Effect of the dopamine D-1/5 antagonist SCH 23390 on the acquisition of conditioned fear

The authors previously reported that typical and atypical antipsychotic dru gs inhibited the acquisition but not expression of conditioned fear. The pr esent study examined the effects of the selective dopamine D-1/5 agonist (S KF 38393) and antagonist (SCH 23390) on the acquisition and expression of c onditioned fear. Drugs were administered subcutaneously to male Sprague-Daw ley rats 30 min before foot shock (2.5 mA for 5 min). Twenty-four hours aft er foot shock, rats were again placed and observed in the shock chamber wit hout shocks (conditioned fear). Freezing behavior induced by conditioned fe ar, an index of anxiety or fear, was recorded using a time-sampling procedu re. SCH 23390 (0.1-1 mg/kg) inhibited the acquisition of conditioned freezi ng. The administration of SCH 23390 at a dose of 0.1 mg/kg 30 min after foo t shock did not affect conditioned freezing. Taken together. it is conclude d that D-1/5 antagonism inhibits the acquisition of conditioned fear. SKF 3 8393 (3-20 mg/kg) failed to change the acquisition of conditioned fear. SCH 23390 or SKF 38393 administered prior to testing did not reduce the expres sion of conditioned fear. These results suggest that D-1/5, receptors may p lay a role in the development of fear or anxiety. (C) 2000 Elsevier Science Inc.