The posteromedial barrel subfield of the somatosensory cortex of mice was examined histochemically for cytochrome oxidase activity (cytochrome c oxidase; ferrocytochrome c:oxygen oxidoreductase, EC 1. 9. 3. 1). In normal mice a high enzymatic activity was found within the barrel hollows, rather than in the sides and septa. Electron microscopic examination indicated that within the hollows reactive mitochondria reside in many dendrites, in some axonal terminals, and in a few neuronal perikarya. After neonatal cauterization of selected row(s) of vibrissae, the corresponding row(s) of barrels appeared as narrowed fused band(s) and their cytochrome oxidase activity was much reduced. Removal of vibrissae in the adult, by either cauterization or repeated plucking, did not cause size changes of cortical barrels. However, there was a significant decrease in the oxidative enzymatic activity within these barrels VSports手机版. Thus, the deprivation of sensory input through damage to, or removal of, the peripheral sensory organ induces an enzymatic response in neurons that are at least two to three synapses away from the periphery. .