Synaptic Diversity and Quantification of Intra-Hippocampal Contextual Memory

Authors: Mitsushima D*

DOI: 10.23880/nnoaj-16000113

Volume 2, Issue 2

Abstract

The hippocampal neurons seem to process both space and time information within a specific episode. However, the integrated system how to sustain a piece of specific memory or what associates the memory fragment each other is largely unknown. Bliss & Lømo (1973) reported long-term potentiation (LTP) in rabbit hippocampus, which has been considered as a cellular model of hippocampal memory. Hayashi, et al. (1999) clearly showed that the synaptic delivery of AMPA receptor is a molecular mechanism of LTP. Although the molecular mechanism of in vivo hippocampal learning had been unknown, we showed that learning-dependent synaptic delivery of AMPA receptors into the CA3-CA1 synapses is required for contextual learning. More importantly, contextual learning not only induces synaptic delivery of AMPA receptors but also strengthens GABAA receptor-mediated inhibitory synapses onto the CA1 neurons. Although each CA1 neurons showed different strength of the excitatory/inhibitory synapses in untrained animals, contextual learning clearly diversified the strength of excitatory/inhibitory synapses. Entropy analysis of the diversity may allow us to quantify the amount of information in trained animals.

Keywords: AMPA receptor; Glutamate; GABAA receptor; GABA; Synaptic diversity; Self-entropy; Plasticity; Learning

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