Nociception is enhanced after low doses and reduced after high doses of the serotonin receptor agonist 5-methoxy-N,N-dimethyltryptamine.
Neuroscience letters September 1, 1980 O G Berge, K Hole, H Dahle 34 citations
Injecting 5-methoxy-N,N-dimethyltryptamine into the brain's ventricles altered pain sensitivity in rats, measured by the tail-flick test. Low doses (1.6 to 25 micrograms) reduced tail-flick latencies by 13-24%, indicating hyperalgesia (increased pain sensitivity), likely from decreased activity in descending serotonergic neurons. Moderate doses (50 and 100 micrograms) produced a biphasic response: initial hyperalgesia followed by analgesia. The highest dose (400 micrograms) increased latencies by 28-39%, indicating analgesia, probably by stimulating spinal postsynaptic serotonergic receptors.