Differential effects of heroin on opioid levels in the rat brain

Dependence on the potent narcotic agent heroin in rats was produced by the implication of double-coated pellets. Chronic administration of this drug induced significant alterations in dynorphin B and [Met5]enkephalin-Arg6-Gly7-Leu8 (ME-RGL) levels in discrete areas of the rat brain. The level of the latter increased by 53.6% in the substantia nigra while the levels of dynorphin B increased in the globus pallidus and ventral tegmental area (188.0 and 41.8%, respectively).