Dihydrobenzofuran analogues of hallucinogens. 4. Mescaline derivatives

Dihydrobenzofuran and tetrahydrobenzodifuran functionalities were employed as conformationally restricted bioisosteres of the aromatic methoxy groups in the prototypical hallucinogen, mescaline (1). Thus, 4-(2-aminoethyl)-6,7-dimethoxy-2,3-dihydrobenzofuran hydrochloride (8) and 1-(8-methoxy-2,3,5,6-tetrahydrobenzo[1,2-b:5,4-b']difuran-4-yl)-2- aminoethane hydrochloride (9) were prepared and evaluated along with 1 for activity in the two-lever drug discrimination (DD) paradigm in rats trained to discriminate saline from LSD tartrate (0.08 mg/kg). Also, 1, 8, and 9 were assayed for their ability to displace [3H]ketanserin from rat cortical homogenate 5-HT2A receptors and [3H]8-OH-DPAT from rat hippocampal homogenate 5-HT1A receptors. In addition, these compounds were evaluated for their ability to compete for agonist and antagonist binding to cells expressing cloned human 5-HT2A, 5-HT2B, and 5-HT2C receptors. Finally, agonist efficacy was assessed by measurement of phosphoinositide hydrolysis in NIH 3T3 cells expressing the rat 5-HT2A or 5-HT2C receptors. Although 1 fully substituted for LSD in the DD assays (ED50 = 33.5 mumol/kg), neither 8 nor 9 substituted for LSD, with just 50% of the rats administered 8 selecting the drug lever, and only 29% of the rats administered 9 selecting the drug lever. All of the test compounds had micromolar affinity for the 5-HT1A and 5-HT2A receptors in rat brain homogenate. Curiously, the rank order of affinities of the compounds at 5-HT2A sites was opposite their order of potency in the behavioral assay. An evaluation for ability to stimulate phosphoinositide turnover as a measure of functional efficacy revealed that all the compounds were of approximately equal efficacy to serotonin in 5-HT2C receptors. At 5-HT2A receptors, however, 8 and 9 were significantly less efficacious, eliciting only 61 and 45%, respectively, of the maximal response. These results are consistent with the proposed mechanism of action for phenethylamine hallucinogens, that such compounds must be full agonists at the 5-HT2A receptor subtype. In contrast to the 2,5-dimethoxy-substituted phenethylamines, where rigidification of the methoxy groups had no deleterious effect on activity, the loss of activity in the 3,4,5-trioxygenated mescaline analogues may suggest that the 3 and 5 methoxy groups must remain conformationally mobile to enable receptor activation.

Transient reinforcing effects of phenylisopropylamine and indolealkylamine hallucinogens in rhesus monkeys

Relatively few studies have assessed the reinforcing effects of hallucinogenic compounds, and no such studies have attempted to engender contingent responding for these compounds in animals with behavioral histories that include experience with serotonergically mediated reinforcing effects. The objectives of the present study were to investigate the capacity of several hallucinogenic compounds to maintain self-administration behavior in rhesus monkeys with a previous history of 3,4-methylenedioxymethamphetamine (MDMA) self-administration, and to compare these effects across a range of doses of drugs from two structural classes (indolealkylamines and phenylisopropylamines). The results indicate that no compound generated reliable responding and that no subject ever self-administered 4-iodo-2,5-dimethoxyphenylisopropylamine (DOI) at rates above those engendered by contingent saline. However, 3 out of 4 subjects did respond at rates between 0.75 and 3.0 responses/s in one or more sessions where N,N-dimethyltryptamine (DMT), mescaline or psilocybin were available. During some of these sessions in which self-administration was maintained, animals earned a majority of all available infusions and appeared intoxicated by the end of the session. This pattern of transient self-administration may indicate that these compounds have weak reinforcing effects, or mixed reinforcing and aversive effects.

Phencyclidine, lysergic acid diethylamide, and mescaline: cerebral artery spasms and hallucinogenic activity

Phencyclidine (PCP), lysergic acid diethylamide (LSD), and mescaline produced potent contractile responses on isolated basilar and middle cerebral arteries, where, in terms of potency, LSD greater than mescaline greater than PCP. All three drugs produced cerebrovasospasm in a concentration range which parallels that needed for their psychotomimetic and intoxicating actions. Specific receptors for PCP, which subserve contraction and differ from those for LSD and mescaline, are found in cerebral arteries. Concentrations of PCP that produced near-maximum contractile responses on cerebral arteries were similar to those in the blood and brain of human subjects who had died from PCP overdoses. A specific calcium antagonist, verapamil, readily prevented (and reversed) PCP-induced vasospasm. This study provides direct evidence for PCP receptors in cerebral blood vessels, the biologic action of which can be reversed by a calcium antagonist; the clinical use of the latter could prove invaluable in treating PCP-intoxicated victims.

The discriminative stimulus properties of 2,5-dimethoxy-4-methylamphetamine (DOM): differentiation from amphetamine

Rats were trained in a two-lever operant procedure to discriminate either 1.0 mg/kg (+)amphetamine or 1.5 mg/kg DOM from saline. Rats trained to discriminate DOM from saline showed generalization with the DOM training condition when tested with mescaline or 2,5-dimethoxy-4-ethylamphetamine (DOET), but not when tested with (+)amphetamine or methylphenidate. Both isomers of DOM generalized with racemic training compound, the (-)isomer being more potent. The DOM stimulus was completely blocked by the serotonin (5-HT) antagonists cinanserin and methysergide, but not by the peripheral 5-HT antagonist xylamidine nor the dopamine antagonist haloperidol. Rats trained to discriminate (+)amphetamine from saline generalized with the amphetamine training condition when tested with methylphenidate but not when tested with mescaline, DOET, racemic DOM, or either isomer of DOM. The amphetamine stimulus was blocked by pretreatment with haloperidol but not by cinanserin, methysergide, or xylamidine. The results show that, despite their structural similarity, amphetamine and DOM induce pharmacologically distinct stimuli.

