SENSITIZATION TO THE PSYCHOMOTOR EFFECTS OF AMPHETAMINE AND MORPHINE-INDUCED BY FOOD RESTRICTION DEPENDS ON CORTICOSTERONE SECRETION

Food restriction has been shown to enhance the behavioral sensitivity to addictive drugs. The biological factors involved in this effect are largely unknown. Since food restriction, among other factors, increas es corticosterone secretion, the role of this hormone in the effects o f food restriction on the response to psychostimulants and opioids was investigated. The effects of food restriction on amphetamine- and mor phine-induced locomotor activity were compared in: (i) animals with an intact hypothalamo-pituitary-adrenal axis; (ii) animals in which food restriction-induced corticosterone secretion was suppressed by adrena lectomy, but which received exogenous corticosterone from a subcutaneo us implant, which slowly releases corticosterone, producing a stable p lasma level within the normal physiological range over a period of 20 days. It was found that food restriction enhanced sensitivity to the p sychomotor effects of amphetamine (1 mg/kg i.p.) and morphine (1 mg/kg i.p.) in animals with an intact hypothalamo-pituitary-adrenal axis, b ut not in animals in which endogenous corticosterone secretion was eli minated. These results suggest that corticosterone secretion may be on e of the mechanisms by which food restriction amplifies the behavioral responses to amphetamine and morphine. Since an enhanced locomotor re activity to addictive drugs has been found to be frequently associated with an enhanced vulnerability to drug self-administration, these fin dings point to a role for glucocorticoids in the susceptibility to dru g abuse.