Descending pain modulation shaping spinal signalling of colorectal nociception

Signalling of colorectal pain is regulated by descending pain mechanisms in the spinal cord. This study aimed to establish if the influence of descending pain modulation of colorectal pain signalling differs between spinal cord regions known to receive input from colorectal sensory fibres- the thoracolumbar (TL) and lumbosacral (LS) spinal cord. This was assessed by using immunolabelling for serotonin and tyrosine hydroxylase to identify descending input into the TL and LS spinal cord and their association with neurons activated by colorectal distension. This was followed by applying pharmacological mediators of descending transmission into either TL and LS spinal cord regions and measuring their affects on visceromotor responses evoked by in vivo colorectal distension. Then the expression of receptors mediating descending transmission was assessed and compared between TL and LS spinal cord full thickness and within dorsal horn regions isolated by laser microdissection. The resulting data is summarised in the attached PDF.