Effect of noxious bucal trigeminal high frequency electrical stimulation on lumbar spinal cord evaluated by evoked potentials in the rat

Abstract

Aims: trigeminal contribution to the pain modulation system and its effects over distant spinal areas are unknown. Materials and methods: 5 male Sprague-Dawley adult rats were used, anesthetized with thiobarbital 60mg/Kg-1; i.p. and laminectomized (T11-L5) for recording the lumbar evoked potentials (LEP) by electrical trigeminal stimulation of the oral mucosa (25V; 0.05ms; 0.2Hz). From an average of 1200 LEPs typical N and P wave sequence was detected with stable amplitudes during basal conditions. Results: high frecuency stimulation (5Hz; 5 min) induces a significant amplitude reduction more intense for P wave (-70.7%) than for N wave (56.4%; P=0.00001), which was reverted by the return to basal stimulation frequency (0.2Hz) showing an increased N and P wave amplitude correlation (76%) when compared to basal value (25%; P-0.00001). Conclusion: these results suggest that the electrical trigeminal tetanic stimulation induces a reversible tetanic inhibition in the lumbar spinal dorsal horn interneurons with sign of a postetanic potentiation effect.