Piperidinyltetralin sigma ligands

Sigma receptor ligands have been proposed to be potential antipsychotic drugs based on their activity profile in animal behavioral models and their indirect modulation of dopaminergic function. Compound 15 (DuP 734) is a combined antagonist of sigma-1 and serotonin 5HT2 receptors, which has been entered into phase I clinical trials as a potential antipsychotic drug. Tetralins 1 and 2 were prepared to determine whether restriction of the conformation of 15 and its analogs may lead to differences in binding selectivity or in vivo profile. The syntheses and the structure-activity relationships of these compounds are reported herein. A reduced derivative, 14, had high affinity for sigma-1 and serotonin 5HT2 receptors as well as excellent oral activity in some animal antipsychotic models. Furthermore, compound 14 failed to cause catalepsy in the rat up to 90 mg/kg (po).

Occupancy of central neurotransmitter receptors by risperidone, clozapine and haloperidol, measured ex vivo by quantitative autoradiography

Risperidone (Risperdal) is a novel antipsychotic drug, with beneficial effects on both positive and negative symptoms of schizophrenia, and with a low incidence of extrapyramidal side effects (EPS). These particular properties have been attributed to the predominant and very potent serotonin 5-HT2 receptor antagonism of the drug combined with less potent dopamine D2 antagonism. In order to provide data on the degree to which various central neurotransmitter receptors are occupied in vivo, we performed ex vivo receptor occupancy studies with risperidone in comparison with clozapine and haloperidol in rats and guinea pigs. Various types of receptors, to which the compounds were known to bind to in vitro, were investigated precisely using receptor autoradiography in sections of the same rat brain except for histamine H1 receptors that were measured in the guinea-pig cerebellum. Risperidone (2 h after s.c. treatment) occupied 5-HT2 receptors at very low doses (ED50 = 0.067 mg/kg). Nearly full occupancy (> 80%) was achieved before H1, D2, alpha 1 and alpha 2 receptors became occupied (ED50 = 0.45, 0.66, 0.75 and 3.7 mg/kg, respectively). Clozapine displayed occupancy of H1 and alpha 1 receptors at low doses (ED50 = 0.15 and 0.58 mg/kg, respectively) and of 5-HT2, 5-HT1C, D2, alpha 2, cholinergic muscarinic and 5-HT1A receptors at higher doses (ED50 = 1.3, 1.8, 9.0, 9.5, 11 and 15 mg/kg, respectively). Haloperidol occupied D2 and alpha 1 receptors at low doses (ED50 = 0.13 and 0.42 mg/kg, respectively) and 5-HT2 receptors at a higher dose (ED50 = 2.6 mg/kg). Occupancy of receptor types occurred with similar ED50-values in various brain areas, e.g. D2 receptors in striatum and mesolimbic areas. The ED50-values for the ex vivo measured occupancy of 5-HT2 and D2 receptors were in good agreement with ED50-values for functional effects putatively mediated by these central receptors. The dose-dependent occupancy of D2 receptors proceeded more gradually with risperidone (slope in the caudate-putamen: 0.85) than with clozapine (slope: 1.44) or haloperidol (slope: 1.51). It has previously been suggested that partial D2 receptor occupancy may suffice to control the positive symptoms of schizophrenia, whereas higher D2 receptor occupancy would induce extrapyramidal symptoms (EPS). The dose ratio for high (75%) vs. low (25%) D2 receptor occupancy in the caudate-putamen, was 37.3 for risperidone, 8.4 for clozapine, and 7.9 for haloperidol.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of mescaline and some of its analogs on cholinergic neuromuscular transmission

Mescaline (3,4,5-trimethoxyphenylethylamine; MES) and its analogs, anhalinine (ANH) and methylenemescaline trimer (MMT) were investigated, using sciatic-sartorius preparations of the frog and cortical tissue from the rat. The effects of MES and its analogs were examined with respect to muscle twitch, resting membrane potential and nicotinic receptor binding. Mescaline and its analogs (10-100 microM) blocked both directly and neurally evoked twitches but their effects on neurally evoked twitches were greater than those on directly evoked twitches. Mescaline, ANH and MMT decreased amplitude of the miniature endplate and endplate potentials, decreased acetylcholine (ACh) quantal content, hyperpolarized the resting membrane potential and prolonged duration of the action potential. They did not significantly displace the binding of [125I]-alpha-bungarotoxin (alpha-BTX) to nicotinic receptors, at concentrations which blocked neuromuscular transmission. These results suggest that MES and its analogs inhibit cholinergic neuromuscular transmission by blocking release of ACh; they also affect K+ conductance.

