Incipient cauda equina syndrome as a model of somatovisceral pain in dogs:Spinal cord structures involved as revealed by the expression of c-fos andNADPH diaphorase activity

Segmental and laminar distribution of Fos-like immunoreactive, reduced nico tinamide adenine dinucleotide phosphate diaphorase (NADPHd)-exhibiting and double-labeled (Fos-like immunoreactive and NADPHd-exhibiting) neurons was examined in lower lumbar and sacral segments of the dog spinal cord using t he model of multiple cauda equina constrictions. NADPHd histochemistry was used as marker of nitric oxide synthase-containing neurons. The appearance and the time-course of Fos-Like immunoreactive, NADPHd and double-labeled n eurons was studied at 2 h and 8 h postconstriction characterized as the inc ipient phase of cauda equina syndrome. The occurrence of Fos-like immunorea ctive and NADPHd-exhibiting neurons in fully developed cauda equina syndrom e was studied at five days postconstriction. An increase in Fos-like immuno reactivity in superficial laminae (I-II) and an enhanced NADPHd staining of lamina Vm neurons were found. A statistically significant increase in Fos- like immunoreactive neurons was found in laminae I-II and Vm-X sh postconst riction, and in contrast, a prominent decrease in Fos-like immunoreactive n eurons was found in laminae I-II, accompanied by a statistically significan t increase in Fos-like immunoreactive neurons in more ventrally located lam inae VIT-X at five days postconstriction. Quantitative analysis of laminar distribution of constriction-induced NADPHd-exhibiting neurons revealed a c onsiderable increase in these neurons in laminae VIII-IX 8 h postconstricti on and a statistically highly significant increase in NADPHd-exhibiting neu rons in laminae VII-X five days postconstriction. Concurrently, the number of NADPHd-exhibiting neurons in laminae I-II was greatly reduced. While a l ow number of double-labeled neurons was found throughout the gray matter of lower lumbar and sacral segments at 2 h postconstriction, a statistically significant number of double-labeled neurons was found in lamina X 8 h and in laminae W-X five days postconstriction. The course and distribution of a nterograde degeneration resulting five days after multiple cauda equina con strictions are compared with segmental and laminar distribution of Fos-like immunoreactive and NADPHd-exhibiting neurons. Prominent involvement of the spinal cord neurons appearing in the lumbosacr al segments at the early beginning and in fully developed cauda equina synd rome results in a Fos-like immunoreactivity and strongly enhanced NADPHd st aining of some neuronal pools. Under such circumstances, an early cauda equ ina decompression surgery is advisable aimed at decreasing or preventing th e derangement of the neural circuits in the lumbosacral segments. (C) 1999 IBRO. Published by Elsevier Science Ltd.