Prolongation of Relaxation Time in Extraocular Muscles With Brain Derived Neurotrophic Factor in Adult Rabbit.
OBJECTIVE
We tested the hypothesis that short-term treatment with brain derived neurotrophic factor (BDNF) would alter the contractile characteristics of rabbit extraocular muscle (EOM).


METHODS
One week after injections of BDNF in adult rabbit superior rectus muscles, twitch properties were determined in treated and control muscles in vitro. Muscles were also examined for changes in mean cross-sectional areas, neuromuscular junction size, and percent of myofibers expressing specific myosin heavy chain isoforms, and sarcoendoplasmic reticulum calcium ATPases (SERCA) 1 and 2.


RESULTS
Brain derived neurotrophic factor-treated muscles had prolonged relaxation times compared with control muscles. Time to 50% relaxation, time to 100% relaxation, and maximum rate of relaxation were increased by 24%, 27%, and 25%, respectively. No significant differences were seen in time to peak force, twitch force, or maximum rate of contraction. Brain derived neurotrophic factor treatment significantly increased mean cross-sectional areas of slow twitch and tonic myofibers, with increased areas ranging from 54% to 146%. Brain derived neurotrophic factor also resulted in an increased percentage of slow twitch myofibers in the orbital layers, ranging from 54% to 77%, and slow-tonic myofibers, ranging from 44% to 62%. No significant changes were seen SERCA1 or 2 expression or in neuromuscular junction size.


CONCLUSIONS
Short-term treatment with BDNF significantly prolonged the duration and rate of relaxation time and increased expression of both slow-twitch and slow-tonic myosin-expressing myofibers without changes in neuromuscular junctions or SERCA expression. The changes induced by BDNF treatment might have potential therapeutic value in dampening/reducing uncontrolled eye oscillations in nystagmus.
Department of Ophthalmology and Visual Neurosciences, University of Minnesota, Minneapolis, Minnesota, United States.
Krysta R
KR
Nelson
Department of Ophthalmology and Visual Neurosciences, University of Minnesota, Minneapolis, Minnesota, United States.
Shanlee M
SM
Stevens
Department of Ophthalmology and Visual Neurosciences, University of Minnesota, Minneapolis, Minnesota, United States.
Linda K
LK
McLoon
D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology*; D004195:Disease Models, Animal; D005133:Eye Movements / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects; D009759:Nystagmus, Pathologic / Q000188:drug therapy* / Q000503:physiopathology; D009801:Oculomotor Muscles / Q000187:drug effects / Q000502:physiology*; D011817:Rabbits
D019208:Brain-Derived Neurotrophic Factor