Resting and stimulated respiration in vitro in the central nervous system. Regional distribution and relation to cell density.

1. The respiratory rates in vitro of ten structures of the rabbit brain were measured in the presence of a normal (5mm) and an elevated (50mm) concentration of K(+) ions. The results were expressed on a dry-weight basis and in terms of cell density. 2. On a dry-weight basis, with a normal concentration of K(+), there was a steady decrease in respiratory rate on passing from the cerebral cortex through successively lower centres to the brain-stem, i.e. respiration was negatively correlated with phylogenetic age. 3. When the resting respiratory rates were expressed in terms of cell density there was no correlation with phylogenetic age. The neuron-containing structures of the cerebrum and brain-stem had identical respiratory rates with the exception of the cerebral cortex which had a higher rate. 4. The K(+)-stimulated respiratory rates/cell also showed a negative correlation with phylogenetic age; the higher centres responded with a greater percentage increase than the lower. 5. The results from the cerebellar cortex were anomalous. 6. There were variations of respiratory rate within the diencephalon. The thalamus had a relatively high respiratory rate, the anterior and ventral regions relatively low and the hypothalamus intermediate. 7. The oxygen consumption of white matter was not increased by a high external concentration of K(+).