Behavioral and neurochemical pharmacology of six psychoactive substituted phenethylamines: Mouse locomotion, rat drug discrimination and in vitro receptor and transporter binding and function

Rationale: Psychoactive-substituted phenethylamines 2,5-dimethoxy-4- chlorophenethylamine (2C-C); 2,5-dimethoxy-4-methylphenethylamine (2C-D); 2,5-dimethoxy-4-ethylphenethylamine (2C-E); 2,5-dimethoxy-4-iodophenethylamine (2C-I); 2,5-dimethoxy-4-ethylthiophenethylamine (2C-T-2); and 2,5-dimethoxy-4-chloroamphetamine (DOC) are used recreationally and may have deleterious side effects. Objectives: This study compares the behavioral effects and the mechanisms of action of these substituted phenethylamines with those of hallucinogens and a stimulant. Methods: The effects of these compounds on mouse locomotor activity and in rats trained to discriminate dimethyltryptamine, (-)-DOM, (+)-LSD, (±)-MDMA, and S(+)-methamphetamine were assessed. Binding and functional activity of the phenethylamines at 5-HT_1A, 5-HT_2A, 5-HT_2C receptors and monoamine transporters were assessed using cells heterologously expressing these proteins. Results: The phenethylamines depressed mouse locomotor activity, although 2C-D and 2C-E stimulated activity at low doses. The phenethylamines except 2C-T-2 fully substituted for at least one hallucinogenic training compound, but none fully substituted for (+)-methamphetamine. At 5-HT_1A receptors, only 2C-T-2 and 2C-I were partial-to-full very low potency agonists. In 5-HT_2A arachidonic acid release assays, the phenethylamines were partial to full agonists except 2C-I which was an antagonist. All compounds were full agonists at 5-HT_2A and 5-HT_2C receptor inositol phosphate assays. Only 2C-I had moderate affinity for, and very low potency at, the serotonin transporter. Conclusions: The discriminative stimulus effects of 2C-C, 2C-D, 2C-E, 2C-I, and DOC were similar to those of several hallucinogens, but not methamphetamine. Additionally, the substituted phenethylamines were full agonists at 5-HT_2A and 5-HT_2C receptors, but for 2C-T-2, this was not sufficient to produce hallucinogen-like discriminative stimulus effects. Additionally, the 5-HT_2A inositol phosphate pathway may be important in 2C-I's psychoactive properties.