A New Look at Astrocytes
Astrocytes Are Found to Have Complex Functions Within the Brain
Jul 21, 2008
Astrocytes are cells in the brain that support the function of neurons. There are several types of supporting cells in the brain, which as a group are commonly called glial cells. Astrocytes are also sometimes called astroglia.
Other glial cells include the oligodendrocytes, ependymal cells and micoglia. Astrocytes get their name due to their star shape with arm-like processes. The processes reach out and connect to many neurons and other glial cells.
Astrocytes as "Nannies"
For many years, astrocytes have been thought of as the "nannies" of the brain, relegated to nondescript support functions for the more active and well-known neurons. The astrocytes were known for supplying nutritional molecules such as glucose to the neurons and as part of the blood-brain barrier via their connection with endothelial cells. Astrocytes were also understood to have roles in absorbing or neutralizing excesses of neurotransmitter that has leaked from neurons and for physical support of neuronal tissue. When neurons become damaged, astrocytes become phagocytes and recycle the neuronal detritus.
More Important Roles
As essential as the functions of supply and recycling are in the brain, the astroglia may have a more direct role in the actual development of the brain. A number of studies in brain development are pursuing the idea that astroglia may function as signposts for growing neurons. Colon-Ramos and Shen report these glia may be chemically marking the preferable connections for the growing neurons. There are also other research programs looking into the moderating effect of astroglia on the actions within the synaptic cleft.
Moderating Neuronal Signaling
Signals are sent between neurons by chemical messengers, the neurotransmitters, across the synaptic cleft which separates the neurons. In the brain, astroglia are found encircling the synaptic areas as protection and containment. It has long been known that astroglia could absorb some neurotransmitters that were excess to the signaling process.
Now, a number of researchers are finding that astrocytes have a more assertive role in the brain’s signaling system. Liza Gross notes that astrocytes have been found dampening the signaling between neurons when those neurons have been overstimulated. They have also been found to be participating in a signaling cascade between neighboring astrocytes, generating their own cellular communication.
The Incredibly Complex Brain
As researchers look deeper and deeper into the anatomy and physiology of the nervous system, there appears to be no end in sight to its complexity. The astroglia are one such case. From the status of nannies, they have risen to the ranks of neuronal growth directors and cellular regulators.
 |
