma concentrations of LH increased in HP rams following exposure to estrous ewes, but not following exposure to rams. Concentrations of LH were unchanged in LP and MO rams regardless of sex of the stimulus animal. Multivariate discriminate analysis based on soma size of neurons within the amygdala, preoptic region (POA), bed nucleus of the stria, terminalis (BNST), and ventromedial hypothalamus discriminated LP rains from BP and MO rams, but did not discriminate between BP and MO rams. Numbers of neurons present in quantified nuclei had no discriminating power. Low-performing rams exposed to estrous ewes had more neurons staining positive for fos immunoreactivity in the POA and BNST when compared to LP rams exposed to rams or MO rams but were not different from HP rams. High-performing rams appear to discriminate sex of stimulus animals and exhibit a neuroendocrine response when exposed to estrous ewes. Low-performing rams apparently detected sensory signals from estrous females, however, a neuroendocrine response or further investigation was not provoked. Male-oriented rams exhibited a low level of investigatory behavior towards both male and female stimulus animals and did not exhibit a neuroendocrine response or increased neural c-fos activity. Thus, MO rams may not be receiving sexual signals in a fashion similar to LP rams. Volumetric analysis of soma size revealed subtle differences in LP rams that may have resulted from developmental changes occurring in utero, or as a consequence of behavioral experience.