CHARACTERIZATION OF NICOTINIC RECEPTOR-MEDIATED [H-3] DOPAMINE RELEASE FROM SYNAPTOSOMES PREPARED FROM MOUSE STRIATUM

This study establishes that presynaptic nicotinic receptors modulate dopamine release in the mouse striatum. Nicotinic agonists elicit a dose-dependent increase in the release of [H-3]dopamine from synaptosomes prepared from mouse striatum. At low concentrations, this release is Ca2+ dependent, whereas at higher concentrations Ca2+-independent, mecamylamine-insensitive release was also observed. The Ca2+-dependent nicotine-evoked release was not blocked by alpha-bungarotoxin but was effectively blocked by neuronal bungarotoxin as well as several other nicotinic receptor antagonists. The relationship between potency for stimulation of release for agonists and potency for inhibition of release for antagonists was compared to the affinity of these compounds for the [H-3]nicotine binding site. The overall correlation between release and binding potency was not high, but the drugs may be classified into separate groups, each of which has a high correlation with binding. This finding suggests either that more than one nicotinic receptor regulates dopamine release or that not all agonists interact with the same receptor in an identical fashion.