Reduction in thermal hyperalgesia by intrathecal administration of glycine and related compounds.

We have previously shown in animal models that enhanced segmental glycine release is produced by neuroaugmentation techniques commonly used to control pain in humans. Our current hypothesis is that glycine administered intrathecally reduces the pain response evoked by the hotplate analgesia meter method. Neuropathic rats created by unilateral partial ligation of the sciatic nerve were treated with intrathecal infusion of glycine, strychnine, MK-801, or 5-7 DKA at 0.1 mumol for 2 hours at a rate of 10 microliters/min. Time required for limb withdrawal at 42 degrees C was significantly increased after glycine administration but not altered by strychnine, a specific glycine receptor antagonist. Administration of the NMDA receptor antagonist, MK-801, blocked the influence of glycine, with a less obvious antagonistic response from 5.7 DKA. Our results provide evidence that glycine and related compounds significantly modify thermal hyperalgesia, and may operate primarily through the NMDA receptor complex.