A sex difference in the pattern of substance P-like immunoreactivity in the bed nucleus of the stria terminalis.

The caudal part of the dorsomedial bed nucleus of the stria terminalis (BNST) contained a discrete region of dense substance P (SP) staining in both male and female rats. However, the pattern of this staining differed markedly between the sexes. Males exhibited a densely stained capsule surrounding a less dense core. In females, this core was barely detectable (small and present on only 1 or 2 sections) or absent. The perimeter of this area of dense staining was traced and the area inside calculated. The mean area was found to be 2.4 times larger in males. The component of the BNST which receives this SP innervation was identified on Cresyl violet-stained sections. The area occupied by this distinct cell group was 32% larger in males. The areas of the suprachiasmatic nuclei and whole coronal sections through the BNST were measured in the same way and found not to differ between the sexes.