ULTRASTRUCTURE OF RETROGRADE DEGENERATION IN THALAMUS OF RAT 1. NEURONAL SOMATA DENDRITES

The degenerative reaction to axotnic injury of neurons of the lateral nucleus of rat thalamus was observed electron microscopically one, 2, 3, 5 and 10 days after localized unilateral decorticectomy. In 2-day survivals dispersion of rosette ribosomes into single units was the most distinctive feature although occasional fused groups of mitochondria were also noteworthy. At 3 days vacuolar dilatation of ER cisterns which were depleted of attached ribosomes, microtubular hyperplasia and an apparent increase in mitochondrial numbers marked many neurons. An overall diminution in ER elements was present at this and later stages. Foci of cytoplasmic degradation prominently consisting of myeloid bodies were conspicuous. Golgi cisterns showed dilatation concurrently with alterations in the membranous ER. Focal dilatation of the Golgi system led to formation of large cytoplasmic vacuoles in 5- and 10-day animals. Although some Golgi complexes retained characteristic appearances in degenerating neurons, the preservation of this organelle was only relative in comparison to the ER. Other morphologic abnormalities included swelling of mitochondria and appearance of rare lipid droplets and glycogen granules in the cytoplasm. There was no evidence of neurofilamentous hyperplasia.