Differences in spinal distribution and neurochemical phenotype of colonic afferents in mouse and rat

Abstract

Visceral pain is a prevalent clinical problem and one of the most common ailments for which patients seek medical attention. Recent studies have described many of the physiological properties of visceral afferents, but not much is known regarding their anatomical characteristics. To determine the spinal distribution and neurochemical phenotype of colonic afferents in rodents, Alexa Fluor-conjugated cholera toxin-beta (CTB) was injected subserosally into the proximal and distal portions of the descending colon in Sprague Dawley rats and C57Bl/6 mice. Dorsal root ganglia (T10-S2) were processed for fluorescent immunohistochemistry and visualized by confocal microscopy. In the mouse, CTB-positive neurons were most numerous in the lumbosacral region (LS; L6-S1), with a smaller contribution in the thoracolumbar ganglia (TL; T13-L1). In contrast, CTB-positive neurons in the rat were most numerous in the TL ganglia, with a smaller contribution in the LS ganglia. The vast majority of CTB-positive neurons in both mouse and rat were positive for TRPV1 and CGRP and most likely unmyelinated, in that most colonic afferents were not positive for neurofilament heavy chain. In the mouse, the TL ganglia had a significantly higher percentage of TRPV1- and CGRP-positive neurons than did the LS ganglia, whereas no differences were observed in the rat. The high incidence of TRPV1-positive colonic afferents in rodents suggests that hypersensitivity from the viscera may be partially a TRPV1-mediated event, thereby providing a suitable target for the treatment of visceral pain.

Convergence of bladder and colon sensory innervation occurs at the primary afferent level

“…Similar to previous studies, we found the fluorescent conjugates of CTB to be very efficient in labeling visceral afferents of the pelvis in the rat and mouse (Christianson et al 2006a;Christianson et al 2006b;Wang et al 1998). As expected and in agreement with existing literature (Jancso and Maggi 1987;Robinson et al 2004;Wang et al 1998;Zhong et al 2003), most bladder afferents projected from the L6-S1 DRG in both rodents, while a smaller, but still notable, population was present in TL DRG.…”

“…As expected and in agreement with existing literature (Jancso and Maggi 1987;Robinson et al 2004;Wang et al 1998;Zhong et al 2003), most bladder afferents projected from the L6-S1 DRG in both rodents, while a smaller, but still notable, population was present in TL DRG. In our studies, the distribution of retrogradelylabeled distal colon afferents also paralleled that of the bladder and, in general, was in agreement with the bimodal LS and TL peaks as noted in the Wistar rat (Vizzard et al 2000) and C57Bl/6 mice (Christianson et al 2006b;Robinson et al 2004). In support of the specificity of our labeling studies, dually-labeled cells were identified only at DRG levels that have previously been shown to contain both distal colon and urinary bladder afferents (Christianson et al 2006b;de Groat et al 1987;Keast and De Groat 1992;Robinson et al 2004).…”

“…In our studies, the distribution of retrogradelylabeled distal colon afferents also paralleled that of the bladder and, in general, was in agreement with the bimodal LS and TL peaks as noted in the Wistar rat (Vizzard et al 2000) and C57Bl/6 mice (Christianson et al 2006b;Robinson et al 2004). In support of the specificity of our labeling studies, dually-labeled cells were identified only at DRG levels that have previously been shown to contain both distal colon and urinary bladder afferents (Christianson et al 2006b;de Groat et al 1987;Keast and De Groat 1992;Robinson et al 2004). Further supporting the specificity of our findings, bladder denervation substantially reduced labeling of bladder afferents and consequentially the number of dually-labeled cells.…”

“…Previously we have applied 5μL of CTB onto the serosal surface of the distal colon (and adjacent tissues) to determine the extent of retrograde labeling that might arise from dye leakage (n=3). On average, this resulted in only 2 CTB-positive cells per section in the L6 ganglia (Christianson et al 2006b). …”

TRP channels in neurogastroenterology: opportunities for therapeutic intervention

“…bradykinin, 5-HT, neuronal growth factor, tryptase), but also mild acidosis are able to sensitize TRPV1 and enhance the probability of channel gating by heat and capsaicin (Chuang et al, 2001;Ji et al, 2002;Amadesi et al, 2004;Sugiuar et al, 2004). Because TRPV1 was suggested to play a crucial role in nociception based on its expression on mostly unmyelinated visceral afferents (Ward et al, 2003;Brierley et al, 2005;Christianson et al, 2006), a vast number of studies investigating its role in visceral sensation and pain emerged (Caterina et al, 2000). (Reviews by Di Marzo et al, 2002;Geppetti and Trevisani, 2004;Holzer, 2008b;Blackshaw et al, 2010).…”