The ventral tegmental area (VTA) is located in the midbrain and contains massive dopaminergic neurons. The VTA has received considerable attention as a potentially important brain region for the action of psychoactive drugs such as nicotine. The present study was conducted to determine the characteristics of dopaminergic neurons by focusing on the relative contribution of nicotinic and muscarinergic receptors and on sensitivity to alpha-bungarotoxin in nicotinic receptors. Under the urethane anaesthesia, the activity of dopaminergic neurons was recorded in Sprague-Dawley rats. Cholinergic agents including nicotine, muscarine, methyllycaconitine, and dihydro-beta-erythroidine were ejected iontophoretically. The activity of mesoaccumbens neurons was more increased by nicotine than muscarine. Iontophoretically ejected dihydro-beta-erythroidine inhibited the excitatory effects of nicotine. In particular, methyllycaconitine more greatly inhibited the excitatory effects of nicotine in the VTA. The distribution of the neuronal subtype sensitive to alpha-bungarotoxine was relatively high compared to the insensitive subtype located in the VTA. These results suggest that midbrain dopaminergic neurons showed highly sensitive excitatory response upon iontophoretic application of nicotine and that midbrain VTA neurons reveal the distinct characteristics in terms of nicotinic receptors.

Keywords: ventral tegmental area, nucleus accumbens, nicotine, alpha-bungarotoxin, cholinergic receptors