Previous research suggests that body odorants, including anal scents and urinary odors, contribute to sex discrimination and mate identification in European ferrets of both sexes. We assessed the possible role of the vomeronasal organ (VNO) in these functions by surgically removing the organ bilaterally in sexually experienced female ferrets. Lesioned (VNOx) and sham-operated control (VNOi) females reliably discriminated between male- and female-derived anal scent gland as well as fresh urinary odors in habituation/dishabituation tests. However, VNOi females spent significantly more time than VNOx subjects investigating male urinary odors in these tests. Also, VNOi females, but not VNOx subjects, preferred to investigate day-old male versus female urine spots as well as wooden blocks that had previously been soiled by male versus female ferrets. Both groups of female ferrets preferred to approach volatile odors from a breeding male instead of an estrous female in Y-maze tests and both groups showed similar levels of receptive sexual behavior in response to a male's neck grip. The VNO is apparently not required for olfactory sex discrimination or mate recognition in this carnivore, but instead may play a role in promoting continued contact with nonvolatile body odors previously deposited by opposite-sex conspecifics during territorial scent marking.

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Previous studies showed that bilateral lesions of the male ferret's preoptic area/anterior hypothalamus (POA/AH), centered in the sexually dimorphic nuclei present in this region, caused subjects to seek out a same-sex male, as opposed to a female conspecific. Male subjects with POA/AH lesions (which were also castrated and given estradiol) displayed female-typical receptive behavior in response to neck gripping by a stimulus male, implying that subjects' approaches to a same-sex conspecific were sexually motivated. We asked whether the effect of POA/AH lesions on males' partner preference reflects a shift in the central processing of body odorant cues so that males come to display a femaletypical preference to approach male body odorants. Sexually experienced male ferrets in which electrolytic lesions of the POA/AH caused bilateral damage to the sexually dimorphic male nucleus (MN) resembled sham-operated females by preferring to approach body odors emitted from anesthetized male as opposed to female stimulus ferrets confined in the goal boxes of a Y-maze. This lesion-induced shift in odor preference was correlated with a significant increase in the ability of soiled male bedding to induce a Fos response in the medial POA of males with bilateral damage to the MN-POA/AH. No such partner preference or neural Fos responses were seen in sham-operated males or in other groups of males with POA/AH lesions that either caused unilateral damage or no damage to the MN-POA/AH. Male-typical hypothalamic processing of conspecifics' body odorants may determine males' normal preference to seek out odors emitted by female conspecifics, leading to mating and successful reproduction.

Previous research [J. Neurosci. 21 (2001) 5832-5840] showed that ferrets of both sexes require olfactory signals to identify opposite-sex mating partners at a distance. The present experiments assessed the contributions of anal scent gland and urinary odorants to these preferences. Sexually experienced, ovohysterectomized female and castrated male ferrets were injected daily with estradiol benzoate and testosterone propionate, respectively. When tested in an airtight Y-maze, subjects of both sexes preferred to approach volatile odors emitted from opposite- versus same-sex stimulus ferrets that were anesthetized and placed in the goal boxes, regardless of whether the anal scent glands of stimulus ferrets had been surgically removed or left intact. Subjects of each sex showed an equal preference to approach volatile odors emitted from anesthetized opposite-sex ferrets that were scent-gland intact as opposed to descented. Female subjects preferred to approach volatile anal scent gland odorants, as well as urinary odorants from male, as opposed to female conspecifics. Male subjects preferred to approach volatile anal scents from females versus males; however, males showed no preference for female over male urinary odorants. Our results suggest that anal scent gland odorants are sufficient, but not required, for mate recognition in the ferret. Instead, a combination of body odorants including, but not restricted to, those derived from anal scent gland secretions apparently underlie olfactory sex discrimination and partner preference in this carnivore.

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