Synaptic blockade plays a major role in the neural disturbance of experimental spinal cord compression

We analyzed dynamic processes of neural excitation propagation in the experimentally compressed spinal cord using a high-speed optical recording system. Transverse slices of the juvenile rat cervical spinal cord were stained with a voltage-sensitive dye (di-4-ANEPPS). Two components were identified in the depolarizing optical responses to dorsal root electrical stimulation: a fast component of short duration corresponding to pre-synaptic excitation and a slow component of long duration corresponding to post-synaptic excitation. In the directly compressed dorsal horn, the slow component was attenuated more (attenuated to 37.4 +/- 9.1 % of the control) than the fast component (to 70.5 +/- 14.9%) (p < 0.01) at 400 msec after stimulation. Depolarizing optical responses to compression and to chemical synaptic blockade were similar. There was a regional difference between white matter (attenuated to 86.2 +/- 10.5%) and gray matter (to 72.6 +/- 10.4%) (p < 0.03) in compression-induced changes of the fast components; neural activity in the white matter was resistant to compression, especially in the dorsal root entry zone. Depolarizing optical signals in the region adjacent to the directly compressed site were also attenuated; the fast component was attenuated to 77.6 +/- 10.4% and the slow component to 31.8 +/- 11.3% of the control signals (p < 0.01). Spinal cord dysfunction induced by purely mechanical compression without tissue destruction was virtually restored with early decompression. We suggest that a disturbance of synaptic transmission plays an important role in the pathophysiological mechanisms of spinal cord compression, at least under in vitro experimental conditions of juvenile rats.