DuP 734 [1-(cyclopropylmethyl)-4-(2'(4''-fluorophenyl)-2'- oxoethyl)piperidine HBr], a potential antipsychotic agent: preclinical behavioral effects

It has been suggested that sigma receptors may be involved in the etiology of psychosis and that 5-hydroxytryptamine2 (5-HT2) antagonists may have utility in treating the negative symptoms of psychosis as well as reducing the side effects associated with the typical antipsychotic haloperidol. We have evaluated the potential antipsychotic effects of 1-(cyclopropylmethyl)-4-(2'(4''-fluorophenyl)-2'-oxoethyl)piper i din e HBr (DuP 734), a selective and potent sigma and 5-HT2 receptor ligand with weak affinity for D2 receptors, in behavioral animal models that are not necessarily dependent on dopamine antagonism. DuP 734 potently blocked mescaline-induced scratching (ED50 = 0.35 mg/kg, p.o.) and aggressive activity (ED50 = 1.9 mg/kg, p.o.) and was relatively much weaker as an apomorphine antagonist (ED50 = 12 mg/kg, p.o.). This was in contrast to the typical antipsychotic agents such as haloperidol and chlorpromazine, which were very potent in all three tests. In rats, DuP 734 did not antagonize avoidance behavior or induce catalepsy, and, therefore, differed from the potent dopamine receptor antagonist antipsychotics. It did, however, reduce lever response rates in a random interval 60-sec food reward schedule of reinforcement (ED50 = 6.0 mg/kg, p.o.) in rats. The results suggest that DuP 734 may have antipsychotic activity without the liability of motor side effects typical of neuroleptics. Although DuP 734 itself did not antagonize avoidance activity, it significantly enhanced the potency of haloperidol in blocking avoidance behavior by 3-fold (by shifting the ED50 from 0.94 to 0.36 mg/kg, p.o.), whereas the ED50 of haloperidol for blockade of escape behavior and induction of catalepsy was not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Nootropic candidates inhibit head-twitches induced by mescaline in mice

The effects of various nootropic candidates on mescaline-induced head-twitches were studied in mice. The number of head-twitches induced by mescaline (100 mg/kg, s.c.) was significantly reduced by idebenone (32 and 100 mg/kg, i.p.), minaprine (0.32-10 mg/kg, p.o.) and nebracetam (100 mg/kg, p.o.). Cholinesterase inhibitors such as tetrahydroaminoacridine (1 and 10 mg/kg, p.o.), NIK-247 (10 and 18 mg/kg, p.o.) and physostigmine (0.32 mg/kg, i.p.) also suppressed the head-twitch response to mescaline. These results suggest that the direct or indirect cholinergic-activating effects of these drugs may be involved in inhibiting mescaline-induced head-twitches.

Naphthosultam derivatives: a new class of potent and selective 5-HT2 antagonists

A series of 2-(aminoalkyl)naphth[1,8-cd]isothiazole 1,1-dioxides was synthesized and examined in various receptor binding tests. Most compounds demonstrated high affinity for the 5-HT2 receptor with moderate to high selectivity. A member of this series, compound 24 (RP 62203), displays high 5-HT2 receptor affinity (Ki = 0.26 nM), which is respectively more than 100 and 1000 times higher than its affinity for alpha 1 (Ki = 38 nM) and D2 (Ki greater than 1000 nM) receptors. This compound is a potent orally effective and long lasting 5-HT2 antagonist in the mescaline-induced head-twitches test in mice and rats.

