An ultrastructural study of axonal changes following constriction of postganglionic branches of the superio cervical ganglion in the rat

Abstract

Postganglionic branches were ligated or cut 1 to 2 mm from the superior cervical ganglion in 48 Wistar rats. The axons were examined at intervals from 6 h to 143 days postoperatively. At 6 h the axons were swollen for about 0.6 mm proximal to the ligature, the distended segments containing chiefly vesiculotubular smooth endoplasmic reticulum , 60 to 110 nm dense-cored vesicles and some mitochondria. These organelles were tightly packed close to the ligature and dispersed in amorphous axoplasm further away. Over the next 12 to 30 h many mitochondria became grouped in compact clusters, associated with filaments, near the proximal end of the zone of densely packed organelles, and other organelles appeared in increasing numbers in the same region. These included clumps of small vesicles (some with dense cores), multivesicular bodies of regular form, loops or flattened sacs of membrane, and tubules with an electron-dense content (all of which were probably transported from the cell bodies), and autophagic vacuoles and large cytoplasmic dense bodies, which appeared to form locally within the intra-axonal accum ulations. The autophagic vacuoles and dense bodies formed part of a reaction of intra-axonal digestion of the material initially accumulated. This digestive reaction coincided with the onset of a phase of intracytoplasmic digestion in the cell bodies. The flattened sacs of membrane and the tubules with electron-dense content, and possibly also the multivesicular bodies, appeared to provide material for the intra-axonal formation of autophagic vacuoles and dense bodies. Close to the ligature the tips of the congested axons degenerated and were phagocytosed by Schwann cells. Regenerative axon sprouting (not described in detail in this paper) began within 24 to 38 h and was associated with the appearance of a wispy material in the axons. It was concluded that the relative output of various types of material from the cell bodies may change during the retrograde reaction to axonal injury in these neurons, as part of a coordinated response involving correlation of events in widely separated parts of the neuron.