Electrophysiological characteristics of substantia nigra neurons in organotypic cultures: Spontaneous and evoked activities

Morphological and electrophysiological characteristics of dopaminergic and non-dopaminergic neurons in the substantia nigra and their postsynaptic res ponses to stimulation of the tegmental pedunculopontine nucleus were studie d in rat organotypic triple cultures. These cultures consisted of the subth alamic nucleus explant, ventral mesencephalic explant, inclusive of the sub stantia nigra and the mesopontine tegmentum explant, inclusive of the tegme ntal pedunculopontine nucleus, prepared from one- to two-day-old rats. Intr acellular sharp and whole-cell recordings were obtained from three- to eigh t-week-old organotypic cultures. Recorded neurons were identified as dopami nergic and non-dopaminergic neurons with tyrosine hydroxylase immunohistoch emistry. Dopaminergic neurons had long duration action potentials, prominen t afterhyperpolarization, time-dependent inward and outward rectification a nd strong frequency adaptation. Spontaneous firing patterns varied from reg ular, irregular to burst firing. Non-dopaminergic neurons had short duratio n action potentials, in general no rectifying currents, and maintained high firing frequencies. Spontaneous firing patterns in these neurons were irre gular or burst firing. Morphological analysis of the recorded neurons label ed with neurobiotin revealed that non-dopaminergic neurons had more extensi ve arborization of higher-order dendrites than dopaminergic neurons. Dopami nergic and non-dopaminergic neurons receive glutamatergic and cholinergic e xcitatory inputs from the tegmental pedunculopontine nucleus. These results indicate that morphological and electrophysiological characte ristics of substantia nigra neurons in the organotypic culture are generall y similar to those reported in in vitro slice and in vivo studies. However, spontaneous activities of dopamine neurons observed in the organotypic cul ture preparation more closely resemble those in in vivo preparation compare d to in vitro preparation. (C) 2000 IBRO. Published by Elsevier Science Ltd .