Effects of mandibular distraction osteogenesis on the inferior alveolar nerve: an experimental study in monkeys.

A series of experimental studies were performed in monkeys to study the effect of mandibular distraction osteogenesis on the inferior alveolar nerve at different times before and after distraction. A mandible osteotomy was performed and distraction was carried out unilaterally in 10 young rhesus monkeys and bilaterally in six. The intact nerves on the contralateral side of the 10 monkeys were used for the control. Care was taken to avoid destroying the integrity of the inferior alveolar nerve during the surgical procedure. After a 5-day latency period, the distraction device was activated at a rate of 0.5 mm twice each day for 15 days. Sensory nerve action potential testing was applied before and 1 day after the operation, at completion of distraction, and at 2, 4, 6, 9, and 12 weeks of fixation. Necropsy was performed at the completion of distraction and 2, 4, 6, and 12 weeks of fixation. The mental nerves were taken, sectioned, and stained with lead citrate and uranyl acetate, and examined with a transmission electron microscope. The inferior alveolar nerves in the distraction gap were obtained, and paraffin slides were made and stained with hematoxylin and eosin, Luxol fast blue, and Bodian methods. The authors found that immediately after the mandible osteotomy, most nerves showed signs of slight acute injury; the latency was increased by 5.553 percent, and the amplitude was decreased to 1808 microV. This might be caused by the surgical procedure or by compressions produced by swelling tissues around the nerves. When distraction was completed, the latency was prolonged for an average of 22.18 percent, and the amplitude average had attenuated to 28.54 percent (804 microV) of the preoperative value on the distracted side. Most nerve fibers exhibited signs of degeneration, such as myelin disruption, swelling of cell organs greatly increased in axoplasm, axon tearing, and myelin fragments engulfed by macrophages. These were nerve reactions to the tensions produced by mandible lengthening. As time elapsed, the nerve's action potential recovered gradually because of its repairing ability, the latency shortened, amplitude increased, Schwann cells proliferated and formed new myelin sheaths, and the tearing axons reconnected. After 12 weeks of consolidation, there was still a latency of 12.384 percent prolongation because of the prolonged conduction distance, and the average amplitude was restored to 2786 microV, the approximate preoperative value. The nerve seemed to be repaired completely; its myelin thickness, axon diameter, and ultrastructure were all similar to those of the control. It was concluded that mandibular distraction osteogenesis can produce some degree of harmful effects on the function and structure of inferior alveolar nerves, but it is reversible and relatively slight. Along with the regeneration of the nerve's myelin and axon, the nerve function can gradually rehabilitate to a normal level.

Restoration of normal conduction properties in demyelinated spinal cord axons in the adult rat by transplantation of exogenous Schwann cells.

Although remyelination of demyelinated CNS axons is known to occur after transplantation of exogenous glial cells, previous studies have not determined whether cell transplantation can restore the conduction properties of demyelinated axons in the adult CNS. To examine this issue, the dorsal columns of the adult rat spinal cord were demyelinated by x-irradiation and intraspinal injections of ethidium bromide. Cell suspensions of cultured astrocytes and Schwann cells derived from neonatal rats transfected with the (beta-galactosidase) reporter gene were injected into the glial-free lesion site. After 3-4 weeks nearly all of the demyelinated axons were remyelinated by the transplanted Schwann cells. The dorsal columns were removed and maintained in an in vitro recording chamber; conduction properties were studied using field potential and intra-axonal recording techniques. The demyelinated axons exhibited conduction slowing and block, and a reduction in their ability to follow high-frequency stimulation. Axons remyelinated by transplantation of cultured Schwann cells exhibited restoration of conduction through the lesion, with reestablishment of normal conduction velocity. The axons remyelinated after transplantation showed enhanced impulse recovery to paired-pulse stimulation and greater frequency-following capability as compared with both demyelinated and control axons. These results demonstrate the functional repair of demyelinated axons in the adult CNS by transplantation of cultured myelin-forming cells from the peripheral nervous system in combination with astrocytes.

Deficiencia cronica de hexosaminidasa A asociada a neuropatia periferica sensitiva pura / Chronic hexosaminidase A deficiency associated to pure sensory peripheral neuropathy

Se presenta a un paciente con deficiencia de hexosaminidasa A (Hx A), que conduce a la gangliosidosis GM2, que desarrolla un cuadro neurológico progresivo cuyo comienzo pudo fijarse a los 10 años y que se caracterizó por deterioro intelectual, compromiso cerebeloso, alteración de neuromas motoras superior e inferior y neuropatía sensitiva sin aparente compromiso de las fibras motoras que integran el nervio mixto. La biopsia del nervio safeno externo mostró pérdida de fibras mielínicas, en especial de aquellas de mayor y menor diámetro, agrupamiento axonal, axones con cubiertas mielínicas anormalmente finas en relación con su diámetro, degeneración axonal, desmielinización segmentaria y paranodal y remielinización. La microscopia electrónica reveló cuerpos de inclusión electrodensos no específicos e incusiones laminares concéntricas dentro del citoplasma de las células de Schwann. Los hallazgos hechos señalan que la neuropatía sensitiva pura puede formar parte del espectroclínico de la deficiencia de HxA (AU)