THE EFFECT OF PROLONGED TREATMENT WITH IMIPRAMINE AND ELECTROCONVULSIVE SHOCK ON THE LEVELS OF ENDOGENOUS ENKEPHALINS IN THE NUCLEUS-ACCUMBENS AND THE VENTRAL TEGMENTUM OF THE RAT

The present study was designed to find out whether the prolonged admin istration of imipramine (IMI) or electroconvulsive shock (ECS) influen ces levels of endogenous enkephalins in the nucleus accumbens (NAS) an d the ventral tegmentum (VTA) of the rat. Ressults indicate that treat ment with IMI as well as with ECS has a profound effect on the levels of enkephalins in both structures. In the NAS both treatments lead to an increase in the levels of endogenous enkephalins and this effect is accompanied by an increase in mRNA coding for proenkephalin (measured by in situ hybridization) in this structure, indicating the enhanceme nt of biosynthesis of endogenous enkephalinergic peptides following an tidepressant treatment. The results are discussed in the light of the hypothesis concerning the influence of endogenous enkephalins on mesol imbic dopamine neurons, the activity of which plays a crucial role in the etiology of depression.