Postnatal cell proliferation and death in a lateralized, gender-related, asymmetric nucleus.

Sexual differentiation and lateralization of neurone number in a discrete forebrain nucleus (SDApc) related to masculine vocal emission, occur contemporaneously in postnatal (P0-P15) gerbils. Stereological estimates of cell proliferation and death during SDApc organization were made by BrdU labelling and pyknosis, respectively. Results confirmed that rates of apoptosis were greater in females and lateralized in males. Immunoreactive BrdU cells, located in the SDApc at P0-P6, with low levels at P15, were not numerically different between the sexes. Only at one age, P0, in males, was a left-right difference seen in BrdU-immunoreactive cell numbers. Microglia, identified by isolectin immunostaining, were numerically similar to BrdU cells. We suggest that apoptosis, rather than neurogenesis, differentiates and lateralizes SDApc organization, and proliferating cells are microglia, phagocytosing debris.