Species differences in the vasopressin-immunoreactive pathways in the bed nucleus of the stria terminalis and medial amygdaloid nucleus in prairie voles (Microtus ochrogaster) and meadow voles (Microtus pennsylvanicus), Behav. Neurosci

Vasopressin-immunoreactive (AVP-ir) cells in the bed nucleus of the stria terminalis (BST) and medial amygdaloid nucleus (MA) and their AVP-ir projections to the lateral septum were studied in monogamous prairie voles (Microtus ochrogaster) and promiscuous meadow voles (M. pennsylvani-cus). A sexually dimorphic AVP-ir pathway was found in both species; males had more AVP-ir cells in the BST and MA, as well as denser AVP-ir fibers in the lateral septum, than did females. A significant species difference was also found. Overall, meadow voles had more AVP-ir cells in the BST and MA than did prairie voles. Male prairie voles, however, had a higher density of AVP-ir fibers in the lateral septum than male meadow voles. The species difference in the sexually dimorphic AVP-ir projections in the BST and MA is implicated in the rodents ' different life strategy and behavior. Rodents show remarkable diversity in social organization and parental behavior. At one end of the spectrum, animals such as meadow voles (Microtuspennsylvanicus) live in mother-young cohorts in which mothers are the unique providers of parental care. At the other end of the spectrum, animals such as prairie voles (M. ochrogaster) live in extended-family groups in which both parents share the responsibility for rearing of young (Gruder-Adams & Getz, 1985; Oliveras & Novak, 1986; Wang & Novak, 1992). To explain this variation in reproduc-tive strategies, studies have been carried out to correlate ecological factors with behavior and to examine the selective pressures that are responsible for the evolution of behavio