Background: Data on structural variations in the neuronal composition of myenteric ganglia along the small intestine of various species are scarcely available. The aim of this study was to compare morphologically the ganglia and neurons of different parts of this organ in the pig.
Methods: Wholemounts from jejunum and ileum of two 14-week-old pigs were silver impregnated. The number of morphologically defined neuron types I-VI were counted per cm2. To relate these numbers to the putative whole neuron population, all impregnated neuronal nucleoli were counted in the same areas.
Results: Morphologically classifiable, impregnated neurons ranged between 17.9 and 23.1% of the putative whole population as determined by neuronal nucleoli counting. The proportions of type I neurons (jejunum, 22-25%; ileum, 19%) and type II neurons (jejunum, 30%; ileum, 37%) were considerable in both segments. The proportion of type III neurons was about 30% in jejunum and 2% in ileum whereas the percentages of type IV (jejunum, 10%; ileum, 18%), type V (jejunum, 2%; ileum, 12%) and type VI neurons (jejunum, 3%; ileum, 11%) were higher in the ileum. All differences between jejunal and ileal percentages were significant as determined by chi square test.
Conclusions: Ganglia from the upper jejunum and the lower ileum reveal distinct differences in terms of neuron type composition. We suggest that these morphological differences reflect well known functional differences, e.g. in terms of motility, between different parts of the small intestine.