Reversal of learned helplessness by morphine in rats: involvement of a dopamine mediation
by
Besson A, Privat AM, Eschalier A, Fialip J
Laboratoire de Pharmacologie,
Faculte de Pharmacie,
Equipe NPPUA,
Clermont-Ferrand, France.
Pharmacol Biochem Behav 1998 Jun; 60(2):519-25

ABSTRACT

The aim of this study was to examine the role of dopamine neurotransmission in the effects of morphine in the learned helplessness paradigm in rats, a generally recognized model of depression. In this model, rats first exposed to inescapable shocks (stressed rats) exhibited an escape deficit in a subsequent shuttle-box test performed 48 h later for 3 consecutive days. The numbers of escape failures and intertrial crossings (motor activity during each intertrial interval) were recorded. Morphine was injected twice daily for 5 days (6 mg/kg/day, s.c.), and haloperidol, a preferential D2-dopamine receptor antagonist, was injected i.p. 15 min before each shuttle-box session. At the highest dose tested (150 microg/kg) haloperidol mimicked the behavioral deficit produced by inescapable shocks. A 37.5 microg/kg dose of haloperidol, which was ineffective by itself, reversed the morphine-induced improvement of escape behavior in previously stressed rats and the morphine-induced increase in intertrial activity in both stressed and nonstressed animals. These results support roles (a) for a dysregulation of dopaminergic neuronal activity in the expression of escape deficit subsequent to an inescapable aversive situation, and (b) for a dopaminergic mediation in the effects of morphine in the learned helplessness paradigm.

Morphine
Tolerance
Dependence
Endomorphins
Morphine: structure
Morphine and serotonin
Morphine and magnesium
Opioids, mood and cognition
Morphine as an antipsychotic?
Is morphine an antidepressant?
Depression, opioids and the HPA
Methadone, morphine and heroin
Morphine for endogenous depressives
Tolerance, sensitization and dependence
Methadone and morphine as antidepressants
Opioids, depression and learned helplessness

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