General synaptic platicity

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Figure 1: The Input and Output Pathways of Hippocampal Formation. Entorhinal cortex (EC) is the main input to the hippocampus. EC projects to the dentate gyrus (DG) via perforant fiber pathway and provides the critical input to CA3 via mossy fiber pathway, then to CA1 by means of the Schaffer collateral pathway. Additionally, EC can also project directly to CA3, CA1 and subiculum (Sub). Meantime, EC is the major output of the hippocampus. Arrows denote the direction of impulse flow.

CA3 has a positive feedback mechanism for amplification

Transmission through

AMPA and NMDA receptors:

1.

Tettanic stimulation of the presynaptic neuron

will eventually lead to the release of glutamate into the synaptic cleft and

will bind to AMPA and NMDA receptors

2.

Binding to AMPA receptors open the channel and

allow an influx of Na ions which depolarise the postsynaptic terminal

3.

This depolarisation allows the displacement of a

blocking Mg+ ion from the NMDA channel and along with glutamate binding will

lead to the influx of Ca through the channel

4.

Ca activates 2 kinases: PKC and

calcium-calmodulin-dependent protein kinase II (CamKII) which leads to

mechanisms which increases the synapses response to stimulation by:

5.

Changes in synaptic structure>> increase

in dendritic spines

6.

Increasing the conductance of AMPA receptors by

phosphorylation (via CamKII/ PKC)

7.

Insertion of new AMPA receptors via exocytosis

(CamKII activated- see below)

hippocampal pathways

NMDA and AMPA