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Optical imaging of spreading depolarization waves triggered by spinal nerve stimulation in the chick embryo: possible mechanisms for large-scale coactivation of the central nervous system.

Using a multiple-site optical recording technique with a voltage-sensitive dye, we found that widely spreading depolarization waves were evoked by dorsal root stimulation in embryonic chick spinal cords. Spatiotemporal maps of the depolarization waves showed that the signals were mainly distributed in the ventral half of the slice, with the highest activity in the ventrolateral area. The propagation velocity of the waves was estimated to be in the order of mm/s. Depolarization waves were evoked in the ventral root-cut preparation, but not in the dorsal root-cut preparation, suggesting that the wave was triggered by synaptic inputs from the primary afferents, and that activation of the motoneurons was not essential for wave generation. In intact spinal cord-brain preparations, the depolarization wave propagated rostrally and caudally for a distance of several spinal segments in normal Ringer's solution. In a Mg(2+)-free solution, the amplitude and extent of the signals were markedly enhanced, and the depolarization wave triggered in the cervical spinal cord propagated to the brainstem and the cerebellum. The depolarization wave demonstrated here had many similarities with the vagus nerve-evoked depolarization wave reported previously. The results suggest that functional cell-to-cell communication systems mediated by the depolarization wave are widely generated in the embryonic central nervous system, and could play a role in large-scale coactivation of the neurons in the spinal cord and brain.

Animals↗

Early effects of nucleus pulposus application on spinal nerve root morphology and function.

It is known that 24 h or more after epidural application of autologous nucleus pulposus, functional and structural changes are established in adjacent nerve roots. It is, however, not known how soon after the application these changes appear. The aim of this study was to reduce the exposure duration to 3 h and to evaluate nerve function and histological changes in the nerve tissue during this time period. A total of 12 pigs was used. In ten pigs, autologous nucleus pulposus (NP) was applied epidurally on the cauda equina. Nerve function was then monitored for 3 h by measurements of muscle action potentials (MAP) in the tail muscles, following nerve root stimulation cranial to the exposed zone. In five of the ten pigs with NP application, nerve root compression to 50 mm Hg was added by means of an inflatable balloon. In two control animals, neither NP nor compression was applied. At the end point, nerve root specimens were harvested for histological assessment. No reduction of MAP amplitude was detected in any of the series. However, there was an epidural accumulation of leucocytes and mast cells, as well as minor axonal and Schwann cell changes in both the NP and NP+ compression series, as compared to the control series. Morphological changes in terms of an epidural inflammatory reaction and minor axonal and Schwann cell damage may thus be demonstrated within 3 h of NP application, with or without compression. However, there is no functional deterioration of the nerve roots detectable within this time period.

Animals↗