Diminished retrograde transport causes axonal dystrophy in the nucleus gracilis. Electron- and light-microscopic study.

To examine a possible cause of axonal dystrophy in the nucleus gracilis, dorsal root ganglion (DRG) neurons of rats were investigated by means of electron-microscopic autoradiography and horseradish peroxidase (HRP) tracing method. Following injections of tritiated amino acids into the L6 and S1 DRG, labeling was observed on the initial and halfway developed dystrophic terminals in the ipsilateral gracile nucleus. However, no grains or few, if any, were found on the well developed huge dystrophic endings. Compared with the thoracic and upper lumbar DRG, a decrease in velocity and amount of retrograde HRP transport was demonstrated in the lower lumbar and sacrococcygeal DRG neurons, especially of large cell diameter, irrespective of age of rats. These findings led us to conclude that the axonal dystrophy reflects a state of an anterograde overtransport of the axoplasm caused by a diminished retrograde transport which is specific to lower lumbar and sacrococcygeal DRG large neurons.