Locomotor and discriminative stimulus effects of four novel hallucinogens in rodents

Molecular and Medical Aspects of Psychedelics

Psychedelics belong to the oldest psychoactive drugs. They arouse recent interest due to their therapeutic applications in the treatment of major depressive disorder, substance use disorder, end-of-life anxiety,= and anxiety symptoms, and obsessive-compulsive disorder. In this review, the current state of preclinical research on the mechanism of action, neurotoxicity, and behavioral impact of psychedelics is summarized. The effect of selective 5-HT2A receptor agonists, 25I- and 25B-NBOMe, after acute and repeated administration is characterized and compared with the effects of a less selective drug, psilocybin. The data show a significant effect of NBOMes on glutamatergic, dopaminergic, serotonergic, and cholinergic neurotransmission in the frontal cortex, striatum, and nucleus accumbens. The increases in extracellular levels of neurotransmitters were not dose-dependent, which most likely resulted from the stimulation of the 5-HT2A receptor and subsequent activation of the 5-HT2C receptors. This effect was also observed in the wet dog shake test and locomotor activity. Chronic administration of NBOMes elicited rapid development of tolerance, genotoxicity, and activation of microglia. Acute treatment with psilocybin affected monoaminergic and aminoacidic neurotransmitters in the frontal cortex, nucleus accumbens, and hippocampus but not in the amygdala. Psilocybin exhibited anxiolytic properties resulting from intensification of GABAergic neurotransmission. The data indicate that NBOMes as selective 5-HT2A agonists exert a significant effect on neurotransmission and behavior of rats while also inducing oxidative DNA damage. In contrast to NBOMes, the effects induced by psilocybin suggest a broader therapeutic index of this drug.

Hallucinogenic activity, neurotransmitters release, anxiolytic and neurotoxic effects in Rat's brain following repeated administration of novel psychoactive compound 25B-NBOMe

2-(4-Bromo-2,5-dimethoxyphenyl)-N-(2-methoxybenzyl)etanoamine (25B-NBOMe) is a highly selective 5-HT2A receptor agonist, exhibiting a potent hallucinogenic activity. In the present study, we investigated the effect of a 7-day treatment with 25B-NBOMe in a dose of 0.3 mg/kg on the following: the neurotransmitter release in vivo using microdialysis in freely moving animals, hallucinogenic activity measured in the Wet Dog Shake (WDS) test, anxiety level as measured in the light/dark box (LDB) and locomotor activity in the open field (OF) test, DNA damage with the comet assay, and on a number of neuronal and glial cells with immunohistochemistry. Repeated administration of 25B-NBOMe decreased the response to a challenge dose (0.3 mg/kg) on DA, 5-HT and glutamatergic neurons in the rats' frontal cortex, striatum, and nucleus accumbens. The WDS response dropped drastically after the second day of treatment, suggesting a rapid development of tolerance. LDB and OF tests showed that the effect of 25B-NBOMe on anxiety depends on the treatment and environmental settings. Results obtained with the comet assay indicate a genotoxic properties in the frontal cortex and hippocampus. An increase in immunopositive glial but not neuronal cells was observed in the cortical regions but not in the hippocampus. In conclusion, our study showed that a chronic administration of 25B-NBOMe produces the development of tolerance observed in the neurotransmitters release and hallucinogenic activity. The oxidative damage of cortical and hippocampal DNA implies the generation of free radicals by the drug, resulting in genotoxicity but rather not in neurotoxic tissue damage. Behavioral tests show that 25B-NBOMe exerts anxiogenic effect after single and repeated treatment.

25X-NBOMe compounds - chemistry, pharmacology and toxicology. A comprehensive review

Recently, a growing number of reports have indicated a positive effect of hallucinogenic-based therapies in different neuropsychiatric disorders. However, hallucinogens belonging to the group of new psychoactive substances (NPS) may produce high toxicity. NPS, due to their multi-receptors affinity, are extremely dangerous for the human body and mental health. An example of hallucinogens that have been lately responsible for many severe intoxications and deaths are 25X-NBOMes - N-(2-methoxybenzyl)-2,5-dimethoxy-4-substituted phenethylamines, synthetic compounds with strong hallucinogenic properties. 25X-NBOMes exhibit a high binding affinity to serotonin receptors but also to dopamine, adrenergic and histamine receptors. Apart from their influence on perception, many case reports point out systemic and neurological poisoning with these compounds. In humans, the most frequent side effects are tachycardia, anxiety, hypertension and seizures. Moreover, preclinical studies confirm that 25X-NBOMes cause developmental impairments, cytotoxicity, cardiovascular toxicity and changes in behavior of animals. Metabolism of NBOMes seems to be very complex and involves many metabolic pathways. This fact may explain the observed high toxicity. In addition, many analytical methods have been applied in order to identify these compounds and their metabolites. The presented review summarized the current knowledge about 25X-NBOMes, especially in the context of toxicity.

