The effect of intrathecal administration of the GABA A receptor antagonist bicuculline methylbromide on jaw muscle electromyographic (EMG) activity evoked by mustard oil injection into the rat temporomandibular joint was studied. Bicuculline given prior to mustard oil augmented the EMG activity evoked by mustard oil, and 'rekindling' of EMG activity was induced by bicuculline given 30 min after mustard oil. These results suggest that central GABA A receptors modulate reflex responses to noxious craniofacial stimuli.