INCREASED 5-HT2 RECEPTOR-MEDIATED BEHAVIOR 11 DAYS AFTER SHOCK IN LEARNED HELPLESSNESS RATS

In the learned helplessness procedure, rats can be differentiated into two distinct groups, Learned helplessness (LH) rats do not learn to e scape a controllable shock while non-learned helplessness (NLH) rats l earn this response. This deficit in performance in LH rats lasted for 11 days. In LH rats, pretreatment with acute desipramine (15 mg/kg i.p .) or chronic diazepam (0.95 mg/kg/day p.o. for 7 days) did not produc e recovery from this deficit of performance, but pretreatment with chr onic desipramine (17.7 mg/kg/day p.o. for 7 days) or chronic mianserin (6.1 mg/kg/day p.o. for 7 days) led to recovery. Before presentation of uncontrollable shock, there was no difference between LH and NLH ra ts, but 11 days after the shock, head shakes induced +/-)-1-(2,5-demet hoxy-4-iodophenyl)-2-aminopropane (DOI) in LH rats was significantly m ore frequent than those in NLH and naive rats without change of [H-3]k etanserin binding. The basal corticosterone level was higher in LH rat s than in NLH rats. These findings suggest that the learned helplessne ss model is a reliable animal model of depression accompanied by 5-HT2 receptor hypersensitivity.