Diffuse noxious inhibitory controls triggered by heterotopic CO2 laser conditioning stimulation decreased the SEP amplitudes induced by electrical tooth stimulation with different intensity at an equally inhibitory rate

Abstract

The purpose of this study was to investigate (1) whether selective Adelta-fiber stimulation with CO(2) laser produces a diffuse noxious inhibitory controls (DNIC) effect in the trigeminal nerve territory; and (2) whether the DNIC effect differs depending on test stimulus intensities under constant conditioning stimuli. To examine whether the CO(2) laser radiation on the dorsum of the hand selectively stimulates Adelta-fibers, laser evoked potentials (LEP) were recorded. The mean peak latency of LEP was 381.4 ms. The findings revealed that the CO(2) laser selectively stimulated Adelta-fibers. Electrical tooth stimuli with 3 levels of intensities (1.2, 1.4, 1.6 times the pain threshold) were applied to subjects as test stimulation in randomized order, with a CO(2) laser stimulus of 18 mJ/mm(2) applied to the dorsum of the hand for 4 min as the noxious conditioning stimulus. Somatosensory evoked potentials (SEP) induced by electrical tooth stimulation were recorded and tooth pain intensity was evaluated using a visual analogue scale (VAS). The amplitudes of the SEP late component and VAS values were significantly decreased only during the conditioning stimuli without aftereffect. The inhibitory rates of the amplitudes ranged from 31.3% to 34.6% and the VAS values from 29.0% to 31.2%. There were no significant differences in their inhibitory rates between the 3 test stimulus intensities. The result indicated that selective Adelta-fiber stimulation with the CO(2) laser produces a DNIC effect in the trigeminal nerve territory and suggested that the DNIC effect does not depend on the intensity of the test stimuli.

Effects of dexmedetomidine on conditioned pain modulation in humans

“…A painful CO2 laser beam applied to the peripheral skin and hand induced ascending sensory signals which are mediated by Ad fibres (Kakigi et al, 1991;Oono et al, 2008), consistent with previous studies (Kakigi et al, 1989(Kakigi et al, , 1991Tran et al, 2001). A painful CO2 laser beam applied to the peripheral skin and hand induced ascending sensory signals which are mediated by Ad fibres (Kakigi et al, 1991;Oono et al, 2008), consistent with previous studies (Kakigi et al, 1989(Kakigi et al, , 1991Tran et al, 2001).…”

“…2 shows individual examples of SEP waveforms during the first session with and without CO2 laser stimuli. In the first session, noxious conditioning stimuli using the CO2 laser stimuli in this study can induce CPM in accordance with our previous study in humans (Oono et al, 2008). Table 1 shows the latencies of SEP in both the first and second sessions of three types.…”

“…The stimulus intensity, 9-12 W (approximately 16-20 mJ/ mm 2 ), was determined according to previous reports (Tran et al, 2001;Obi et al, 2007;Oono et al, 2008). Noxious laser stimulation with a wavelength of 10.6 mm and laser radiation size of about 12 mm in diameter was delivered with a stimulus duration of 200 ms at about 3-s intervals.…”

Movement-Related Cortical Potentials Associated with Oral and Facial Functions in Humans

“…To estimate objective pain intensity, the late component of SEPs recorded from the vertex was analyzed. On the basis of Oono's method (Oono et al, 2008), a monopolar electrode was fixed to the surface of the upper central incisors and single electrical square pulses were administrated at 1 Hz. In this study, stimuli inducing bearable pain sensation (VAS = 5 -7) were administered.…”

Neurophysiological observation of the nociceptive system using electrocutaneous stimulation

“…Largest effect of CPT were found near pain threshold and no effect for stimuli below pain threshold [115]. On the contrary, laser modulating stimuli resulted in almost equal inhibitory effects regardless of stimulus amplitudes of electrical tooth stimulation [111]. Talbot et al [134] also showed inhibition of both perceived non-noxious and noxious heat stimuli by CPT.…”