سهم سلول های گلیال در پتانسیل های خود انگیخته و برانگیخته

The mechanism by which brain cells generate alpha and other rhythms remains obscure, and the possible articipation of glial cells in the process continues to be debated. We will present data obtained from freely moving rats in which flashes produced by a light emitting diode implanted under the skin of the scalp evoke retinal and cortical responses recorded through electrodes implanted behind the eye and over visual cortex. In the retina, which is a brain-like structure isolated in the periphery during embryology, the b-wave evoked response is thought to be produced by the Müller glial cells as they maintain potassium ion homeostasis in the extracellular space during the synaptic events initiated by rod and cone activation. We will report on the results of a search int his retinal analogue of the brain for spontaneous activity in the EEG spectrum. © 1997 Elsevier Science B.V.

During this conference Riitta Hari said `to make sense of alpha events we should proceed from single cell dynamics to population dynamics'. We heartily agree, and offer for your consideration the neuropile visualized in any good electron micrograph of mammalian cortex as the brain cell population whose dynamics are most worthy of analysis. Neuropile is an intimately intertwined collection of microscopic membranes within which interactions such as glia–glial, glia–neuronal, and neuro–neuronal are constantly taking place across the fluid-filled extracellular space. Neuropile is ubiquitous, and understanding its population dynamics will surely help unravel some of the mysteries of brain function. The first author of this paper began thinking this way in 1961, when he declared an interest in the physiology of glial cells (Galambos, 1961), and has speculated further on the matter since then (Galambos, 1989). Very recently, after 35 years of searching, we have at last discovered a way to study normal glia in situ, and have begun to use the preparation for testing the idea that dynamic interactions between astrocytes and neurons contribute to the electrical activities recorded through scalp electrodes. We recently published the first report of these experiments (Galambos et al., 1994); they deal with evoked potentials, not alpha rhythms, but perhaps after considering these earliest results you may agree the method could uncover useful new facts about the electrogenesis of rhythmic brain oscillations as well.

This essay asks the reader to examine the evidence that electrogenesis of spontaneous and evoked brain potentials involves two interrelated phenomena. The first is the injection of electrical currents into the extracellular space by depolarizing and repolarizing neuronal membranes, a widely-accepted and classical point of view. The second is the capacity of many glial cells to monitor, control, and adjust the potassium ion concentration in extracellular space: [K+]o is at every given moment being altered by synaptic activities and readjusted toward its optimal value by glial spatial buffering, a pair of linked events that creates intracellular transport of potassium ions and the appearance of measurable extracellular currents. The question to be answered is this: How much of the electrical current flowing across a pair of electrodes pasted on the scalp can be traced to purely neuronal activity, and how much to the potassium homeostasis function the glial cells constantly perform?