Lateral entorhinal, perirhinal, and amygdala-entorhinal transition projections to hippocampal CA1 and dentate gyrus in the rat: a current source density study
Abstract
In urethane-anesthetized rats, cortical regions which provide distal dendritic excitation of the dentate gyrus and CA1 of the dorsal hippocampus were studied using current source density analysis. Electrical stimulation of the lateral perforant path (LPP) in the lateral angular bundle, lateral entorhinal cortex (LEC), and amygdala-entorhinal transition (TR) resulted in a current sink in the outer molecular layer of the dentate gyrus accompanied by proximal sources; this sink-source pattern is distinctly different from the source-sink-source pattern evoked by medial perforant path stimulation. The progressive decrease of the sink latency following stimulation of the TR, LEC, and LPP (11.6, 7.8, and 3.6 ms, respectively, at the dorsal blade of the dentate gyrus) suggests a possible sequence of orthodromic activation of these structures. Stimulation of the LEC or TR (collectively termed cortical stimulation) differed from LPP (fiber) stimulation. A low threshold and small chronaxie were characteristic of fiber rather than cortical stimulation. In addition, cortical stimulation, possibly through excitation of intracortical circuits, evoked larger paired-pulse facilitation of the excitatory postsynaptic currents in dentate gyrus and...Continue Reading
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