Hallucinogen-Like Action of the Novel Designer Drug 25I-NBOMe and Its Effect on Cortical Neurotransmitters in Rats

25I-NBOMe, a synthetic hallucinogen related to the 2C family, increases extracellular levels of dopamine, serotonin, and glutamate in the rat frontal cortex, as measured by microdialysis in freely moving animals. It also raises tissue content of serotonin and its metabolite 5-HIAA but does not affect tissue dopamine or its metabolites. The drug elicits head-twitch response in rats, a behavioral marker of hallucinogenic effect in humans. Dose-response curves were inverted U-shaped for dopamine and serotonin release, but U-shaped for glutamate release and head-twitch response. The findings suggest that the hallucinogenic activity of 25I-NBOMe is linked to increased extracellular glutamate mediated by cortical 5-HT2A receptors, with modulation by 5-HT2C and 5-HT1A receptors.

Study at a glance

Abstract

NBOMes are N-benzylmethoxy derivatives of the 2C family hallucinogens. 4-Iodo-2,5-dimethoxy-N-(2-methoxybenzyl)phenethylamine (25I-NBOMe) is one of the commonly used illicit drugs. It exhibits high binding affinity for 5-HT 2A/C and 5-HT 1A serotonin receptors. Activation of 5-HT 2A receptor induces head-twitch response (HTR) in rodents, a behavioral marker of hallucinogen effect in humans. There is not much data on neurochemical properties of NBOMes. Therefore, we aimed to investigate the effect of 25I-NBOMe on extracellular level of dopamine (DA), serotonin (5-HT), and glutamate (GLU) in the rat frontal cortex, tissue contents of monoamines, and hallucinogenic activity in rats. The extracellular levels of DA, 5-HT, and GLU were studied using microdialysis in freely moving animals. The tissue contents of DA, 5-HT and their metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were determined in the rat frontal cortex. We also tested a drug-elicited HTR. 25I-NBOMe at doses 1, 3, and 10 mg/kg (sc) increased extracellular DA, 5-HT, and GLU levels, enhanced tissue content of 5-HT and 5-HIAA, but did not affect tissue level of DA and its metabolites. The compound exhibited an inverted U -shaped dose-response curve with respect to the effect on extracellular DA and 5-HT levels, but a U -shaped dose-response curve was observed for its effect on GLU release and HTR. The data from our study suggest that hallucinogenic activity of 25I-NBOMe seems to be related with the increase in extracellular GLU level-mediated via cortical 5-HT 2A receptors. The influence of 25I-NBOMe on 5-HT 2C and 5-HT 1A receptors may modulate its effect on neurotransmitters and HTR.