Immunocytochemical identification of axons containing coexistent serotonin and substance P in the cat lumbar spinal cord.
Axons containing both serotonin-like (5-HT)-LI and substance P-like (SP)-LI immunoreactivity were identified in all laminae of the cat spinal cord at the level of the lumbar enlargement. Using an immunologically-specific, double immunofluorescence method, coexistent 5-HT-LI and SP-LI immunoreactivity could be visualized in the same tissue section with appropriate FITC and rhodamine fluorescent filter sets. The fewest number of coexistent axons were observed in the superficial laminae of the dorsal horn, while their number increased in the more ventral dorsal horn laminae. Numerous coexistent axons were observed in the area adjacent to the central canal. The greatest number of coexistent axons was found in the ventral horn, especially in the motoneuronal cell groups. This study demonstrates that axons containing coexistent 5-HT-LI and SP-LI immunoreactivity are found in all laminae of the cat lumbar spinal cord and are thus involved in both sensory and motor functions. Their more frequent occurrence in the ventral horn suggests a greater role for coexistent 5-HT and SP in motor function. Since axons containing coexistent 5-HT and SP, and those containing only 5-HT, likely originate from different populations of neurons, our observations provide evidence for a diverse origin of descending 5-HT afferents to the different spinal laminae.
D000818:Animals; D001369:Axons / Q000648:ultrastructure*; D002415:Cats; D016650:Fluorescein-5-isothiocyanate; D005452:Fluoresceins; D005455:Fluorescent Antibody Technique; D005456:Fluorescent Dyes; D012235:Rhodamines; D012701:Serotonin / Q000032:analysis*; D013116:Spinal Cord / Q000166:cytology*; D013373:Substance P / Q000032:analysis*; D013861:Thiocyanates
D005452:Fluoresceins; D005456:Fluorescent Dyes; D012235:Rhodamines; D013861:Thiocyanates; D012701:Serotonin; D013373:Substance P; D016650:Fluorescein-5-isothiocyanate