Enlargement of motoneuron peripheral field following partial denervation with or without dorsal rhizotomy

• Published in: Neuroscience Vol. 84; no. 1; pp. 151 - 161
• Main Authors: Cuppini, R, Ambrogini, P, Sartini, S
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.05.1998; Elsevier
• Subjects: Animals; Biological and medical sciences; Cell Size - physiology; Denervation; dorsal rhizotomy; Evoked Potentials, Motor - physiology; extensor digitorum longus muscle; Fundamental and applied biological sciences. Psychology; Male; Motor Endplate - physiology; Motor Neurons - cytology; Motor Neurons - physiology; motor unit enlargement; Neuromuscular Junction - physiology; partial muscle denervation; rat; Rats; Rats, Sprague-Dawley; Rhizotomy; Striated muscle. Tendons; Synapses - physiology; Vertebrates: osteoarticular system, musculoskeletal system; motor unit enlargement; MEPP, miniature end-plate potential; rat; extensor digitorum longus muscle; L4, fourth lumbar segment; EPP, end-plate potential; L3, third lumbar segment; partial muscle denervation; dorsal rhizotomy; EDL, extensor digitorum longus; L5, fifth lumbar segment; NMDA, N-methyl- d-aspartate; Vertebrata; Mammalia; Enlargment; Rat; Rodentia; Electrophysiology; Motor neuron; Rhizotomy; Extensor digitorum muscle; Motor unit; Denervation
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(97)00506-X

In partially denervated skeletal muscle, spared motor fibres sprout, enlarging motor unit size. Neuritogenesis and sprouting are known to depend on the synaptic input to the neurons. This suggests that spared motoneuron reaction to partial muscle denervation might be controlled by primary sensory neurons which directly or indirectly project to motoneurons. In two groups of rats, different surgical procedures were carried out: partial denervation of the extensor digitorum longus muscle without or with homolateral dorsal rhizotomy. Spared motoneuron peripheral field was evaluated by nerve-evoked tension measures. Following partial muscle denervation, spared motoneurons enlarged their projection peripheral field five to six times, innervating most of the denervated portion of the muscle. When dorsal rhizotomy was carried out together with partial denervation, the enlargement of the motoneuron's peripheral field occurred later; however, the peripheral field size was the same or greater than that found in partially denervated muscles without dorsal rhizotomy in the long term. Excitatory postsynaptic potential recordings at neuromuscular junctions consistently showed that innervation of denervated muscle cells by spared motoneurons was impaired when the dorsal roots were cut. Finally, in both groups of operated rats an increase in motor unit number occurred early after surgery, anticipating a process normally occurring in the same age range. These findings are consistent with the idea that sensory input trans-synaptically controls motoneuron peripheral field size.