Activation of “Secondary” Impulse Trigger Sites in Hippocampal Neurones

Abstract

INTRACELLULARLY recorded spike potentials of hippocampal neurones occasionally exhibit fast prepotentials superimposed on spontaneous slow depolarizations and excitatory postsynaptic potentials evoked by stimulation of the subiculum¹. Although the origin and nature of fast prepotentials have not been determined, available data suggest that they represent electrotonic reflexions of partial spikes evoked in dendrites by pathways arising in the subiculum¹. Two investigations which are summarized here have permitted further analysis of fast prepotentials as well as the definition of some of the factors conditioning their development in hippocampal neurones. The results are illustrated in contrast with findings in elements which did not exhibit fast prepotentials during a long period of spontaneous activity or in response to low frequency (1/sec) stimulation of the perforant pathway in the subiculum.