The effects of olfactory and somatosensory desensitization on Fos-like immunoreactivity in the brains of pup-exposed postpartum rats.

Fos-like immunoreactivity (fos-lir) was examined in sites within the "maternal circuit" in postpartum female rats that received various sensory desensitizations and were exposed to pups for 1 or 2 hr. Neither olfactory bulbectomy nor thelectomy (nipple removal) significantly reduced the fos-lir in the anterior medial preoptic area (MPOA), although reductions following bulbectomy in medial amygdala did occur. Peripherally induced hyposmia by ZnSo4 reduced fos-lir in the olfactory structures (olfactory bulbs, piriform cortex, and olfactory tubercle), in medial and cortical nuclei of the amygdala, but not in anterior MPOA. Application of the topical anesthetic Emla to the ventrum only reduced fos-lir in the somatosensory cortex. Combined olfactory and ventral desensitizations produced marginal reductions in posterior MPOA. It is suggested that the MPOA is primarily involved as part of the effector system in the expression of the behavior. In contrast, the amygdala is involved in processing sensory cues received from pups during dam-litter interactions.