Variations in oxidative enzyme type profiles among prenatal rat lumbar motoneurons

We have used cytochrome oxidase histochemical staining to evaluate whether immature rat lumbar motoneurons show intrinsic separation into high or low oxidative enzyme types. Relative oxidative enzyme levels are frequently used to help differentiate between muscle fibres of various types and to differentiate between mature neurons. Here we show a wide variation in motoneuron cytochrome oxidase levels from prenatal times, although the range of staining levels as measured densitometrically is greater for mature than for prenatal animals. We find variation in cytochrome oxidase levels among motoneurons prior to the formation of mature patterns of connectivity or electrical activity, and conclude therefore that this differentiation is unlikely to have arisen by differential usage and probably arose as a function of cell lineage.