Correlation between the potency of hallucinogens in the mouse head-twitch response assay and their behavioral and subjective effects in other species

Serotonergic hallucinogens such as lysergic acid diethylamide (LSD) induce head twitches in rodents via 5-HT_2A receptor activation. The goal of the present investigation was to determine whether a correlation exists between the potency of hallucinogens in the mouse head-twitch response (HTR) paradigm and their reported potencies in other species, specifically rats and humans. Dose-response experiments were conducted with phenylalkylamine and tryptamine hallucinogens in C57BL/6J mice, enlarging the available pool of HTR potency data to 41 total compounds. For agents where human data are available (n = 36), a strong positive correlation (r = 0.9448) was found between HTR potencies in mice and reported hallucinogenic potencies in humans. HTR potencies were also found to be correlated with published drug discrimination ED₅₀ values for substitution in rats trained with either LSD (r = 0.9484, n = 16) or 2,5-dimethoxy-4-methylamphetamine (r = 0.9564, n = 21). All three of these behavioral effects (HTR in mice, hallucinogen discriminative stimulus effects in rats, and psychedelic effects in humans) have been linked to 5-HT_2A receptor activation. We present evidence that hallucinogens induce these three effects with remarkably consistent potencies. In addition to having high construct validity, the HTR assay also appears to show significant predictive validity, confirming its translational relevance for predicting subjective potency of hallucinogens in humans. These findings support the use of the HTR paradigm as a preclinical model of hallucinogen psychopharmacology and in structure-activity relationship studies of hallucinogens. Future investigations with a larger number of test agents will evaluate whether the HTR assay can be used to predict the hallucinogenic potency of 5-HT_2A agonists in humans. "This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

DARK Classics in Chemical Neuroscience: NBOMes

N-Benzylphenethylamines, commonly known as NBOMes, are synthetic psychedelic compounds derived from the phenethylamine class of psychedelics (2C-X compounds), which originally have been derived from the naturally occurring alkaloid mescaline. Analogously to their parent compounds and other classical psychedelics, such as psilocybin and lysergic acid diethylamide (LSD), NBOMes are believed to exert their main pharmacological effects through activation of serotonin 2A (5-HT_2A) receptors. Since their introduction as New Psychoactive Substances (NPSs) in 2010, NBOMes have been widely used for recreational purposes; this has resulted in numerous cases of acute toxicity, sometimes with lethal outcomes, leading to the classification of several NBOMes as Schedule I substances in 2013. However, in addition to their recreational use, the NBOMe class has yielded several important biochemical tools, including [¹¹C]Cimbi-36, which is now being used in positron emission tomography (PET) studies of the 5-HT_2A and 5-HT_2C receptors in the mammalian brain, and 25CN-NBOH, one of the most selective 5-HT_2A receptor agonists developed to date. In this Review, the history, chemistry, structure-activity relationships, ADME (absorption, distribution, metabolism, and excretion) properties, and safety profiles of NBOMes will be outlined and discussed.

Pharmacological characterizations of the 'legal high' fluorolintane and isomers

1,2-Diarylethylamines represent a class of molecules that have shown potential in the treatment of pain, epilepsy, neurodegenerative disease and depression. Examples include lefetamine, remacemide, and lanicemine. Recently, several 1,2-diarylethylamines including the dissociatives diphenidine, methoxphenidine and ephenidine as well as the opioid MT-45, have appeared as 'research chemicals' or 'legal highs'. Due to their recent emergence little is known about their pharmacology. One of these, 1-[1-(2-fluorophenyl)-2-phenylethyl]pyrrolidine (fluorolintane, 2-F-DPPy), is available for purchase with purported dissociative effects intended to resemble phencyclidine (PCP) and ketamine. To better understand this emerging class, pharmacological investigations were undertaken for the first time on fluorolintane and its five aryl-fluorine-substituted isomers. In vitro binding studies revealed high affinity for N-methyl-D-aspartate (NMDA) receptors with fluorolintane (K_i = 87.92 nM) with lesser affinities for related compounds. Additional affinities were seen for all compounds at several sites including norepinephrine (NET), serotonin (SERT) and dopamine (DAT) transporters, and sigma receptors. Notably high affinities at DAT were observed, which were in most cases greater than NMDA receptor affinities. Additional functional and behavioral experiments show fluorolintane inhibited NMDA receptor-induced field excitatory postsynaptic potentials in rat hippocampal slices and inhibited long-term potentiation induced by theta-burst stimulation in rat hippocampal slices with potencies consistent with its NMDA receptor antagonism. Finally fluorolintane inhibited prepulse inhibition in rats, a measure of sensorimotor gating, with a median effective dose (ED₅₀) of 13.3 mg/kg. These findings are consistent with anecdotal reports of dissociative effects of fluorolintane in humans.

