Unique molecular characteristics of visceral afferents arising from different levels of the neuraxis: location of afferent somata predicts function and stimulus detection modalities

Visceral organs receive neural innervation from sensory ganglia located adjacent to multiple levels of the brainstem and spinal cord. Here we examined whether molecular profiling could be used to identify functional clusters of colon afferents from thoracolumbar (TL), lumbosacral (LS), and nodose ganglia (NG) in the mouse. Profiling of TL and LS bladder afferents was also done. Visceral afferents were back-labeled using retrograde tracers injected into proximal and distal regions of colon or bladder, followed by single cell RT-qPCR and analysis via an automated hierarchical clustering method. Genes were chosen for assay (32 for bladder; 48 for colon) based on their established role in stimulus detection, regulation of sensitivity/function or neuroimmune interaction. A total of 132 colon afferents (from NG, TL and LS) and 128 bladder afferents (from TL and LS) were analyzed. Retrograde labeling from the colon showed NG and TL afferents innervate proximal and distal regions of the colon whereas 98% of LS afferents only project to distal regions. There were clusters of colon and bladder afferents, defined by mRNA profiling, that localized to either TL or LS ganglia. Mixed TL/LS clustering also was found. In addition, transcriptionally, NG colon afferents were almost completely segregated from colon DRG (TL or LS) neurons. These results indicate that populations of primary visceral afferents are functionally ″tuned″ to detect and interact with the internal environment and that information from all levels is integrated at higher (CNS) levels, not only for regulation of homeostatic functions, but for conscious visceral sensations including pain.