“The antinociceptive effects of cannabinoids and opioids have been known for centuries.

Serotonin and its receptors are also known to play important roles in nociception. However, the contribution of spinal 5-HT5A receptors in antinociceptive effects of cannabinoids and opioids has not been studied.

We conducted this study to clarify spinal mechanisms of the actions of the antinociceptive effects of cannabinoids and opioids.

Our findings show that spinal 5-HT5A receptors are involved in the antinociceptive effects of WIN 55,212-2 and morphine.”

https://www.ncbi.nlm.nih.gov/pubmed/29406831

http://www.nrcresearchpress.com/doi/10.1139/cjpp-2017-0567#.Wnr8P2inHrc