title: Effects of the sustained release of IGF-1 on extraocular muscle of the infant non-human primate: adaptations at the effector organ level.
abstract: OBJECTIVE
  The authors have demonstrated that prolonged exposure of adult rabbit extraocular muscle (EOM) to insulin-like growth factor-1 (IGF-1) results in significantly increased cross-sectional area and muscle force generation lasting over 3 months. Here the authors assess the effects on EOM of sustained IGF-1 treatment on normal binocular infant Macaca mulatta.
  
  
  METHODS
  Sustained-release IGF-1 pellets were implanted bilaterally in each medial rectus (MR) muscle of two normal infant non-human primates. Eye position was examined using corneal light reflex testing. After 3 months, morphometric analyses of myofiber cross-sectional area and innervation density in treated MR muscles were compared with an age-matched control and with antagonist lateral rectus (LR) muscles.
  
  
  RESULTS
  After 3 months, the slow-release pellets remained at the implantation site in all four MR muscles treated. The treated MR showed pronounced increases in cross-sectional area and nerve density, mirrored in the untreated antagonist LR.
  
  
  CONCLUSIONS
  Three months of bilateral sustained IGF-1 release in infant non-human primate MR resulted in increased muscle size and innervation density, mirrored in the untreated antagonist LR. It appears that bilateral MR treatment resulted in slow adaptation of both treated MR and contralateral LR muscles over time such that functional homeostasis and near-normal alignment were maintained. Further work is needed to determine what signaling mechanisms maintain proportional innervation when EOMs are forced to adapt to an externally applied perturbation.
authors: Department of Ophthalmology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors: Christy L
authors: CL
authors: Willoughby
authors: Stephen P
authors: SP
authors: Christiansen
authors: Michael J
authors: MJ
authors: Mustari
authors: Linda K
authors: LK
authors: McLoon
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000473:pathology; D003692:Delayed-Action Preparations / Q000008:administration & dosage; D004343:Drug Implants; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage*; D008253:Macaca mulatta; D008279:Magnetic Resonance Imaging; D009413:Nerve Fibers, Myelinated / Q000473:pathology; D009801:Oculomotor Muscles / Q000187:drug effects* / Q000294:innervation / Q000473:pathology; D009802:Oculomotor Nerve / Q000473:pathology*
chemical_list: D003692:Delayed-Action Preparations; D004343:Drug Implants; D007334:Insulin-Like Growth Factor I