Effect of opioid peptides on dopamine release from nucleus accumbens after repeated treatment with methamphetamine.

The effect of opioid peptides on extracellular dopamine levels in the nucleus accumbens was compared between rats treated with methamphetamine and saline repeatedly (for 9 days) by using microdialysis. After the period of repeated treatment, the rats in both groups were kept for an additional 9 days without further treatment. Repeated administration of methamphetamine reduced the decreasing effect of dynorphin (10 microM), applied locally in the perfusate, and enhanced the increasing effect of [D-Ala2,MePhe4,Gly-ol5]enkephalin (DAGO, 10 microM) on the extracellular dopamine levels in the nucleus accumbens. It is possible that repeated treatment with methamphetamine leads to attenuation of the inhibition and enhancement of the stimulation of dopamine release from the nucleus accumbens via presynaptic dynorphin- and enkephalin-sensitive receptors, respectively.