MPOA cytotoxic lesions and maternal behavior in the rat: effects of midpubertal lesions on maternal behavior and the role of ovarian hormones in maturation of MPOA control of maternal behavior

Small neurotoxin lesions in the medial preoptic area (MPOA) block maternal behavior (MB) in adults but large lesions are required to produce the same effect in juvenile rats (23-27 days of age). To study the maturation of MPOA control of MB, in Experiment I, we compared the effects of small versus large neurotoxin MPOA lesions at midpuberty (38 days of age) on MB. Midpubertal females with large MPOA lesions showed severe impairment in MB affecting retrieving, crouching, and nest building, but 85% of females with small MPOA lesions exhibited all components of MB and performed like control females without MPOA lesions. To study the role of ovarian hormones during puberty on the maturation of MPOA mediation of MB (Experiment IIA), females were ovariectomized either before or after puberty and small MPOA cytotoxic lesions were made at 53 days of age. At 60 days of age both groups showed similar deficits in MB which indicated that the maturation of the MPOA mediation of MB is not dependent on pubertal ovarian hormones. In Experiment IIB, we administered estradiol benzoate (sc) and this overcame the deficit in MB after small MPOA lesions in females that had been deprived of estrogen for shorter periods (30 days) but had not been deprived for longer periods (60 days). In addition, ovary-intact females with circulating estrogen and small lesions in the MPOA at 53 days of age did not show deficits in MB.