Lysergic acid diethylamide (LSD) administration selectively downregulates serotonin2 receptors in rat brain

A dosage regimen of lysergic acid diethylamide (LSD) that reliably produces behavioral tolerance in rats was evaluated for effects on neurotransmitter receptor binding in rat brain using a variety of radioligands selective for amine receptor subtypes. Daily administration of LSD [130 micrograms/kg (0.27 mumol/kg) intraperitoneally (IP)] for 5 days produced a decrease in serotonin2 (5-hydroxytryptamine2, 5-HT2) binding in cortex (measured 24 hours after the last drug administration) but did not affect binding to other receptor systems (5-HT1A, 5-HT1B, beta-adrenergic, alpha 1- or alpha 2-adrenergic, D2-dopaminergic) or to a recognition site for 5-HT uptake. The decrease was evident within 3 days of LSD administration but was not demonstrable after the first LSD dose. Following 5 days of LSD administration the decrease was still present 48 hours, but not 96 hours, after the last administration. The indole hallucinogen psilocybin [1.0 mg/kg (3.5 mumol/kg) for 8 days] also produced a significant decrease in 5HT2 binding, but neither the nonhallucinogenic analog bromo-LSD [1.3 mg/kg (2.4 mumol/kg) for 5 days] nor mescaline [10 mg/kg (40.3 mumol/kg) for 5 or 10 days] affected 5-HT2 binding. These observations suggest that LSD and other indole hallucinogens may act as 5-HT2 agonists at postsynaptic 5-HT2 receptors. Decreased 5-HT2 binding strikingly parallels the development and loss of behavioral tolerance seen with repeated LSD administration, but the decreased binding per se cannot explain the gamut of behavioral tolerance and cross-tolerance phenomena among the indole and phenylethylamine hallucinogens.

5HT-2 mediation of acute behavioral effects of hallucinogens in rats

In rats tested during their first exposure to a Behavioral Pattern Monitor chamber, acute injections of the 5HT-2 agonists mescaline, quipazine, 2,5-dimethoxy-4-iodoamphetamine (DOI), 2,5-dimethoxy-4-methylamphetamine (DOM), or 2,5-dimethoxy-4-ethylamphetamine (DOET) produced an inhibition of locomotor and investigatory behavior during the first 30 min of the test session. This suppression of exploratory behavior was attenuated when rats were familiarized with the testing chamber prior to the administration of DOI. Hence, as previously observed with both LSD and DOM, 5HT-2 agonists appear to potentiate the normal neophobic reaction to a novel environment. The mixed 5HT-1 and 5HT-2 agonist 5-methoxy-N,N-dimethyltryptamine (5MeODMT) also produced a decrease in activity when animals were tested in the novel environment. However, as previously found with 5HT-1A agonists, this effect was unchanged when animals were tested in the familiar environment and may therefore reflect a generalized sedation. The receptor specificity of these differential effects of 5HT-1 and 5HT-2 agonists in this paradigm was tested by assessing the ability of selective 5HT-2 antagonists to block the effects of the agonists. A dose of the 5HT-2 antagonist ketanserin which had no effect by itself significantly reduced the behavioral effects of mescaline, DOM, and quipazine. Similarly, the selective 5HT-2 antagonist ritanserin blocked the effect of quipazine. In contrast, ketanserin had no significant effect on the suppression of activity produced by the 5HT-1A agonist 8-hydroxy-2(di-n-propylamino)tetralin (8OHDPAT).(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of 5-HT receptor subtypes in the discriminative stimulus properties of mescaline

In order to further evaluate the extent to which particular 5-HT receptor subtypes (5-HT1, 5-HT2) might be involved in the behavioral effects of hallucinogenic drugs, rats were trained to discriminate mescaline (10 mg/kg i.p.) from saline and were given substitution (generalization) and combination (antagonism) tests with putatively selective serotonergic and related neuroactive compounds. The mescaline cue generalized to relatively high doses of the 5-HT2 agonists, 2,5-dimethoxy-4-methylamphetamine (DOM), LSD and psilocybin; the extent of generalization to 5-HT1 agonists (8-hydroxy-2-[diethylamino]tetralin (8-OHDPAT), RU-24969 and 8-hydroxy-2-[di-n-propylamino]tetralin (TFMPP] was unclear. Combinations of the training drug and sufficiently high doses of 5-HT2 antagonists (ketanserin, LY-53857, pirenperone) were followed by saline-lever responding; less selective central 5-HT (metergoline), and DA (SCH-23390, haloperidol) antagonists, did not block the mescaline cue. These data suggest that 5-HT2 receptors are involved in the stimulus properties of mescaline.

