Anti-nociceptive mechanism of baicalin involved in intervention of TRPV1 in DRG neurons in vitro

Ethnopharmacological relevance: Scutellaria baicalensis Georgi (Lamiaceae) is often included as an ingredient in traditional Chinese compound prescriptions for the treatment of fever-related or inflammatory conditions. Aim of the study: The present work was to further uncover the analgesic mechanisms of baicalin (a known principal constituent of Scutellaria baicalensis) by investigating its effects on the expression of TRPV1 mRNA as well as on its functions as mediators of calcium entrance into the cytoplasm of dorsal root ganglion (DRG) neurons in vitro. Materials and methods: By using CPT as an agent to eliminate the non-neuronal cells and using serum-free neurobasal as culture medium, primary cultures of rat DRG neurons with high purity and viability were established. On this basis, effects of baicalin on both the expression of TRPV1 mRNA and on the function of TRPV1 in vitro under two various temperature conditions were studied. The TRPV1 mRNA expression levels were examined by using qRT-PCR and analyzed by the method of 2(-Delta Delta CT). The elevation amplitudes of intracellular [Ca(2+)]i evoked by TRPV1 agonist capsaicin in DRG neurons were examined by the calcium fluorescence imaging method under confocal microscopy. Results: Baicalin was shown to down-regulate the mRNA expression levels of TRPV1 at both 37 and 39 degrees C, and under the latter temperature, the intracellular fluorescent intensity evoked by capsaicin was significantly decreased following incubation with baicalin in vitro. We also demonstrated that the actions of baicalin to TRPV1 were not achieved through pathways of TRPA1 or TRPV subfamily members. Conclusions: Collectively, these results provide compelling evidence that the down-regulated actions of baicalin to TRPV1 in DRG neurons might account for part of the anti-nociceptive mechanism of baicalin. (C) 2010 Elsevier Ireland Ltd. All rights reserved.