MALE FACES AND ODORS EVOKE DIFFERENTIAL PATTERNS OF NEUROCHEMICAL RELEASE IN THE MEDIOBASAL HYPOTHALAMUS OF THE EWE DURING ESTRUS - AN INSIGHT INTO SEXUAL MOTIVATION

During behavioural oestrus female sheep, like females of many species, become both attracted to and sexually receptive towards males, wherea s at other times they will avoid them, The mediobasal hypothalamus is the main site for the feedback action of sex steroids to induce sexual behaviour in the sheep and in previous studies we have shown that nor adrenaline and serotonin are released in this region during sexual int eractions with males, The current study investigated whether such chan ges are specific to interactions with males and if visual or olfactory cues or somatosensory stimulation during mating are critical. In vivo microdialysis sampling was carried out in the mediobasal hypothalamus of ovariectomized ewes submitted to artificial oestrous cycles. Relea se of monoamines and amino acid transmitters was first measured in ani mals during and after oestrus when they were exposed to interactions w ith either males or females or presentation of food. Noradrenaline con centrations only increased significantly when the females were in oest rus and interacted with males irrespective of whether intromissions we re permitted. Females were then exposed to visual (faces) or odour (a home pen) cues from males or to the males themselves. Slide images of male faces increased concentrations of amines, glutamate and GABA duri ng early oestrus, when females spent most time looking at them, During late oestrus noradrenaline, glutamate and GABA concentrations also in creased in response to the male faces but no transmitter changes were seen during the luteal phase or at any time where the females were exp osed to female faces, or inverted male faces. Exposure to male odour p roduced a lower increase in noradrenaline concentrations when females were in early oestrus but marked increases 20 and 30 min after exposur e to male odours in late oestrus. No other transmitters were affected. Exposure to a male and mating with him when females were in early or late oestrus produced increased noradrenaline concentrations similar t o those seen with face stimuli alone although other neurotransmitters were unaffected. These results show that noradrenaline, and to a lesse r extent dopamine, serotonin, glutamate and GABA release in the mediob asal hypothalamus, can be modulated specifically in the oestrous femal e by sensory information coming from the male during oestrus, The diff erential effects of male cues during early and late oestrus suggest th eir involvement in (i) preceptive or anticipatory sexual responses sho wn by the female to male cues, and (ii) receptive sexual responses, an d suggest that the mediobasal hypothalamus plays a key role in the int egration of hormonal action on sexual motivation and processing of sen sory information during oestrus.