ELECTROPHYSIOLOGY OF HIPPOCAMPAL NEURONS: IV. FAST PREPOTENTIALS

Abstract

In an intracellular microelectrode analysis of hippocampal neurons in anesthetized cats, a small, abrupt prespike potential, called a fast prepotential (FPP), was seen in about 25% of the units studied. The following observations suggest that the FPPs represent spike activity generated within the impaled neuron, (i) They appeared as a rebound to intracellularly delivered hyper polarizing pulses in "normal" cells in an all-or-none fashion, (ii) They exhibited uniform contour in a given cell whenever they appeared, (iii) They fired at higher frequencies when cells showed signs of injury, (iv) When seen in isolation, the time course of the falling phase was more rapid than our estimates of purely passive decay would allow. The small amplitude of the FPPs suggests an origin remote from the soma. Since FPPs were never seen during antidromic activation, it seems unlikely that they arise from the axon. Therefore it is suggested that they arise within the dendritic tree of these cells.