Emodin inhibits the expression of receptor and calcitonin-gene-related peptide release in trigeminal ganglia of trigeminal neuralgia rats.

Trigeminal neuralgia (TN) is one of the most intense forms of facial pain. It has been reported that the P2X receptor plays a crucial role in facilitating pain transmission, and the calcitonin-gene-related peptide (CGRP) from trigeminal ganglia (TGs) might perform differing function in nociceptive afferent input transmission. The present study investigated whether emodin can affect TN pain transmission by suppressing the expression of P2X receptors and CGRP in TGs. Chronic constriction injury of the infraorbital branch of the trigeminal nerve (CCI-ION) was used as TN model. The TN rats were randomly divided into the following 4 groups: (1) a sham group (Sham), (2) a sham rats treated with emodin group (TN + E), (3) a TN rats treated with 0.5% sodium carboxymethyl cellulose (CMC) as vehicle group (TN) and (4) a TN rats treated with emodin group (TN + E). The mechanical hyperalgesia threshold of TN rats was tested by Electric Von Frey filaments. The change of the expression of P2X receptors and CGRP in rat's TG was detected with RT-PCR, immunohistochemical staining, and Western blotting. The phosphorylation of p38 and ERK1/2 pathway of TG was detected by Western blotting. After CCI-ION injury, the threshold of mechanical hyperalgesia for the territory of ligated infraorbital nerve in TN group decreased significantly compared with that in sham group. On day 14 after operation of CCI-ION, there was also an evident increase in the expression of P2X receptors and CGRP in the TG of TN group. However after treatment with emodin, the response of mechanical hyperalgesia of TN rats was clearly increased while the enhanced expression of P2X receptor and CGRP in TN rats was significantly decreased. The phosphorylation of p38 and ERK1/2 in TN group was stronger than that in Sham group. But these phosphorylation changes in the TN rats were much weaker after treatment with emodin. In conclusion, P2X receptor may cooperate with CGRP in the pain transmission of TN, and emodin can inhibit the expression and activation of P2X receptor and CGRP in TG to relieve TN.