Receptor Binding Profiles for Tryptamine Psychedelics and Effects of 4-Propionoxy-N,N-dimethyltryptamine in Mice

Analogues of 4-phosphoryloxy-N,N-dimethyltryptamine (psilocybin) are being sold on recreational drug markets and developed as potential medications for psychedelic-assisted therapies. Many of these tryptamine-based psilocybin analogues produce psychedelic-like effects in rodents and humans primarily by agonist activity at serotonin 2A receptors (5-HT2A). However, the comprehensive pharmacological target profiles for these compounds compared to psilocybin and its active metabolite 4-hydroxy-N,N-dimethyltryptamine (psilocin) are unknown. The present study determined the receptor binding profiles of various tryptamine-based psychedelics structurally related to psilocybin across a broad range of potential targets. Specifically, we examined tryptamine psychedelics with different 4-position (hydroxy, acetoxy, propionoxy) and N,N-dialkyl (dimethyl, methyl-ethyl, diethyl, methyl-propyl, ethyl-propyl, diisopropyl, methyl-allyl, diallyl) substitutions. Further, the psilocybin analogue 4-propionoxy-N,N-dimethyltryptamine (4-PrO-DMT) was administered to mice in experiments measuring head twitch response (HTR), locomotor activity, and body temperature. Overall, the present pharmacological profile screening data show that the tryptamine psychedelics target multiple serotonin receptors, including serotonin 1A receptors (5-HT1A). 4-Acetoxy and 4-propionoxy analogues of 4-hydroxy compounds displayed somewhat weaker binding affinities but similar target profiles across 5-HT receptors and other identified targets. Additionally, differential binding screen profiles were observed with N,N-dialkyl position variations across several non-5-HT receptor targets (i.e., alpha receptors, dopamine receptors, histamine receptors, and serotonin transporters), which could impact in vivo pharmacological effects of the compounds. In mouse experiments, 4-PrO-DMT displayed dose-related psilocybin-like effects to produce 5-HT2A-mediated HTR (0.3-3 mg/kg s.c.) as well as 5-HT1A-mediated hypothermia and hypolocomotion (3-30 mg/kg s.c.). Lastly, our data support a growing body of evidence that the 5-HT2A-mediated HTR induced by tryptamine psychedelics is attenuated by 5-HT1A receptor agonist activity at high doses in mice.

Acute pharmacological profile of 2C-B-Fly-NBOMe in male Wistar rats—pharmacokinetics, effects on behaviour and thermoregulation

Introduction:N-2-methoxy-benzylated (“NBOMe”) analogues of phenethylamine are a group of new psychoactive substances (NPS) with reported strong psychedelic effects in sub-milligram doses linked to a number of severe intoxications, including fatal ones. In our present work, we provide a detailed investigation of pharmacokinetics and acute behavioural effects of 2C-B-Fly-NBOMe (2-(8-bromo-2,3,6,7-tetrahydrobenzo [1,2-b:4,5-b′]difuran-4-yl)-N-[(2-methoxybenzyl]ethan-1-amine), an analogue of popular psychedelic entactogen 2C-B (4-Bromo-2,5-dimethoxyphenethylamine).

Methods: All experiments were conducted on adult male Wistar rats. Pharmacokinetic parameters of 2C-B-Fly-NBOMe (1 mg/kg subcutaneously; s. c.) in blood serum and brain tissue were analysed over 24 h using liquid chromatography-mass spectrometry (LC/MS). For examination of behavioural parameters in open field test (OFT) and prepulse inhibition (PPI) of acoustic startle reaction (ASR), 2C-B-Fly-NBOMe (0.2, 1 and 5 mg/kg s. c.) was administered in two temporal onsets: 15 and 60 min after administration. Thermoregulatory changes were evaluated in individually and group-housed animals over 8 h following the highest dose used in behavioural experiments (5 mg/kg s. c.).

