Behavioral effects of centrally administered arginine vasopressin in the rat fetus.

Arginine8 vasopressin (AVP) was administered to rat fetuses on Embryonic Day 20 via intracisternal (IC), intrahemispheric (IH), or intrathecal (IT) injection. The IC administration of AVP promoted a 4-fold increase in motor activity, including the uncommon patterns of mouthing, licking, and facial wiping. The IH injection of AVP had little effect on fetal behavior, but IT injection resulted in pronounced increases in fetal activity, including mouthing, licking, and wiping. The IT administration of a V1 antagonist blocked AVP effects, whereas IH injection potentiated AVP-induced changes in fetal behavior. The IC blockade of V1 receptors suppressed facial wiping to a chemosensory fluid (lemon) and reduced oral grasping of an artificial nipple, whereas IH injection of the V1 antagonist promoted facial wiping responses and increased grasping of the nipple. These data suggest that AVP may play a role in the development of responsiveness to stimuli encountered in the context of suckling.