Effect of bilateral accessory olfactory bulb lesions on volatile urinary odor discrimination and investigation as well as mating behavior in male mice

Abstract

Previous research raises the possibility that urinary volatiles from estrous female mice activate mitral cells in the accessory olfactory bulb (AOB) of male mice following detection via the main olfactory epithelium as opposed to the vomeronasal organ. We asked whether bilateral lesions of the AOB would disrupt the ability of male mice to discriminate between urinary volatiles from mice of different sexes or endocrine states, or affect their interest in investigating these odors when they were presented sequentially in home-cage habituation/dishabituation tests. Males with either partial or complete bilateral lesions of the AOB resembled sham-operated control males in their ability to discriminate between ovariectomized and estrous female urinary volatiles as well as between male and estrous female urinary volatiles. However, males with either complete or partial AOB lesions spent significantly less time than sham-operated control males investigating urinary volatiles from estrous females, especially during tests when the alternative stimulus presented was male urine. Placement of AOB lesions failed to disrupt males' mating performance. Our results suggest that the incentive value of opposite-sex (female) volatile urinary odors which are initially detected by the main olfactory system is enhanced when they are further processed by the male's AOB.

Fig. 1

Schematic representations of complete (n=5) as well as partial (n=5) bilateral lesions of the accessory olfactory bulb (AOB) in male mice. Drawings of the glomerular, mitral and granule cell layers of the AOB from a sham-operated control male are shown in sagittal sections taken from the lateral, middle, and medial segments of the entire olfactory bulb. AOB lesion reconstructions are also shown from the left and right hemispheres. Gray shading represents the area of overlap of AOB lesions in all members of each group. Black shading represents the area of greatest extent of the AOB lesion in any member of each group.

Fig. 2

Effect of accessory olfactory bulb lesions on the time spent by male mice investigating urinary volatiles from ovariectomized female vs. estrous female mice in home-cage habituation/dishabituation tests. The sequence of urinary odor stimuli was reversed in the two tests (Panels A and B) given on consecutive days. Wilcoxon Signed Rank Tests were used to make within groups comparisons of the time spent investigating the third presentation of one odor and the first presentation of the next odor: &, #, $ indicate a significant difference ( p<0.05) in investigation times for males in the sham-operated, complete AOB lesion, and partial AOB lesion groups, respectively. Δ indicates a significant overall group difference in investigation times by a Kruskal Wallis One-Way ANOVA on ranks. Data are expressed as mean±SEM; group numbers are given in parenthesis.

Fig. 3

Effect of accessory olfactory bulb lesions on the time spent by male mice investigating urinary volatiles from gonadally intact male vs. estrous female mice in home-cage habituation/dishabituation tests. The sequence of urinary odor stimuli was reversed in the two tests (Panels A and B) given on consecutive days. Wilcoxon Signed Rank Tests were used to make within groups comparisons of the time spent investigating the third presentation of one odor and the first presentation of the next odor: &, #, $ indicate a significant difference ( p<0.05) in investigation times for males in the sham-operated, complete AOB lesion, and partial AOB lesion groups, respectively. Δ indicates a significant overall group difference in investigation times by a Kruskal Wallis One-Way ANOVA on ranks. Data are expressed as mean±SEM; group numbers are given in parenthesis.