Electrophysiology of pars compacta cells in the in vitro substantia nigra--a possible mechanism for dendritic release.

The electrophysiological properties of neurons in the pars compacta of the substantia nigra have been examined in vitro in guinea pig mesencephalic slices. These cells display a set of voltage- and Ca2+-dependent ionic conductances which confer upon them rather unique electrophysiological characteristics. In particular, the results indicate the presence of two separate dendritic Ca2+ conductances. One is inactivated at rest membrane potential and is de-inactivated by membrane hyperpolarization. The second resembles that responsible for dendritic spikes in other neurons. These conductances fulfil most of the physiological and pharmacological requirements for the ionic mechanisms underlying Ca2+-dependent dendritic release.