Multiscale interactions between chemical and electric signaling in LTP induction, LTP reversal and dendritic excitability

Synaptic plasticity leads to long-term changes in excitability, whereas cellular homeostasis maintains excitability. Both these processes involve interactions between molecular events, electrical events, and network activity. Here I explore these intersections with a multilevel model that embeds molecular events following synaptic calcium influx into a multicompartmental electrical model of a CA1 hippocampal neuron. I model synaptic plasticity using a two-state (bistable) molecular switch that controls glutamate receptor insertion into the post-synaptic density. I also model dendritic activation of the MAPK signaling pathway, which in turn phosphorylates and inactivates A-type potassium channels. I find that LTP-inducing stimuli turn on individual spines and raise dendritic excitability. This increases the amount of calcium that enters due to synaptic input triggered by network activity. As a result, LTD is now induced in some synapses. Overall, this suggests a mechanism for cellular homeostasis where strengthening of some synapses eventually balances out through weakening of a possibly overlapping set of other synapses. Even in this very narrow slice of cellular events, interesting system properties arise at the interface between multiple scales of cellular function. (C) 2011 Elsevier Ltd. All rights reserved.