When people think about activity in the brain they usually think about neurons. Neurons are the brain cells that send signals to and receive signals from other neurons. They communicate electrically by supporting electrical impulses known as action potentials. When an action potential reaches another neuron it communicates with it through a special structure known as a synapse, which includes a very small space between the sending and receiving neurons. The action potential causes a chemical, known as a neurotransmitter, to be released from the sending neuron, which then crosses the space in the synapse, and binds to receptors on the receiving neuron where it influences electrical signaling.

Another kind of brain cell known as glia are often thought of as “supporting” cells (glia literally means glue in Greek) and are often ignored when scientists think about how the brain does its signal processing to support, for example, sensation or perception. New research adds to the evidence that glia may be just as important as neurons for signal processing in the brain. The paper “Channel-Mediated Tonic GABA Release from Glia” (published November 5, 2010 in Science) demonstrates that glia are an important source for at least some of the tonic inhibition found through much of the brain.

Tonic inhibition is like keeping the brakes engaged in an automobile that is revved up and ready to go. If you release the brakes, the car is off and running until you brake again. In the brain, many neurons would be revved up and ready to fire a lot of action potentials if the “brakes” weren’t kept on through tonic inhibition. In fact, the loss of appropriate tonic inhibition is one possible reason for epileptic seizures.

In their new paper, the research team demonstrates that the glial cells in a particular part of the brain known as the cerebellum have ion channels (bestrophin 1) that chronically release an inhibitory neurotransmitter (most likely GABA) onto neurons known as granule cells and a particular set of axons known as parallel fibers. The resulting tonic inhibition is clearly in the position to play a significant role in signal processing in the cerebellum. Future research should provide insight into what that role is and if the same or similar mechanisms involving glial cells can account for tonic inhibition in other parts of the brain.