Origin and distribution of neuropeptide-FF-like immunoreactivity in the spinal cord of rats

Neuropeptide FF, or F8Famide (Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-NH2; "morphine-modulating peptide"), isolated from bovine brain, is an FMRF-NH2-like peptide with morphine-modulating effects. Neuropeptide FF (NFF) is highly concentrated in spinal cords of various mammalian species. There is evidence that NFF participates in the modulation of nociceptive mechanisms. The present study was aimed at describing the distribution and origin of the neuropeptide-FF-like immunoreactivity (LI) in the rat spinal cord. For distribution studies spinal cord sections from colchicine-treated animals were processed according to the indirect immunofluorescence method. Retrograde fluorescent tracer was injected in the lumbar dorsal spinal cord to study descending NFF-LI-containing spinal pathways. NFF-immunoreactive (ir) cell bodies were detected in the substantia gelatinosa, marginal zone, laminae III, IV, and X at all levels of the spinal cord, and the dorsolateral funiculus, and dorsal gray commissure of the lumbosacral transition zone. NFF-ir fibers and terminals were identified in laminae I-IV and X, dorsolateral funiculus, intermediolateral cell column, dorsal gray commissure, sacral parasympathetic nucleus, and ventral horn. A spinal NFF-LI-containing descending pathway originating in the lamina X neurons was observed, but a supraspinal origin of descending NFF-ir fibers was not identified. According to this study the NFF-LI of the spinal cord is of intrinsic spinal origin. The anatomical distribution supports the concept that the NFF-like peptides have a role in the nociception. They may also be involved in sensory-visceral reflex arcs.