Implication of endogenous opioid system
in the learned helplessness model of depression

by
Tejedor-Real P, Mico JA, Maldonado R,
Roques BP, Gibert-Rahola J
Department of Neurosciences,
School of Medicine, Cadiz, Spain
Pharmacol Biochem Behav 1995 Sep; 52(1):145-52


ABSTRACT

The involvement of opioid system on the learned helplessness model of depression was investigated. Animals preexposed to inescapable shocks were treated with either Met-enkephalin, Leu-enkephalin, morphine, imipramine, naloxone, RB 38A (a mixed inhibitor of enkephalin degrading enzymes), or RB 38B (a selective inhibitor of neutral endopeptidase EC 3.4.24.11). Stimulation of opioid system by either opioid agonists or enkephalin catabolism inhibitors reversed the escape deficit induced by shock pretreatment. In contrast, administration of naloxone potentiated the effect of inescapable shocks. Imipramine reduced the number of escape failures in this test, and this effect was antagonized by naloxone. These results point to the involvement of the endogenous opioid system in this model of depression.
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