Antidepressants and endogenous opioid peptide systems.

The influence of antidepressants on the brain and pituitary content of immunoreactive beta-endorphin (ir-beta E) and dynorphin (ir-DYN) was studied in rats. Chronic administration of the first and second generation antidepressants imipramine, citalopram and rolipram, and of the antidepressant neuroleptics levomepromazine and chlorprothixene elevated the level of ir-beta E in the hypothalamus. Imipramine and levomepromazine also increased the level of ir-DYN in this tissue. Imipramine administered chronically potentiated stress-induced as well as morphine analgesia. The results obtained suggest that chronic antidepressants enhance the brain opioid system activity and increase the sensitivity of opiate receptors.