Return of the lysergamides. Part V: Analytical and behavioural characterization of 1-butanoyl-d-lysergic acid diethylamide (1B-LSD)

The psychedelic properties of lysergic acid diethylamide (LSD) have captured the imagination of researchers for many years and its rediscovery as an important research tool is evidenced by its clinical use within neuroscientific and therapeutic settings. At the same time, a number of novel LSD analogs have recently emerged as recreational drugs, which makes it necessary to study their analytical and pharmacological properties. One recent addition to this series of LSD analogs is 1-butanoyl-LSD (1B-LSD), a constitutional isomer of 1-propanoyl-6-ethyl-6-nor-lysergic acid diethylamide (1P-ETH-LAD), another LSD analog that was described previously. This study presents a comprehensive analytical characterization of 1B-LSD employing nuclear magnetic resonance spectroscopy (NMR), low- and high-resolution mass spectrometry platforms, gas- and liquid chromatography (GC and LC), and GC-condensed phase and attenuated total reflection infrared spectroscopy analyses. Analytical differentiation of 1B-LSD from 1P-ETH-LAD was straightforward. LSD and other serotonergic hallucinogens induce the head-twitch response (HTR) in rats and mice, which is believed to be mediated largely by 5-HT_2A receptor activation. HTR studies were conducted in C57BL/6J mice to assess whether 1B-LSD has LSD-like behavioral effects. 1B-LSD produced a dose-dependent increase in HTR counts, acting with ~14% (ED₅₀  = 976.7 nmol/kg) of the potency of LSD (ED₅₀  = 132.8 nmol/kg). This finding suggests that the behavioral effects of 1B-LSD are reminiscent of LSD and other serotonergic hallucinogens. The possibility exists that 1B-LSD serves as a pro-drug for LSD. Further investigations are warranted to confirm whether 1B-LSD produces LSD-like psychoactive effects in humans.

2-Aminoindan and its ring-substituted derivatives interact with plasma membrane monoamine transporters and α2-adrenergic receptors

RATIONALE

Over the last decade, many new psychostimulant analogues have appeared on the recreational drug market and most are derivatives of amphetamine or cathinone. Another class of designer drugs is derived from the 2-aminoindan structural template. Several members of this class, including the parent compound 2-aminoindan (2-AI), have been sold as designer drugs. Another aminoindan derivative, 5-methoxy-2-aminoindan (5-MeO-AI or MEAI), is the active ingredient in a product marketed online as an alcohol substitute.

METHODS

Here, we tested 2-AI and its ring-substituted derivatives 5-MeO-AI, 5-methoxy-6-methyl-2-aminoindan (MMAI), and 5,6-methylenedioxy-2-aminoindan (MDAI) for their abilities to interact with plasma membrane monoamine transporters for dopamine (DAT), norepinephrine (NET) and serotonin (SERT). We also compared the binding affinities of the aminoindans at 29 receptor and transporter binding sites.

RESULTS

2-AI was a selective substrate for NET and DAT. Ring substitution increased potency at SERT while reducing potency at DAT and NET. MDAI was moderately selective for SERT and NET, with tenfold weaker effects on DAT. 5-MeO-AI exhibited some selectivity for SERT, having sixfold lower potency at NET and 20-fold lower potency at DAT. MMAI was highly selective for SERT, with 100-fold lower potency at NET and DAT. The aminoindans had relatively high affinity for α₂-adrenoceptor subtypes. 2-AI had particularly high affinity for α_2C receptors (K_i = 41 nM) and slightly lower affinity for the α_2A (K_i = 134 nM) and α_2B (K_i = 211 nM) subtypes. 5-MeO-AI and MMAI also had moderate affinity for the 5-HT_2B receptor.

CONCLUSIONS

2-AI is predicted to have (+)-amphetamine-like effects and abuse potential whereas the ring-substituted derivatives may produce 3,4-methylenedioxymethamphetamine (MDMA)-like effects but with less abuse liability.

Comparison of the behavioral effects of mescaline analogs using the head twitch response in mice

BACKGROUND

In recent years, there has been increasing scientific interest in the effects and pharmacology of serotonergic hallucinogens. While a large amount of experimental work has been conducted to characterize the behavioral response to hallucinogens in rodents, there has been little systematic investigation of mescaline and its analogs. The hallucinogenic potency of mescaline is increased by α-methylation and by homologation of the 4-methoxy group but it not clear whether these structural modifications have similar effects on the activity of mescaline in rodent models.

METHODS

In the present study, the head twitch response (HTR), a 5-HT_2A receptor-mediated behavior induced by serotonergic hallucinogens, was used to assess the effects of mescaline and several analogs in C57BL/6J mice. HTR experiments were conducted with mescaline, escaline (4-ethoxy-3,5-dimethoxyphenylethylamine) and proscaline (3,5-dimethoxy-4-propoxyphenylethylamine), their α-methyl homologs TMA (3,4,5-trimethoxyamphetamine), 3C-E (4-ethoxy-3,5-dimethoxyamphetamine) and 3C-P (3,5-dimethoxy-4-propoxyamphetamine), and the 2,4,5-substituted regioisomers TMA-2 (2,4,5-trimethoxyamphetamine), MEM (4-ethoxy-2,5-dimethoxyamphetamine) and MPM (2,5-dimethoxy-4-propoxyamphetamine).

RESULTS

TMA induced the HTR and was twice as potent as mescaline. For both mescaline and TMA, replacing the 4-methoxy substituent with an ethoxy or propoxy group increased potency in the HTR assay. By contrast, although TMA-2 also induced the HTR with twice the potency of mescaline, potency was not altered by homologation of the 4-alkoxy group in TMA-2.

CONCLUSIONS

The potency relationships for these compounds in mice closely parallel the human hallucinogenic data. These findings are consistent with evidence that 2,4,5- and 3,4,5-substituted phenylalkylamine hallucinogens exhibit distinct structure-activity relationships. These results provide additional evidence that the HTR assay can be used to investigate the structure-activity relationships of serotonergic hallucinogens.

