PHYSIOLOGICAL-PROPERTIES OF ANATOMICALLY IDENTIFIED BASKET AND BISTRATIFIED CELLS IN THE CA1 AREA OF THE RAT HIPPOCAMPUS IN-VITRO

Basket and bistratified cells form two anatomically distinct classes o f GABAergic local-circuit neurons in the CA1 region of the rat hippoca mpus, A physiological comparison was made of intracellularly recorded basket (n = 13) and bistratified neurons (n = 6), all of which had bee n anatomically defined by their efferent target profile (Halasy et al. , 1996). Basket cells had an average resting membrane potential of -64 .2 +/- 7.2 vs. -69.2 +/- 4.6 mV in bistratified cells. The latter had considerably higher mean input resistances (60.2 +/- 42.1 vs. 31.3 +/- 10.9 M Omega) and longer membrane time constants (18.6 +/- 8.1 vs. 9. 8 +/- 4.5 ms) than basket cells. Differences were also apparent in the duration of action potentials, those of basket cells being 364 +/- 77 and those of bistratified cells being 527 +/- 138 mu s at half-amplit ude. Action potentials were generally followed by prominent, fast afte rhyperpolarizing potentials which in basket cells were 13.5 +/- 6.7 mV in amplitude vs. 10.5 +/- 5.1 in bistratified cells. The differences in membrane time constant, resting membrane potential, and action pote ntial duration reached statistical significance (P < 0.05). Extracellu lar stimulation of Schaffer collateral/commissural afferents elicited short-latency excitatory postsynaptic potentials (EPSPs) in both cell types. The average 10-90% rise time and duration (at half-amplitude) o f subthreshold EPSPs in basket cells were 1.9 +/- 0.5 and 10.7 +/- 5.6 ms, compared to 3.3 +/- 1.3 and 20.1 +/- 9.7 ms in bistratified cells , the difference in EPSP rise times being statistically significant. B asket and bistratified EPSPs were highly sensitive to a bath applied a ntagonist of non-N-methyl-D-aspartate (NMDA) receptors, whereas the re maining stow-rise EPSP could be abolished by an NMDA receptor antagoni st. Increasing stimulation intensity elicited biphasic inhibitory post synaptic potentials (IPSPs) in both basket and bistratified cells. In conclusion, basket and bistratified cells in the CA1 area show promine nt differences in several of their membrane and firing properties. Bot h cell classes are activated by Schaffer collateral/commissural axons in a feedforward manner and receive inhibitory input from other, as ye t unidentified, local-circuit neurons. (C) 1996 Wiley-Liss, Inc.