EVIDENCE AGAINST THE INVOLVEMENT OF ACTH CRF RELEASE OR CORTICOSTEROID RECEPTORS IN THE ANXIOLYTIC EFFECT OF CORTICOSTERONE

The present study was designed to evaluate the role of ACTH and/or CRF release and corticosteroid receptors (glucocorticoid and mineralocort icoid) in the anxiolytic effect of corticosterone (CORT). Costicostero id receptor mediation was evaluated using a dose-response analysis of the effect of CORT and by the action of dexamethasone (DEX), which bin ds to glucocorticoid receptors but not to mineralocorticoid receptors. DEX administration also permits indirect evaluation of the effect of ACTH/CRF release on the anxiolytic effect of CORT. Male Wistar rats (3 months old) weighing 250-350 g were treated sc with vehicle (N = 38), CORT 1.25 (N = 18), 2.5 (N = 13) and 5.0 (N = 24) mg/kg, or DEX 5.0 ( N = 19) and 10.0 (N = 17) mg/kg and tested in the elevated plus-maze 2 h later. The group that received the highest dose of CORT (5.0 mg/kg) showed a significant increase in percent open arm entries (38 +/- 2.6 , mean +/- SEM) as well as in percent time spent in open arms (27 +/- 4.0) when compared with the vehicle-treated rats (24.3 +/- 2.8 and 12. 4 +/- 1.9, respectively; both P<0.05). There were no other significant differences among groups in the two parameters tested or in total arm entries. These data corroborate previous findings of the anxiolytic e ffect of CORT and suggest that inhibition of ACTH/CRF release and cort icosteroid receptors do not play a major role in the anxiolytic effect of CORT.