Pharmacological characterization of the LSD analog N-ethyl-N-cyclopropyl lysergamide (ECPLA)

RATIONALE

The lysergamide lysergic acid diethylamide (LSD) is a prototypical classical hallucinogen with remarkably high potency. LSD remains a popular recreational drug but is also becoming an important research tool for medical and neuroscience studies. Recently, several lysergamides that are close structural analogs of LSD have been sold as recreational drugs, which suggests that further studies are needed to explore the pharmacological properties of these compounds.

OBJECTIVE

In this present investigation, another LSD congener, N-ethyl-N-cyclopropyl lysergamide (ECPLA), which to date has not been marketed as a recreational substance, was evaluated for its pharmacological features relative to those previously reported for LSD. The experiments focused on interactions with the 5-HT_2A receptor, which is responsible for mediating the psychedelic effects of LSD and other hallucinogens.

METHODS

Competitive binding assays were performed to measure the affinity of ECPLA for 27 monoamine receptors. The ability of ECPLA to activate human 5-HT₂ receptor subtypes was assessed using calcium mobilization assays. Head twitch response (HTR) studies were conducted in C57BL/6J mice to determine whether ECPLA activates 5-HT_2A receptors in vivo. Two other N-alkyl substituted lysergamides, N-methyl-N-isopropyl lysergamide (MIPLA) and N-methyl-N-propyl lysergamide (LAMPA), were also tested in the HTR paradigm for comparative purposes.

RESULTS

ECPLA has high affinity for most serotonin receptors, α₂-adrenoceptors, and D₂-like dopamine receptors. Additionally, ECPLA was found to be a potent, highly efficacious 5-HT_2A agonist for Gq-mediated calcium flux. Treatment with ECPLA induced head twitches in mice with a median effective dose (ED₅₀) of 317.2 nmol/kg (IP), which is ~ 40% of the potency observed previously for LSD. LAMPA (ED₅₀ = 358.3 nmol/kg) was virtually equipotent with ECPLA in the HTR paradigm whereas MIPLA (ED₅₀ = 421.7 nmol/kg) was slightly less potent than ECPLA.

CONCLUSIONS

These findings demonstrate that the pharmacological properties of ECPLA, MIPLA, and LAMPA are reminiscent of LSD and other lysergamide hallucinogens.

Correction to: Pharmacological characterization of the LSD analog N-ethyl-N-cyclopropyl lysergamide (ECPLA)

The author of this article wanted to change the Acknowledgments section to: These studies were supported by an award from NIDA (R01 DA041336), as well as by the Veteran's Administration VISN 22 Mental Illness Research, Education, and Clinical Center. Receptor binding and functional data were generously.

Comparison of the behavioral responses induced by phenylalkylamine hallucinogens and their tetrahydrobenzodifuran ("FLY") and benzodifuran ("DragonFLY") analogs

In recent years, rigid analogs of phenylalkylamine hallucinogens have appeared as recreational drugs. Examples include 2-(8-bromo-2,3,6,7-tetrahydrobenzo[1,2-b:4,5-b']difuran-4-yl)ethan-1-amine (2C-B-FLY) and 1-(8-bromobenzo[1,2-b;4,5-b']difuran-4-yl)-2-aminopropane (Bromo-DragonFLY, DOB-DFLY). Although some rigid compounds such as DOB-DFLY reportedly have higher potency than their non-rigid counterparts, it is not clear whether the same is true for 2C-B-FLY and other tetrahydrobenzodifurans. In the present study, the head twitch response (HTR), a 5-HT2A receptor-mediated behavior induced by serotonergic hallucinogens, was used to assess the effects of 2,5-dimethoxy-4-bromoamphetamine (DOB) and its α-desmethyl homologue 2,5-dimethoxy-4-bromophenethylamine (2C-B), as well as their benzodifuranyl and tetrahydrobenzodifuranyl analogs, in C57BL/6J mice. DOB (ED50 = 0.75 μmol/kg) and 2C-B (ED50 = 2.43 μmol/kg) induced the HTR. The benzodifurans DOB-DFLY (ED50 = 0.20 μmol/kg) and 2C-B-DFLY (ED50 = 1.07 μmol/kg) had significantly higher potency than DOB and 2C-B, respectively. The tetrahydrobenzodifurans DOB-FLY (ED50 = 0.67 μmol/kg) and 2C-B-FLY (ED50 = 1.79 μmol/kg), by contrast, were approximately equipotent with their non-rigid counterparts. Three novel tetrahydrobenzodifurans (2C-I-FLY, 2C-E-FLY and 2C-EF-FLY) were also active in the HTR assay but had relatively low potency. In summary, the in vivo potency of 2,5-dimethoxyphenylalkylamines is enhanced when the 2- and 5-methoxy groups are incorporated into aromatic furan rings, whereas potency is not altered if the methoxy groups are incorporated into dihydrofuran rings. The potency relationships for these compounds in mice closely parallel the human hallucinogenic data. The high potency of DOB-DFLY is probably linked to the presence of two structural features (a benzodifuran nucleus and an α-methyl group) known to enhance the potency of phenylalkylamine hallucinogens.

