Asymmetric Distribution of Membrane-Glycogen Complexes in Multiply Innervated Fibers of Rabbit Extraocular Muscle

Abstract

Membrane-glycogen complexes were recently described in multiply innervated fibers (MIF) of extraocular muscle (EOM) of mature rabbits (1,2). They have not been reported in EOM of other species. The present study finds that such complexes are not evenly distributed along the length of MIF but are largely confined to the ends of these fibers and well removed from the muscle's thickened belly portion where sampling might most likely be concentrated. The m. superior rectus of prepubertal (2 Kg. ) New Zealand white rabbit was embedded whole and serially sectioned at 5 microns (3). Fibers along the orbital surface of the muscle were followed by light microscopy whereby the endings of MIF could be detected. The locus of MIF populations within the muscle was determined, and approximately 30 samples per fiber were taken for EM examination. Two major populations of MIF were observed among the orbital surface fibers.