Elsevier

Brain Research

Volume 398, Issue 2, 29 November 1986, Pages 242-252
Brain Research

Hippocampal sharp waves: Their origin and significance

https://doi.org/10.1016/0006-8993(86)91483-6Get rights and content

This study investigated the spatial distribution and cellular-synaptic generation of hippocampal sharp waves (SPW) in the dorsal hippocampus of the awake rat. Depth analyses of SPWs were performed by stepping the recording electrode in 82.5 μm increments. SPWs were present during slow wave sleep, awake immobility, drinking, grooming and eating (0.01–2/s). The largest negative SPWs were recorded from the middle part of the stratum radiatum of CA1, the stratum lucidum of CA3, the inner molecular layer of the dentate gyrus and from layer I of the subiculum, in that order. The polarity of the SPWs was positive in layers II–IV of the subiculum, in stratum oriens and stratum pyramidale of CA1 and CA3, and in the hilus of the dentate gyrus. The electrical gradients across the null zones of the field SPWs were as large as 8–14 mV/mm. SPWs were associated with population bursts of pyramidal cells and increased discharges of interneurons and granule cells. During the SPW the excitability of granule cells and pyramidal cells to afferent volleys increased considerably. Picrotoxin and atropine and aspiration lesion of the fimbria-fornix increased either the amplitude or the frequency of SPWs. Diazepam and Nembutal could completely abolish SPWs. It is suggested that: (1) hippocampal SPWs are triggered by a population burst of CA3 pyramidal cells as a result of temporary disinhibition from afferent control; and (2) field SPWs represent summed extracellular PSPs of CA1 and subicular pyramidal cells, and dentate granular cells induced by the Schaffer collaterals and the associational fibers of hilar cells, respectively. The relevance of the physiological SPWs to epileptic interictal and long-term potentiation is discussed.

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