As the gut ages: Timetables for aging of innervation vary by organ in the Fischer 344 rat

To explore the effects of aging on the vagal innervation of the gastrointes tinal (GI) tract, male Fischer 344 rats at 3 and 24 months of age were inje cted in the left nodose ganglion with 3 gel m cholera toxin subunit B-horse radish peroxidase (to label motor endings). The stomach and duodenum were p repared as wholemounts and processed with tetramethyl benzidine. In additio n, to study age-related changes in the myenteric plexus, the stomachs, smal l intestines, and large intestines from 3-, 12-, 21-, 24- and 27-month-old rats were prepared as wholemounts and processed with Cuprolinic Blue (to st ain the neurons). Vagal afferent endings, motor terminal profiles, and myen teric neurons were counted and mapped with a sampling grid. In the stomach, loth the vagal and myenteric innervation were stable between the ages of 3 and 24 months; however, a decrease in the number of myenteric neurons in t he forestomach was noted at 27 months. In the small and large intestines, m yenteric cell loss occurred by 12 months of age, progressed with age, and a ppeared to be governed by several general principles: (1) the rate of cell loss was organ-specific, with a gradient of increasing severity from proxim al to distal in the gut, (2) within organs of the GI tract, the rate of cel l lost; differed between regions; and (3) for given regions, cell losses pr ogressed linearly with increasing age. The findings suggest that a positive relationship exists between the density of vagal extrinsic innervation and myenteric neuron survival; however, whether this results from the vagal in nervation and/or other factor is) protecting or rescuing myenteric neurons from age-related attrition remains to be determined. (C) 2001 Wiley-Liss, I nc.