Electron microscopic study of sprouting dendrites in the ciliary ganglia of cat and monkey (Macaca fascicularís) following pre- and post-ganglionic axotomy

Abstract

The present paper reports the ultrastructure of dendritic sprouting and formation of associated synapses in the ciliary ganglion of cat and monkey induced by pre- and post-ganglionic axotomy. In both series of experiments, sprouting dendrites were observed mostly at 3-5 days postoperatively; such profiles were identified by their dense packing of mitochondria and glycogen-like granules. In longitudinal section, such profiles appeared as expanded extensions from the normal-looking dendritic trunks. None were observed to arise directly from the neuronal soma. After preganglionic nerve section, the cross-sectional diameters of such profiles measured 2.211 .O pm (range: 0.9-6.2 pm) in cat and 2.4I0.7 y m (range: 0.9-5.5 pm) in monkey. After postganglionic nerve section, the crosssectional diameters of such profiles measured 2.110.7 pm (range: 0.8-4.5 pm) in cat and 2.811.4 pm (range: 1.1-7 .O p m) in monkey. After preganglionic axotomy, in both cat and monkey, the axon terminals began to degenerate at 3 days postoperatively and disappeared by 5 days postoperatively. However, at later postoperative survival periods, the axon terminals reappeared and were observed to make synaptic contacts with the sprouting dendrites. Some of the sprouting dendrites were observed to degenerate, some as early as 3 days postoperatively; such profiles did not appear to have any synapse on them. After postganglionic axotomy, such sprouting dendritic profiles were also observed to make synaptic contacts with axon terminals; some were only closely associated with profiles filled with synaptic vesicles. The results thus suggest that through the formation of new synapses, sprouting of dendrites may have a role to play in neuronal survival after axotomy.