Reproductive and maternal performance in the mouse following removal of the olfactory bulbs.

Abstract

Removal of the olfactory bulbs in pregnant and non-pregnant mice has been shown to lead to a loss ofmaternal behaviour (Gandelman, Zarrow, Denenberg & Myers, 1971). Cannibalism of the young occurs in practically all cases, and in the few instances when cannibalism does not take place, the young invariably die from neglect. In mice, therefore, the olfactory system must be functional for maternal behaviour to occur. By contrast, data obtained from the rat indicate that no one sensory system is necessary for the exhibition of maternal behaviour (Beach & Jaynes, 1956). In our original experiment (Gandelman, Zarrow, Denenberg & Myers, 1971), multiparous mice were bulbectomized on Day 12 ofgestation, allowed to litter, and were killed immediately after the death of their young in order to verify the brain lesions. It was not known, therefore, whether multiple experiences with pregnancy and parturition occurring subsequent to olfactory bulb removal could overcome the debilitating effect of the lack of olfaction upon maternal behaviour, or whether another sensory system might eventually assume the role originally played by the olfactory system. The present experiment inves¬ tigated this hypothesis. Twelve, 60-day-old, nulliparous mice of the Rockland-Swiss albino strain had both olfactory bulbs removed. The operation consisted of drilling a 2-mm hole in the skull over the bulbs and removing the tissue by aspiration. The animals were then housed individually in 5 7 11 in. translucent cages and allowed free access to food and water. Since it has been shown that sham operations do not affect maternal behaviour in 'mice (Gandelman, Zarrow, Denenberg & Myers, 1971; Zarrow, Gandelman & Denenberg, 1971), such controls were not employed. Five days after surgery, one adult male Rockland-Swiss albino mouse was placed into each cage and the females were checked every morning for the presence of a vaginal plug. After a plug was discovered, the male was removed and the female was left in isolation throughout pregnancy, parturition and the lactation period. During lactation, the females and their young were observed twice a day until the death of the offspring, after which the male was returned to the female's cage. If a vaginal plug was not found within 2 weeks, the male was removed and replaced by another male. If a vaginal plug was not found within 7 days after the second male was introduced, the female was killed and its