An Electronic Circuit Model of the Interpostsynaptic Functional LINK Designed to Study the Formation of Internal Sensations in the Nervous System

Figure 5

Illustration explaining long-term potentiation (LTP) based on the formation of interpostsynaptic functional LINKs. (a) Regular stimulation of the Shaffer collaterals (stimulated fibers are shown in orange) before inducing LTP. None of the postsynapses (double rings in green) of the CA1 neuron are inter-LINKed with other postsynapses belonging to other CA1 neurons (not shown). Note the presence of existing interpostsynaptic functional LINKs (in red) forming islets of inter-LINKed postsynapses between postsynapses (double rings in black) that belong to other CA1 neurons that are not shown in the figure. Since there are no functional LINKs that connect to the postsynapses of the shown CA1 neuron, regular stimulation at the Schaffer collaterals will not reach the soma of the shown CA1 neuron. If some of the postsynapses of the CA1 neuron from where we record make few functional LINKs connecting to the postsynapses that are activated by stimulation at the Schaffer collaterals, then the response can be recorded from the given CA1 neuron; however, it will not show any potentiated effect. (b) During LTP induction, high frequency stimulation of the Schaffer collaterals results in formation of a large number of interpostsynaptic functional LINKs between abutted dendritic spines that belong to different CA1 neurons (all stimulated Schaffer collaterals are in orange). Note that all the postsynapses are activated to form reversible interpostsynaptic functional LINKs between them (in red, those interpostsynaptic functional LINKs formed with the postsynapses of the CA1 neuron are shown in blue). Potentials traversing through all the interpostsynaptic functional LINKs and finally reaching the dendritic spines of the shown CA1 neuron result in a potentiated effect when recorded from this CA1 neuron. Swelling of the dendritic spines [44–47] can favor interpostsynaptic membrane hemifusion and blockers of lipid membrane fusion can attenuate LTP [48]. Also note that LTP can be recorded from either extracellular recording (recording electrode 1) or patch clamp recording of the neuronal soma (recording electrode 2). (c) Immediately following LTP induction, a regular stimulus can reach the CA1 neuron through the LTP-induced interpostsynaptic functional LINKs showing a potentiated effect. Since the newly formed interpostsynaptic functional LINKs are reversible, their reversal over time causes gradual decline in the strength of LTP. Postsynapses are shown in double rings to represent membrane bilayer in a cross-sectional view. Short red boxes between the postsynapses indicate interpostsynaptic functional LINKs. Short blue boxes represent the interpostsynaptic functional LINKs to the postsynapses of the CA1 neuron. Presynaptic terminals are not shown. For convenience, stimulating electrode is not shown in (b) and (c).

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