The medial preoptic area, necessary for adult maternal behavior in rats, is only partially established as a component of the neural circuit that supports maternal behavior in juvenile rats

To determine whether the neurons of the medial preoptic area (MPOA) are necessary for pup-induced maternal behavior (MB) in juvenile and adult rats, subjects received bilateral injections of the neurotoxin N-Methyl-D-Aspartic acid into the MPOA. Controls were intact or were sham treated by surgical placement of the syringe barrel. The rats were then induced into MB by constant pup exposure. Starting at 27 (juvenile) or 60 (adult) days of age, rats were tested for MB for 12 consecutive days. After histological analysis, rats were categorized as having either large or small lesions of the MPOA. In juveniles, large lesions of the MPOA blocked retrieval and impaired nest-building, but crouching behavior was unaffected; small lesions had no effect on MB. In contrast, in adults, large or small lesions severely impaired all components of MB. The results suggest that in juvenile rats, the role of the MPOA neurons in MB is only partially established, whereas by 60 days of age, the unsubstitutable role of the MPOA in the neural circuit that mediates MB is fully established.