Effects of intraocular mescaline and LSD on visual-evoked responses in the rat

The effects of mescaline and LSD on the flash-evoked cortical potential (FEP) were determined in unrestrained rats with chronically-implanted electrodes. Systemic administration of mescaline or LSD significantly attenuated the primary component of the FEP at three stimulus intensities with the greatest effect observed 60-90 minutes following drug administration. The magnitude and specificity of the effects of these agents on the primary response suggest that they produce deficits in conduction through the retino-geniculato-cortical system. The serotonin receptor antagonists, cyproheptadine and methysergide, antagonized the mescaline-induced depression of the FEP in accordance with neurochemical and behavioral evidence that mescaline acts as a partial agonist on serotonin receptors. Topical or intraocular administration of atropine antagonized the actions of systemically-administered mescaline. In addition, intraocular administration of mescaline or LSD attenuated the FEP indicative of an action of these hallucinogens on visual processing in the retina which is modulated by muscarinic receptor activity.

LSD and other related hallucinogens elicit myoclonic jumping behavior in the guinea pig

1. We evaluated the behavioral response of guinea pigs to hallucinogenic agents in order to characterize the response of this species to a variety of known hallucinogenic drugs. 2. The systemic injection of LSD in the guinea pig elicited a "myoclonic-like" response the frequency of which was dose-dependent. This behavior exhibited rapid tolerance which was more prominent at higher doses. 3. Subacute mescaline pretreatment reduced the myoclonic response to LSD suggesting cross-tolerance. 4. Mescaline, DOM, TMA, DMA and 5 Me-ODMT also elicited myoclonus in a dose-dependent manner and in potency ratios which approximate the human experience for hallucinogenic activity. 5. Brom-LSD failed to induce myoclonus. 6. Since the myoclonic response of the guinea pig shares a number of pharmacologic characteristics with the human hallucinogenic event, this species may be useful in the study of hallucinogenic compounds.

Behavioral and electroencephalographic effects of zopiclone, a cyclopyrrolone derivative

Behavioral effects of zopiclone were investigated in mice and rats and compared with the data on diazepam, nitrazepam and flurazepam. The electroencephalographic effect of the drug was also examined in unanesthetized rabbits with chronic electrode implants and compared with that of diazepam. The present results indicate that zopiclone possesses pharmacological properties qualitatively similar to benzodiazepines, which are characterized by potent anticonflict and antiaggressive effects and much weaker anticonvulsant, muscle relaxant, ataxiogenic, sedative and anesthesia potentiating effects; the properties of this drug were compared with those of diazepam, nitrazepam and flurazepam. Zopiclone suppressed the EEG arousal responses and inhibited afterdischarges induced by electrical stimulation of the hippocampus and amygdala. The effects of zopiclone on EEG and afterdischarges were approximately 1/10 those of diazepam.

Specific antagonists of the acute behavioral response to centrally-administered vasopressin in mice

Vasopressin and related peptides cause behavioral excitation after intracerebroventricular injection in mice. This behavioral excitation is characterized by excessive scratching and grooming behavior in the unrestrained animal and enhanced escape-directed activity in stressful situations. These effects of vasopressin were found to be blocked by the administration of analogs which act as competitive antagonists of the pressor-activity of vasopressin. The potencies of these analogs in suppressing the behavioral effect paralleled the pressor antagonist potencies. The antagonists did not cause the characteristic behavioral alterations by themselves, nor did they block grooming and/or scratching behavior induced by the structurally-unrelated substances, mescaline, bombesin and substance P. It is suggested that these antagonists provide useful tools for studying the role of endogenous vasopressin in behavior.

