PATHWAY OF POSTSYNAPTIC INHIBITION IN THE HIPPOCAMPUS

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Abstract
Three lines of evidence suggest that interneurones are concerned in the production of inhibitory postsynaptic potentials [IPSP] in hippocampal pyramidal cells: the latency, the long and varying rise time of the IPSP with sometimes a ripple of about 700/sec, and the wide dispersal of IPSP production by each of the four inputs employed. Unitary spike potentials could be detected in the stratum oriens and the pyramidal layer which had properties appropriate for these postulated inter -neurones. The various types of basket cells have a location and a synaptic distribution on pyramidal cell somas that fit them exactly for the role of the inhibitory cells, and that there are no alternatives. Thus, inhibitory cells have been identified for the first time in the central nervous system. It is further postulated that some pyramidal cells discharge impulses along their axons and so up the axon collaterals to activate basket cells to discharge impulses along their widely ramifying axons. Activation of the synapses formed on the somas of pyramidal cells by these axonal terminals produces the IPSP that are widely distributed to pyramidal cells.