The Forgotten Brain Emerges--Scientific American Mind Article

In an article from Scientific American Mind entitled "The Forgotten Brain Emerges," by Krebs, Huttmann and Steinhauser, it is found by many neuroscientists that glial cells are nearly as important to thinking as neurons. There are nine times as many glial cells in the gray matter of our brains as neurons. It was thought of for many years that glial only provided support for neurons in ways such as fighting pathogens, maintaining a good ion balance and insulation. But this is not true. Glial cells are apparently involved in all aspects of the brain's information processing.
As we all know, there are three main glial cell types: microglia, oligodendrocytes and astrocytes. Microglia act like an immune system for the brain whereas oligodendrocytes form myelin sheaths around the neuronal axons acting as insulation. The important glial cell in this article were the astrocytes, which are involved in a number of aspects of our brain's functioning.
Astrocytes supply neurons with nutrients from blood vessels, absorb neurtransmitters (NT) and make sure ion concentrations remain constan. Astrocytes are also known to "talk" to one another. In essence, the above characteristics of astrocytes are important in how glia affect of neurons communicate.
Though glia are important, they differ in how they conduct information. Neurons use electrical impulses (action potentials) to conduct information whereas astrocytes use chemical messages controlled by rising and falling Ca2+ concentrations. Though they used different ways to conduct information, they may use the same types of messenger molecules. Often, astrocytes will release the same NT's as neurons.
In this article, epilipsy was examined in order to find out how glia communicate. In epileptic episodes, neurons in one region of the brain suddenly fire in complete synchrony with only a few misfiring. Tissue from the hippocampus of epileptic patients were studied because the hippocampus is involved in the onset and spread of seizures. Thins sections of the hippocampus were removed and ion streams flowing through the cell membranes of single astrocytes were tracked. The activity of indivudual ion channels and NT receptros were then measured.
Non-epileptic brains have two types of astrocytes: glu T cells and glu R cells. glu T cells are completely lacking in patients in a certain form of epilepsy noted temporal lobe epilepsy. In healthy brains, though, these glu T cells absorb glutamate that has been released by neurons. This inhibits the prolonged stimulation of the neurons. Along with this glutamate absorption, glu T cells can also remove K+ ions from the intracellular space of neurons also helping to shut down neurons.
glu T cells are connected together by gap junctions. This helps them work together to remobved molecules and ions from neurons simultaneously. This further helps the brain from overactive transmission. In epileptic patients, with this lack of glu T cells, the rapid removal of messenger molecules and ions is absent and the substances instead collect around neurons which overstimulates them. Another consequence of glu T cell loss is that neurons become energy depleted. Healthy brains have glu T cells that absorb glucose and transform it into lactic acid which enables neurons to generate energy. This severly impairs the brain from receiving the supply of nutrients it needs.
On the otherhand, glu R cells have specialized receptors that a used for a variety of messenger substances, which also includes glutamate. Unlike glu T cells, glu R cells do not have gap junctions and thus do not have the ability to remove ions such as K+. Patients with epilepsy have glu R ceclls but K+ channels in their cell membranes is significantly lower compared to that of a healthy brain. Their operation is much slower.
It is still unknown as to whether the deficiency or changes in glia actually cause this type of epilepsy or is a consequence of it. The authors of this article state further research is needed which can go in the direction of looking into pathological problems in the brain that includes neuronal activity AND glial activity. A new understanding of glia must be developed.