Abstract
Sexual differentiation of the brain-pituitary system of pigs occurs prenatally, since it is possible to alter the positive feedback response of LH to oestrogen in the postnatal female by prenatal treatment with testosterone (T). In the adult male pig feedback responses of LH to either T or 5α-dihydrotestosterone (5α-DHT) are mediated via the amygdala (AMY) and hypothalamus. Microimplants or microinjections of either substance into the AMY or mediobasal hypothalamus show that both, T and 5α-DHT can stimulate and inhibit LH-secretion. Catechol-oestrogens are one link between androgens metabolizable to oestrogens and LH control mechanisms. An altogether different action of steroids in the pigs brain is given by the boar pheromone 5α-androst-16-en-3-one and T when applied as an aerosol to the pigs nasal mucosa. Both androgens change olfactory bulb unit activity. Transmission through the lateral olfactory tract may eventually reach the limbic hypothalamic system.
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