The effect of ageing on the innervation and total collagen content of human colon

This thesis addressed the enteric innervations and total collagen content and its distribution within the functional sublayers, namely: mucosa, submucosa and muscularis externa (circular muscle (CM) and taenia coli (TC)) in ageing human colon. Macroscopically normal ascending (AC) and descending (DC) colon was obtained at surgery from cancer patients without diagnosis of diverticular disease or inflammatory bowel disease. Masson’s trichrome and Picrosirius red stains were employed to identify the total collagen content and distribution within the colonic wall. A hydroxyproline assay evaluated the total collagen concentration in the formalin-fixed, paraffin-embedded human colonic samples. Assessment of the subtypes of enteric glial cells (EGCs) and calretinin- immunoreactive (IR) enteric neurons were demonstrated by immunohistochemical method. Standardized procedures were utilised to ensure unbiased counting and densitometric evaluation for further quantitative analysis. The results of the present study demonstrated that greater collagen content was present in the submucosa and muscularis externa, particularly the TC in the elderly (≥ 65 years) samples compared to adult (< 65 years). The density of S100-IR EGCs declined among the elderly in the CM and within the myenteric plexus (MP) per ganglionic area. There was little or no GFAP-IR EGCs in both adult and elderly colon. Among the elderly, the density of calretinin-IR neurons and fibres were decreased in the submucosal plexus of AC but not clearly in the DC. In the mucosal layer of both AC and DC, the decrease in density of calretinin-IR fibres was greater in the AC compared to DC. Sex related differences were not found when data combined in both the AC and DC samples. Collectively, these results indicate that there are region and sublayer dependent changes in the distribution of total collagen fibres, EGCs and calretinin-IR enteric neurons in ageing human colon. This age-related structural change may differentially impact upon specialised functions and affect colonic physiology.