Transformation of synaptic vesicle phenotype in the intramedullary axonal arbors of cat spinal motoneurons following peripheral nerve injury

• Published in: Experimental brain research 2001-08, Vol.139 (3), p.297-302
• Main Authors: HAVTON, Leif A, KELLERTH, Jan-Olof
• Format: Article
• Language: English
• Subjects: Animals; Axons; Axons - physiology; Axons - ultrastructure; Axotomy; Biological and medical sciences; Cats; Cranial nerves. Spinal roots. Peripheral nerves. Autonomic nervous system. Gustation. Olfaction; Dense core vesicles; Genetic transformation; Horseradish peroxidase; Medical sciences; Medulla Oblongata - ultrastructure; Motor neurons; Motor Neurons - physiology; Motor Neurons - ultrastructure; Muscle, Skeletal - innervation; Nervous system (semeiology, syndromes); Neurology; Peripheral nerves; Peripheral Nerves - physiology; Phenotype; Phenotypes; Presynapse; Spinal cord; Spinal cord injuries; Synaptic Vesicles - physiology; Synaptic Vesicles - ultrastructure; Ultrastructure
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s002210100766

Permanent transection of a peripheral motor nerve induces a gradual elimination of whole axon collateral systems in the axotomized spinal motoneurons. There is also an initial concurrent decrease in the amount of recurrent inhibition exerted by these arbors in the spinal cord for up to 6 weeks after the injury, whereas the same reflex action returns to normal by the 12-week postoperative state. The aim of the present investigation was to study the fine structure of the intramedullary axonal arbors of axotomized alpha-motoneurons in the adult cat spinal cord following a permanent peripheral motor nerve lesion. For this purpose, single axotomized alpha-motoneurons were labeled intracellularly with horseradish peroxidase at 12 weeks after permanent transection of their peripheral motor nerve. The intramedullary portions of their motor axon and axon collateral arbors were first reconstructed at the light microscopic level and subsequently studied ultrastructurally. This study shows that the synaptic contacts made by the intramedullary axon collateral arbors of axotomized motoneurons have undergone a change in synaptic vesicle ultrastructure from spherical and clear vesicles to spherical and dense-cored vesicles at 12 weeks after the transection of their peripheral axons. We suggest that the present transformation in synaptic vesicle fine structure may also correspond to a change in the contents of these boutons. This may, in turn, be responsible for the strengthening and recovery of the recurrent inhibitory reflex action exerted by the axotomized spinal motoneurons following a prolonged permanent motor nerve injury.