Behavioral effects of non-opioid fragments of beta-endorphin.

The opioid peptide beta-endorphin (beta E) is converted by brain enzymes to a variety of non-opioid peptide molecules. Several of these peptides specifically affect brain processes in a different manner as assessed in behavioral test procedures. The peptide beta E-(2-9) exhibits behavioral effects resembling psychostimulant drugs in certain aspects and potentiates apomorphine-induced stereotypy following peripheral and intrastriatal treatment. The peptide beta E-(10-16), like serotonin and antidepressant drugs antagonizes the behavioral effects of intra-accumbens injected melatonin. The peptide beta E-(6-17) induces several effects which resemble those of neuroleptic drugs, including an antipsychotic action, and may control the activity of specific dopaminergic systems present in the nucleus accumbens. Thus, non-opioid fragments of beta-endorphin may be involved in the modulation of neurotransmitter systems and consequently in brain homeostasis and possibly in psychopathological syndromes.