Maternal behavior in rats: evidence for the involvement of preoptic projections to the ventral tegmental area.

This study provides evidence that a neural system extending from the preoptic region to the ventral tegmental area (VTA) of the midbrain is important for the normal expression of maternal behavior in lactating rats. In the first experiment, bilateral electrolytic lesions of the VTA severely disrupted the maternal behavior of postpartum rats. In the second experiment, lactating rats that received a unilateral knife cut severing the lateral connections of the medial preoptic area (MPOA) paired with a contralateral lesion of the VTA showed more severe maternal behavior deficits than females that received one of the following treatments: (a) a unilateral knife cut severing the lateral connections of the MPOA paired with an ipsilateral VTA lesion; (b) a unilateral knife cut severing the lateral connections of the MPOA paired with a contralateral lesion of the medial hypothalamus posterior to the MPOA; (c) a unilateral knife cut severing the lateral connections of the lateral preoptic area paired with a contralateral VTA lesion. The oral components of maternal behavior (retrieving and nest building) were particularly affected as a result of bilateral damage to the system extending from the preoptic area to the VTA.