Intracellular studies of dopamine neurons in vitro: pacemakers modulated by dopamine.

Intracellular recordings from dopamine (DA)-sensitive neurons in rat substantia nigra tissue slices revealed that these neurons exhibit spontaneous pacemaker-like activity. DA-sensitive neurons had higher input resistances, larger time constants and less linear voltage responses to current injection than did non-DA-sensitive neurons in the zona compacta. The administration of DA produced an inhibition of firing rate, a hyperpolarization and a decrease in input resistance. These effects were blocked by (-)sulpiride, a selective D2 antagonist. A reversal potential of -88 +/- 14 mV was calculated for the DA-induced hyperpolarization suggesting the involvement of potassium ions in the mechanism of DA action.