Results: Peak drug concentrations were detected 30 and 60 min after the drug application in serum (28 ng/ml) and brain tissue (171 ng/g), respectively. The parental compound was still present in the brain 8 h after administration. Locomotor activity was dose-dependently reduced by the drug in both temporal testing onsets. ASR was also strongly disrupted in both temporal onsets, drug’s effect on PPI was weaker. 2C-B-Fly-NBOMe did not cause any significant thermoregulatory changes.

Discussion: Our results suggest that 2C-B-Fly-NBOMe penetrates animal brain tissue in a relatively slow manner, induces significant inhibitory effects on motor performance, and attenuates sensorimotor gating. Its overall profile is similar to closely related analogue 2C-B and other NBOMe substances.

(2-Aminopropyl)benzo[β]thiophenes (APBTs) are novel monoamine transporter ligands that lack stimulant effects but display psychedelic-like activity in mice

Derivatives of (2-aminopropyl)indole (API) and (2-aminopropyl)benzofuran (APB) are new psychoactive substances which produce stimulant effects in vivo. (2-Aminopropyl)benzo[β]thiophene (APBT) is a novel sulfur-based analog of API and APB that has not been pharmacologically characterized. In the current study, we assessed the pharmacological effects of six APBT positional isomers in vitro, and three of these isomers (3-APBT, 5-APBT, and 6-APBT) were subjected to further investigations in vivo. Uptake inhibition and efflux assays in human transporter-transfected HEK293 cells and in rat brain synaptosomes revealed that APBTs inhibit monoamine reuptake and induce transporter-mediated substrate release. Despite being nonselective transporter releasers like MDMA, the APBT compounds failed to produce locomotor stimulation in C57BL/6J mice. Interestingly, 3-APBT, 5-APBT, and 6-APBT were full agonists at 5-HT2 receptor subtypes as determined by calcium mobilization assays and induced the head-twitch response in C57BL/6J mice, suggesting psychedelic-like activity. Compared to their APB counterparts, ABPT compounds demonstrated that replacing the oxygen atom with sulfur results in enhanced releasing potency at the serotonin transporter and more potent and efficacious activity at 5-HT2 receptors, which fundamentally changed the in vitro and in vivo profile of APBT isomers in the present studies. Overall, our data suggest that APBT isomers may exhibit psychedelic and/or entactogenic effects in humans, with minimal psychomotor stimulation. Whether this unique pharmacological profile of APBT isomers translates into potential therapeutic potential, for instance as candidates for drug-assisted psychotherapy, warrants further investigation.

Effect of -NBOMe Compounds on Sensorimotor, Motor, and Prepulse Inhibition Responses in Mice in Comparison With the 2C Analogs and Lysergic Acid Diethylamide: From Preclinical Evidence to Forensic Implication in Driving Under the Influence of Drugs

In the last decade, the market for new psychoactive substances has been enriched by numerous psychedelic phenethylamines, which mimic the psychoactive effect of lysergic acid diethylamide (LSD). In particular, the -NBOMe series, which are more potent than their 2C compounds analogs, are considered worthy substitutes for LSD by users. The purpose of this study was to assess the effects of 25H-NBOMe and its halogenated derivatives (25I-NBOMe and 25B-NBOMe) in comparison to their 2C compounds analogs and LSD on the sensorimotor (visual, acoustic, and overall tactile), reaction time, spontaneous (total distance traveled) and stimulated (drag, accelerod test) motor activity, grip strength test, and prepulse inhibition (PPI) responses in mice. Systemic administration of -NBOMe, 2C compounds analogs, and LSD (0.001-10 mg/kg) differently impaired the sensorimotor, reaction time, motor, and PPI responses in mice. In particular, halogenated (25I and 25B)-NBOMe derivatives appear to be more effective than the entire class of 2C compounds analogs in altering visual and acoustic responses, affecting reaction time, and motor and sensory gating in PPI test. In fact, the specific rank order of compounds potency for nearly all of the experiments showed that (25I and 25B)-NBOMe were more potent than 2C compounds analogs and LSD. -NBOMe and 2C compounds analogs impaired not only the reception of incoming sensory stimuli (visual and acoustic), but their correct brain processing (PPI) in an equal and sometimes stronger way than LSD. This sensory impairment directly affected the spontaneous motor response and reaction time of mice, with no change in performance in stimulated motor activity tests. These aspects should be carefully considered to better understand the potential danger that psychedelic phenethylamines, in particular -NBOMe, may pose to public health, with particular reference to decreased performance in driving and hazardous works that require special sensorimotor skills.

