The vomeronasal organ is required for the expression of lordosis behaviour, but not sex discrimination in female mice - PubMed (original) (raw)

Comparative Study

The vomeronasal organ is required for the expression of lordosis behaviour, but not sex discrimination in female mice

Matthieu Keller et al. Eur J Neurosci. 2006 Jan.

Abstract

The role of the vomeronasal organ (VNO) in mediating neuroendocrine responses in female mice is well known; however, whether the VNO is equally important for sex discrimination is more controversial as evidence exists for a role of the main olfactory system in mate recognition. Therefore, we studied the effect of VNO removal (VNOx) on the ability of female mice to discriminate between volatile and non-volatile odours of conspecifics of the two sexes and in different endocrine states using Y-maze tests. VNOx female mice were able to reliably distinguish between male and female or male and gonadectomized (gdx) male volatile odours. However, when subjects had to discriminate between male and female or gdx male non-volatile odours, VNOx females were no longer able to discriminate between sex or different endocrine status. These results thus show that the VNO is primarily involved in the detection and processing of non-volatile odours, and that female mice can use volatile odours detected and processed by the main olfactory system for mate recognition. However, VNO inputs are needed to promote contact with the male, including facilitation of lordosis responses to his mounts. A single subcutaneous injection with gonadotropin-releasing hormone (GnRH) partially reversed the deficit in lordosis behaviour observed in VNOx females suggesting that VNO inputs may reach hypothalamic GnRH neurons to influence the display of sexual behaviour.

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Figures

Fig. 1

Fig. 1

Samples of male and oestrous female urine and the HMW (high molecular weight) and LMW (low molecular weight) fractions run on a standard 15% sodium dodecyl sulphate–polyacrylamide gel electrophoresis. The molecular weight of the major urinary proteins is approximately 18 kDa.

Fig. 2

Fig. 2

Representative photomicrographs showing sagittal sections stained with SBA–HRP of the AOB of female mice who had either undergone sham removal of (VNOi) or a bilateral surgical removal of the vomeronasal organ (VNOx). The absence of SBA–HRP staining in the glomerular layer of VNOx animals was taken as evidence of successful VNO removal. Gl, glomerular cell layer; Gr, granular cell layer; Mi, mitral cell layer. Scale bar, 100 μm.

Fig. 3

Fig. 3

Mean (± SEM) amount of time spent by VNOi or VNOx females investigating (A) volatile (no access) and (B) non-volatile (direct access) olfactory cues when given a choice between intact male odours and gonadectomized male odours or between intact male odours and oestrous female odours in a Y-maze. *P < 0.05, effect of odour stimulus; #P < 0.05, effect of the VNO lesion.

Fig. 4

Fig. 4

Mean (± SEM) amount of time spent by VNOi or VNOx females investigating the low-molecular-weight (LMW) urinary fraction or high-molecular-weight (HMW) urinary fraction, when given a choice between intact male odours and oestrous female odours in a Y-maze. *P < 0.05, effect of odour stimulus; #P < 0.05, effect of the VNO lesion.

Fig. 5

Fig. 5

(A) Mean (± SEM) lordosis quotient expressed by VNOi and VNOx females in response to the male’s mount during three consecutive tests. *P < 0.05; effect of the VNO lesion. (B) Mean (± SEM) lordosis quotient expressed by VNOi and VNOx females in response to the male’s mount after injection of GnRH or saline. *P < 0.05, effect of the lesion; #P < 0.05, effect of GnRH (vs. saline) injection.

Fig. 6

Fig. 6

Representative sagittal sections showing Fos-immunoreactive protein in the AOB of VNOi and VNOx females following stimulation with 30 μL of male urine (VNOx and VNOi) or water (VNOi). Scale bar, 100 μm.

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