Disruption of maternal behaviour in virgin and postparturient rats following sagittal plane knife cuts in the preoptic area-hypothalamus

Parasagittal knife cuts along the medial preoptic area-medial anterior hypothalamus were placed at either the medial (near lateral or NL cuts) or lateral (far lateral or FL cuts) border of the medial forebrain bundle in separate groups of virgin (Experiment 1) and postparturient (Experiment 2) rats. FL cuts were placed so as to spare preoptic-hypothalamic efferent connections with the medial forebrain bundle. NL and FL knife cuts were equally effective in preventing the induction of maternal behaviour produced by repeated exposure of virgin rats to foster pups. Both types of cuts also reduced nest building in virgins. In postparturient rats, NL and FL cuts both abolished pup retrieval and reduced nursing behaviour. However, only NL cuts disrupted lactation and nest building. NL cuts also produced chronic hyperthermia. The deficits in maternal behaviour and nest building may be independent of this hyperthermia, as shaving the fur in animals with NL cuts reduced body temperatures to control levels but did not restore these behaviours. These findings indicate that while preoptic/hypothalamic connections through the medial forebrain bundle are important for nest building and possibly lactation, other lateral connections must also be important for pup retrieval and nursing behaviour. The identity of these connections remains to be determined.