A study on the submandibular ganglion of the monkey with special reference to ultrastructural changes after lingual nerve sectioning.

This study describes normal light and electron microscopic features of the monkey submandibular ganglion. The intraglandular ganglion is composed of a collection of smaller ganglia distributed mainly at the hilum of the submandibular gland: one or two large ganglia were often found along with the main duct, while the smaller ones were located at the periphery. All ganglion cells were covered by satellite cells. Ultrastructurally, the ganglion cells showed the usual features of autonomic neurons, being round to oval with a prominent nucleus and nucleolus. Their cytoplasm contained numerous randomly distributed organelles. Occasional ganglion cells showed darkened dendrites. The majority of the synapses observed were of the axo-dendritic type, although the axo-somatic type was not uncommon. In the latter, the axon terminals were sometimes seen to deeply invaginate the soma of the ganglion cells forming synaptic contacts. Non-synaptic desmosome-like junctional complexes were common between the ganglion cells. Following the severance of the lingual nerve, the ganglion showed structural alterations beginning 1 day after the operation. The earliest sign of change was the increase in the number of macrophages surrounding the ganglion. Three and five days after the lingual nerve sectioning, the number of darkened dendrites considerably increased. Associated with this change were neuronal nuclei displaying irregular outlines. Other changes involved the disintegration of the preganglionic fibres and their axon terminals. The latter were observed to be engulfed by the infiltrated macrophages and Schwann cells. By 7 days after the preganglionic parasympathectomy, the ganglion cells resumed normal features, suggesting the acute and reversible nature of the transneuronal degeneration of the monkey submandibular ganglion cells. This is further supported by the absence of cell death during the period examined.