Nicotinic excitation of rat ventral tegmental neurones in vitro studied by intracellular recording.

1. Intracellular recordings were made from presumed dopamine-containing neurones in the ventral tegmental area (VTA) in rat brain slices. 2. Nicotine (10-100 microM) and acetylcholine (ACh) depolarized the neurones. The depolarization caused by ACh was typically biphasic; both components were increased by neostigmine (0.1-10 microM), but only the slower component was blocked by scopolamine (1-10 microM). 3. The nicotinic action of ACh, studied in the presence of neostigmine and scopolamine, persisted in the presence of tetrodotoxin (1 microM) and cobalt (2-5 mM). 4. ACh or carbachol (30 microM) caused inward currents in neurones voltage-clamped near the resting potential. These currents reversed polarity at around -4 mV, were blocked by hexamethonium (1-100 microM) in a voltage-dependent manner, and showed desensitization with prolonged or repeated agonist applications. 5. Depolarizations caused by ACh and carbachol were reduced in slices pretreated with kappa-bungarotoxin, but were not changed by alpha-bungarotoxin. 6. These responses to ACh and nicotine resemble those previously described on autonomic ganglion cells. The direct action on VTA neurones may contribute to the positive reinforcement associated with nicotine consumption.