Maternal odours induce Fos in the main but not the accessory olfactory bulbs of neonatal male and female ferrets

Previous research demonstrated that exposing gonadectomized adult ferrets t o odours in oestrous female bedding induced nuclear Fos-immunoreactivity (F os-IR; a marker of neuronal activity) in the main as opposed to the accesso ry olfactory system in a sexually dimorphic fashion, which was further augm ented in both sexes by treatment with testosterone propionate. Ferrets are born in an altricial state and presumably use maternal odour cues to locate the nipples until the eyes open after postnatal (P) day 23. We investigate d whether maternal odours augment neuronal Fos preferentially in the main v ersus accessory olfactory system of neonatal male and female ferret kits, C irculating testosterone levels peak in male ferrets on postnatal day P15, a nd mothers provide maximal anogenital stimulation (AGS) to males at this sa me age. Therefore, we assessed the ability of maternal odours to augment Fo s-IR in the accessory olfactory bulb (AOB), the main olfactory bulb (MOB) a nd other forebrain regions of male and female ferret kits on P15 and invest igated whether artificial AGS (provided with a paintbrush) would further en hance any effects of maternal odours. After separation from their mothers f or 4 h, groups of male and female kits that were placed for 1.5 h with thei r anaesthetized mother had significantly more Fos-IR cells in the MOB granu le cell layer and in the anterior-cortical amygdala, but not in the AOB cel l layer, compared to control kits that were left on the heating pad. Artifi cial AGS failed to amplify these effects of maternal odours. Maternal odour s (with or without concurrent AGS) failed to augment neuronal Fos-IR in med ial amygdaloid and hypothalamic regions that are activated in adult ferrets by social odours. In neonatal ferrets of both sexes, as in adults, sociall y relevant odours are detected by the main olfactory epithelium and initial ly processed by the MOB and the anterior-cortical amygdala. In neonates, un like adults, medial amygdaloid and hypothalamic neurones either do not resp ond to these inputs or respond in a manner that fails to induce Fos express ion.