On the cellular localization and distribution of carbonic anhydrase II immunoreactivity in the rat brain

Evidence is provided that carbonic anhydrase-II is localized in the central nervous system to wide spread systems of oligodendrocytes and restricted astroglia populations, involving both fiber bundles and neuropil. It is suggested that CO₂ formed in activated axons may, via carbonic anhydrase-II, give rise to protons controlling the excitability of surrounding neuropil. Thus, CO₂ may represent an important, highly diffusible, signal in brain, involved in the tonic control of neuronal activity.