P2X and NMDA receptor involvement in temporomandibular joint-evoked reflex activity in rat jaw muscles

Abstract

We have previously shown that injection of the excitatory amino glutamate into the rat temporomandibular joint (TMJ) evokes reflex activity in both anterior digastric (DIG) and masseter (MASS) muscles that can be attenuated by prior TMJ injection of a N-methyl-Daspartate (NMDA) receptor antagonist. The aim of the present study was to test if jaw muscle activity could also be evoked by P2X receptor agonist injection into the rat TMJ region and if the reflex activity could be modulated by TMJ injection of P2X receptor antagonist or NMDA receptor antagonist. The selective P2X subtype agonist α,β-methylene adenosine 5′-triphosphate (α,β-me ATP) and vehicle (phosphate-buffered saline) or the selective P2X antagonist, 2′-(or-3′)-O-(2,4,6-trinitrophenyl) adenosine 5′-triphosphate (TNP-ATP) or selective NMDA antagonist (±)-D-2-amino-5-phosphonovalerate(APV) were injected into the rat TMJ region. Electromyographic (EMG) reflex activity was recorded in both DIG and MASS muscles. Compared with the baseline EMG activity, α,β-me-ATP injection into the TMJ (but not its systemic administration) following pre-injection of the vehicle significantly increased the magnitude and the duration of ipsilateral DIG and MASS EMG activity in a dose-dependent manner. The α,β-me-ATP-evoked responses could be antagonized by pre-injection of TNP-ATP into the same TMJ site but contralateral TMJ injection of TNP-ATP proved ineffective. Furthermore, the α,β-me-ATP-evoked responses could also be antagonized by APV injected into the same TMJ site but not by its systemic injection. These results indicate the interaction of peripheral purinergic as well as glutamatergic receptor mechanisms in the processing of TMJ nociceptive afferent inputs that evoke reflex activity in jaw muscles.

Dura-evoked neck muscle activity involves purinergic and N-methyl-D-aspartate receptor mechanisms

“…On the day of the experiment, the weight of the animals was between 225 and 350 g. All surgical and experimental procedures were approved by the University of Toronto Animal Care Committee, and were in accordance with the regulations of the Ontario Animal Research Act (Canada). The procedures were generally similar to those previously described in detail [1,5,15], and thus are only briefly outlined here.…”

“…As craniofacial noxious stimulation may evoke reflex effects in jaw, facial or tongue muscles as well as neck muscles [1,5,15], bipolar EMG electrodes were placed into neck (semispinalis), periorbital (orbicularis oculi) and jaw (masseter, anterior digastric) muscles bilaterally, as well as into the tongue (genioglossus) musculature. The right frontal dura was then exposed by using a dental drill to remove part of the skull (1–2mm from the central suture and bregma), and attention was paid to avoid damage to the superior sagittal sinus.…”

“…The chemicals TNP-ATP (a selective antagonist of P2 × 1 , P2× 3 , and P2× 2/3 receptor subtypes; catalogue number: SML0740), α,β-meATP (a selective agonist of P2 × 1 , P2× 3 , and P2× 2/3 receptor subtypes; catalogue number: M6517) [17] and APV (an NMDA receptor antagonist; catalogue number: A8054) [15] were purchased from Sigma-Aldrich (St Louis, Missouri, USA). α, β-meATP was freshly dissolved in normal saline (NS), and TNP-ATP and APV were freshly dissolved in PBS (catalogue number: P4417) at pH 7.4 (Sigma-Aldrich).…”

“…Furthermore, there is evidence that ATP may regulate glutamate release via an action involving both P2X and NMDA receptor mechanisms in the spinal dorsal horn and MDH [9,11]. Both NMDA and P2X receptor mechanisms have also been shown to contribute to modulating trigeminal nociceptive afferent inputs to the MDH in the brainstem and contribute to processes underlying brainstem sensorimotor circuits [5,6,10,13 –15]. Therefore, it is possible that P2X and NMDA receptor mechanisms contribute to the reflex effects of dural stimulation on neck muscle activity.…”

Inflammation, Pain, and Pressure—Purinergic Signaling in Oral Tissues

“…The P2X 3 receptor is expressed in the TMJ (Ichikawa et al, 2004), and injection of the P2X agonist α,β-meATP into the rat TMJ increased behavioral nociceptive responses, while blockage of P2X receptors with antagonist PPADS decreased the inflammatory hyperalgesia accompanying injection of carrageenan into rat TMJ (Oliveira et al, 2005). P2X receptors also contribute to reflexive actions in the TMJ, since the antagonist α,β-meATP reduced the reflex response (Watanabe et al, 2010). Given the role of purinergic receptors in inflammation (Ferrero, 2011) and the importance of inflammation in the TMJ (Sessle, 2011), it is likely that purines may also contribute here, although there was no change in the expression of the P2Y 12 receptor from microglia in rat models of TMJ inflammation (Villa et al, 2010).…”