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Abstract
This is a study of the effects of the endogenous opioid peptides, enkephalins, on
learned helplessness, an experimental model of depression in rats. For this purpose,
the responses induced by RB 38A, a mixed inhibitor of enkephalin catabolism, and RB
38B, a selective inhibitor of neutral endopeptidase EC 3.4.24.11, were compared with
the antidepressive effect induced by imipramine, RB 38A and RB 38B induced an imipramine-like
effect in reducing helpless behavior, as illustrated by the decrease in the number
of escape failures. According to the different pharmacological potential of both inhibitors
to reduce enkephalin metabolism, complete inhibition of enkephalins (RB 38A) produced
a higher response than that obtained with a partial inhibitor (RB 38B). On the other
hand, naloxone (NLX) was found to facilitate the induction of learned helplessness,
and to antagonize the effect of both enkephalin-degrading enzyme inhibitors. These
results suggest that modifications in the activity of the endogenous opioid system
could take place in this model of depression. The antidepressant-like effects induced
by RB 38B, and especially by RB 38A, in the learned helplessness paradigm suggest
that new mixed enkephalinase inhibitors, able to cross the blood-brain barrier, could
provide a new strategy in the treatment of affective disorders.
Keywords
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Article info
Publication history
Received in revised form:
March 17,
1993
Received:
February 28,
1992
Footnotes
☆This work was partly supported by DGICYT grant number PN89-0166 and Acción Integrada Hispano-Francesa number 229-03 and 313-A.
Identification
Copyright
© 1993 Published by Elsevier Inc.