Evidence for dopamine-storing interneurons and paraneurons in rhesus monkey sympathetic ganglia

In order to study and quantify the small, intensely fluorescent (SIF) cells and to examine their synaptology, the superior cervical sympathetic ganglia of rhesus monkeys were examined by a sequential glyoxylic acid (GA) monoamine fluorescence and electron microscopic technique. Correlated data concerning the sensitivity of the ganglia to dopamine were gathered by measuring the rise in cyclic AMP levels following incubation in vitro with exogenous dopamine. Cyclic AMP levels after incubation for 12 min with 50 micron dopamine showed marked increases, averaging 288% of control values. This indicates that these ganglia contain a dopamine receptor-adenylate cyclase complex. The number of SIF cells per mg of tissue was about half that found in the cow and rabbit, and only 1% of the number observed in the rat. Morphological data support the view that, in this species, there are almost equal numbers of type I (hypothesized interneuron) and type II (paraneuron) SIF cells. Presumptive SIF cell efferent synapses were observed by electron microscopy, the postsynaptic elements being dendritic spines or very fine nerve processes.