Identifying Chinese medicinal materials with antinociceptive activities using a Drosophila model

Nociception is the reception of signals in the central nervous system (CNS) triggered by specialized sensory receptors which received stimuli such as electrical, thermal, mechanical, or chemical and response to escape from danger. Similar to humans, the fruitfly Drosophila display evolutionarily conserved nociceptive response that makes it suitable for in vivo nociceptive study. In this study, Drosophila larvae were used as initial screening model to investigate the antinociceptive effect that was caused by 61 randomly selected Chinese Medicinal Materials (CMMs). Upon noxious heat stimulation, 73% of larvae in the control group produced a stereotypical rolling behavior within 1 s. Among those tested CMMs, the results indicated that 4 aqueous CMMs extracts from Citrus aurantium L. (family: Rutaceae), Angelica dahurica (Fish. ex Hoffm.) Benth. et Hook (family: Umbelliferae), Vitex trifolia L. var. simplicifolia Cham. (family: Verbenaceae) and Panax notoginseng (Burk.) F. H. Chen (family: Araliaceae) were found to have strong antinociceptive effect on Drosophila larvae since less than 40% of the larvae have produced stereotypical rolling behavior within 1 s upon noxious heat stimulation.;An alternative complementary approach was used to verify the antinociceptive effect of 4 CMMs aqueous extracts in a Drosophila adult model. Drosophila adults were subjected to CMM treatments and then placed on an in-house-designed heating device for noxious heat stimulation. Their behavioral outputs were quantified and expressed as heat avoidance index (AI) for revealing the degree of antinociceptive effect of CMMs. By comparing the AI value of non-CMM treated control group with CMM-treated groups at temperature challenge 32°C, it was found that an AI value of 0.2 was obtained for non-CMM-treated control group whereas CMMs-treated groups showed AI values ranged from 0.33 to 0.4. The increase of AI value in those CMM-treated groups means that Drosophila adults became more susceptible to noxious heat stimulation. This indicates that those identified CMMs by the larvae model possess strong and versatile antinoceiceptive activities in Drosophila adults.;In addition, reverse transcription PCR (RT PCR) analysis was performed to study the effects of CMMs on the mRNA expression of three nociceptive-related genes painless, nompC and CG4536. These three genes all belong to the Transient Receptor Potential (TRP) families and have been shown to be involved in heat response. The results indicate that the gene expression level for nompC was significantly down-regulated with fold changes ranging from 0.2 to 0.7 upon 2 hrs treatment of three aqueous CMM extracts Citrus aurantium, Angelica dahurica and Vitex trifolia. However, there is no significant difference in gene expression level for painless and CG4536.;In this study, it has been demonstrated that Drosophila are feasible to use for screening CMMs with antinociceptive activity. While the data of the relative gene expression level for those target genes observed in this study may also serve as biomarkers for providing more evidence to investigate drugs have antinociceptive effects. In the future, such information paves the way for further development in the study of antinociceptive drugs.