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Long-term synaptic plasticity in deep layer-originated associational projections to superficial layers of rat entorhinal cortex

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  • 학습
  • 기억
  • 해마
  • 내후뇌피질
  • 시냅스 가소성
  • 도파민
  • 아세틸콜린
  • Biology
  • Pharmacology


Superficial layers of the entorhinal cortex (EC) relay the majority of cortical input projections to the hippocampus, whereas deep layers of the EC mediate a large portion of hippocampal output projections back to other cortical areas, suggesting a functional segregation between superficial and deep layers of the EC as input and output structures of the hippocampus, respectively. However, deep layers of the EC send associational projections to superficial layers, suggesting a potential interaction between neocortical input and hippocampus-processed output in superficial layers. This possibility was investigated by examining whether deep to superficial EC projections support long-term synaptic plasticity, and whether they interact with other pathways in superficial layers in rat medial EC slice preparations. Synaptic responses of the deep-to-superficial layer projections were verified based on field potential profiles, pairedpulse facilitation, physical separation between superficial and deep layers, and pharmacological manipulation. Longterm potentiation (LTP) was reliably induced in the deep-tosuperficial layer projections by burst stimulations that emulated or sharp wave electroencephalogram (EEG), and it was blocked by an N-methyl-D-aspartate receptor antagonist (D-2-amino-5-phosphonopentanoic acid) and a calcium channel blocker (nifedipine). Prolonged low frequency stimulation induced long-term depression. A weak stimulation of deep layers, which induced a small degree of LTP by itself, generated a much larger degree of LTP when paired with a strong stimulation of superficial layers, indicating that the deep-tosuperficial layer projections cooperate with other pathways in the superficial EC to enhance synaptic weights. Our results suggest that neocortical input and hippocampal output information are integrated in superficial layers of the EC.

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