Effects of β-Phenylethylamine on Psychomotor, Rewarding, and Reinforcing Behaviors and Affective State: The Role of Dopamine D1 Receptors

Beta-phenylethylamine (β-PEA) is a well-known and widespread endogenous neuroactive trace amine found throughout the central nervous system in humans. In this study, we demonstrated the effects of β-PEA on psychomotor, rewarding, and reinforcing behaviors and affective state using the open-field test, conditioned place preference (CPP), self-administration, and ultrasonic vocalizations (USVs) paradigms. We also investigated the role of the dopamine (DA) D1 receptor in the behavioral effects of β-PEA in rodents. Using enzyme-linked immunosorbent assay (ELISA) and Western immunoblotting, we also determined the DA concentration and the DA-related protein levels in the dorsal striatum of mice administered with acute β-PEA. The results showed that acute β-PEA increased stereotypic behaviors such as circling and head-twitching responses in mice. In the CPP experiment, β-PEA increased place preference in mice. In the self-administration test, β-PEA significantly enhanced self-administration during a 2 h session under fixed ratio (FR) schedules (FR1 and FR3) and produced a higher breakpoint during a 6 h session under progressive ratio schedules of reinforcement in rats. In addition, acute β-PEA increased 50-kHz USV calls in rats. Furthermore, acute β-PEA administration increased DA concentration and p-DAT and TH expression in the dorsal striatum of mice. Finally, pretreatment with SCH23390, a DA D1 receptor antagonist, attenuated β-PEA-induced circling behavior and β-PEA-taking behavior in rodents. Taken together, these findings suggest that β-PEA has rewarding and reinforcing effects and psychoactive properties, which induce psychomotor behaviors and a positive affective state by activating the DA D1 receptor in the dorsal striatum.

Tolerance to neurochemical and behavioral effects of the hallucinogen 25I-NBOMe

RATIONALE

4-Iodo-2,5-dimethoxy-N-(2-methoxybenzyl)phenethylamine (25I-NBOMe) is a potent serotonin 5-HT2A/2C receptor agonist with hallucinogenic activity. There is no data on the 25I-NBOMe effect on brain neurotransmission and animal performance after chronic administration.

OBJECTIVES

We examined the effect of a 7-day treatment with 25I-NBOMe (0.3 mg/kg/day) on neurotransmitters' release and rats' behavior in comparison to acute dose.

METHODS

Changes in dopamine (DA), serotonin (5-HT), acetylcholine (ACh), and glutamate release were studied using microdialysis in freely moving rats. The hallucinogenic activity was measured in the wet dog shake (WDS) test. The animal locomotion was examined in the open field (OF) test, short-term memory in the novel object recognition (NOR) test. The anxiogenic/anxiolytic properties of the drug were tested using the light/dark box (LDB) test.

RESULTS

Repeated administration of 25I-NBOMe decreased the response to a challenge dose of DA, 5-HT, and glutamatergic neurons in the frontal cortex as well as weakened the hallucinogenic activity in comparison to acute dose. In contrast, striatal and accumbal DA and 5-HT release and accumbal but not striatal glutamate release in response to the challenge dose of 25I-NBOMe was increased in comparison to acute treatment. The ACh release was increased in all brain regions. Behavioral tests showed a motor activity reduction and memory deficiency in comparison to a single dose and induction of anxiety after the drug's chronic and acute administration.

CONCLUSIONS

Our findings suggest that multiple injections of 25I-NBOMe induce tolerance to hallucinogenic activity and produce alterations in neurotransmission. 25I-NBOMe effect on short-term memory, locomotor function, and anxiety seems to be the result of complex interactions between neurotransmitter pathways.

2-(4-Iodo-2,5-dimethoxyphenyl)-N-[(2-methoxyphenyl)methyl]ethanamine (25I-NBOME): A Harmful Hallucinogen Review

