CHLORIDE-DEPENDENT POTENTIALS AND THEIR EFFECTS ON FIRING PATTERN IN GUINEA-PIG CINGULATE CORTICAL-NEURONS

Intracellular recordings were made from pyramidal neurons in the anter ior cingulate cortex layer V of the guinea-pig slice preparation. An o scillation in membrane potential occurred when the membrane was depola rized to a subthreshold level (e.g. -60 mV), and the oscillation trigg ered repetitive firing. The frequency of the spontaneous firing varied with the membrane potential: frequencies were 2.9+/-1.4, 6+/-1, 13+/- 3, and 17+/-3 Hz at the membrane potentials of -60, -58, -55, and -40 mV, respectively. Bicuculline (500 nM to 10 mu M) increased the firing rate when the membrane potential was kept around threshold level by D C current injection. 2-Hydroxysaclofen and low Cl- (43 mM) also increa sed the firing rate, but tamido-4'-isothiocyanatostilbene-2,2'-disulph onate (SITS, 250 mu M) did not change the firing rate. Strychnine (1 t o 3 mu M) had no effect on the spontaneous firing. These results sugge st that the firing frequency of cingulate pyramidal neurons is modulat ed by GABA tonically released by interneurons.