Destruction of the main olfactory epithelium reduces female sexual behavior and olfactory investigation in female mice

Abstract

We studied the contribution of the main olfactory system to mate recognition and sexual behavior in female mice. Female mice received an intranasal irrigation of either a zinc sulfate (ZnSO4) solution to destroy the main olfactory epithelium (MOE) or saline (SAL) to serve as control. ZnSO4-treated female mice were no longer able to reliably distinguish between volatile as well as nonvolatile odors from an intact versus a castrated male. Furthermore, sexual behavior in mating tests with a sexually experienced male was significantly reduced in ZnSO4-treated female mice. Vomeronasal function did not seem to be affected by ZnSO4 treatment: nasal application of male urine induced similar levels of Fos protein in the mitral and granule cells of the accessory olfactory bulb (AOB) of ZnSO4 as well as SAL-treated female mice. Likewise, soybean agglutinin staining, which stains the axons of vomeronasal neurons projecting to the glomerular layer of the AOB was similar in ZnSO4-treated female mice compared to SAL-treated female mice. By contrast, a significant reduction of Fos in the main olfactory bulb was observed in ZnSO4-treated females in comparison to SAL-treated animals, confirming a substantial destruction of the MOE. These results show that the MOE is primarily involved in the detection and processing of odors that are used to localize and identify the sex and endocrine status of conspecifics. By contrast, both the main and accessory olfactory systems contribute to female sexual receptivity in female mice.

Figure 1

The mean (±SEM) amount of time that female mice spent investigating volatile (A, B) and nonvolatile (C, D) odor stimuli derived from intact male versus castrated (gdx) male in a Y-maze. Females had received either intranasal irrigation with zinc sulfate to destroy the MOE (ZnSO₄) or saline to serve as control (SAL), prior to behavioral testing. *P < 0.05, post hoc comparisons between time spent investigating intact male versus castrated male odor by SAL females.

Figure 2

Mean (±SEM) lordosis quotients (%) of female mice which had received either intranasal irrigation with zinc sulfate to destroy the MOE (ZnSO₄) or saline to serve as control (SAL). *P < 0.05, significant effect of ZnSO₄ treatment (overall ANOVA).

Figure 3

Representative photomicrographs showing sagital sections stained with SBA–HRP of the AOB of female mice which had either undergone ZnSO₄ or SAL treatment. The presence of SBA–HRP staining in the glomerular layer of both groups of animals was taken as evidence of intact VNO function in ZnSO₄-treated females. Gl, glomerular cell layer; Mi, mitral cell layer; Gr, granular cell layer. Scale bar: 100 μm.

Figure 4

(A) Mean (±SEM) numbers of Fos-immunoreactive cells in the mitral and granular cell layers of both the MOB and AOB. Female mice which were either treated with zinc sulfate to destroy the MOE (ZnSO₄)or SAL were either exposed to male urine or water placed directly on the nose. *P < 0.05, significantly different between SAL females exposed to water and SAL and ZnSO₄ females exposed to male urine. #P < 0.05, significantly different between SAL females exposed to urine and SAL females exposed to water or ZnSO₄ females exposed to male urine. (B) Representative sagital sections showing Fos-immunoreactive cells in the mitral and granular cell layers of the MOB and AOB. Female mice in which the MOE was destroyed by intranasal application of ZnSO₄ did not show a significant induction of c-fos in both cell layers of the MOB after exposure to male urine. By contrast, they showed a similar Fos induction in both cell layers of the AOB. Scale bar: 100 μm.