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

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.