This study investigated the possible involvement of brain stem excitatory amino acid receptor mechanisms and the trigeminal subnucleus caudalis (Vc) in temporomandibular joint (TMJ)evoked reflex jaw muscle activity. Glutamate injected into the TMJ of anesthetized rats reflexly evoked activity in the jaw muscles. Application of lidocaine, but not saline, to the surface of the caudal brainstem overlying Vc significantly suppressed TMJ-evoked jaw muscle activity, while application of NMDA or non-NMDA receptor antagonists also significantly attenuated jaw muscle activity. These results provide evidence that Vc is a critical relay in the TMJ-evoked reflex activation of the jaw muscles, and that both NMDA and non-NMDA receptor mechanisms may contribute to these effects. NeuroReport 12: 1875-1878 (C) 2001 Lippincott Williams & Wilkins.