Return of the lysergamides. Part IV: Analytical and pharmacological characterization of lysergic acid morpholide (LSM-775)

Lysergic acid diethylamide (LSD) is perhaps one of the best-known psychoactive substances and many structural modifications of this prototypical lysergamide have been investigated. Several lysergamides were recently encountered as 'research chemicals' or new psychoactive substances (NPS). Although lysergic acid morpholide (LSM-775) appeared on the NPS market in 2013, there is disagreement in the literature regarding the potency and psychoactive properties of LSM-775 in humans. The present investigation attempts to address the gap of information that exists regarding the analytical profile and pharmacological effects of LSM-775. A powdered sample of LSM-775 was characterized by X-ray crystallography, nuclear magnetic resonance spectroscopy (NMR), gas chromatography mass spectrometry (GC-MS), high mass accuracy electrospray MS/MS, high performance liquid chromatography (HPLC) diode array detection, HPLC quadrupole MS, and GC solid-state infrared analysis. Screening for receptor affinity and functional efficacy revealed that LSM-775 acts as a nonselective agonist at 5-HT1A and 5-HT2A receptors. Head twitch studies were conducted in C57BL/6J mice to determine whether LSM-775 activates 5-HT2A receptors and produces hallucinogen-like effects in vivo. LSM-775 did not induce the head twitch response unless 5-HT1A receptors were blocked by pretreatment with the antagonist WAY-100,635 (1 mg/kg, subcutaneous). These findings suggest that 5-HT1A activation by LSM-775 masks its ability to induce the head twitch response, which is potentially consistent with reports in the literature indicating that LSM-775 is only capable of producing weak LSD-like effects in humans.

Effect of Hallucinogens on Unconditioned Behavior

Because of the ethical and regulatory hurdles associated with human studies, much of what is known about the psychopharmacology of hallucinogens has been derived from animal models. However, developing reliable animal models has proven to be a challenging task due to the complexity and variability of hallucinogen effects in humans. This chapter focuses on three animal models that are frequently used to test the effects of hallucinogens on unconditioned behavior: head twitch response (HTR), prepulse inhibition of startle (PPI), and exploratory behavior. The HTR has demonstrated considerable utility in the neurochemical actions of hallucinogens. However, the latter two models have clearer conceptual bridges to human phenomenology. Consistent with the known mechanism of action of hallucinogens in humans, the behavioral effects of hallucinogens in rodents are mediated primarily by activation of 5-HT2A receptors. There is evidence, however, that other receptors may play secondary roles. The structure-activity relationships (SAR) of hallucinogens are reviewed in relation to each model, with a focus on the HTR in rats and mice.

Return of the lysergamides. Part III: Analytical characterization of N6 -ethyl-6-norlysergic acid diethylamide (ETH-LAD) and 1-propionyl ETH-LAD (1P-ETH-LAD)

The psychoactive properties of lysergic acid diethylamide (LSD) have fascinated scientists across disciplines and the exploration of other analogues and derivatives has been motivated by deepening the understanding of ligand-receptor interactions at the molecular level as well as by the search for new therapeutics. Several LSD congeners have appeared on the new psychoactive substances (NPS) market in the form of blotters or powders. Examples include 1-propionyl-LSD (1P-LSD), AL-LAD, and LSZ. The absence of analytical data for novel compounds is a frequent challenge encountered in clinical and toxicological investigations. Two newly emerging lysergamides, namely N6 -ethyl-6-norlysergic acid diethylamide (ETH-LAD) and 1P-ETH-LAD, were characterized by gas chromatography-mass spectrometry (GC-MS), low and high mass accuracy electrospray MS(/MS), GC solid-state infrared analysis, high performance liquid chromatography diode array detection as well as nuclear magnetic resonance spectroscopy. Limited analytical data for ETH-LAD were previously available, whereas information about 1P-ETH-LAD has not previously been encountered in the scientific literature. This study extends the characterization of lysergamides distributed on the NPS market, which will help to make analytical data available to clinicians, toxicologists, and other stakeholders who are likely to encounter these substances. The analysis of a test incubation of 1P-ETH-LAD with human serum at 37°C by LC single quadrupole MS at various time points (0-6 h, once per hour and one measurement after 24 h) revealed the formation of ETH-LAD, suggesting that 1P-ETH-LAD might serve as a pro-drug. 1P-ETH-LAD was still detectable in serum after 24 h. Copyright © 2017 John Wiley & Sons, Ltd.

Return of the lysergamides. Part II: Analytical and behavioural characterization of N6 -allyl-6-norlysergic acid diethylamide (AL-LAD) and (2'S,4'S)-lysergic acid 2,4-dimethylazetidide (LSZ)

Lysergic acid N,N-diethylamide (LSD) is perhaps one of the most intriguing psychoactive substances known and numerous analogs have been explored to varying extents in previous decades. In 2013, N6 -allyl-6-norlysergic acid diethylamide (AL-LAD) and (2'S,4'S)-lysergic acid 2,4-dimethylazetidide (LSZ) appeared on the 'research chemicals'/new psychoactive substances (NPS) market in both powdered and blotter form. This study reports the analytical characterization of powdered AL-LAD and LSZ tartrate samples and their semi-quantitative determination on blotter paper. Included in this study was the use of nuclear magnetic resonance (NMR) spectroscopy, gas chromatography-mass spectrometry (GC-MS), low and high mass accuracy electrospray MS(/MS), high performance liquid chromatography diode array detection and GC solid-state infrared analysis. One feature shared by serotonergic psychedelics, such as LSD, is the ability to mediate behavioural responses via activation of 5-HT2A receptors. Both AL-LAD and LSZ displayed LSD-like responses in male C57BL/6 J mice when employing the head-twitch response (HTR) assay. AL-LAD and LSZ produced nearly identical inverted-U-shaped dose-dependent effects, with the maximal responses occurring at 200 µg/kg. Analysis of the dose responses by nonlinear regression confirmed that LSZ (ED50  = 114.2 nmol/kg) was equipotent to LSD (ED50  = 132.8 nmol/kg) in mice, whereas AL-LAD was slightly less potent (ED50  = 174.9 nmol/kg). The extent to which a comparison in potency can be translated directly to humans requires further investigation. Chemical and pharmacological data obtained from NPS may assist research communities that are interested in various aspects related to substance use and forensic identification. Copyright © 2016 John Wiley & Sons, Ltd.

