Interhippocampal Impulses

Andersen, P. Interhippocampal Impulses. III. Basal dendritic activation of CA3 neurorzs. The commissural afferents of the hippocampal field CA3 terminate in the layer of the basal dendrites only (Blackstad 1956), making selective basal dendritic activation possible. The response of CA3 in response to a symmetrical contralateral stimulation is a diphasic spike followed by a negative wave, sometimes with a superimposed spike. The diphasic spike represents interhippocampal fibre activity. The negative wave was recorded only from the CA3 basal dendritic layer. It is partly an excitatory postsynaptic potential produced in the basal dendrites by the commissural volley, partly a postsynaptic CA3 neuron discharge. The spike is a more synchronous discharge of the same neurons. The commissural volley elicits spikes more seldom in CA3 than in CA1, where apical dendritic activation is the most prominent, suggesting that a cell discharge is easier produced by apical than by basal dendritic activation. The susceptibility to anoxia is similar for the two fields. Strychnine normally produces great changes in CA1 potentials, but has only minor influence on the CA3 commissural response.