Ultrastructure and function of the granule-containing cells in the anuran sympathetic ganglia

In the sympathetic ganglia of various anuran species clusters of small granule-containing cells (GC cells) appeared more often in the 5th to 7th paravertebral granglia rather than in the 9th and 10th ganglia of the sympathetic chain. The GC cells were classified into four types according to the granular vesicle morphology. Types I, II and III cells probably acted as endocrine cells which secrete catecholamines into blood capillaries or extracellular spaces. Type IV cells, however, resembled sympathetic ganglion cells. They seemed to be a special type of postganglionic adrenergic neuron rather than a type of interneuron. All these four cell types received cholinergic innervations. Ganglion cells in the anuran sympathetic ganglia formed no synapses with the adrenergic elements or the GC cells. Hence, it was unlikely that s-IPSP was mediated by catecholamines released from GC cells. Serial section studies revealed that both B- and C-neurons received only cholinergic innervation. A mechanism of s-IPSP production was discussed in correlation with the morphological findings.