Annulate lamellae in regenerating skeletal muscle fibers of rats treated with cholinesterase inhibitor.

The stacks of annulate lamellae were observed within the soleplate sarcoplasm of the striated muscles of rats after brief and chronic treatment with neostigmine methylsulfate, but these were only rarely encountered in the control specimen. The individual lamellae comprising the stack were continuous with vesicular profiles but infrequent in the direct continuity with the nuclear envelope. Since these appeared during the periods of the myopathic course which can be reversible, these organelles seem to reflect a secondary reaction in myocytes, subsequent to intensive cytoplasmic needs to regenerate.