Mescaline: excitatory effects on acoustic startle are blocked by serotonin2 antagonists

The ability of serotonin2 (5-HT2) antagonists to block the excitatory effects of mescaline on the acoustic startle reflex were analyzed. Mescaline (20 mg/kg) caused a consistent increase in the amplitude of the acoustic startle reflex. This effect was blocked in a dose-related fashion by the 5-HT2 antagonist ritanserin (ED50 dose = 0.25 mg/kg IP). In contrast, even a high dose of ritanserin (2.0 mg/kg) did not block the excitatory effects of amphetamine on startle. Other 5-HT2 antagonists (ketanserin, cinanserin, LY 53857) also blocked mescaline's effect, whereas the 5-HT1 antagonist pindolol (5 mg/kg) did not. These results support the hypothesis that the behavioral effects of hallucinogens are mediated by agonist actions at 5-HT2 receptors.

Comparison of stimulants and hallucinogens on shuttle avoidance in rats

Rats were trained to a high level of performance of a conditioned avoidance response in a shuttlebox to test effects of several classical stimulants in comparison to a variety of hallucinogens. A previously-reported biphasic pattern of effects of mescaline on shuttle avoidance was replicated and extended to 12 other hallucinogens of both phenylethylamine and indolealkylamine classes. Response patterns of hallucinogens could be differentiated from 3 stimulants and from a methoxyamphetamine compound that lacks hallucinogenic activity.

Effect of hallucinogens on spontaneous and sensory-evoked locus coeruleus unit activity in the rat: reversal by selective 5-HT2 antagonists

As previously reported, systemic administration of the hallucinogens D-lysergic acid diethylamide (LSD) (5-10 micrograms/kg) and mescaline (2 mg/kg) in the anesthetized rat produced a decrease in spontaneous activity but, paradoxically, facilitated activation of locus coeruleus (LC) neurons by sciatic nerve stimulation. In the present study, the hallucinogen 2,5-dimethoxy-4-methylamphetamine (DOM) (20-80 micrograms/kg) was found to have similar effects. Systemic administration of the selective 5-HT2 antagonists LY 53857 (0.02-0.8 mg/kg) and ritanserin (0.1-0.3 mg/kg) completely reversed both actions of the hallucinogens on the LC. In contrast, LY 53857 did not reverse the effects of (+)-amphetamine (0.5 mg/kg) on the spontaneous or sensory-evoked activity of the LC. These results suggest that the common actions of indoleamine and phenethylamine hallucinogens displayed in the LC are mediated via 5-HT2 receptors; however, these receptors appear to be located outside the LC itself.

Mescaline-induced motor impairment in rats, assessed by two different methods

Motor impairment, especially ataxia, is often mentioned as a 'side effect' of doses of psychoactive drugs which depress animal behaviour; it is difficult to determine it accurately from visual observation, but relatively few attempts have been made to measure it objectively and quantitatively. Mescaline, in moderate to large doses, can induce biphasic--depressant followed by stimulant--effects on learnt and other performance of laboratory rodents. Motor impairment, using three doses, was accordingly measured during the depressant phase by two methods. An 'ataxia' test, involving analyses of footprints, showed few irregularities of gait splay due to mescaline, but the drug markedly reduced the length of steps ('stride') in a dose-related manner. In a 'tilt plane' test for general motor control, the animals' ability to cling to a tilted plane decreased with 25 mg/kg mescaline, at 30 and 40 minutes after administration. Deficits of this kind can be relevant to interpreting drug actions on forms of behaviour which involve movements for responding, and they also have interesting potential in their own right.

Direct comparison of hallucinogenic phenethylamines and D-amphetamine on dorsal raphe neurons

We compared the effects of the hallucinogens 2,5-dimethoxy-4-methylamphetamine (DOM), mescaline and the simulant D-amphetamine, applied by microiontophoresis to rat dorsal raphe (DR) units. DR neuron firing rate was relatively insensitive to DOM and unaffected by mescaline, but was clearly inhibited by D-amphetamine. Intravenous DOM usually inhibited, but this effect was correlated with blood pressure changes; i.v. D-amphetamine produced inconsistent responses. These results suggest that most of the effects seen on i.v. administration of phenethylamines are not mediated directly on the serotonergic cell.

