Acute effects of methamphetamine applied microiontophoretically to nucleus accumbens neurons in rats.

Microiontophoretic studies were performed to elucidate the acute effects of methamphetamine on the nucleus accumbens (Acc) neurons receiving input from the parafascicular nucleus (Pf) of the thalamus using rats anesthetized with chloral hydrate. Spike generation upon Pf stimulation was inhibited by conditioning stimuli applied to the ventral tegmental area (VTA), which is rich in dopamine-containing neurons, and by iontophoretic application of methamphetamine as well as dopamine. The VTA-, methamphetamine- and dopamine-induced inhibition of the spikes elicited by Pf stimulation was antagonized during simultaneous application of haloperidol. Glutamate-induced firing was also inhibited during iontophoretic application of methamphetamine and dopamine in neurons receiving input from the Pf, and the inhibition was blocked by simultaneously applied haloperidol. In the reserpine-treated animals, however, the Pf-induced spikes were not affected by methamphetamine, but inhibited by dopamine. These results indicate that methamphetamine inhibits the Acc neurons receiving input from the Pf, probably by releasing dopamine from dopaminergic nerve terminals from the VTA.