Pharmacology and Toxicology of N-Benzylphenethylamine ("NBOMe") Hallucinogens

Serotonergic hallucinogens induce profound changes in perception and cognition. The characteristic effects of hallucinogens are mediated by 5-HT2A receptor activation. One class of hallucinogens are 2,5-dimethoxy-substituted phenethylamines, such as the so-called 2C-X compounds 2,5-dimethoxy-4-bromophenethylamine (2C-B) and 2,5-dimethoxy-4-iodophenethylamine (2C-I). Addition of an N-benzyl group to phenethylamine hallucinogens produces a marked increase in 5-HT2A-binding affinity and hallucinogenic potency. N-benzylphenethylamines ("NBOMes") such as N-(2-methoxybenzyl)-2,5-dimethoxy-4-iodophenethylamine (25I-NBOMe) show subnanomolar affinity for the 5-HT2A receptor and are reportedly highly potent in humans. Several NBOMEs have been available from online vendors since 2010, resulting in numerous cases of toxicity and multiple fatalities. This chapter reviews the structure-activity relationships, behavioral pharmacology, metabolism, and toxicity of members of the NBOMe hallucinogen class. Based on a review of 51 cases of NBOMe toxicity reported in the literature, it appears that rhabdomyolysis is a relatively common complication of severe NBOMe toxicity, an effect that may be linked to NBOMe-induced seizures, hyperthermia, and vasoconstriction.

Premature responses in the five-choice serial reaction time task reflect rodents' temporal strategies: evidence from no-light and pharmacological challenges

RATIONALE

The five-choice serial reaction time task (5-CSRTT) is regularly used to study attention and impulsivity. In the 5-CSRTT, rodents initiate a trial, then after an inter-trial interval (ITI), a light appears in one of five holes. Responding in the lit vs. unlit hole reflects attention (accuracy), while responding prematurely before a light appears is suggested to reflect impulsivity/response disinhibition. Comparison of rat and mouse 5-CSRTT performance has raised questions on the validity of premature responses as measuring impulsivity/response inhibition. To minimize effort, rodents may use a temporal strategy, enabling their "timing" of the ITI, minimizing the need to attend during this delay. Greater reliance on this strategy could result in premature responses due to "guesses" if their timing was poor/altered.

OBJECTIVES

To assess the degree to which rats and/or mice utilize a temporal strategy, we challenged performance using infrequent no-light trials during 5-CSRTT performance.

RESULTS

Even when no light appeared when one was expected, rats responded ~60 % compared to ~40 % in mice, indicating a greater reliance on a temporal strategy by rats than by mice. Consistent with this hypothesis, rats made more premature responses than mice. Additional studies using a temporal discrimination task and a 5-CSRTT variant demonstrated that delta-9-tetrahydrocannabinol, the active ingredient in cannabis, slowed temporal perception and reduced premature responses.

CONCLUSIONS

These data provide behavioral and pharmacological evidence indicating that premature responses are heavily influenced by temporal perception. Hence, they may reflect an aspect of waiting impulsivity, but not response disinhibition, an important distinction for translational clinical research.

Return of the lysergamides. Part I: Analytical and behavioural characterization of 1-propionyl-d-lysergic acid diethylamide (1P-LSD)

1-Propionyl-d-lysergic acid diethylamide hemitartrate (1P-LSD) has become available as a 'research chemical' in the form of blotters and powdered material. This non-controlled derivative of d-lysergic acid diethylamide (LSD) has previously not been described in the published literature despite being closely related to 1-acetyl-LSD (ALD-52), which was developed in the 1950s. This study describes the characterization of 1P-LSD in comparison with LSD using various chromatographic and mass spectrometric methods, infrared and nuclear magnetic resonance spectroscopy. An important feature common to LSD and other serotonergic hallucinogens is that they produce 5-HT2A -receptor activation and induce the head-twitch response (HTR) in rats and mice. In order to assess whether 1P-LSD displays LSD-like properties and activates the 5-HT2A receptor, male C57BL/6 J mice were injected with vehicle (saline) or 1P-LSD (0.025-0.8 mg/kg, IP) and HTR assessed for 30 min using magnetometer coil recordings. It was found that 1P-LSD produced a dose-dependent increase in HTR counts, and that it had ~38% (ED50  = 349.6 nmol/kg) of the potency of LSD (ED50  = 132.8 nmol/kg). Furthermore, HTR was abolished when 1P-LSD administration followed pretreatment with the selective 5-HT2A receptor antagonist M100907 (0.1 mg/kg, SC), which was consistent with the concept that the behavioural response was mediated by activation of the 5-HT2A receptor. These results indicate that 1P-LSD produces LSD-like effects in mice, consistent with its classification as a serotonergic hallucinogen. Nevertheless, the extent to which 1P-LSD might show psychoactive effects in humans similar to LSD remains to be investigated. Copyright © 2015 John Wiley & Sons, Ltd.

