Motoneuron Replacement for Reinnervation of Skeletal Muscle in Adult Rats

Abstract

Reinnervation is needed to rescue muscle when motoneurons die in disease or injury. Embryonic ventral spinal cord cells transplanted into peripheral nerve reinnervate muscle and reduce atrophy but low motoneuron survival may limit motor unit formation. We tested whether transplantation of a purified population of embryonic motoneurons into peripheral nerve (mean ± SE: 146,458 ± 4011 motoneurons) resulted in more motor units and reinnervation than transplantation of a mixed population of ventral spinal cord cells (72,075 ± 12,329 motoneurons). Ten weeks after either kind of transplant, similar numbers of neurons expressed choline acetyl transferase and/or Islet-1. Motoneuron numbers always exceeded the reinnervated motor unit count. Most motor end plates were simple plaques. Reinnervation significantly reduced muscle fiber atrophy. These data show that the number of transplanted motoneurons or motoneuron survival do not limit muscle reinnervation. Incomplete differentiation of motoneurons in nerve and lack of muscle activity may result in immature neuromuscular junctions that limit reinnervation and function.

Transplantation of embryonic spinal cord neurons to the injured distal nerve promotes axonal regeneration after delayed nerve repair

“…The muscle atrophy was thereby alleviated. These observations were consistent with those of previous studies (Erb et al ., ; Yohn et al ., ; Casella et al ., ; Grumbles et al ., , ; Su et al ., ; Liu et al ., , ). When the grafted cells were removed and the residual distal stump was cross‐sutured to the proximal end of freshly cut ipsilateral common peroneal (CP) nerve, the axonal regeneration from the proximal stump of the injured CP nerve was promoted, and the muscle function was partially recovered.…”

Morphological Regeneration and Functional Recovery of Neuromuscular Junctions after Tourniquet-Induced Injuries in Mouse Hindlimb

“…Injured peripheral nerves and skeletal muscles have a remarkable ability for tissue regeneration (Scheib and Hoke, 2013; Domingues-Faria et al, 2016), and regeneration of functional NMJs occurs after NMJ injury (McMahan et al, 1980; Darabid et al, 2014). Although, regenerated NMJs are mainly formed at original synaptic sites of the skeletal muscle (McMahan et al, 1980), growing evidence demonstrates that NMJs are also formed on regenerated axons and muscle fibers (Slater, 1982; Slater and Allen, 1985; Ijkema-Paassen et al, 2002; Nishizawa et al, 2003; Li and Thompson, 2011; Grumbles et al, 2012; Kang and Lichtman, 2013). The alteration of regenerated NMJs formed at both original synaptic sites and new synaptic areas, however, is associated with permanent neurological deficiency, and long-term skeletal muscle contractile dysfunction, even to the degree of complete limb paralysis (Creager et al, 2012).…”

Electrical Stimulation of Embryonic Neurons for 1 Hour Improves Axon Regeneration and the Number of Reinnervated Muscles That Function

“…2), a potential mismatch between the neurotransmitters released by regenerating axons (e.g. glutamate and the muscle target [acetylcholine] [94]), although motoneurons retrogradely labeled from reinnervated muscles were ChAT-positive [36]), collapsed intramuscular sheaths following long-term denervation (95), the presence of immature neuromuscular junctions, which are common in our model (50), and/or neuromuscular junctions that were non-functional.…”

“…At week 0, 200,000 ventral spinal cord cells (73% ± 2% of cells were positive for Islet-1, a marker for embryonic motoneurons [50]) were suspended in 5 μl of medium and injected into the tibial nerve 10 to 15 mm from where it enters the gastrocnemii muscles using a Hamilton syringe. Immediately following transplantation, a pair of silver electrodes was placed under the tibial nerve where cells (or medium) had been transplanted.…”

“…( A-C ) Hematoxylin and eosin stained cross-sections (10 μm) of a denervated (medium injected without cells, A ), reinnervated (20 Hz 1 hour, B ), and uninjured medial gastrocnemius (MG) muscle ( C ). ( D ) Mean (±SE) area of reinnervated MG muscle fibers (> 498 μm 2 cross-sectional area (50), and percentage of reinnervated MG muscle fibers ( E ) across groups compared to denervated fibers (No cells; *, p < 0.05, one-way ANOVA). Numbers at the bottom of each bar indicate the number of animals per group.…”