CA1 PYRAMIDAL TO BASKET AND BISTRATIFIED CELL EPSPS - DUAL INTRACELLULAR-RECORDINGS IN RAT HIPPOCAMPAL SLICES

1. Dual intracellular recordings in the CAI region of adult rat hippoc ampal slices and biocytin filling of synaptically connected cells were used to study the excitatory postsynaptic potentials (EPSPs) elicited in basket (n = 7) and bistratified interneurones (n = 7) by action po tentials activated in simultaneously recorded pyramidal cells. 2. Inte rneurones could be subdivided according to their electrophysiological properties into classical fast spiking, burst firing, regular spiking and fast spiking cells with a rounded spike after-hyperpolarization. T hese physiological classes did not, however, correlate with morphologi cal type. EPSPs were not recorded in regular spicing cells. 3. Average EPSP amplitudes were larger in bistratified cells (range, 0.5-9 mV) t han in basket cells (range, 0.15-3.6 mV) and the probability of obtain ing a pyramidal cell-interneurone EPSP was also higher far the bistrat ified cells (1:7) than for the basket cells (1:22). EPSP 10-90% rise t imes in bistratified cells (0.7-2 ms) and their widths at half-amplitu de (3.9-11.2 ms) were slightly longer than in basket cells (rise times , 0.4-1.6 ms; half-widths, 2.2-9.7 ms). 4. The majority of these EPSPs (6 of 8 tested) increased in amplitude and duration with postsynaptic depolarization, although in two (of 4) basket cells the voltage relat ion was conventional. 5. All EPSPs tested in both basket (n = 7) and b istratified cells (n = 5) decreased in amplitude with repetitive presy naptic firing. The average amplitudes of second EPSPs elicited within 15 ms of the first were between 34 and 94% of the average amplitude of the first EPSP. Third and fourth EPSPs in brief trains were further d epressed. This depression was associated with an increase in the incid ence of apparent failures of transmission indicating a presynaptic loc us.