The 5,7-DHT-induced anticonflict effect is dependent on intact adrenocortical function

We have recently reported that the anxiolytic-like effect observed in rats severely depleted of brain serotonin (5-HT) by means of 5,7-DHT is indirect and probably involves the GABA(A)/benzodiazepine chloride ionophore receptor complex (GABAA/BDZ-RC). One tentative explanation for this effect considered the involvement of corticosteroids. In the present series of experiments we have therefore investigated the effect of adrenalectomy (ADX) on the 5,7-DHT-induced anxiolytic-like effect displayed by rats in Vogel's conflict test. ADX totally abolished the anticonflict effect of the 5,7-DHT lesion. Replacement treatment with corticosterone, but not with dexamethasone, reinstated the anticonflict effect. These results indicate that an intact adrenocortical function, possibly via brain steroid type I receptors, is required for the expression of the 5,7-DHT-induced anxiolytic-like effect. It is postulated that ADX lowers the concentration of endogenous positive modulators at the GABAA/BDZ-RC to a level no longer sufficient to produce anxiolytic-like effects in 5,7-DHT-lesioned animals. The finding that 5,7-DHT-lesioned animals were more sensitive than sham-lesioned controls to the anticonflict effect of the barbiturate-like corticosteroid THDOC provides further support for the contention that an increased endogenous activity at the GABAA/BDZ-RCes is involved in the anxiolytic-like effect observed in rats with a severe depletion of brain 5-HT.