Abuse liability profile of three substituted tryptamines

Abstract

The abuse liability profile of three synthetic hallucinogens, N,N-diisopropyltryptamine (DIPT), 5-N,N-diethyl-5-methoxytryptamine (5-MeO-DET), and 5-methoxy-α-methyltryptamine (5-MeO-AMT), was tested in rats trained to discriminate hallucinogenic and psychostimulant compounds, including cocaine, methamphetamine, 3,4-methylenedioxymethylamphetamine (MDMA), lysergic acid diethylamide (LSD), (-)-2,5-dimethoxy-4-methylamphetamine (DOM), and dimethyltryptamine (DMT). Because abused hallucinogens act at 5-hydroxytryptamine 1A (5-HT(1A)) and 5-HT(2A) receptors, and abused psychostimulants act at monoamine transporters, binding and functional activities of DIPT, 5-MeO-DET, and 5-MeO-AMT at these sites were also tested. DIPT fully substituted in rats trained to discriminate DMT (ED(50) = 1.71 mg/kg) and DOM (ED(50) = 1.94 mg/kg), but produced only 68% LSD-appropriate responding. 5-MeO-DET fully substituted for DMT (ED(50) = 0.41 mg/kg) and produced 59% MDMA-appropriate responding. 5-MeO-AMT did not fully substitute for any of the training drugs, but produced 67% LSD-appropriate responding. None of the compounds produced substitution in rats trained to discriminate cocaine or methamphetamine. All three compounds showed activity at 5-HT(1A) and 5-HT(2A) receptors as well as blockade of reuptake by the serotonin transporter. In addition, 5-MeO-AMT produced low levels of serotonin release and low potency blockade of dopamine uptake. DIPT, 5-MeO-DET, and 5-MeO-AMT produced behavioral and receptor effects similar to those of abused hallucinogens, but were not similar to those of psychostimulants. DIPT and 5-MeO-DET may have abuse liability similar to known hallucinogens and may be hazardous because high doses produced activity and lethality.

Fig. 1.

Discriminative stimulus effects of DIPT, 5-MeO-DET, and 5-MeO-AMT in separate groups of rats trained to discriminate DMT, LSD, DOM, MDMA, cocaine, or methamphetamine from saline. Top of each pair, drug-appropriate responding of the test compounds in DMT-, LSD-, DOM-, MDMA-, cocaine-, and methamphetamine-trained rats. Bottom of each pair, rate of responding in responses per second. Each point represents the average of six rats except where indicated.

Fig. 2.

Effect of DIPT, 5-MeO-DET, and 5-MeO-AMT on horizontal activity counts/10 min as a function of dose (top to bottom) and time interval during an 8-h session. Each panel shows one dose group compared with vehicle control. *, p < 0.05 compared with vehicle for depressant or stimulant effect (10–40 min).