Search

Age-related changes in the nitric oxide-producing neurons in the rat rectoanal region were studied with reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry and morphometry. In 15-dayold rats the myenteric plexus of the distal rectum and anal canal, situated in the space between the longitudinal and circular muscle layers, was exposed by NADPH-d positive perikarya. In the anal canal the positive myenteric neurons were more intensively stained than in the rectum. The mean optical density (OD) of positive neurons in the rectum was 115.8±2.4 vs. 89.5±1.6 in the anal canal. Single nerve fibres and small nerve bundles in the circular muscle layer of the anal canal were frequently seen and were more intensively stained than rectal fibres. In 3-month-old rats a larger number of NADPH-d-positive nerve fibres and an increase in their staining intensity were found. The staining intensity of the perikarya in the anal canal was higher than in the rectum (the OD 70.9 ± 1.1 vs. 55.5 ± 1.5). In the circular muscle layer thicker nerve strands were observed. In 26-month-old rats the staining intensity of NADPHd-positive perikarya in the myenteric plexus was weaker than in the 3-month-old rats. In the rectum their OD was lower than in the anal canal (93.8 ± 2.05 vs. 78.9 ± 1.7). The nerve strands were sparse and less intensely stained than in 3-month-old rats. Our results are consistent with the hypothesis that NO is an important neurotransmitter of the recto-anal motility in the ageing gut.