42. The effects of THC on Cutaneous Silent Period

Abstract

The analgesic effects of cannabinoids are mediated through the activity on the endogenous cannabinoid system. (−)-trans-Δ 9 -tetrahydrocannabinol (THC) is the principal psychoactive constituent of cannabis and it shows a partial agonist activity on cannabinoid receptors, in particular CB1 receptor, mainly expressed by neurons of the central and peripheral nervous system. Several studies demonstrate the effects of THC on pain perception. The aim of this study was to evaluate the effects of THC in 13 healthy volunteers (HV) through the analysis of Cutaneous Silent Period (CSP), a nociceptive spinal inhibitory reflex, considered a defense response, specific for the human upper limbs. CSP parameters have been recorded from the abductor digiti minimi (ADM) before and after an hour from the administration of a cannabis-based preparation. We recorded the same parameters before and after the administration of placebo in the same volunteers. The results showed that the CSP latency and amplitude left unchanged in HV after the drug administration at the dose commonly used to suppress nociceptive reflexes in humans. These differential effects of a narcotic-analgesic drug provide evidence that the Cutaneous Silent Period is not a THC-sensitive nociceptive reflex.