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On the ultrastructure of the rat anococcygeus muscle

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The rat anococcygeus muscle, which is known from previous functional and histochemical investigations to be a smooth muscle with a dense adrenergic innervation, was studied by electron microscopic methods. The muscle was found to be organized in small bundles of 2 to 8 muscle cells, which were interconnected by desmosome-like junctions and by gap junctions. Small Schwann cell-axon complexes with 1 to 5 axons appeared to represent the functional terminal nerve pathway. Such axon complexes were located at the periphery of the small smooth muscle bundles, they never penetrated into them. A ratio of approximately 6 small axon complexes per 100 muscle cells was found. After glutaraldehyde fixation axon varicosities contained mainly small empty vesicles. After treatment with 5-hydroxydopamine and permanganate fixation mainly small vesicles with a dense core were found. The neuromuscular distances ranged from 550 to 5000 Å, with a mean of about 2600 Å. True close neuromuscular contacts at a distance below 500 Å with a fusing of basal laminae were absent.

The present observations provide a morphological base for the findings of previous electrophysiological and pharmacological studies on the anococcygeal muscle.

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Gillespie, J.S., Lüllmann-Rauch, R. On the ultrastructure of the rat anococcygeus muscle. Cell Tissue Res. 149, 91–104 (1974). https://doi.org/10.1007/BF00209052

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Key words

  • Anococcygeal muscle
  • Smooth muscle
  • Rat
  • Innervation, adrenergic