Tritiated leucine incorporation in the developing hamster facial nucleus with injury: a liquid scintillation study.

Tritiated leucine incorporation was examined after either crush or axotomy of the hamster facial nerve at specific stages in the maturation of the neuronal nucleolus. Changes in the neuronal metabolic response to injury in development were demonstrated with liquid scintillation examination of tritiated leucine incorporation into the trichloroacetic acid (TCA)-insoluble and TCA-soluble fractions derived from whole reactive and normal facial nuclear groups. Changes in incorporation seen in the developmental sequence were attributed to actual changes in neuronal protein metabolism, and not to changes in the amino acid pool, glial changes or hyperemic capillary changes. The ability to increase leucine incorporation over the normal as a result of injury in development coincided with the time of final nucleolar maturation in the facial motor neurons, beginning at approximately 20 days postnatal age. Thus, there is a correlation between a specific morphological event, the attainment of the mature nucleolar configuration, and the acquisition of the mature synthetic capacity as indicated by the ability to respond to injury in the mature manner.