The hormonal influences on the slow extinction rate of a conditioned taste aversion shown by male rats and the fast extinction rate shown by female rats were investigated. When males were castrated, they extinguished as quickly as females. When castrated males were given testosterone propionate replacement, they had a slow extinction rate. Castration had no effect on the extinction rate of females. But when testosterone propionate was administered to castrated or intact females, they had a slow, malelike extinction rate. Thus, sexual dimorphism in the extinction rate of a conditioned taste aversion seems to be due to the activational effects of testosterone.A rat will avoid the taste of a novel food when poisoned after consuming that food (Garcia, Kimeldorf, & Koelling, 1955;Richter, 1953;Rz6ska, 1953). The rat will continue to avoid the taste for a considerable time, even when tasting is no longer followed by poisoning (Barnett, 1963; Rzoska, 1953). It will, however, eventually begin to consume the food again (Garcia, Ervin, & Koelling, 1966;Garcia et al., 1955). The amount of time it takes the rat to begin consuming the food has been found to be dependent on the dosage level of the poison (Elkins, 1973), deprivation level (Grote & Brown, 1973), and the measurement technique (Elkins, 1973;Garcia et al., 1966;Garcia et al., 1955). Recently, Chambers and Sengstake (1976) found that the rate of extinction of a conditioned taste aversion is also dependent on the sex of the rat. When rats are under ad lib food and water conditions, males extinguish more slowly than females.
