Steroid control of sexual behaviour

Sexual behaviour can be described in terms of two components. The first, ‘appetitive’ component includes the search for a partner and the display of courtship behaviour that stimulates the partner’s sexual interest. This component is linked to the degree of motivation. The second, ‘consummatory’ component includes the display of behaviour that will lead to mating: adoption of a correct posture by the female and intromission and ejaculation by the male. In males, the intensity of sexual behaviour is most often measured by the latencies and the frequencies with which these behaviours occur. However, these parameters provide only a partial insight into sexual behaviour and, in particular, its motivational aspects. Specific methods have been developed to study particular motivational aspects in males (Everitt, 1990). In females, the term ‘consummatory‘ is rarely used and the two components are labelled proceptivity and receptivity after Beach (1976). Proceptive behaviours are the expression of the appetitive component and depend, at least in part, on the motivational state of the animal. Sexual receptivity consists of those behaviours that allow copulation and, in most species, includes immobility. In cats and laboratory rodents, the female adopts a posture called lordosis which is a reflexive arching of the back. This posture is the most commonly used parameter to quantify female sexual behaviour, but the fact that it is only a sign of receptivity with no obvious motivational component and that it is not necessarily applicable to all species is sometimes ignored. Although it is simplistic, the view of two distinct components having different neuroendocrine bases has proved to be very useful in our understanding of the mechanisms underlying sexual behaviour (Everitt, 1990). The probability of sexual behaviour being displayed by an adult animal in response to the appropriate stimulation is modulated by gonadal steroids. The importance of this steroid modulation varies markedly since males and females in several species, including humans and some other primates, show sexual behaviour after gonadectomy (Dixson, 1983). However, even in these species, steroids have been shown to modulate expression of some aspects of sexual behaviour (Bancroft, 1984). In general, sexual behaviour is sexually dimorphic: males and females have different behavioural repertoires and prefer to engage in sexual behaviour with a partner of the opposite sex. Little is known about the sexual differentiation of partner preference but the development of the sexual behavioural repertoire has been shown, in most species, to depend on the presence of gonadal testosterone, acting directly or through its metabolite oestradiol, during the embryonic or perinatal period (Baum, 1979).