The importance of the basolateral/basomedial amygdala for goal-directed maternal responses in postpartum rats

A model of the neural regulation of maternal behavior in rats proposes that the basolateral amygdala (BLA) provides pup-related sensory inputs to the nucleus accumbens–ventral pallidum (NA–VP) circuit and that medial preoptic area activation of the mesolimbic dopamine system potentiates the ability of BLA neurons to stimulate goal-directed maternal responses, such as pup retrieval behavior. Previous research using electrical lesions has provided some direct support for the importance of BLA. In the current study, we examined the effects of temporary inactivation of neurons within BLA and the adjoining basomedial nucleus of the amygdala (BMA) on maternal behavior in postpartum rats. For an anatomical control, muscimol was injected into the medial amygdala (MeA). Since research has shown that MeA plays an inhibitory role in maternal behavior, it was predicted that muscimol injections restricted to that site would not disrupt maternal behavior. The results showed that muscimol injections into BLA/BMA, at dosage levels between 100 and 200 ng/side, produced major deficits in retrieval behavior and minor deficits in nursing behavior. In contrast, muscimol injections into MeA left maternal behavior relatively unaffected. These results show that neuron-specific inactivation of BLA/BMA causes severe deficits in what can be considered a goal-directed and appetitive maternal response, pup retrieval, while leaving the consummatory aspect of maternal behavior, nursing, relatively unaffected. Since oxytocin is important for maternal behavior, and since both BMA and MeA neurons contain OT-binding sites, perhaps OT stimulates BMA output and suppresses MeA output to influence aspects of maternal behavior.