L-type calcium channels modulate glutamate-driven bursting activity in thenucleus accumbens in vivo

The majority of adult nucleus accumbens medium spiny neurons exhibit a bist able membrane potential that fluctuates between a relatively hyperpolarized (Down) state (average = -76 mV) and a less hyperpolarized (Up) state (aver age = -60 mV) near tiring threshold. During in vivo extracellular recording s from nucleus accumbens neurons, we used microiontophoresis to apply gluta mate and selected neurons that fired in bursting patterns reflecting a subt hreshold bistable membrane potential. The average frequency of bursts event s was 0.85 Hz. The average burst duration was 392+/-3.5 ms, with an average of 13.4 spikes and an average spike frequency of 30.6+/-3.1 Hz, per burst. To determine the involvement of the L-type calcium channel in the bursting pattern, we applied the benzothiazepine L-type calcium channel blocker, di ltiazem. Diltiaem rapidly (<2 min) and reversibly decreased the burst durat ion by 29% and the frequency of spikes within a burst by 30% without changi ng the overall burst event frequency. The results provide the first in vivo electrophysiological evidence implicating an L-type calcium channel that m odulates glutamate-induced burst firing of nucleus accumbens neurons. (C) 2 000 Elsevier Science B.V. All rights reserved.