Lesion of the main olfactory epithelium facilitates maternal behavior in virgin rabbits

Maternal behavior is induced in virgin female rabbits (normally unresponsive to foster pups) by removing the accessory olfactory bulbs. To determine if the main olfactory system (MOS) plays a similar inhibitory role in the present work we investigated the effect of lesioning the olfactory epithelium with a ZnSO₄ spray on the facilitation of maternal behavior in New Zealand white virgin rabbits. Four days after the chemical lesion 40% of females showed behaviors indistinguishable from those of normal mothers, i.e.: rapid entrance into the nest box containing the pups, adoption of a crouching posture over them, acceptance of suckling, and exit from the nest box after ca. 3 min. The proportion of females showing these behaviors rose to 70% by day 14 post-lesion. Ovariectomized rabbits sprayed with ZnSO₄ or animals sprayed with NaCl did not behave maternally. ZnSO₄ also provoked a transient reduction in olfactory perception: before the lesion animals from all groups directed significantly more sniffs to a flask containing male urine than to one containing water. This difference was abolished in ZnSO₄-sprayed females (intact and ovariectomized) for 3–6 days post-lesion and was re-established by 7–9 days. NaCl did not provoke such transitory hyposmia. ZnSO₄ lesions did not provoke malaise in the animals, as determined by food intake and the frequency of scent-marking and ambulation. Results suggest that olfactory cues from the pups are aversive to virgin rabbits and that a transitory reduction in their perception (accompanied by the action of ovarian secretions) is enough to facilitate maternal responsiveness.