Alterations in [Met5]- and [Leu5]enkephalin and neurotensin content in basal ganglia induced by the long-term administration of dopamine agonist and antagonist drugs to rats.

Treatment of rats for 18 months with trifluoperazine increased [Met5]- and [Leu5]enkephalin and neurotensin content in striatum and nucleus accumbens. However, in substantia nigra the content of [Met5]enkephalin was decreased, [Leu5]enkephalin unchanged and that of neurotensin increased. Administration of L-DOPA plus carbidopa, bromocriptine or pergolide for 12 months decreased [Met5]enkephalin (except bromocriptine) and neurotensin, but not [Leu5]enkephalin, levels in striatum. L-DOPA decreased and bromocriptine increased neurotensin levels in substantia nigra. But neurotensin levels in nucleus accumbens were unaffected.