Endogenous AVP systems regulate oral behavior in the rat fetus: neuropeptide systems as ontogenetic adaptations.

Pharmacological manipulation of V1 receptors in rostral and caudal brain regions alters perioral responsiveness in the E20 rat fetus. Blockade of caudal V1 receptors or activation of rostral V1 receptors reduces fetal responsiveness to perioral cutaneous stimulation. Activation of caudal V1 receptors or blockade of rostral V1 receptors increases fetal responsiveness to perioral stimulation, including oral capture and grasping of an artificial nipple. These results suggest that V1 receptor-containing neurons regulate perioral responsiveness in the E20 rat fetus and that the 2 populations of neurons exhibit functional differences. The caudal part of the arginine8-vasopressin (AVP) system increases whereas the rostral part decreases responsiveness to different types of perioral stimuli. The neuropeptide AVP may affect suckling behavior immediately after birth by regulating perioral sensory responsiveness.