Strychnine alters response properties of trigeminal nociceptive neurons inthe rat

The purpose of this study was to examine the role of glycine in sensory pro cesses in the spinal trigeminal nucleus oralis (Sp5O). We evaluated the eff ect of intravenous administration of strychnine, a glycine receptor antagon ist, on the responses of Sp5O convergent neurons evoked by innocuous periph eral electrical and mechanical stimuli in halothane-anesthetized rats. Stry chnine significantly increased the A beta -fiber-evoked activities of Sp5O neurons to electrical stimulation in a dose-dependent (0.2-0.8 mg/kg) fashi on. The response to air-jet stimulation was also significantly enhanced at the highest dose of strychnine. These findings indicate that glycinergic ne urons participate in the control of the flow of information conveyed to Sp5 O nociceptive neurons by myelinated low-threshold mechanoreceptive afferent s. Thus, alteration of trigeminal glycinergic modulation may contribute to the dynamic mechanical allodynia that occurs in trigeminal neuropathies.