Jeffrey P Garrett

Wake Forest University, Winston-Salem, North Carolina, United States

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Publications (5)17.51 Total impact

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    ABSTRACT: Botulinum neurotoxin-A (BoNTA) is a potent neurotoxin used to alter muscle tone to manage spasticity and to provide tendon bioprotection; however, the appropriate dose and injection volume to administer is not defined. Male mice (n = 120) received BoNTA injections into one gastrocnemius with either a constant volume (10 µl) with a variable dose (1, 3, 6 U/kg) or a constant dose (3 U/kg) in a variable volume (2.5, 5, 10, 20, 30 µl). Electromyographic (EMG) examination, muscle force generation (MFG), and wet muscle mass were measured in the ipsilateral and contralateral limbs at 1, 2, 4, or 12 weeks post-injection. MFG and EMG responses decreased to approximately 40% of contralateral after a 1 U/kg injection and 0% of contralateral by 3 and 6 U/kg injection at 1 week after injection. Neuromuscular blockade was greatest with a 10 µl injection volume. MFG, EMG examination, and wet muscle mass reached contralateral values 12 weeks after injection for all injection doses and volumes tested. Effective injection doses and volumes were identified for producing full and partial neuromuscular blockade in the mouse gastrocnemius. These findings have important clinical implications in the intramuscular administration of BoNTA to manage muscle tone.
    Preview · Article · Nov 2011 · Journal of Orthopaedic Research
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    ABSTRACT: The management of peripheral nerve injuries with segmental defects is a challenge to both patient and surgeon. Repairs under tension have a poor prognosis; sensory nerve allografts have donor site morbidity and suboptimal motor recovery, but remain the gold standard. The development of conduit-based repair strategies has evolved and these are promising for sensory nerves and short defects; however, no conduit filler is clinically available that improves motor recovery equivalent to sensory autografts. In this study, motor recovery using keratin-based hydrogel filler was compared with that for sensory nerve autografts and empty conduits. Fifty-four mice were randomized into 3 treatment groups: empty conduit, sural nerve autograft, and keratin hydrogel-filled conduit. Animals were followed for 6 weeks, 3 months, and 6 months. Outcomes included compound motor action potential (CMAP), nerve area, myelinated axon number and density, and myelinated axon diameter. Neuromuscular recovery with keratin was greater than with empty conduits in most outcome measures. Nerves that regenerated through the keratin hydrogel had lower conduction delays, greater amplitudes, more myelinated axons, and larger axons than nerves that regenerated through empty conduits. Sensory nerve autografts and keratin hydrogel were statistically equivalent in CMAP measurements at 6 months. Moreover, keratin-filled conduits demonstrated greater axon density and larger average axon diameter than both empty conduits and autograft at 6 months. In a mouse tibial nerve model, keratin hydrogels significantly improved electrophysiological recovery, compared with empty conduits and sensory nerve autografts, at an early time point of regeneration. Keratin hydrogels also produce long-term electrical and histological results superior to empty conduits and equivalent to sensory nerve autografts.
    No preview · Article · Dec 2008 · The Journal of hand surgery
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    ABSTRACT: The management of trauma-associated nerve defects is difficult because of the absence of autologous donor motor or sensory nerves. Pre-clinical development and clinical experience has shown that damaged nerves can be surgically repaired using a tubular conduit interposed across the defect. Acceptable patient outcomes are achieved so long as the gap distance does not exceed a few centimeters. Although research in animals has demonstrated that nerve repair can be facilitated across slightly larger gaps by introducing a biomaterial filler into the conduit lumen, these biomaterials are not typically "neuroinductive" (i.e. capable of acting directly on regenerative cells to enhance nerve tissue formation beyond clinical limits). Moreover, their use does not often result in functional recovery equivalent to nerve autograft, the clinical gold standard. Here we show that a biomaterial gel made from the proteins found in human hair can mediate a robust nerve regeneration response, in part through activation of Schwann cells. In vitro, keratins extracted from human hair enhance the activity of Schwann cells by a chemotactic mechanism, increase their attachment and proliferation, and up-regulate expression of important genes. Moreover, these characteristics translate to improved functional nerve recovery in an animal model. These results suggest that a biomaterial derived from human hair keratins is neuroinductive and can facilitate an outcome comparable to autograft in a nerve injury model.
    No preview · Article · Feb 2008 · Biomaterials
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    ABSTRACT: Neuromuscular junction destabilization following nerve injury contributes to irreversible functional impairment. Myogenic Regulatory Factors (MRF's) including myoblast determination factor (MyoD), MRF-4, Myogenin, and myogenic factors-5 (myf-5), and Growth-associated protein 43 KDa (GAP43) regulate gene expression of nicotinic acetylcholine receptor (nAChR) subunits (alpha, beta, delta, gamma, and epsilon). We hypothesized that nerve injury induces altered gene expression of MRF's, nAChRs, and GAP-43 in the skeletal muscle which destabilize neuromuscular junctions. The tibial nerve was transected in 42 juvenile male Sprague-Dawley rats. Denervated and contralateral control gastrocnemius m. mRNA for nAChR subunits, MRF's, and GAP-43 were determined by real time reverse transcription polymerase chain reaction (real time RT-PCR). After transection, muscle mass decreased for 1 year with a nadir of 75% at 3 months. Alpha, gamma, and epsilon subunit genes increased by 3 and peaked at 7 days before returning to control levels (P < 0.05). Beta subunits and GAP-43 tended to increase. Delta subunits peaked at 3 days returning to control levels by 30 days. By one month, most of the nAChR subunits had returned to control levels. Alpha, beta, gamma, and delta subunit expression remained significantly lower than control up to 1 year later (P < 0.05). MRF4, Myogenin, and MyoD expression paralleled that of alpha, gamma, and epsilon nAChR subunits (P < 0.05). Gene expression of nAChR alpha, gamma, delta and epsilon subunits was biphasic in the first month after nerve injury, similar to that of MRF's. nAChR subunits and MRF's may play a critical role in neuromuscular junction stability.
    No preview · Article · Nov 2007 · Journal of Orthopaedic Research

  • No preview · Article · Aug 2006 · Journal of Reconstructive Microsurgery

Publication Stats

188 Citations
17.51 Total Impact Points


  • 2011
    • Wake Forest University
      • Department of Orthopaedic Surgery
      Winston-Salem, North Carolina, United States
  • 2008
    • Wake Forest School of Medicine
      • Department of Orthopaedic Surgery and Rehabilitation
      Winston-Salem, North Carolina, United States