CHARACTERIZATION OF BLINK REFLEX INTERNEURONS BY ACTIVATION OF DIFFUSE NOXIOUS INHIBITORY CONTROLS IN MAN

The blink reflex consists of an early, pontine R1-component and a late , medullary R2-component. R1 and R2 can be evoked by innocuous stimuli , but only the R2 also by painful heat, suggesting that the R2 is medi ated by wide dynamic range neurons (WDR) of the spinal trigeminal :nuc leus. Remote noxious stimuli suppress the activity in WDR neurons via activation of diffuse noxious inhibitory controls (DNIC), whereas low- threshold mechanoreceptive neurons (LTM) are unaffected. In order to c haracterize the trigeminal interneurons of R1. and R2 we investigated the modulation of the blink reflex by remote painful heat. The blink r eflex was elicited in 11 healthy subjects by innocuous electrical puls es applied to the left supraorbital nerve. The remote, painful heat st imuli were applied by a Peltier type thermode to the left volar forear m. Remote painful heat of 44 to 46 degrees C significantly suppressed the R2 by 15% (p < 0.01), while the R1 remained unchanged. These resul ts provide further evidence that the R2 is mediated by medullary WDR n eurons and the R1 by pontine LTM neurons. (C) 1998 Elsevier Science B. V. All rights reserved.