Effect of bilateral transection of the lateral olfactory tract on the male-induced implantation failure (the Bruce effect) in mice.

Bilateral transection of the lateral olfactory tract (LOT) at the rostral level induced anosmia in female mice; by contrast, sectioning of the LOT at more caudal levels failed to induce anosmia in females. Transection of the LOT at all the levels inhibited the alien male-induced implantation failure in newly inseminated mice (the Bruce effect). Sham-operated as well as intact females exhibited a high rate of implantation failure following alien male exposure. The results suggest that the inhibition of the Bruce effect in LOT-transected females is not due to anosmia induced by the operation procedure, but due to interruption of the primary olfactory bulb projections to the posterior parts of the olfactory cortex. Our results rule out the involvement of the nervus terminalis in the Bruce effect. The present report lends support to the involvement of the accessory olfactory system in the transmission of the pheromonal stimulus involved in the male-induced implantation failure.