Long-term changes in myosin heavy chain composition after botulinum toxin a injection into rat medial rectus muscle.

PURPOSE: To study long-term changes of extraocular muscles after botulinum toxin (Botx) A-induced paralysis, with special emphasis on myosin heavy chain (MyHC) isoform pattern in muscle fibers. METHODS: Botx A (5 IU) was injected into the ocular medial rectus (MR) muscles of adult rats. After 1, 5, and 8 months muscle cross sections were examined immunohistochemically, histochemically, and morphometrically. MyHC content was analyzed by gel electrophoresis. RESULTS: Paralyzed MR muscles displayed mildly atrophic and hypertrophic muscle fibers and decreased oxidative metabolism, due to decreased succinate dehydrogenase activity. However, muscle morphology was not grossly disturbed. MyHC profile was shifted toward slower isoforms. Electrophoretic analysis showed that the share of MyHCI, and especially of MyHCIIa and MyHCIIx/d, increased several fold, whereas the share of MyHCIIb decreased heavily during the first 5 months. Immunohistochemical analysis generally mirrored the results obtained by electrophoresis. Moreover, specific extraocular MyHC isoform MyHCeom disappeared and could not be detected during the whole experimental period. The portion of MyHCIIb relatively increased 8 months after Botx A injection, although the MyHC profile was still far from normal. CONCLUSIONS: These long-lasting changes in Botx A-paralyzed ocular MR muscles most probably reflect their inability to regain their unique functional characteristics after new motor end plate formation and recovery of muscle contraction.

Fibre types and myosin heavy chain expression in the ocular medial rectus muscle of the adult rat.

Myosin heavy chain (MHC) expression was determined immunohistochemically in individual muscle fibre types characterised by activities of ATPase and the key oxidative and glycolytic enzymes in rat ocular medial rectus (MR) muscles. In the global layer (GL), glycolytic activity of muscle fibres was higher and oxidative activity lower, than in the orbital layer (OL). Muscle fibres in the former displayed rosette-like organisation with a slow fibre surrounded by several fast fibres, which expressed either MHCIIa or MHCIIb, but many co-expressed both isoforms. In the OL some slow fibres co-expressed MHCIIa. Extraocular MHC isoform (MHCeom) could not be determined immunohistochemically and no pure MHCIIx/d containing fibres were found, suggesting that these isoforms, demonstrated electrophoretically, are co-expressed with others. Slow muscle fibres in both layers co-expressed MHCbeta slow, MHCalpha cardiac and MHC-slow tonic. Neonatal isoform (MHCneo) was co-expressed in several fast and slow muscle fibres in the orbital, but not global layer. Slow fibres in the GL displayed very low oxidative activity. Electrophoretic analysis of ocular MR muscle homogenates revealed that about 50% of total MHC was MHCIIb, MHCeom was quite prominent (25%), and MHCIIa, MHCIIx/d and MHCI contributed each about 8%. MHCneo, MHCslow tonic and MHCalpha cardiac could not be identified as separate bands.

Bilateral macular dysplasia in fragile X syndrome.

PURPOSE: Few studies have investigated the eye and vision dysfunctions of children with the fragile X syndrome. CASE REPORT: We report on a preschool boy with bilateral macular dysplasia and fragile X syndrome. His ocular features and phenotypic and genetic expressions are described. His mentally normal mother was identified as an expansion mutation carrier, and his older sister has learning disabilities, astigmatic refractive error, squint, and mild ptosis. Intrauterine infection has been excluded. CONCLUSION: To our knowledge, the association of macular dysplasia with fragile X syndrome has not been reported. The finding of macular dysplasia might be a coincidental developmental disorder and not a part of the syndrome. It could be considered a condition causing visual deficit with nystagmus in fragile X syndrome.