Segmental distribution of peptide- and 5HT-like immunoreactivity in nerve terminals and fibers of the thoracolumbar sympathetic nuclei of the cat.

The distribution of leucine-enkephalin, methionine-enkephalin, neurotensin, somatostatin, substance P, oxytocin, vasopressin, neurophysin II, and serotonin in nerve terminals and fibers of sympathetic autonomic areas of the thoracolumbar (T-L) spinal cord was studied immunohistochemically in cats. Densities of these immunoreactive terminals and fibers were estimated in the intermediolateral nucleus pars principalis (IMLp) and pars funicularis (IMLf), the nucleus intercalatus (IC), and the central autonomic area (CA). Results for leucine- and methionine-enkephalin-like immunoreactivity (ENK) were similar and immunoreactivity for vasopressin was not observed. The greatest numbers of terminals and fibers in the IMLp region contained ENK, neurotensin-(NT), and serotonin-like immunoreactivity (5HT); terminals and fibers containing substance P-(SP) and neurophysin II-like immunoreactivity (NP2) were intermediate in number, and those containing somatostatin-(SS) and oxytocin-like immunoreactivity (OXY) were generally sparse. In the IC and CA, terminals and fibers containing ENK and NT were dense, those containing SP were moderate, and those containing OXY, NP2, and 5HT were sparsely represented. In the IMLp, where the largest proportion of sympathetic preganglionic neurons (SPN) is found, the greatest concentration of terminals and fibers containing ENK was found in segments T1-T8; for NT these segments were T1-T5 and T11-L1, for SP-C8-T2 and T11-L1, for NP2-T4-T7 and L2 to L3, and for 5HT-T1-T5. Terminals and fibers containing SS and OXY were present in segments C8-T10 and segments C8, T2-T8, T13, and L2 to L3, respectively. These results indicate that while ENK, NT, SP, NP2, and 5HT fibers and terminals are widely distributed throughout the T-L cord, they may influence to a greater degree the SPN in segments where they are present in greater numbers. As SS and OXY were not found at all levels of the IMLp, their functions may be more organ specific.