On the effect of motor nerve degeneration on the fine-structural localization of esterases in the mammalian motor end-plate

Electron-microscopic localizations of acetylcholinesterase and non-specific esterases have been studied in the motor end-plates of the rat diaphragm, using a modified Koelle acetylthiocholine technique for acetylcholinesterase, the Holt technique for non-specific esterases (substrates: indoxyl acetate and indoxyl butyrate) and the Crevier-Bélanger technique for thiolacetic acid esterases. Acetylcholinesterase is located in the pre- and post-synaptic membranes and in the junctional folds built up by the latter. Indoxyl acetate esterase shows a homogeneous localization in primary and secondary synaptic clefts. Indoxyl butyrate esterase is located in the ‘middle dense layer’ of the synaptolemma. Thiolacetic acid esterase is predominantly post-synaptic, accompanied by a slighter pre-synaptic activity. Eleven days after motor nerve transection, the synaptic gutter is occupied by a large number of collagenous fibres, and only small granular fragments of the degenerated nerve fibres remain. These fragments are devoid of acetyl- and non-specific esterases, but exert a thiolacetic acid esterase activity, probably demonstrating proteolytic enzymes. The post-synaptic membrane exhibits a slightly reduced enzyme activity without any major alteration in the fine-structural localization of acetyl- and non-specific esterases.