Immunocytochemical studies of the peptidergic content of fibers and terminals within the lateral spinal and lateral cervical nuclei

As part of a series of studies in which we are attempting to determine the roles of the lateral spinal (LSn) and lateral cervical (LCn) nuclei in somatic sensation, we have examined the fibers and terminals within these nuclei in the rat using the indirect immunofluorescence technique. Eleven antisera were used. Within the LSn, antisera against dynorphin 1-8 (DYN), substance P (SP), and Met-enkephalin (ENK) produced labeling of a large number of processes in all segmental levels examined. Processes labeled with these antisera frequently apposed the cell bodies and dendrites of LSn neurons. Antisera against somatostatin (SOM) and FMRF-NH₂ (FMRF) labeled smaller numbers of processes within the LSn. Few, if any, processes in the LSn were labeled using antisera against serotonin, cholecystokinin octapeptide, oxytocin, neurotensin, corticotrophin-releasing factor, and vasoactive intestinal polypeptide. In contrast to the LSn, the LCn contained virtually no labeled processes irrespective of the antiserum employed. An area was found adjacent to the LCn in the medial portion of the dorsal lateral funiculus (DLf) of C2 that resembled the LSn in several of its anatomical characteristics: (1) like the LSn, the medial portion of the C2 DLf contained small multipolar neurons; (2) it was similar to the LSn in its medial-lateral extent; and (3) following staining with each antiserum, the LSn and the medial DLf of C2 contained a similar number of labeled processes. The peptide-containing area in the medial DLf of C2 was found to be continuous with the LSn. We therefore propose that this region is a rostral extension of the LSn. The relative abundance of immunoreactive processes in apposition to neurons within the LSn and LCn was confirmed by observers who were unaware of the antiserum employed or the nucleus being evaluated. These findings support our previous suggestion that the DLf in the rat contains two functionally and anatomically distinct nuclei. The LCn of the cat was also examined after immunostaining with DYN, SP, ENK, SOM, and FMRF antisera. A small number of fibers and terminals were labeled by SP antiserum within the medial most part of the LCn. The remaining antisera failed to label processes in the LCn.