SOME NEUROHISTOCHEMICAL PROPERTIES OF NERVE ELEMENTS IN MYENTERIC PLEXUS OF RABBIT ILEUM - SIMILARITIES AND DISSIMILARITIES TO THE RODENT PATTERN

Enteric neurons have distinct neurochemical codings in each species. T he basal tone of the gastrointestinal tract of the rabbit is low and p roduces neurally evoked pendular movements. Therefore, it might have a n innervation pattern different from that of other laboratory animals. We have characterised myenteric neuron populations in rabbit ileum wi th neurochemical markers that are known to be associated with distinct cell types and/or fibre systems in the myenteric plexus. The density of nerve cells estimated with the NADH-diaphorase technique was about 2500 cells/cm(2) and most, if not all, neurons contained microtubule-a ssociated protein 2. NADPH-diaphorase-positive cells were numerous. On e cell type was large and emitted long straight processes, whereas sma ll cells bore thin filamentous dendrites. Neurons immunoreactive for 2 8-kDa calcium-binding protein were rare. Over 70% of them had very str ongly labelled lamellar dendrites. Their axons were beaded and formed pericellular baskets around unstained somata. We found very few small tyrosine-hydroxylase-positive cells. The fibre network in the plexus w as very strong; the axons formed many pericellular baskets. In double labelling studies, no co-localisation was revealed between the 28-kDa calcium-binding protein and NADPH-diaphorase. Some fibres containing 2 8-kDa calcium-binding protein formed only a few contacts on somata of NADPH-diaphorase-positive cells. None of the NADPH-diaphorase-labeled cells were found to be stained for tyrosine hydroxylase. Tyrosine-hydr oxylase-positive fibres rarely made pericellular baskets on the surfac e of NADPH-diaphorase-positive somata. Strongly immunolabelled pericel lular baskets were never observed around NADPH-diaphorase-positive cel l somata. The results suggest that myenteric neurons in rabbit compris e distinct and characteristic neurochemical properties that are differ ent from the rodent pattern. Therefore, the explanation of the motilit y pattern of rabbit intestine can be approached on a chemical neuroana tomical basis.