Olfactory bulbectomy blocks mating-induced ovulation in musk shrews (Suncus murinus)

In many species, reproductive function can be modified by olfactory inputs. We employed bilateral olfactory bulbectomy (BULBX) to examine the effects of disruption of olfactory inputs on mating behavior and ovulation in female musk shrews. On several measures, sexual behavior was delayed in BULBX females compared to controls. When females were mated on five consecutive days, the majority of unoperated and sham-operated (SHAM) shrews ovulated; only one female subjected to BULBX ovulated. Administration of GnRH induced ovulation in the majority of females. We performed immunocytochemistry to assess the effects of bulbectomy on mating-induced responses of the neural GnRH system. In BULBX and SHAM females, the numbers of cells containing proGnRH immunoreactivity in the medial septum (MS)/diagonal band (DB) were significantly elevated 1 h after mating. Bulbectomy increased the numbers of GnRH-immunoreactive peptide-containing cells in the preoptic area, but it reduced neuron numbers in the MS/DB, as compared with those in SHAM controls. In addition, the GnRH-immunoreactive fiber area in the median eminence was greater in BULBX than in SHAM females. In sum, female musk shrews can display receptivity and engage in copulation without olfactory inputs. However, the olfactory system is essential for mating-induced ovulation.