The synthetic cathinone mephedrone (MEPH) has two mirror-image forms (enantiomers), R-MEPH and S-MEPH, which produce different effects in rats. Both enantiomers similarly release dopamine, but R-MEPH is much weaker than S-MEPH at releasing serotonin. R-MEPH caused more repetitive movements, produced sensitization to those movements after repeated doses, and was rewarding in a conditioned place preference test, whereas S-MEPH was not. In a brain-stimulation reward test, both enantiomers showed biphasic effects, but R-MEPH produced greater facilitation. These findings indicate that R-MEPH's stronger dopamine actions and weaker serotonin actions make it more stimulant-like than S-MEPH.
Psilocybin, a psychedelic compound, causes repetitive, stereotyped movements and reduces defensive reactions in planarian flatworms. These effects are mediated by the neurotransmitter serotonin (5-hydroxytryptamine). The findings suggest that psilocybin's behavioral actions in this simple animal model are linked to serotonergic signaling.
Psilocybin, the active compound in Psilocybe mushrooms, reduced pain-related behaviors in adult male rats exposed to formalin-induced noxious stimuli, a model of both acute and persistent inflammatory pain. Doses of 0.1 and 0.3 mg/kg significantly decreased flinching and licking during both early and late pain phases. Pretreatment with volinanserin, a selective blocker of the 5-HT 2A receptor, eliminated this pain-relieving effect, indicating that psilocybin produces analgesia at least partly by activating that receptor.