Nrxn3 reduces myofascial nociceptive pain

Neurexin 3 (Nrxn3) has a role in neuronal signaling. Previous reports indicated that reducing Nrxn3 expression in the central amygdala increased orofacial neuropathic pain. A common temporomandibular disorder is myofascial pain. Thus, we hypothesized that Nrxn3 would reduce myofascial hypersensitivity. To test this hypothesis Nrxn3 shRNA was infused into the central amygdala of male rats. Then a ligature of the tendon attachment of the anterior superficial portion of the masseter muscle was performed to induce inflammatory orofacial pain. Dark phase meal duration was measured continuously, and von Frey filament testing was completed every 7 days for 21 days to measure the nociceptive response. After testing tissues were collected and the amount of Nrxn3 was measured. Neuronal activity in the orofacial pain pathway was quantitated by c-Fos staining of the central amygdala, lateral parabrachial nucleus, trigeminal ganglia and trigeminal nucleus caudalis. Knockdown of Nrxn3 in the central amygdala significantly increased the pain response and increased the levels of c-Fos. This increased response was observed for greater than two weeks. The data suggests Nrxn3 expression within the central amygdala attenuates nociceptive orofacial pain by reducing neuronal activity.