Role of the brain and accessory olfactory system in the block to pregnancy in mice.

Selective lesions have been made to the receptors in the main and accessory olfactory systems. In the absence of the accessory receptors, female mice are not able to show a neuroendocrine response to male pheromones but are able to detect male odours which induce the response. In the absence of main olfactory receptors, such discrimination of male odours is not possible, but the neuroendocrine response resulting in a block to pregnancy is maintained. These experiments suggest that cognitive aspects of olfaction are not essential for pregnancy block to occur and that in mice the dual olfactory systems are functional as well as anatomically distinct. Moreover, strain recognition can occur at the level of the accessory olfactory system without the female being able to display a behavioural awareness of this 'recognition'.