Effects of colchicine on nucleic acid metabolism during metamorphosis of Tenebrio molitor L. and in some mammalian tissues

1. Administration of 10mug. of colchicine/pupa of the beetle Tenebrio molitor L. arrests its differentiation, the pupa remaining alive for 2-3 weeks. 2. The same concentration of colchicine inhibits DNA synthesis and stimulates RNA synthesis (as shown by incorporation into the nucleic acids of labelled adenine, labelled uridine and labelled thymidine). The effects of colchicine on nucleic acid metabolism are first detected 3 days after its administration to first-day pupae. 3. No effects of colchicine are seen on [1-(14)C]glycine incorporation into protein in vivo. 4. Relatively high concentrations of colchicine (e.g. 10mm) suppress incorporation of [8-(14)C]adenine into RNA in dorsal abdominal wall in vitro. Such concentrations have no effect on its incorporation into acid-soluble nucleotides. 5. Colchicine (1mm) suppresses incorporation of [8-(14)C]adenine into DNA to a greater extent than into RNA in various mammalian tissues in vitro (e.g. rat spleen, regenerating rat liver, rat embryo, guinea-pig intestinal mucosa, Ehrlich ascites cells). Colchicine (1mm) has no effect on the rate of respiration of, or on incorporation of radioactivity into acid-soluble nucleotides in, the mammalian tissues tested. 6. Further evidence indicates complex-formation between colchicine and DNA, and it is suggested that the effect of colchicine in suppressing DNA synthesis is due to its combination with the DNA primer (template).

The reflection of ejecting and retaining currents in the time-course of neuronal responses to microelectrophoretically applied drugs

The role of ejecting and retaining currents in determining the time-course of neuronal responses to microelectrophoretically applied drugs (acetylcholine, glutamate, noradrenaline, 5-hydroxytryptamine, and mescaline) was investigated. Comparing the parameters of excitatory responses to ejecting currents of successively increasing intensity, the following changes were observed: the response latency became progressively shorter, the plateau became higher, and the recovery time was prolonged. An increase in the intensity or duration of the pre-ejection retaining current resulted in the prolongation of the response latency and the latency to plateau, but did not alter the plateau itself. An increase in the intensity of the post-ejection retaining current reduced the recovery time of the response.

LSD mescaline and serotonin injected into medial raphe nucleus potentiate apomorphine hypermotility

Microinjections of LSD (0.05 microgram), mescaline (0.5 microgram) and serotonin (10 microgram) into the medial raphe nucleus of rats resulted in a strong potentiation of apomorphine (1 mg/kg i.p.)-induced hypermotility. The potentiating effect of LSD or serotonin was suppressed by simultaneous injections of methysergide (0.05 microgram) or cyproheptadine (0.05 microgram) into the medial raphe nucleus. The same doses of LSD injected into the dorsal raphe nucleus and of LSD and mescaline injected into the nucleus accumbens failed to influence locomotor activity, whereas injections of higher doses of LSD and mescaline into the nucleus accumbens inhibited spontaneous and apomorphine-stimulated locomotor activity. It is concluded that the potentiating effect of systemically administered low doses of hallucinogens was triggered by preferential actions on the serotonergic system in the medial raphe nucleus.

Behavioural models of psychosis

Studies on the biological basis of psychosis are currently being conducted in a variety of disciplines and using a wide range of techniques (Smythies, 1968). These include studies of the basic mechanism of action of drugs which mimic, exacerbate or ameliorate psychosis. A major sub-section of the field is composed of structure-activity relationship (S.A.R.) studies in which we determine what effect the systematic manipulation of the molecular structure has on the activity of a drug. In this way valuable data can be obtained as to its possible mode of action. This in turn may suggest hypotheses as to the biochemical lesions in the naturally occurring psychoses. Secondly, specific behavioural responses can be made the dependent variable we measure in experiments where the levels of brain amines, activity of brain enzymes, etc., can be manipulated by any of the many techniques now available.

Role of serotonin in the discriminative stimulus properties of mescaline

Rats were trained to discriminate intraperitoneally administered mescaline from saline in a two-lever operant chamber for food reinforcement. Reward was contingent upon responses made greater than 15 sec apart (DRL-15) on the appropriate lever paired with either drug or saline administration. Following the establishment of discriminative response control by mescaline, the animals were tested for stimulus generalization produced by mescaline after: (a) blockade of periphreral and central serotonin (5-HT) receptors with cinanserin, methysergide, or cyproheptadine; (b) blockade of peripheral 5-HT receptors with xylamidine tosylate; and (c) depletion of brain 5-HT with the tryptophan hydroxylase inhibitor p-chlorophenylalanine (PCPA). The results show that all three central 5-HT antagonists greatly reduced the discriminability of mescaline while the peripheral antagonist, xylamidine tosylate, was without effect. Furthermore, these agents at the doses employed did not effect the discriminability of saline. Depletion of 5-HT with PCPA potentiated the effects of a sub-threshold dose of mescaline and slightly reduced the discriminability of saline. The results indicate that mescaline produces its discriminative stimulus properties by directly stimulating central serotonergic receptors.