Some morphological and histochemical features of the midgut myenteric plexus of the common european frog, Rana Esculenta

Abstract

The neuron morphology and distribution of four putative transmitters were investigated in the myenteric plexus of frog (Rana esculents) midgut. The gross morphology was revealed by NADH-diaphorase histochemistry, and the shape of the neurons by silver impregnation. Nerve cells had heterogeneous distribution: they either formed ganglia or placed as solitary neurons in the duodenum, while in the rest of the midgut only solitary neurons were observed. Three morphologically distinct cell types were rcvealed by silver impregnation: mainly type I and type I1 neurons cells were seen in the duodenum, while the rest of the intestine contained type I1 and I11 cells. Catecholamine fluorescence was revealed in nerve fibres in the duodenum, while few small nerve cells were observed in the small intestinal region. Acetylcholinesterase histochemistry showed strongly reactive nerve cells that were associated with the main fibre bundles in the duodenum. Only longitudinally oriented fibres and occasionally stained neurons were seen in the small intestine. Substance P immunocytochemistry revealed an extensive plexus, which contained a moderate number of stained perikarya in the full length of the midgut. Gammaaminobutyric acid showed non-uniform distribution in the two parts of the midgut: a stronger and more regular fibre staining was found in the duodenum then in the rest of the intestine. Ultrastructural observations demonstrated that intrinsic neurons received synaptic inputs from the profiles contained agranular vesicles. while ~PD- t y pper ofiles established close contacts with neurons. Both profile types formed close contacts with the smooth muscle cells. In spite of the several neuromorphological and ultrastructural similarities to the mammalian species, the transmitter distribution described here does not match in all respects to that found in the enteric nervous system of Offprint requests to: Dr. E. Fekete, Jate, Department of Zoology, Szeged, Egyetem U. 2., P.O. Box. 659, H-6722, Hungary those animals. This finding reflects the view, that the neurochemical coding system and the projection pattern within the plexus may vary considerably among different classes of vertebrates.