A reexamination of the effects of intracerebroventricular glucocorticoids in adrenalectomized rats

Abstract

Several investigators have reported that many of the behavioral and metabolic effects of ADX can be reversed by appropriate levels of glucocorticoids administered either peripherally or centrally. The present studies were conducted to offer a comparison of the effects of orally administered corticosterone (CORT) with ICV glucocorticoids [CORT, CORT acetate, or dexamethasone (DEX)]. Of particular interest were the effects of glucocorticoid treatment on body weight gain and on macronutrient self-selection. Adult male Sprague-Dawley rats were fitted with ICV cannulae and either bilaterally ADX or given sham operations. In the first experiment, ADX animals were initially treated systemically with CORT (20 μg/ml in their drinking water). After a wash-out period during which no steroids were administered, ADX rats were given daily ICV CORT injections (100 μg/day in 10 μl). Systemic CORT treatment promotes weight gain and normal food choice patterns in ADX rats. ICV injections failed to promote weight gain in ADX rats, and daily injection of the vehicle promoted a weight loss in sham-operated controls. Four additional experiments were conducted. ADX, glucocorticoidtreated animals and ADX, vehicle-treated controls as well as sham-operated, vehicle-treated controls were used to assess the effects of both steroid and vehicle on body weight gain and dietary selection patterns. ADX ICV-glucocorticoid-treated animals typically failed to gain weight at the rate observed when ADX rats are treated with CORT systemically. Under one condition, ADX-CORT-treated animals gained weight at a rate comparable to untreated controls, but their ICV-injected control group failed to gain weight. These results are consistent with the hypothesis that glucocorticoids act principally to modify metabolism, and only secondarily have effects on the central control of appetite.