Glial Cells and Epilepsy

Is there a connection? Neurons are not the only cells in the brain. In fact, 90% of brain matter consists of glial cells. Astrocytes, the most common glial cell type, don't have enough sodium channels to carry on the active electrochemical signaling characteristic of neurons, but they can communicate with other cells through the diffusion of messenger molecules.

Furthermore, astrocytes can partially or wholly enwrap neuronal synapses, the message sending or receiving ends of the neuron. This facilitates neutron-astrocyte interactions, and even neuron-neuron communications via astrocytes. Formerly glia were thought to play a passive role in the nervous system---cleaning up the potassium needed in the neural firing mechanism. But increasingly scientists believe that glia play a more active role in enhancing or inhibiting action in the synapse.

Suhita Nadkarni and Peter Jung at Ohio University believe that glia participate in the making of epilepsy. There is no accepted theory of epilepsy; does it arise from neurons talking in synchrony or is it a sort of "thunderstorm" of spontaneous activity among neurons? Jung argues that under some conditions the neuron might "listen" so much to its astrocyte environment (by an overexpression of certain receptor molecules) that it enters into a bistable state; even in the absence of outside (normal) stimulation the neuron could fire indiscriminately in the manner characteristic of epilepsy. It is therefore necessary to undertake a sort of electrical engineering study of neural-glial circuitry.

Jung, a physicist (presently at the Kavli Institute for Theoretical Physics at UC Santa Barbara, 805-893-7333, jungp@kitp.ucsb.edu), has demonstrated some of this glial-neural behavior in computer simulations and is working with neurobiologists who might shortly put the model to an experimental test. (Nadkarni and Jung, Physical Review Letters, 31 December 2003.)