Carbonic anhydrase activity in ependymoglial cells of lower vertebrates

Carbonic anhydrase (CA) activity in ependymal cells was investigated in brains of rats, mice, lizards, frogs, tadpoles, and teleost fish using Hansson's modification of Waldeyer and Häusler's histochemical method. No activity was observed in neurons. CA activity was present in perineural and perivascular glial cells of rodents and lizards, but activity was usually not demonstrable in ependymal cells. In amphibians and fish however, ependymal cells and their sub-ependymal prolongations displayed high levels of CA activity. Acetazolamide, 2×10^-5M, blocked all histochemically demonstrable enzyme activity, as did distilled water at 100° C. Carbonic anhydrase in astroglia may be involved in regulation of electrolyte transfer between blood and brain. The observations reported here are consonant with hypotheses suggesting that in lower vertebrates with thin walled brains, ependymal cells may serve functions normally restricted to perineural and perivascular parenchymal glia in higher animals.