Journal of Neuroscience, Vol 8, 4138-4150, Copyright © 1988 by Society for Neuroscience
Evidence for two functionally distinct subpopulations of neurons within the rat striatum
ES Nisenbaum, WB Orr and TW Berger
Department of Behavioral Neuroscience, University of Pittsburgh, Pennsylvania 15260.
Type I and Type II extracellular action potential waveforms were recorded
from the rat striatum and studied with respect to their dependence on
recording conditions, response to paired impulse stimulation of the
corticostriatal pathway, and iontophoretic application of dopamine (DA).
Results showed that the distinguishing characteristics of Type I and Type
II waveforms are relatively independent of the degree of filtering,
distance of the electrode tip from the target neuron, type of recording
electrode, and firing rate of the neuron. Very low impedance electrodes,
however, were found to mask the difference in spike shape. Electrical
stimulation of cortical afferents results in excitation of both action
potential waveforms, though the Type II class exhibits a significantly
shorter latency than the Type I class. Paired impulse analyses revealed
that both waveforms exhibit variation in the probability of discharge
(facilitation or inhibition) to the second impulse of each impulse pair
that are a function of the interimpulse interval. Most importantly,
however, the probabilities of discharge of Type I and Type II neurons to
the second impulse are inversely related, i.e., when one cell type exhibits
facilitation, the other displays inhibition. These data demonstrate that
Type I and Type II waveforms represent the activity of functionally
different subpopulations of striatal neurons. Moreover, Type II neurons are
found much more often than Type I cells, suggesting that the 2 cell classes
may be represented with different frequencies within striatum. Finally,
Type II neurons display at least a 5 times greater sensitivity to
iontophoretically applied DA than Type I cells, suggesting that the 2 cell
populations also are affected differentially by dopaminergic input from the
substantia nigra.