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

Pharmacol Biochem Behav. 1995 Sep;52(1):145-52. doi: 10.1016/0091-3057(95)00067-7.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antidepressive Agents, Tricyclic / pharmacology
  • Avoidance Learning / drug effects
  • Depression / physiopathology*
  • Depression / psychology
  • Electroshock
  • Endorphins / physiology*
  • Enkephalins / metabolism
  • Enkephalins / pharmacology
  • Helplessness, Learned*
  • Hydroxamic Acids / pharmacology
  • Imipramine / antagonists & inhibitors
  • Imipramine / pharmacology
  • Male
  • Morphine / pharmacology
  • Naloxone / pharmacology
  • Narcotic Antagonists / pharmacology
  • Narcotics / pharmacology
  • Neprilysin / antagonists & inhibitors
  • Phenylalanine / analogs & derivatives
  • Phenylalanine / pharmacology
  • Protease Inhibitors / pharmacology
  • Rats
  • Rats, Wistar

Substances

  • Antidepressive Agents, Tricyclic
  • Endorphins
  • Enkephalins
  • Hydroxamic Acids
  • Narcotic Antagonists
  • Narcotics
  • Protease Inhibitors
  • 3-(N-hydroxycarboxamido-2-benzylpropanoyl)phenylalanine
  • Naloxone
  • Phenylalanine
  • Morphine
  • Neprilysin
  • Imipramine