Morphology of cardiac nerves in experimental infarction of rat hearts. II. Electron microscopical findings.

Alterations of cardiac nerves in myocardial infarction were investigated by electron microscopy after differing intervals in 28 rats. During the first 4 h there are, in non-myelinated nerves within the myocardium, a swelling of the axoplasm with the occurrence of 'pale' axons and swelling of axonal mitochondria and neurosecretory granules. After bursting of the axolemma, these are spilled into the adjacent interstitial space. After 4 h first myelin figures are observed, and in some axons an accumulation of neurofilaments takes place. During the second to seventh day an extensive vesicular disintegration of axonal structures develops. Because of regressive changes, axons cannot be identified with certainty within the necrosis. After two or three weeks nerves with lamellar enfoldings of cytoplasmic processes corresponding to Büngner bands can be seen at the infarction border. These nerves may contain only a few residual axons. Myelinated nerves show a mainly vesicular disintegration. The results are discussed with regard to their functional significance and the special conditions of the animal model, in which ligature of the coronary artery may not only produce ischemia, but may also, by simultaneous ligature of the adjacent cardiac nerves, induce Wallerian degeneration.