Activation of the Dentate Area by Septal Stimulation

A ndersen , P., H. B ruland , and B. R. K aada , Activation of the dentate area by septal stimulation. In rabbits under urethane‐chloralose anesthesia potentials were recorded bilaterally from the dentate area in response to stimulation of the large‐celled posterior part of the medial septal nucleus. The septo‐dentate response consisted of an initial negative spike followed by a slower positive wave. On the basis of recordings from the various cell layers, excitability properties, resistance to anoxia and repetitive stimulation, the initial spike is interpreted as discharges of the dentate granule cells, monosynaptically excited. The following positive wave may partly represent the subsequent spread of excitation along the dendrites of the granule cells, and partly the activation of CA4 neurons.–Stimulation of the contralateral field CA3 of the hippocampus evoked within the dentate area a potential similar in form, but with a greater amplitude and shorter latency than the septo‐dentate response. This crossed CA3‐dentate potential is similarly most likely due to activation of the same granule cells. The crossed projection appears to be more efficient and consists of thicker fibres than the septo‐dentate path.