VOMERONASAL ORGAN-MEDIATED INDUCTION OF FOS IN THE CENTRAL ACCESSORY OLFACTORY PATHWAYS IN REPETITIVELY MATED FEMALE RATS

Removal of the VNO significantly reduced the enhancement of lordosis a nd the induction of fos immunoreactivity in luteinizing hormone-releas ing hormone (LHRH) neurons in ovariectomized estrogen-primed rats. The re was a significant positive correlation between the two variables. I n the accessory olfactory bulb (AOB) of the repetitively mated rats, t he number of fos-positive cells in the granule (G) cell layer was sign ificantly lower in the VNO-removed rats, whereas that in the mitral (M ) cell layer was not significantly different between VNO-removed ad VN O-sham females. The G/M ratio (calculated by dividing the mean number of fos-positive cells in the G cell layer by that in the M cell layer) , taken as an estimate of the output of the AOB, was relatively larger in the VN-sham as compared with the VNO-removed rats. There were sign ificant positive correlations between G/M ratio and the increase in LQ and between the G/M ratio and the percentage of fos-positive LHRH cel ls. The positive correlation between the number of fos-positive cells in the posterodorsal medial amygdala (PDMA) and the increase in LQ and that between the number of fos-positive cells in the PDMA and the per centage of fos-positive LHRH cells were significant, supporting the ro le of the medial nucleus of amygdala in lordosis. However, the correla tion between G/M ratio and the number of fos-positive cells in the PDM A was not significant, indicating that fos immunoreactivity in the PDM A is not directly related to that in the AOB. In conclusion, the resul ts support the involvement of the accessory olfactory system in mediat ing the facilitatory effects of repeated mating on lordosis in female rats and suggest that the influence of the accessory olfactory system is mediated likely through the LHRH neuronal system. Integration and f iltering of sensory information may take place at various levels of th e brain, such as the AOB and the medial amygdala, before being transmi tted to higher brain centers controlling lordosis behavior in female r ats.