Rationale

The lysergamide lysergic acid diethylamide (LSD) is a prototypical classical hallucinogen with remarkably high potency. LSD remains a popular recreational drug but is also becoming an important research tool for medical and neuroscience studies. Recently, several lysergamides that are close structural analogs of LSD have been sold as recreational drugs, which suggests that further studies are needed to explore the pharmacological properties of these compounds.

Objective

In this present investigation, another LSD congener, N-ethyl-N-cyclopropyl lysergamide (ECPLA), which to date has not been marketed as a recreational substance, was evaluated for its pharmacological features relative to those previously reported for LSD. The experiments focused on interactions with the 5-HT 2A receptor, which is responsible for mediating the psychedelic effects of LSD and other hallucinogens.

Methods

Competitive binding assays were performed to measure the affinity of ECPLA for 27 monoamine receptors. The ability of ECPLA to activate human 5-HT 2 receptor subtypes was assessed using calcium mobilization assays. Head twitch response (HTR) studies were conducted in C57BL/6J mice to determine whether ECPLA activates 5-HT 2A receptors in vivo. Two other N-alkyl substituted lysergamides, N-methyl-N-isopropyl lysergamide (MIPLA) and N-methyl-N-propyl lysergamide (LAMPA), were also tested in the HTR paradigm for comparative purposes.

Results

ECPLA has high affinity for most serotonin receptors, α 2 -adrenoceptors, and D 2 -like dopamine receptors. Additionally, ECPLA was found to be a potent, highly efficacious 5-HT 2A agonist for Gq-mediated calcium flux. Treatment with ECPLA induced head twitches in mice with a median effective dose (ED 50 ) of 317.2 nmol/kg (IP), which is ~ 40% of the potency observed previously for LSD. LAMPA (ED 50 = 358.3 nmol/kg) was virtually equipotent with ECPLA in the HTR paradigm whereas MIPLA (ED 50 = 421.7 nmol/kg) was slightly less potent than ECPLA.

Conclusions

These findings demonstrate that the pharmacological properties of ECPLA, MIPLA, and LAMPA are reminiscent of LSD and other lysergamide hallucinogens.