Changes in neuronal activity in rat primary cortical cultures induced by illicit drugs and new psychoactive substances (NPS) following prolonged exposure and washout to mimic human exposure scenarios.

The effects of several new psychoactive substances (NPS) and illicit drugs on neuronal activity were tested in rat brain cells grown on microelectrode arrays. After 30 minutes of exposure, all compounds reduced neuronal activity in a dose-dependent manner. Extending exposure to 5 hours did not cause further decreases. After a 19-hour washout period, activity fully recovered only for methamphetamine, cocaine, and benzylpiperazine; partially recovered for MDMA, PMMA, and α-PVP; and did not recover at the highest concentrations of MDPV, 2C-B, 25B-NBOMe, and TFMPP. Low concentrations of methylone and 2C-B actually increased activity after washout. The ability of neural networks to regain activity after drug exposure appears unrelated to drug class or potency. Complete recovery was rare, which is concerning.

Study at a glance

Abstract

The use of new psychoactive substances (NPS) is increasing despite associated health risks and limited pharmacological and toxicological knowledge. Information is available mainly for acute effects on specific targets like monoamine transporters and receptors. Recently, we have shown the ability of several NPS and illicit drugs to modulate neuronal activity during acute exposure. While these acute measurements provide valuable information regarding the potency and possible structure-activity relationships, an exposure scenario more representative of human exposure would increase insight and aid translation to the human situation. Therefore, we investigated the effects on neuronal activity after acute (30 min) and prolonged (5 h) exposure to amphetamine-type stimulants, cathinones, hallucinogens, piperazines and cocaine using rat primary cortical cultures grown on multi-well microelectrode arrays. To investigate the reversibility of effects, activity was also measured after a washout period of 19 h. During acute exposure, all compounds concentration-dependently decreased neuronal activity. Compared to acute exposure, prolonged exposure did not further decrease neuronal activity. Following washout, effects of 3 out of 11 drugs (methamphetamine, cocaine, and benzylpiperazine) were fully reversible, whereas effects induced by MDMA, PMMA and α-PVP were partially reversible. Neuronal activity did not recover after 19 h washout following exposure to the highest concentration of MDPV, 2C-B, 25B-NBOMe, and TFMPP. On the contrary, exposure to low concentrations of methylone, and to some extent of 2C-B, increased neuronal activity after the washout period. Hazard characterization of emerging NPS should include at least an acute exposure to determine a potency rank order. Supplementing the (acute and prolonged) exposure scenario with a washout period allows investigation of the reversibility of effects. The possibility of a neuronal network to regain activity after drug exposure appears independent of drug class or IC50 values for acute and prolonged exposure. Even though neuronal activity (partly) recovers after washout following exposure to most drugs, it is perturbing that complete recovery of neuronal activity is observed only for a minority of the tested drugs.