Decanoic acid attenuates the excitability of nociceptive trigeminal primary and secondary neurons associated with hypoalgesia

Abstract

Background: Acute application of decanoic acid (DA) in vivo suppresses the excitability of spinal trigeminal nucleus caudalis (SpVc) wide dynamic range (WDR) neurons associated with the short-term mechanical hypoalgesia via muscarinic M 2 receptor signaling; however, the effect of DA on nociceptive trigeminal ganglion (TG) and SpVc nociceptive-specific (NS) neuronal excitability under in vivo conditions remains to be determined. The present study investigated whether this effect could be observed in naive rats. Results: Extracellular single-unit recordings were made from TG and SpVc NS neurons of pentobarbital-anesthetized rats in response to orofacial noxious mechanical stimuli. DA inhibited the mean firing frequency of both TG and SpVc NS neurons, reaching a maximum inhibition of discharge frequency within 1–5 minutes and reversing after approximately 10-minutes; however, this DA-induced suppression of SpVc NS neuronal firing frequency did not occur in rats administered with methoctramine intravenously prior to stimulation. Conclusion: This in vivo study indicated that firing of TG and SpVc NS neurons induced by mechanical hypoalgesia through peripheral M 2 receptors could be inhibited by acutely administered DA, implicating the potential of DA in the future treatment of trigeminal pain. Perspective: This article presents that the acute DA application suppresses the excitability of TG and SpVc NS neurons associated with mechanical hypoalgesia via peripheral M 2 receptor signaling, supporting DA as a potential therapeutic agent in complementary and alternative medicine for the attenuation of nociception.