Effect of GaALAs semiconductor laser irradiation on activities of the neurons in the trigeminal subuncleus caudalis was electrophysiologically investigated in rats. Extrace llular potentials of the caudal neurons were induced by electric stimulation of the ipsilateral lower incisor pulp and laser irradiation was carried out on the cervical surface of the incisor. Changes in firing discharges and numbers of evoked spikes of the caudal neurons were compared before and after irradiation of the laser.
1. Laser irradiation suppressed significantly the late discharges evoked by excitatory inputs from C-fiber afferents, but did not the early discharges evoked by inputs from A δ-afferent fibers.
2. Laser irradiation could not suppress wind-up phenomenon of the caudal neurons which was induced by repetitive stimulation of the tooth pulp. However, previous irradiation of the laser before tooth pulp stimulation was effective not to induce wind-up of neurons.
3. Non-laser light of a tungsten lamp did not suppress the spike discharges of caudal neurons.
4. Reduction in the spike numbers was not significantly observed by the irradiation applied on the “GOUKOKU” point.
5. Further investigations about the effect of low power laser irradiation on free nerve endings of C-fiber should be required.