Synaptic plastcity and optimization by astrocytes

S. Nadkarni and Peter Jung, Department of Physics, Ohio University,

The brain is an extremely complex system. Billions of neurons are connected synaptically to form circuits and loops on multiple scales of organization. To make things even more complex, another type of brain cell, the astrocyte, even more numerous than neurons in the human brain, have recently been identified to form a second, functional network layer. Astrocytes are chemically excitable, although on a much slower time-scale than the electrically excitable neurons, and interact with neurons bidirectionally. They can modulate neuronal synaptic transmission and excitability, and provide neuronal circuitry with additional capabilities through dynamic, and activity-dependent rewiring. I will start with a brief review on astrocyte-biology and our basic strategies to supplement the framework of computational neuroscience with elements of neuron-astrocyte interactions. I will then report on our recent study of the "tripartite-synapse" (i.e. presynaptic neuron + postsynaptic neuron + and synaptic astrocyte) which predicts an optimum for astrocytic enhancement of low-fidelity cortical synapses, with experimental values lying close to the optimum. We further explore the effect of astrocytes on synapses with various designs. I will conclude with speculations about how the synaptic signaling machinery of the tripartite synapse may find its "sweet spot".