Abstract
Neurotoxic signs suggested by abnormalities of the posterior extremities are sometimes observed in rats and mice given high doses of certain test substances in acute toxicity studies, but abnormal morphological changes are not always detected in the nervous system and skeletal muscles of these animals during routine histopathological examinations. In such cases, toxicities are attributable to the onset of motor endplate neuropathy. In this article, we focus on the ultrastructural changes in neuromuscular junctions induced by several neurotoxic substances, based on the results of a search in the literature and data obtained in our laboratory. The literature survey indicated that nerve endings of the peripheral motor nerves are initially damaged in the neurotoxicity of venoms of snakes such as β-bungarotoxin, notexin and taipoxin, as well as chemically synthesized substances such as DTB, sarin, Vacor and DTBHQ, and various kinds of morphological changes as a result of the destruction of motor endplates could be observed in neuromuscular junctions of the animals exposed to these toxic substances. When paralysis of posterior extremities occurs in rats treated with certain test substances, a part of the lumbrical muscles in the foot pad should be fixed and subjected to electron microscopic examinations to eliminate misjudgments concerning neurotoxicity.
