Neurogenesis of galanin cells in the bed nucleus of the stria terminalis and centromedial amygdala in rats: a model for sexual differentiation of neuronal phenotype.

Male rats possess twice as many cells that express arginine-vasopressin (AVP) in the bed nucleus of the stria terminalis (BST) and centromedial amygdala (CMA) as do females. This sex difference may arise from sex differences in the induction of AVP expression in galanin (GAL)-expressing cells, which themselves do not differ in number between males and females. To test whether AVP expression could arise from a single pool of galaninergic cells, we determined whether the cell birth profile of GAL-immunoreactive (ir) cells was similar to that of AVP-ir cells. Dams were injected with the cell birth marker bromodeoxyuridine (BrdU) on one of seven gestational dates, ranging from embryonic day 11 (E11) to E17. The resulting offspring were sacrificed at 3 months of age. Processing their brains for the presence of either GAL and BrdU, or AVP and BrdU immunoreactivity revealed that in both the BST and CMA, the majority of GAL-ir and AVP-ir cells were labeled with BrdU on E12 and E13. In contrast, most other cells in the same region were labeled on E14 and E15. The similarity in the timing of cell birth of the GAL-ir and AVP-ir cells is consistent with the idea that GAL-ir cells in the BST/CMA constitute a single pool of cells that may be induced to express AVP during development.