Contacts: Eric Newman, Physiology Department, (612) 625-2699, [email protected] Deane Morrison, News Service, (612) 624-2346, [email protected]
Movies of the calcium wave are at http://enlil.med.umn.edu/www/phsl/work/caw.htm and can run on computers with a Quicktime plug-in.
New Form of Brain Communication Identified at U of Minnesota
Communication among glial cells--once regarded as just "glue" for the brain--has been identified in intact retinal tissue by researchers at the University of Minnesota. The discovery is a step forward in understanding the function of these cells, which play a role in multiple sclerosis and Parkinson's disease, as well as in regulating the transmission of impulses along nerve fibers and regenerating injured or severed nerves. The discovery is the cover story in the Feb. 7 issue of Science. Working with fresh rat retina, physiologists Eric Newman and Kathleen Zahs studied the behavior of astrocytes, a type of cell named for its star shape. Astrocytes belong to a group of non-nerve cells abundant in brain, spinal cord and the peripheral nervous system. This group, collectively called glia, were once thought to be mere handmaids of nerve cells, with no function but to support and nourish them. But Newman and Zahs showed that astrocytes have lives of their own; they communicate without any help from nerve cells. This type of communication had previously been observed in glial cells grown in a petri dish, but until now, it wasn't known whether this phenomenon occurred in intact tissue. "When I first started, very few neuroscientists cared about what glia did," said Newman. "Now, most of them accept that glia play an essential role in brain function." The glial-cell communication appeared when the researchers stimulated single astrocytes either by electricity, poking or exposure to a chemical known as ATP. In response, calcium levels within the astrocyte skyrocketed, and this condition spread like a ripple through the local astrocyte population. Newman and Zahs used a special dye to track the wave of calcium increases, which they clocked at about 23 microns (nearly one-thousandth of an inch) per second--millions of times slower than nerve transmission. This speed is plenty fast enough, however, for astrocytes and other glial cells to modulate the activity of neurons. Other researchers have found evidence that calcium waves in glial cells can change the electrical behavior of neurons when both types of cells are cultured together in a petri dish, Newman said. He plans similar experiments with intact tissue, recording the electrical activity of neurons as he triggers calcium waves in neighboring glial cells. If nerve cells change their behavior in response to glial cell activity, that would support the idea that glial cells modulate nerve cells--and thus influence slower processes such as changes in mood or state of arousal--in living brains. "Glial cells are in a position to integrate activities of neurons over space and time," said Newman. "For example, a high level of nerve activity in an area might trigger a calcium wave in nearby glial cells, which could negatively feed back on the nerves." Glial cells are already known to have many vital functions, said Newman. Glia maintain proper levels of potassium and other ions in the extracellular environment. When nerve cells signal each other by passing "neurotransmitter" chemicals across synapses (tiny gaps between nerve cells), glial cells remove neurotransmitter molecules from the synapse and thus limit the duration of the signal. In the brain and spinal cord, glial cells called oligodendrocytes produce the fatty myelin sheath that insulates nerve fibers; in multiple sclerosis, oligodendrocytes die, leaving the patient with impaired nervous function. Outside the brain and spinal cord, the counterparts of oligodendrocytes--called Schwann cells--produce myelin and help the nerves regenerate after injury. In Parkinson's disease, according to one theory, chemicals in the environment kill cells that use the neurotransmitter dopamine. Astrocytes may be involved in the disease because they produce a chemical that keeps dopamine-using News releases also on WWW at http://www.umn.edu/urelate/news.html
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