Effects of the psychotomimetic benzomorphan N-allylnormetazocine (SKF 10,047) on prepulse inhibition of startle in mice

N-allylnormetazocine (NANM; SKF 10,047) is a benzomorphan opioid that produces psychotomimetic effects. (+)-NANM is the prototypical agonist for the sigma-1 (σ1) receptor, and there is a widespread belief that the hallucinogenic effects of NANM and other benzomorphan derivatives are mediated by interactions with σ1 sites. However, NANM is also an agonist at the κ opioid receptor (KOR) and binds to the PCP site located within the channel pore of the NMDA receptor, interactions that could potentially contribute to the effects of NANM. NMDA receptor antagonists such as phencyclidine (PCP) and ketamine are known to disrupt prepulse inhibition (PPI) of acoustic startle, a measure of sensorimotor gating, in rodents. We recently found that racemic NANM disrupts PPI in rats, but it is not clear whether the effect is mediated by blockade of the NMDA receptor, or alternatively whether interactions with KOR and σ1 receptors are involved. The present studies examined whether NANM and its stereoisomers alter PPI in C57BL/6J mice, and tested whether the effects on PPI are mediated by KOR or σ1 receptors. Racemic NANM produced a dose-dependent disruption of PPI (3-30mg/kg SC). (+)-NANM also disrupted PPI, whereas (-)-NANM was ineffective. Pretreatment with the selective KOR antagonist nor-binaltorphimine (10mg/kg SC) or the selective σ1 antagonist NE-100 (1mg/kg IP) failed to attenuate the reduction in PPI produced by racemic NANM. We also found that the selective KOR agonist (-)-U-50,488H (10-40mg/kg SC) had no effect on PPI. These findings confirm that NANM reduces sensorimotor gating in rodents, and indicate that the effect is mediated by interactions with the PCP receptor and not by activation of KOR or σ1 receptors. This observation is consistent with evidence indicating that the σ1 receptor is not linked to hallucinogenic or psychotomimetic effects.

Pharmacological Investigations of the Dissociative 'Legal Highs' Diphenidine, Methoxphenidine and Analogues

1,2-Diarylethylamines including lanicemine, lefetamine, and remacemide have clinical relevance in a range of therapeutic areas including pain management, epilepsy, neurodegenerative disease and depression. More recently 1,2-diarylethylamines have been sold as ‘legal highs’ in a number of different forms including powders and tablets. These compounds are sold to circumvent governmental legislation regulating psychoactive drugs. Examples include the opioid MT-45 and the dissociative agents diphenidine (DPH) and 2-methoxy-diphenidine (2-MXP). A number of fatal and non-fatal overdoses have been linked to abuse of these compounds. As with many ‘legal highs’, little is known about their pharmacology. To obtain a better understanding, the effects of DPH, 2-MXP and its 3- and 4-MeO- isomers, and 2-Cl-diphenidine (2-Cl-DPH) were investigated using binding studies at 46 central nervous system receptors including the N-methyl-D-aspartate receptor (NMDAR), serotonin, dopamine, norepinephrine, histamine, and sigma receptors as well as the reuptake transporters for serotonin, dopamine and norepinephrine. Reuptake inhibition potencies were measured at serotonin, norepinephrine and dopamine transporters. NMDAR antagonism was established in vitro using NMDAR-induced field excitatory postsynaptic potential (fEPSP) experiments. Finally, DPH and 2-MXP were investigated using tests of pre-pulse inhibition of startle (PPI) in rats to determine whether they reduce sensorimotor gating, an effect observed with known dissociative drugs such as phencyclidine (PCP) and ketamine. The results suggest that these 1,2-diarylethylamines are relatively selective NMDAR antagonists with weak off-target inhibitory effects on dopamine and norepinephrine reuptake. DPH and 2-MXP significantly inhibited PPI. DPH showed greater potency than 2-MXP, acting with a median effective dose (ED₅₀) of 9.5 mg/kg, which is less potent than values reported for other commonly abused dissociative drugs such as PCP and ketamine.

Analytical characterization of N,N-diallyltryptamine (DALT) and 16 ring-substituted derivatives

Many N,N-dialkylated tryptamines show psychoactive properties in humans and the number of derivatives involved in multidisciplinary areas of research has grown over the last few decades. Whereas some derivatives form the basis of a range of medicinal products, others are predominantly encountered as recreational drugs, and in some cases, the areas of therapeutic and recreational use can overlap. In recent years, 5-methoxy-N,N-diallyltryptamine (5-MeO-DALT) has appeared as a new psychoactive substance (NPS) and 'research chemical' whereas 4-acetoxy-DALT and the ring-unsubstituted DALT have only been detected very recently. Strategies pursued in the authors' laboratories included the preparation and biological evaluation of previously unreported N,N-diallyltryptamines (DALTs). This report describes the analytical characterization of 17 DALTs. Fifteen DALTs were prepared by a microwave-accelerated Speeter and Anthony procedure following established procedures developed previously in the authors' laboratories. In addition to DALT, the substances included in this study were 2-phenyl-, 4-acetoxy-, 4-hydroxy-, 4,5-ethylenedioxy-, 5-methyl-, 5-methoxy-, 5-methoxy-2-methyl-, 5-ethoxy-, 5-fluoro-, 5-fluoro-2-methyl-, 5-chloro-, 5-bromo-, 5,6-methylenedioxy-, 6-fluoro-, 7-methyl, and 7-ethyl-DALT, respectively. The DALTs were characterized by nuclear magnetic resonance spectroscopy (NMR), gas chromatography (GC) quadrupole and ion trap (EI/CI) mass spectrometry (MS), low and high mass accuracy MS/MS, photodiode array detection, and GC solid-state infrared analysis, respectively. A comprehensive collection of spectral data was obtained that are provided to research communities who face the challenge of encountering newly emerging substances where analytical data are not available. These data are also relevant to researchers who might wish to explore the clinical and non-clinical uses of these substances. Copyright © 2016 John Wiley & Sons, Ltd.

