The effect of age on the anatomy and function of the human colon is incompletely understood. The prevalence of disorders in adults such as constipation increase with age but it is unclear if this is due to confounding factors or age-related structural defects. The aim of this study was to determine number and subtypes of enteric neurons and neuronal volumes in the human colon of different ages. Normal colon (descending and sigmoid) from 16 patients (9 male) was studied; ages 33–99. Antibodies to HuC/D, ChAT, nNOS, and PGP9.5 were used. Effect of age was determined by testing for linear trends using regression analysis. In the myenteric plexus, number of Hu-positive neurons declined with age (slope = −1.3 neurons/mm/10yrs, p =0.03). The number of ChAT-positive neurons also declined with age (slope = −1.1 neurons/mm/10yrs of age, p=0.02). The number of nNOS-positive neurons did not decline with age. As a result, the ratio of nNOS to Hu increased (slope= 0.03 per 10yrs of age, p=0.01). In the submucosal plexus, the number of neurons did not decline with age (slope = − 0.3 neurons/mm/10 yrs, p =0.09). Volume of nerve fibers in the circular muscle and volume of neuronal structures in the myenteric plexus did not change with age. In conclusion, the number of neurons in the human colon declines with age with sparing of nNOS- positive neurons. This change was not accompanied by changes in total volume of neuronal structures suggesting compensatory changes in the remaining neurons.

Interstitial cells of Cajal (ICC) are specialized mesenchyme-derived cells that regulate contractility and excitability of many smooth muscles with loss of ICC seen in a variety of gut motility disorders. Maintenance of ICC numbers is tightly regulated, with several factors known to regulate proliferation. In contrast, the fate of ICC is not established. The aim of this study was to investigate whether apoptosis plays a role in the regulation of ICC numbers in the normal colon. ICC were identified by immunolabeling for the c-Kit receptor tyrosine kinase and by electron microscopy. Apoptosis was detected in colon tissue by immunolabeling for activated caspase-3, terminal dUTP nucleotide end labeling, and ultrastructural changes in the cells. Apoptotic ICC were identified and counted in double labeled tissue sections. Apoptotic ICC were identified in all layers of the colonic muscle. In the muscularis propria 1.5 ± 0.2% of ICC were positive for activated caspase-3 and in the circular muscle layer 2.1 ± 0.9% of ICC were positive for TUNEL. Apoptotic ICC were identified by electron microscopy. Apoptotic cell death is ongoing in ICC. The level of apoptosis in ICC in healthy colon indicates that these cells must be continually regenerated to maintain intact networks.

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