Carbonic Anhydrase in Myelin and Glial Cells in the Mammalian Central Nervous System

Abstract

During the past 10 years, immunocytochemical methods have been used for localization of carbonic anhydrase (CA) in glial cells and myelin in the mammalian central nervous system. Those immunocytochemical studies were, however, preceded by several decades of biochemical research, and the possible localization in the oligodendrocytes, which comprise one glial cell type, was first suggested over 45 years ago, after CA was assayed in homogenates of spinal cords and cerebra from seven species.1 At that time, large numbers of oligodendrocytes had been observed predominantly in myelinated regions, where they were often found in rows between myelinated axons. Later, the oligodendrocytes were shown to be the cells that myelinate axons in the central nervous system (reviewed in reference 50). The astrocytes, which are the other major glial cells of brain and spinal cord, are quite diverse in their structures and putative functions, which include the transport of ions, water, and other compounds and the formation of scar tissue within the brain after injury.23,33,40 In this chapter, the evidence for CA in myelin and in glial cells of both types will be discussed. Possible functions for the CA in myelin and glial cells will also be suggested. In another chapter, there is some discussion of localization in the peripheral nervous system and exceptions to the localization in glial cells in the mammalian central nervous system.36 The high levels of CA in the choroid plexus14 should also be noted.