SEX-HORMONES ENHANCE THE IMPACT OF MALE SENSORY CUES ON BOTH PRIMARY AND ASSOCIATION CORTICAL COMPONENTS OF VISUAL AND OLFACTORY PROCESSINGPATHWAYS AS WELL AS IN LIMBIC AND HYPOTHALAMIC REGIONS IN FEMALE SHEEP

Differential activation of neural substrates was investigated in femal e sheep exposed to a male when they were in oestrus, and sexually rece ptive and attracted to males, as opposed to anoestrus when they were n ot. Changes in neuronal activation were visualized in ovariectomized, hormone-treated ewes by quantifying changes in cellular expression of c-fos messenger RNA by in situ hybridization histochemistry. Results s howed that, while oestrus induction had no significant effects on c-fo s expression pel se, a 5-min exposure to a male significantly increase d it in a number of primary and association cortical regions (the mitr al and granule cell layers of the olfactory bulb, visual, somatosensor y, orbitofrontal, piriform, cingulate and temporal cortices), the limb ic system (CA1 region of the hippocampus, subiculum, lateral septum, l ateral and basolateral amygdala, bed nucleus of the stria terminalis) and hypothalamus (mediobasal hypothalamus, medial preoptic area and pa raventricular nucleus) as well as the nucleus accumbens and mediodorsa l thalamus. Intromissions did not contribute significantly to these c- fos changes however. In anoestrus females, exposure to a male only pro duced a small significant increase in c-fos messenger RNA expression i n the temporal cortex inspire of receiving similar amounts of visual a nd olfactory cues from him and a number of mating attempts. These resu lts clearly demonstrate that changes in sexual motivation markedly alt er the neural processing of sensory cues from males. They also show th at the hormonal induction of sexual attraction to males cues and the r esultant stimulation of sexual behaviour is due not only to altered re sponsiveness of oestrogen-sensitive brain regions involved in mediatin g behavioural responses towards the male, but also to changes in prima ry and secondary/tertiary somatosensory, olfactory and visual processi ng regions which relay sensory information to them. (C) 1997 IBRO. Pub lished by Elsevier Science Ltd.