Involvement of the central serotoninergic system in the changes of leu-enkephalin level in discrete rat brain areas.

The effects of acute and chronic treatment with LSD and acute treatment with mescaline, m-CPP, citalopram and fenfluramine on leu-enkephalin (LENK) content in rat brain were examined. The acute LSD treatment was found to decrease and chronic treatment to increase the LENK content in the frontal cortex. In the thalamus with hypothalamus the LENK level fell after the administration of LSD, mescaline, citalopram and fenfluramine, while in the striatum it increased significantly, except for fenfluramine treatment. Methergoline and methiothepin prevented the effects of acute and chronic LSD administration. The diminished LENK level was associated with a decrease of 5-HT or 5-HIAA content in the rat brain areas investigated. Therefore, it has been concluded that the serotoninergic system may modulate the LENK pathway.