Behavioral and pharmacokinetic interactions between monoamine oxidase inhibitors and the hallucinogen 5-methoxy-N,N-dimethyltryptamine

Monoamine oxidase inhibitors (MAOIs) are often ingested together with tryptamine hallucinogens, but relatively little is known about the consequences of their combined use. We have shown previously that monoamine oxidase-A (MAO-A) inhibitors alter the locomotor profile of the hallucinogen 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) in rats, and enhance its interaction with 5-HT2A receptors. The goal of the present studies was to investigate the mechanism for the interaction between 5-MeO-DMT and MAOIs, and to determine whether other behavioral responses to 5-MeO-DMT are similarly affected. Hallucinogens disrupt prepulse inhibition (PPI) in rats, an effect typically mediated by 5-HT2A activation. 5-MeO-DMT also disrupts PPI but the effect is primarily attributable to 5-HT1A activation. The present studies examined whether an MAOI can alter the respective contributions of 5-HT1A and 5-HT2A receptors to the effects of 5-MeO-DMT on PPI. A series of interaction studies using the 5-HT1A antagonist WAY-100,635 and the 5-HT2A antagonist MDL 11,939 were performed to assess the respective contributions of these receptors to the behavioral effects of 5-MeO-DMT in rats pretreated with an MAOI. The effects of MAO-A inhibition on the pharmacokinetics of 5-MeO-DMT and its metabolism to bufotenine were assessed using liquid chromatography-electrospray ionization-selective reaction monitoring-tandem mass spectrometry (LC-ESI-SRM-MS/MS). 5-MeO-DMT (1mg/kg) had no effect on PPI when tested 45-min post-injection but disrupted PPI in animals pretreated with the MAO-A inhibitor clorgyline or the MAO-A/B inhibitor pargyline. The combined effect of 5-MeO-DMT and pargyline on PPI was antagonized by pretreatment with either WAY-100,635 or MDL 11,939. Inhibition of MAO-A increased the level of 5-MeO-DMT in plasma and whole brain, but had no effect on the conversion of 5-MeO-DMT to bufotenine, which was found to be negligible. The present results confirm that 5-MeO-DMT can disrupt PPI by activating 5-HT2A, and indicate that MAOIs alter 5-MeO-DMT pharmacodynamics by increasing its accumulation in the central nervous system.

The novel ketamine analog methoxetamine produces dissociative-like behavioral effects in rodents

RATIONALE

Methoxetamine (MXE) is a ketamine analog sold online that has been subject to widespread abuse for its dissociative and hallucinogenic effects. Previous studies have shown that MXE has high affinity for the phencyclidine (PCP) binding site located within the channel pore of the NMDA receptor (NMDAR), but little is known about its behavioral effects. Dissociative anesthetics such as ketamine and PCP produce a characteristic behavioral profile in rats that includes locomotor hyperactivity and disruption of prepulse inhibition (PPI) of acoustic startle.

METHODS

The goal of the present investigation was to determine whether MXE produces PCP-like effects in Sprague-Dawley rats using the PPI paradigm and the behavioral pattern monitor (BPM), which enables analyses of patterns of locomotor activity and investigatory behavior. PPI studies were conducted with several other uncompetitive NMDAR antagonists that produce dissociative effects in humans, including PCP, the S-(+) and R-(-) isomers of ketamine, and N-allylnormetazocine (NANM; SKF-10,047).

RESULTS

MXE disrupted PPI when administered at 3 and 10 mg/kg SC. The rank order of potency of MXE and the other test compounds in the PPI paradigm (PCP > MXE > S-(+)-ketamine > NANM > R-(-)-ketamine) parallels their affinities for the PCP binding site reported in the literature. When tested in the BPM, 10 mg/kg MXE induced locomotor hyperactivity, reduced the number of rearings, increased the roughness of locomotor paths, and produced perseverative patterns of locomotion. Administration of PCP (2.25 and 6.75 mg/kg, SC) produced a similar profile of effects in the BPM.

CONCLUSIONS

These results indicate that MXE produces a behavioral profile similar to that of other psychotomimetic uncompetitive NMDAR antagonists. Our findings support the classification of MXE as a dissociative drug and suggest that it likely has effects and abuse potential similar to that of PCP and ketamine.

