Neurotoxicity screening of new psychoactive substances (NPS): Effects on neuronal activity in rat cortical cultures using microelectrode arrays (MEA).

While the prevalence and the use of new psychoactive substances (NPS) is steadily increasing, data on pharmacological, toxicological and clinical effects is limited. Considering the large number of NPS available, there is a clear need for efficient in vitro screening techniques that capture multiple mechanisms of action. Neuronal cultures grown on multi-well microelectrode arrays (mwMEAs) have previously proven suitable for neurotoxicity screening of chemicals, pharmaceuticals and (illicit) drugs. We therefore used rat primary cortical cultures grown on mwMEA plates to investigate the effects of eight NPS (PMMA, α-PVP, methylone, MDPV, 2C-B, 25B-NBOMe, BZP and TFMPP) and two 'classic' illicit drugs (cocaine, methamphetamine) on spontaneous neuronal activity. All tested drugs rapidly and concentration-dependently decreased the weighted mean firing rate (wMFR) and the weighted mean burst rate (wMBR) during a 30 min acute exposure. Of the 'classic' drugs, cocaine most potently inhibited the wMFR (IC50 9.8 μM), whereas methamphetamine and the structurally-related NPS PMMA were much less potent (IC50 100 μM and IC50 112 μM, respectively). Of the cathinones, MDPV and α-PVP showed comparable IC50 values (29 μM and 21 μM, respectively), although methylone was 10-fold less potent (IC50 235 μM). Comparable 10-fold differences in potency were also observed between the hallucinogenic phenethylamines 2C-B (IC50 27 μM) and 25B-NBOMe (IC50 2.4 μM), and between the piperazine derivatives BZP (IC50 161 μM) and TFMPP (IC50 19 μM). All drugs also inhibited the wMBR and concentration-response curves for wMBR and wMFR were comparable. For most drugs, IC50 values are close to the estimated human brain concentrations following recreational doses of these drugs, highlighting the importance of this efficient in vitro screening approach for classification and prioritization of emerging NPS. Moreover, the wide range of IC50 values observed for these and previously tested drugs of abuse, both within and between different classes of NPS, indicates that additional investigation of structure-activity relationships could aid future risk assessment of emerging NPS.