Nociceptive-specific blink reflex and glyceryl trinitrate infusion in healthy volunteers.

Glyceryl trinitrate (GTN) is known to induce early headache in healthy humans after intravenous infusion. Moreover, in animal models subcutaneous administration produces an increase in Fos expression in brainstem areas that are involved in trigeminal pain processing. In a double-blind crossover study, we tested the blink reflex before, during and immediately after GTN and placebo intravenous infusion in eight healthy volunteers using a new stimulation electrode that preferentially activates A-delta nociceptive afferent fibres. The initial hypothesis that GTN could induce an increase in the magnitude of the nociceptive blink reflex R2 component by stimulating activity of trigeminal nucleus caudalis wide dynamic range interneurones was not confirmed. Although mild headache was induced in six subjects, there was no significant change between the R2 area under the curve before and after drug vs. placebo.