REGIONAL DIFFERENCES IN THE NUMBER OF NEURONS IN THE MYENTERIC PLEXUSOF THE GUINEA-PIG SMALL-INTESTINE AND COLON - AN EVALUATION OF MARKERS USED TO COUNT NEURONS

Background: Subsets of myenteric neurons have been identified. To dete rmine the proportional representation of neurons in each, it is necess ary to relate the number of neurons in the subset to that of the compl ete set. Prior estimates of total numbers of neurons, obtained with ma ny different markers, have varied widely. Methods: Markers were compar ed for counting myenteric neurons in dissected laminar preparations of guinea pig duodenum, jejunum-ileum, and colon; the effect of stretchi ng preparations on these counts was also determined. Markers included the visualization of single-stranded nucleic acid with cuprolinic blue and the immunocytochemical demonstration of neuron specific enolase ( NSE), PGP9.5, 5-100, and the constitutive expression of a Fos related antigen (FRA). Results: Neurons could not be counted accurately by dem onstrating NSE, PGP9.5, or S-100. The number of neurons detected by de monstrating FRA was consistently less than that determined with cuprol inic blue (similar to 65%). Cuprolinic blue-derived estimates of neuro n numbers were higher than most reported in the literature, but compar able to those recently obtained with ''a nerve cell body'' antiserum. Ganglionic area was found to be stretch independent. The rank order of neurons/cm(2) and ganglionic area/unit resting length was colon > duo denum much greater than jejunum-ileum; more neurons were found in the myenteric plexus of the colon (7.3 x 10(6)) than in that of the entire small intestine (6.5 x 10(6)). Conclusions: Prior studies that have o btained denominators for estimating the proportions of myenteric neuro nal subsets with markers that do not reveal the entire population shou ld be re evaluated. The guinea pig colon contains a surprisingly large number of neurons, the physiological significance of which must be de termined. (C) 1996 Wiley-Liss, Inc.