Abstract
Dynorphin (DYN) fragments are the members of the endogenous opioid system and postulated ligands for the opioid receptors. Infusion of DYN1–17 fragment into the rat dorsal striatum caused a significant increase in acetylcholine and decrease in dopamine overflow. Contrary to this, infusions of DYN2–17 fragment into the rat dorsal striatum caused a significant increase in dopamine and decrease in acetylcholine overflow. Intrastriatal infusions of different doses of the acetylcholinesterase blocker, neostigmine, augmented acetylcholine and inhibited dopamine overflow in a dose-dependent manner. The opposing responses of the DYN fragments suggest that the N-terminal residue plays a key role in presynaptic neuromodulation.