Morphology and electrophysiology of ventral mesencephalon nerve cell cultures

In primary neuron cultures obtained from ventral mesencephalon of mouse fetuses, approximately 10-30% of the neurons were dopaminergic, as demonstrated by a rapid glyoxylic acid histofluorescence procedure, and another 10-30% were GABAergic as demonstrated by autoradiography. Resting membrane potentials averaged -58 mV and input resistances averaged 188 M omega. Action potential (AP) firing patterns were of 3 types: in 49% of cells, depolarizing current elicited bursts of APs of constant amplitude, duration, and interspike interval (Type 1); in 44% of cells, bursts consisted of APs of decreasing amplitude, increasing duration, and increasing interspike interval (Type 2); and in 7% of cells, bursts were initiated by a single high amplitude, short duration AP followed by a series of lower amplitude longer duration APs that progressively increased in amplitude and decreased in duration and interspike interval (Type 3). Calcium APs of two distinct types, differing in duration and rate of rise, were observed when cultures were exposed to tetrodotoxin. Abundant postsynaptic activity was recorded. Simultaneous intracellular recording between pairs of cells demonstrated reciprocal innervation. The neurotransmitter antagonists haloperidol, bicuculline, naloxone, atropine, hexamethonium and pirenzepine affected synaptic activity and/or resting membrane potential of some of the cultured neurons.