Regional differences of respiration in the bullfrog brain based on cell density

The comparison of analogous and homologous regions of the anuran and mammalian brains, according to their rate of oxygen uptake per unit weight of DNA, has revealed a lack of correspondence between the respective brain regions. This discrepancy between corresponding regions was observed during incubation either in low-potassium or in high-potassium Ringer. Per unit weight of DNA, the rate of cellular respiration in the amphibian hindbrain exceeded that of the thalamus-midbrain, and cells in the latter region exceeded those in the telencephalon. Hindbrain values were only higher if based on unit weight of DNA, and were actually lower on a wet weight basis. This pattern contrasted with a uniform rate of oxygen consumption for the homologous regions of the mammalian brain. Such inequalities between the regional brain metabolism of two different classes of vertebrates clearly illustrate the unique evolutionary history of both forms. The intensity of potassium-stimulated oxygen uptake in the three brain regions of the amphibian was interpreted as probably being proportional to the number of glial cells in each area. The smallest percentage of stimulation in the hindbrain may signify fewer glia, and the highest percentage of stimulation in the mid- and forebrain may indicate more numerous glia. Histological descriptions of ependymal glia in consecutive regions of the anuran brain appear to confirm this distribution of non-neuronal cells.