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Single neurons from the substantia nigra of the adult guinea-pig were dissociated. Two morphological types of neurons were identified: (i) large multipolar neurons (20-40 microns greatest diameter) and (ii) small fusiform neurons (less than 20 microns diameter). Neurons of both types showed catecholamine fluorescence and were retrogradely labelled by rhodamine-conjugated microspheres injected into the striatum. Two types of neuron (Type A and Type B) were also identified electrophysiologically in perforated patch recordings of membrane potential and whole-cell current. Type A neurons had a low spontaneous firing frequency (5 Hz) broad action potentials (4 ms) and a threshold of approximately -45 mV. They were inhibited by the dopamine D2 receptor agonist, quinpirole. Type B neurons were characterized by a faster firing frequency (25 Hz), shorter action potential duration (1.5 ms) and a threshold of approximately -50 mV. These cells were unaffected by quinpirole. Large multipolar neurons were usually found to be of the A type and small fusiform, neurons of the B type. The properties of the large multipolar, Type A neurons suggest that they form part of the nigrostriatal, dopaminergic population of the pars compacta.

Original publication




Journal article



Publication Date





81 - 93


Action Potentials, Animals, Catecholamines, Dopamine Agents, Electrophysiology, Ergolines, Fluorescence, Guinea Pigs, Immunohistochemistry, In Vitro Techniques, Male, Membrane Potentials, Neurons, Neurotransmitter Agents, Quinpirole, Receptors, Dopamine, Receptors, Dopamine D2, Rhodamines, Substantia Nigra, Sulpiride, Synapses