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UBC Theses and Dissertations

The commissural projection of the hilus of the area dentata in the rat Willcox, John Edward Francis


Stimulation of the commissural afferents to the hippocampal formation evoked responses in the regio superior, regio inferior, and area dentata. Two waves were found in the stratum moleculare of the fascia dentata: the presynaptic volley (MN1), and the population EPSP (MN2). MN2 was caused by simultaneous activity in both the commissural and association fibres. Granule cells were reliably evoked by a commissural stimulus. The excitation of a granule cell was followed by a long period of inhibition. The long period of inhibition and the absence of a granule cell population spike were attributed to feed-forward inhibition. The commissural current source in the area dentata was hidden by field potentials generated in adjacent structures that were activated simultaneously by the commissural stimulus. In the hilar region a compound pyramidal cell action potential that had both orthodromic and antidromic components was found (HN2). A presynaptic volley in the commissural afferents was located in the commissural terminal zone of the regio inferior (HN1). The P wave was first misinterpreted as the commissural current source in the granule cells, but further investigation localized it to the stratum pyramidale of the regio inferior. It was not definitely characterized, but it appeared to be due to passive recovery processes that occurred after the propagation of action potentials in the pyramidal cells of the regio inferior. Hilar neurons project to the contralateral and ipsilateral area dentata, and to the ipsilateral and/or the contralateral regio superior.

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