The term entactogen has recently been introduced to describe a new pharmacological class of compounds best represented by 3,4-methylenedioxymethamphetamine, MDMA, and its alpha-ethyl homologue MBDB. The present study was designed to test the similarities of the discriminative stimulus properties produced by MDMA and MBDB, as well as to elaborate further the distinction between entactogens, hallucinogens and stimulants. Two groups of rats were trained to discriminate saline from either racemic MDMA hydrochloride (1.75 mg/kg) or S-(+)-amphetamine sulfate (1.0 mg/kg) in a two-lever drug discrimination task. The (+/-)-MDMA cue completely generalized to S-(+)-MDMA, S-(+)-amphetamine, (+/-)-MDA, S-(+)-MBDB, (+/-)-MBDB, R-(-)-MDMA, and R-(-)-MBDB, but not to LSD or DOM. The S-(+)-amphetamine cue generalized to (+/-)-methamphetamine, but not to racemic MDMA or MBDB, nor to their optical isomers. The S-(+)-isomers of both MDMA and MBDB were more potent than the R-(-)-isomers. The results indicate that MDMA and MBDB may share a component of their discriminative stimulus properties which is different from both stimulants and hallucinogens. Although MDA and MDMA have been shown to be amphetamine-like, the lack of stimulant effects for MBDB suggests that amphetamine-like stimulant activity is not necessary for a compound to share discriminative stimulus properties with MDMA.
The alpha-ethyl phenethylamine derivative 1-(1,3-benzodioxol-5-yl)-2-butanamine was prepared. An asymmetric synthesis was used to prepare the enantiomers of this compound and the related alpha-methyl homologue (MDA). The racemates and enantiomers of both compounds were evaluated in the two-lever drug discrimination assay in rats trained to discriminate saline from 0.08 mg/kg of LSD tartrate. Stimulus generalization occurred with the racemate and the R-(-) enantiomer of the alpha-methyl homologue and the S-(+) enantiomer of the alpha-ethyl primary amine. No generalization occurred with the other enantiomers or with the N-methyl derivatives of either series. Human psychopharmacology studies revealed that the N-methyl derivative of the title compound was nonhallucinogenic and that it had a new, novel psychoactive effect. It is suggested that this compound is the prototype of a new pharmacologic class that may have value in facilitating psychotherapy and that this class be designated as entactogens.
Four cyclic analogues of the psychoactive phenethylamine derivative 3,4-(methylenedioxy)amphetamine were studied. These congeners, 5,6- and 4,5-(methylenedioxy)-2-aminoindan (3a and 4a, respectively), and 6,7- and 5,6-(methylenedioxy)-2-aminotetralin (3b and 4b, respectively) were tested for stimulus generalization in the two-lever drug-discrimination paradigm. Two groups of rats were trained to discriminate either LSD tartrate (0.08 mg/kg) from saline, or (+/-)-MDMA.HCl (1.75 mg/kg) from saline. In addition, a 2-aminoindan (5a) and 2-aminotetralin (5b) congener of the hallucinogenic amphetamine 1-(2,5-dimethoxy-4- methylphenyl)-2-aminopropane (DOM) were also evaluated. None of the methylenedioxy compounds substituted in LSD-trained rats, while both 3a and 3b fully substituted in MDMA-trained rats. Compounds 4a and 4b did not substitute in MDMA-trained rats. Compounds 5a and 5b did not substitute in MDMA-trained rats, although 5a substituted in LSD-trained rats, but with relatively low potency compared to its open-chain counterpart. In view of the now well-established serotonin neurotoxicity of 3,4-(methylenedioxy)amphetamine and its N-methyl homologue 1, 3a and 3b were evaluated and compared to 1 for similar toxic effects following a single acute dose of 40 mg/kg sc. Sacrifice at 1 week showed that neither 3a nor 3b depressed rat cortical or hippocampal 5-HT or 5-HIAA levels nor were the number of binding sites (Bmax) depressed for [3H]paroxetine. By contrast, and in agreement with other reports, 1 significantly depressed all three indices of neurotoxicity. These results indicate that 3a and 3b have acute behavioral pharmacology similar to 1 but that they lack similar serotonin neurotoxicity.
The racemate and the enantiomers of 1-(3-methoxy-4-methyphenyl)-2- aminopropane (6) and racemic 5-methoxy-6-methyl-2-aminoindan (11) were tested for stimulus generalization in the two-lever drug-discrimination paradigm. Both 6 and 11 were found to substitute with high potency in 3,4-(methylenedioxy)methamphetamine (1) and (S)-1-(1,3-benzodioxol-5-yl)-2-(methylamino)butane (2) trained rats. In the latter assay, both enantiomers of 6 had identical potencies, but their dose-response curves were not parallel. Racemic 6, but not 11, partially substituted for LSD. Racemic 6 and 11 did not substitute in (S)-amphetamine-trained rats. All of the test compounds were potent inhibitors of [3H]-5-HT uptake into synaptosomes in vitro, with the S enantiomer of 6 being most active. Rat brain monoamine levels were unaltered 1 week following a single high dose (10 or 20 mg/kg, sc) of 6 or 11, or two weeks following a subacute dosing regimen (20 mg/kg, sc, twice a day for 4 days). In addition, radioligand-binding parameters in rat brain homogenate with the 5-HT uptake inhibitor [3H]paroxetine were unchanged after subacute dosing with either racemic 6 or 11. The results indicate that compounds 6 and 11 have animal behavioral pharmacology similar to the methylenedioxy compounds 1 and 2, but that they do not induce the serotonin neurotoxicity that has been observed for the latter two drugs.
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