Studies of the relationship between molecular structure and hallucinogenic activity

The nature of the stereochemistry and aromatic ring substituents and their importance to biological activity for phenethylamine-type hallucinogens is presented. The possibility of a hydrophobic site to bind to the 4-substituent and its likely geometry is described. A brief discussion of the structure-activity relationships for tryptamines such as psilocin and DMT is also given, with comments about the stereochemistry of alpha-methyltryptamines. Evaluation of a series of N(6)-alkyl-nor-LSD derivatives indicated that selected members such as N(6)-ethyl, allyl and propyl were as potent as, if not more potent than LSD, both in a two-lever drug discrimination assay in rats, and in man. N(6)-alkyl groups longer than n-propyl, such as n-butyl or 2-phenethyl, gave compounds that were greatly reduced in activity.

A primate model for the study of hallucinogens

An animal model for studying the actions of hallucinogenic drugs using primate social colonies is presented. Although hallucinogens induce a number of behavioral changes in this paradigm, one emergent behavior, limb jerks, appears to be selectively induced by three classes of hallucinogens in doses which correlate with those reported to be hallucinogenic in humans. Several non-hallucinogenic congeners of hallucinogens failed to significantly elicit this response. Other behavioral changes induced by hallucinogens in monkeys such as ptosis and social withdrawal may be useful in studying aspects of hallucinogen intoxication other than hallucinations, or psychosis in general. Upon daily administration, tolerance developed to all hallucinogens tested except two, as is seen in humans. Moreover, cross-tolerance between hallucinogens could be demonstrated. Further experiments with the hallucinogen 5-methoxy N,N-dimethyltryptamine revealed that although certain individual behaviors could be antagonized by serotonin antagonists, dopamine antagonists, and physostigmine, no drug completely reversed the behavioral abnormalities induced by this hallucinogen. It is suggested that this paradigm, which offers an hallucinogen-induced behavior which correlates well with the human hallucinogen response and permits observation of a wide variety of other potentially relevant behaviors in primates, may be useful in developing and testing theories of hallucinogenic drug action. It may be especially valuable in view of the present difficulties of conducting hallucinogen research in humans.

Effects of hallucinogenic drugs on serotonergic neuronal systems

Studies indicate that hallucinogens markedly suppress the discharge of serotonin containing neurons in the dorsal raphe nucleus. Forebrain neurons receiving a major serotonergic input are relatively insensitive to hallucinogens. These actions of hallucinogens are not sufficient to explain the psychoactive effects of these drugs. Evidence is presented to indicate that hallucinogens sensitize serotonin and norepinephrine receptors in the facial nucleus. This receptor sensitizing effect is common to all, and specific for, hallucinogens. It is suggested that a mechanism of receptor sensitization might account for the altered perceptual reactivity produced by hallucinogens.

Action of a chronic administration of mescaline in dynamic behavioural situations

The modifications of the rat behaviour caused by a chronic administration of mescaline were studied in two schedules of operant conditioning. In the "periodic conditioning" test, the schedule of reinforcement was changed from a fixed ratio to a fixed interval schedule. Mescaline (4 mg/kg/day and 10 mg/kg/day) caused no modification of the ability of the rat to adapt its behaviour to the new experimental situation. In the "reversal test" the contingency for food delivery was switched from one lever, where responses were previously reinforced to the other lever where responses had no programmed consequences. A chronic administration of mescaline (4 mg/kg/day) caused a total incapacity of the rat to switch to the lever which became reinforced in the reversal trial. A chronic administration of 9 mg/kg/day of mescaline had an excitatory effect and the number of reinforced responses in the II and III reversals exceeded the unreinforced responses in a measure greater than in the controls.

Mescaline action on "memory decay" and "problem solving" behavior in the rat

The modifications of behavior caused in the rat by a chronic oral administration of mescaline have been studied in three experimental situations. In the staircase maze mescaline accelerated the spontaneous decay on the conditioned reflex (memory decay) during the period without daily training. Only the results observed at 30 mg/kg/day of mescaline were statistically significant. In a T maze two lateral alleys closed by two swinging doors, 30 mg/kg/day of mescaline increased the time spent in opening the first door. When the two doors of the lateral alleys were closed with a latch, mescaline 30 mg/kg/day, caused an increase in the time spent by the rat in opening the doors. Mescaline caused an increase in food consumption. The increase at 30 mg/kg/day is statistically significant.