Biomaterial Database

Incomplete rematching of nerve and muscle properties in motor units after extensive nerve injuries in cat hindlimb muscle. 1998

V F Rafuse, and T Gordon

Department of Pharmacology, Division of Neuroscience, 513 Heritage Medical Research Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2S2.

1. Motor units were characterized in partially denervated or completely denervated and reinnervated cat medial gastrocnemius (MG) muscles where the number of innervating motor axons was severely reduced to determine (1) to what extent the nerve and muscle properties are rematched in enlarged motor units, (2) whether the normal size relationships between axon size, unit tetanic force and contractile speed are re-established, and (3) whether the type of nerve injury and/or repair affects the re-establishment of nerve and muscle properties. 2. Single MG units were sampled in (1) partially denervated muscles and in reinnervated muscles after either (2) crushing or (3) transecting the nerve and suturing its proximal end to either the distal nerve stump (N-N), or (4) directly to the muscle fascia (N-M). 3. The majority (75-88 %) of motor units in all muscles were classified as S (slow), FR (fast fatigue resistant), FI (fast fatigue intermediate) and FF (fast fatigable). However, there was an increased number of FI and unclassifiable motor units compared to normal. These results suggest that motor unit properties are not entirely regulated by the reinnervating motoneurone. 4. Despite more overlap in the range of unit force between different motor unit types the tetanic force of each type increased in all muscles when reinnervated by few (< 50 %) motor axons. This increase in unit force was due to an expansion in motor unit innervation ratio. 5. The normal relationships between axon size, unit tetanic force, and contractile speed were re-established in all muscles except when reinnervated by < 50 % of their normal complement of motor units after N-M suture. This lack of correlation was due to the reduced fast glycolytic (FG) fibre size and the proportionately greater increase in force of the S units. 6. After reinnervation the ranges in fibre cross-sectional area within single FF units were very similar to those found within the entire FG fibre population. 7. These results show that when few axons make functional connections in partially denervated or reinnervated muscles the normal relationships between axon size and motor unit contractile properties are re-established provided the nerves regenerate within the distal nerve sheath. This rematching of motoneurone size and motor unit contractile properties occurs primarily because the size of the motor axon governs the number of muscle fibres it supplies.

UI	MeSH Term	Description	Entries
D008297	Male		Males
D009046	Motor Neurons	Neurons which activate MUSCLE CELLS.	Neurons, Motor,Alpha Motorneurons,Motoneurons,Motor Neurons, Alpha,Neurons, Alpha Motor,Alpha Motor Neuron,Alpha Motor Neurons,Alpha Motorneuron,Motoneuron,Motor Neuron,Motor Neuron, Alpha,Motorneuron, Alpha,Motorneurons, Alpha,Neuron, Alpha Motor,Neuron, Motor
D009119	Muscle Contraction	A process leading to shortening and/or development of tension in muscle tissue. Muscle contraction occurs by a sliding filament mechanism whereby actin filaments slide inward among the myosin filaments.	Inotropism,Muscular Contraction,Contraction, Muscle,Contraction, Muscular,Contractions, Muscle,Contractions, Muscular,Inotropisms,Muscle Contractions,Muscular Contractions
D009121	Muscle Denervation	The resection or removal of the innervation of a muscle or muscle tissue.	Denervation, Muscle,Denervations, Muscle,Muscle Denervations
D009409	Nerve Crush	Treatment of muscles and nerves under pressure as a result of crush injuries.	Crush, Nerve
D009416	Nerve Regeneration	Renewal or physiological repair of damaged nerve tissue.	Nerve Tissue Regeneration,Nervous Tissue Regeneration,Neural Tissue Regeneration,Nerve Tissue Regenerations,Nervous Tissue Regenerations,Neural Tissue Regenerations,Regeneration, Nerve,Regeneration, Nerve Tissue,Regeneration, Nervous Tissue,Regeneration, Neural Tissue,Tissue Regeneration, Nerve,Tissue Regeneration, Nervous,Tissue Regeneration, Neural
D010525	Peripheral Nerves	The nerves outside of the brain and spinal cord, including the autonomic, cranial, and spinal nerves. Peripheral nerves contain non-neuronal cells and connective tissue as well as axons. The connective tissue layers include, from the outside to the inside, the epineurium, the perineurium, and the endoneurium.	Endoneurium,Epineurium,Perineurium,Endoneuriums,Epineuriums,Nerve, Peripheral,Nerves, Peripheral,Perineuriums,Peripheral Nerve
D002415	Cats	The domestic cat, Felis catus, of the carnivore family FELIDAE, comprising over 30 different breeds. The domestic cat is descended primarily from the wild cat of Africa and extreme southwestern Asia. Though probably present in towns in Palestine as long ago as 7000 years, actual domestication occurred in Egypt about 4000 years ago. (From Walker's Mammals of the World, 6th ed, p801)	Felis catus,Felis domesticus,Domestic Cats,Felis domestica,Felis sylvestris catus,Cat,Cat, Domestic,Cats, Domestic,Domestic Cat
D005260	Female		Females
D006614	Hindlimb	Either of two extremities of four-footed non-primate land animals. It usually consists of a FEMUR; TIBIA; and FIBULA; tarsals; METATARSALS; and TOES. (From Storer et al., General Zoology, 6th ed, p73)	Hindlimbs