Immunocytochemical identification of substance P cells and their processes in rat sensory ganglia and their terminals in the spinal cord: light microscopic studies.

The indirect immunofluorescence method and the unlabeled primary antibody peroxidase antiperoxidase method are used to demonstrate the substance P (SP) plexus in the spinal cord and SP cells in the sensory ganglia of the rat. The normal untreated and the control side of the dorsal rhizotomized rat show vast SP immunoreactive plexuses in the substantia gelatinosa, central gray, and ventral gray regions of the spinal cord. In each sensory ganglion, approximately 250 SP immunoreactive cells are found singly or in small groups of 2 or 3, near blood capillaries or among ganglion and satellite cells. They contain intensely immunoreactive cytoplasmic granules 0.1-3.0 mum across. Occasionally, free intensely immunoreactive granules are found in the surrounding tissue near an SP cell but not clearly within the confines of the cell. Another type of immunoreaction has been observed with both methods. A less intense, homogeneous reactivity has been found in lamellae insinuated between ganglion cells and near blood capillaries close to an SP cell; the characteristic disposition of this homogeneous reactivity suggests an extracellular location. Unilateral rhizotomy results in an increased number of immunoreactive SP cells and nerve fibers as well as a more extensive homogeneous immunoreactivity. These results add to existing evidence that SP cells in sensory ganglia send fibers via the dorsal roots to the spinal cord. SP cells, fibers, and terminals do not take up exogenously applied (125)I-labeled [Tyr(8)]SP and cannot be demonstrated by subsequent autoradiography. No neurotensin immunoreactive cells were found in sensory ganglia.