Nanomolar concentrations of nicotine increase the release of [3H]dopamine from rat striatal synaptosomes

Nicotine stimulates the release of several neurotransmitters from brain tissue by acting on presynaptic nicotinic acetylcholine receptors (nAChR). In this study, an in vitro superfusion system was used to measure the nicotine-evoked release of [3H]dopamine (DA) from rat striatal synaptosomes. A 2-min exposure to micromolar nicotine produces a rapid increase in [3H]DA release. With continued exposure the response declines, apparently due to conversion of the nAChRs to a high-affinity desensitized conformation. In contrast, prolonged exposure to nanomolar concentrations of nicotine, while not producing an immediate response, leads to a gradual cumulative enhancement in [3H]DA release. This effect is calcium-dependent and blocked by the nicotinic antagonist, dihydro-beta-erythroidine. It is suggested that the gradual DA release in response to low concentrations of nicotine occurs as a result of either open channel properties of the desensitized receptor or an equilibrium between the high-affinity desensitized and active states of the nAChRs.