Sex and Species Differences in the Vasopressin Innervation of Sexually Naive and Parental Prairie Voles, Microtus ochrogaster and Meadow Voles, Microtus pennsylvanicus

To study whether central systems that are implicated in functions associated with reproduction show different changes in males and females that become parental, the central vasopressin (AVP) innervation was compared in two species of voles: prairie voles, in which males and females provide parental care, and meadow voles, in which only females provide parental care. For both species, the densities of AVP‐immunoreactive (AVP‐ir) fibers in the lateral septum, lateral habenular nucleus, medial preoptic area and paraventricular nucleus of the thalamus were compared in males and females that were sexually inexperienced or had become parents 6 days before sacrifice. The lateral septum and lateral habenular nucleus presumably receive their projections from the bed nucleus of the stria terminalis and medial amygdaloid nucleus, while the other two areas presumably receive their projections from the suprachiasmatic nucleus. Differences between sexually naive and parental animals were found only in the presumed projections of the bed nucleus of the stria terminalis and medial amygdaloid nucleus. In both species, AVP‐ir fiber densities in the lateral habenular nucleus and the lateral septum were much greater in males than in females regardless of parental state. In prairie voles, AVP‐ir fiber density in the lateral septum and lateral habenular nucleus was reduced in parental males, while no differences were found in females. In parental meadow voles, the AVP‐ir fiber density in the lateral septum did not show changes, while the fiber density in the lateral habenular nucleus was increased. The reduction in AVP‐ir fiber density in parental prairie vole males and the absence of such a reduction in meadow vole males may be related to differences in their contribution to parental care.