Effect of 5-HT2A and 5-HT2C receptors on temporal discrimination by mice

Timing deficits are observed in patients with schizophrenia. Serotonergic hallucinogens can also alter the subjective experience of time. Characterizing the mechanism through which the serotonergic system regulates timing will increase our understanding of the linkage between serotonin (5-HT) and schizophrenia, and will provide insight into the mechanism of action of hallucinogens. We investigated whether interval timing in mice is altered by hallucinogens and other 5-HT2 receptor ligands. C57BL/6J mice were trained to perform a discrete-trials temporal discrimination task. In the discrete-trials task, mice were presented with two levers after a variable interval. Responding on lever A was reinforced if the interval was <6.5 s, and responding on lever B was reinforced if the interval was >6.5 s. A 2-parameter logistic function was fitted to the proportional choice for lever B (%B responding), yielding estimates of the indifference point (T50) and the Weber fraction (a measure of timing precision). The 5-HT2A antagonist M100907 increased T50, whereas the 5-HT2C antagonist SB-242,084 reduced T50. The results indicate that 5-HT2A and 5-HT2C receptors have countervailing effects on the speed of the internal pacemaker. The hallucinogen 2,5-dimethoxy-4-iodoamphetamine (DOI; 3 mg/kg IP), a 5-HT2 agonist, flattened the response curve at long stimulus intervals and shifted it to the right, causing both T50 and the Weber fraction to increase. The effect of DOI was antagonized by M100907 (0.03 mg/kg SC) but was unaffected by SB-242,084 (0.1 mg/kg SC). Similar to DOI, the selective 5-HT2A agonist 25CN-NBOH (6 mg/kg SC) reduced %B responding at long stimulus intervals, and increased T50 and the Weber fraction. These results demonstrate that hallucinogens alter temporal perception in mice, effects that are mediated by the 5-HT2A receptor. It appears that 5-HT regulates temporal perception, suggesting that altered serotonergic signaling may contribute to the timing deficits observed in schizophrenia and other psychiatric disorders.

BDNF-Deficient Mice Show Reduced Psychosis-Related Behaviors Following Chronic Methamphetamine

BACKGROUND

One of the most devastating consequences of methamphetamine abuse is increased risk of psychosis. Brain-derived neurotrophic factor has been implicated in both psychosis and neuronal responses to methamphetamine. We therefore examined persistent psychosis-like behavioral effects of methamphetamine in brain-derived neurotrophic factor heterozygous mice.

METHODS

Mice were chronically treated with methamphetamine from 6 to 9 weeks of age, and locomotor hyperactivity to an acute D-amphetamine challenge was tested in photocell cages after a 2-week withdrawal period.

RESULTS

Methamphetamine-treated wild-type mice, but not brain-derived neurotrophic factor heterozygous mice, showed locomotor sensitization to acute 3mg/kg D-amphetamine. Qualitative analysis of exploration revealed tolerance to D-amphetamine effects on entropy in methamphetamine-treated brain-derived neurotrophic factor heterozygous mice, but not wild-type mice.

CONCLUSIONS

Chronic methamphetamine exposure induces contrasting profiles of behavioral changes in wild-type and brain-derived neurotrophic factor heterozygous mice, with attenuation of behaviors relevant to psychosis in methamphetamine-treated brain-derived neurotrophic factor heterozygous mice. This suggests that brain-derived neurotrophic factor signalling changes may contribute to development of psychosis in methamphetamine users.

N-Benzyl-5-methoxytryptamines as Potent Serotonin 5-HT2 Receptor Family Agonists and Comparison with a Series of Phenethylamine Analogues

A series of N-benzylated-5-methoxytryptamine analogues was prepared and investigated, with special emphasis on substituents in the meta position of the benzyl group. A parallel series of several N-benzylated analogues of 2,5-dimethoxy-4-iodophenethylamine (2C-I) also was included for comparison of the two major templates (i.e., tryptamine and phenethylamine). A broad affinity screen at serotonin receptors showed that most of the compounds had the highest affinity at the 5-HT2 family receptors. Substitution at the para position of the benzyl group resulted in reduced affinity, whereas substitution in either the ortho or the meta position enhanced affinity. In general, introduction of a large lipophilic group improved affinity, whereas functional activity often followed the opposite trend. Tests of the compounds for functional activity utilized intracellular Ca(2+) mobilization. Function was measured at the human 5-HT2A, 5-HT2B, and 5-HT2C receptors, as well as at the rat 5-HT2A and 5-HT2C receptors. There was no general correlation between affinity and function. Several of the tryptamine congeners were very potent functionally (EC50 values from 7.6 to 63 nM), but most were partial agonists. Tests in the mouse head twitch assay revealed that many of the compounds induced the head twitch and that there was a significant correlation between this behavior and functional potency at the rat 5-HT2A receptor.

Recent advances in the neuropsychopharmacology of serotonergic hallucinogens

Serotonergic hallucinogens, such as (+)-lysergic acid diethylamide, psilocybin, and mescaline, are somewhat enigmatic substances. Although these drugs are derived from multiple chemical families, they all produce remarkably similar effects in animals and humans, and they show cross-tolerance. This article reviews the evidence demonstrating the serotonin 5-HT2A receptor is the primary site of hallucinogen action. The 5-HT2A receptor is responsible for mediating the effects of hallucinogens in human subjects, as well as in animal behavioral paradigms such as drug discrimination, head twitch response, prepulse inhibition of startle, exploratory behavior, and interval timing. Many recent clinical trials have yielded important new findings regarding the psychopharmacology of these substances. Furthermore, the use of modern imaging and electrophysiological techniques is beginning to help unravel how hallucinogens work in the brain. Evidence is also emerging that hallucinogens may possess therapeutic efficacy.