Evidence for autonomic paraneurons in sympathetic ganglia of a shrew (Tupaia glis).

The morphological relationships between blood vessels and the small monoamine-storing cells have been studied in the superior sympathetic ganglia of Tupaia. Substantial clusters of these cells were found to be associated anatomically with vascular loops or glomeruli. Blood from these glomeruli enters the capillary bed that supplies principal ganglionic neurons. Thus the vascular path for catecholamine transportation is rather clearly defined in Tupaia, providing new morphological evidence for the existence of a portal system for conveying catecholamine from clusters of paraneurons to principal ganglionic neurons. On the basis of vesicle criteria, two populations of small, granule-containing cell were distinguished, and both were encountered in the same cluster. On the basis of fluorescence microscopy, the relatively small number (14.3%) of solitary SIF cells may be true interneurons because, although there has been no electron microscopic identification of efferent synapses, their processes are much longer than those of the paraneurons.