A qualitative and quantitative study of substance P immuno-cytochemistry of the trigeminal ganglion in the monkey.

The immunoreactivity of substance P(SP) in the monkey trigeminal ganglion was examined and the distribution of immunoreactive cells determined. The monkey trigeminal ganglion is composed of clusters of sensory cells arranged in cords parallel to the long axis of the nerve fibres. The cells have prominent nuclei and are surrounded by satellite cells. Abundant organelles are randomly distributed throughout the cytoplasm. A striking feature of the ganglion was the presence of some axon-like prolifes containing mainly dense-cored vesicles and some agranular vesicles. Between 16 and 32% of the ganglion cells displayed SP-immunoreactivity. Most of the SP-IR cells were unipolar, small to medium-sized ganglion cells and they had no specific pattern of distribution. The staining of the SP-IR cells varied considerably, ranging from weak or moderate to heavy staining, although the majority of them were moderately stained. Immuno-electron microscopy showed that the SP-IR products were distributed throughout the soma of ganglion cells and not associated with any particular organelles or inclusions. The reaction products were also found in both myelinated and unmyelinated fibres between the ganglion cells. Another remarkable feature of the trigeminal ganglion was the occurrence of some SP-IR nerve fibres forming a rich "glomerular" network of pericellular arborizations around some of the SP-negative cells. Ultrastructural study showed the presence of some SP-IR nerve terminals in close approximation to some SP-negative cells, but there were no synaptic contacts. The relative frequency of the SP-IR pericellular arborizations paralleled the frequency of all the SP-IR cells.(ABSTRACT TRUNCATED AT 250 WORDS)