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Original Article

Differential Effects of Maturation on Nicotinic- and Muscarinic Receptor–Induced Ion Secretion in Guinea Pig Distal Colon

Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112

The incidence of constipation increases with age. This has been linked to age-related changes in the structure and function of myenteric neurons regulating intestinal motility; however, the role of submucous neurons is unknown. The aim of this study was to determine the effect of maturation on cholinergic receptor–induced ion secretion in guinea pig colon. Changes in the short-circuit current (Isc) and tissue conductance were monitored in muscle-stripped colonic segments from young (3–4-month-old) and mature (12–15-month-old) male guinea pigs. Thirty-one percent of colonic segments from young guinea pigs exhibited ongoing neural activity, which was absent in mature animals. Baseline Isc was significantly higher only in young guinea pig tissues with ongoing activity. Tissue conductance was similar in all tissues. Electrical field stimulation caused a biphasic increase in the Isc. At 15 V/10 Hz, only Peak 1 was attenuated, whereas both peaks were reduced in mature guinea pigs at 10 V/5Hz. 1,1,dimethyl-4-phenyl-piperazinium(DMPP)–induced ion secretion was blunted in mature guinea pigs. Atropine reduced the 1,1,dimethyl-4-phenyl-piperazinium response only in young guinea pigs. Carbachol-induced ion secretion was similar in tissues from both age groups. In conclusion, nicotinic receptor–induced secretion mediated by both cholinergic and noncholinergic secretomotor neurons was blunted; however, epithelial muscarinic receptor activity was unaltered during maturation.

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