Olfactory and vomeronasal system mediation of maternal recognition in the developing rat

Olfactory-mediated arousal and maternal recognition were evaluated in neonatal rat pups. Non-nutritionally deprived pups which underwent bilateral olfactory bulbectomies on day 5, failed to distinguish between the ventral and dorsal surfaces of a nursing rat and a heating pad. They showed virtually no arousal response to any of these surfaces. In contrast, pups with unilateral bulbectomies, and sham controls, graded their arousal response, and were maximally aroused by the mother's ventral surface. Following 24 h of maternal deprivation, bilaterally bulbectomized pups displayed a modest arousal response, directed primarily towards the dorsal surface. Pups with complete vomeronasal nerve sections displayed maximal arousal responses toward the dorsal surface. However, they were far more aroused than the bilaterally bulbectomized pups. Rat pups with incomplete vomeronasal lesions graded their response like controls, with maximal responsiveness directed toward the ventral surface. Shaving the dorsal surface markedly diminished the arousal response of bilaterally bulbectomized pups, but had only modest effects on sham and unilaterally bulbectomized controls. Thus, lesions that destroyed both the main and accessory's olfactory bulb systems severely impaired the pups' ability to effectively recognize a lactating female and markedly diminished maternally-induced arousal. Selective damage to the vomeronasal-accessory olfactory system appeared to disrupt discriminative capacity, but had little effect on the magnitude of the arousal response.