NBOMes are N-benzylmethoxy derivatives of the 2C family compounds with N-2-methoxybenzyl moiety substituted by the methoxy group at the 2- and 5-position and the halogen group at the 4-position of the phenyl ring. These substances are a new class of potent serotonin 5-HT2A receptor agonist hallucinogens with potential harmful effects. The substitution with halogen of the already psychoactive phenethylamine produces a derivative (2C-I) with increased hallucinogenic effects. This class of hallucinogens has chemical structures very similar to natural hallucinogenic alkaloid mescaline and these are sold mainly via internet as a 'legal' alternative to other hallucinogenic drug-lysergic acid diethylamide (LSD). 25I-NBOMe is the first synthesized and one of the most common compound from NBOMes. Knowledge of pharmacological properties of 25I-NBOMe is very limited so far. There are only a few in vivo and in vitro so far published studies. The behavioral experiments are mainly related with the hallucinogenic effect of 25I-NBOMe while the in vitro studies concerning mainly the affinity for 5-HT2A receptors. The 25I-NBOMe Critical Review 2016 reported 51 non-fatal intoxications and 21 deaths associated with 25I-NBOMe across Europe. Case reports describe various toxic effects of 25I-NBOMe usage including tachycardia, hypertension, hallucinations, rhabdomyolysis, acute kidney injury and death. The growing number of fatal and non-fatal intoxication cases indicates that 25I-NBOMe should be considered as a serious danger to public health. This review aims to present the current state of knowledge on pharmacological effects and chemical properties of 25I-NBOMe and to describe reported clinical cases and analytical methods available for identification of this agent in biological material.

25B-NBOMe, a novel N-2-methoxybenzyl-phenethylamine (NBOMe) derivative, may induce rewarding and reinforcing effects via a dopaminergic mechanism: Evidence of abuse potential

An increasing number of N-2-methoxybenzyl-phenethylamine (NBOMe) derivatives are being misused worldwide, including the potent hallucinogen 2-(4-bromo-2,5-dimethoxyphenyl)-N-(2-methoxybenzyl)ethanamine (25B-NBOMe). However, the number of studies characterizing the abuse potential and psychopharmacological properties of 25B-NBOMe is limited; thus, we examined its rewarding and reinforcing effects using conditioned place preference (CPP) and self-administration (SA) tests. Pretreatment with SCH23390 (SCH), Haloperidol (HAL), and ketanserin (KS), antagonists of dopamine D1 (DRD₁ ), dopamine D2 (DRD₂ ), and serotonin 2A (5-HT_2A receptor) receptors, respectively, was utilized during a CPP test to investigate the involvement of the dopaminergic and serotonergic systems in 25B-NBOMe-mediated effects. We also examined the effects of 25B-NBOMe on the expression of dopamine-related proteins in the nucleus accumbens (NAcc) and ventral tegmental area (VTA). Then, we measured the dopamine level, phosphorylated CREB (p-CREB), deltaFosB (ΔFosB), and brain-derived neurotrophic factor (BDNF) in the NAcc. In addition, we explored the involvement of 5-HT_2A receptors in the 25B-NBOMe-induced head twitch response (HTR). We also examined the effects of 25B-NBOMe on brain wave activity using electroencephalography. 25B-NBOMe elicited CPP and SA. SCH and HAL blocked 25B-NBOMe-induced CPP, whereas KS did not. Moreover, 25B-NBOMe altered the DRD₁ , DRD₂ , and dopamine transporter expression and increased dopamine levels. It also induced changes in p-CREB, ΔFosB, and BDNF expression. 25B-NBOMe induced HTR and increased 5-HT_2A receptor mRNA levels, effects inhibited by KS. Furthermore, 25B-NBOMe altered delta and gamma wave activity, which was normalized by SCH and HAL. These findings show that 25B-NBOMe may induce rewarding and reinforcing effects via a dopaminergic mechanism, suggesting its abuse potential.

Designer drugs: a medicinal chemistry perspective (II)

During 2012-2018, the clandestine manufacture of new psychoactive substances (NPS) designed to circumvent substance control regulations increased exponentially worldwide, with concomitant increase in fatalities. This review focuses on three compound classes identified as synthetic opioids, synthetic amphetamines, and synthetic cannabinoids and highlights the medicinal chemistry precedents utilized by clandestine laboratories to develop new NPS with increased brain penetration, longer duration of action, and greater potency. Chemical approaches to illicit drug abuse treatment options, particularly for opioid use disorder, are also discussed.

25C-NBOMe short characterisation

Purpose

N-Methoxybenzyls, a group of toxic phenylethylamine derivatives of the 2C family compounds, are a new class of potent serotonin 5-HT2A receptor agonist hallucinogens with potential harmful effects. This study summarizes current state of knowledge of one of the most dangerous representative of this group—N-(2-methoxybenzyl)-2,5-dimethoxy-4-chlorophenethylamine (25C-NBOMe). Due to hallucinogenic properties similar to those observe after lysergic acid diethylamide (LSD) usage (altered thoughts, feelings, and awareness of one’s surroundings), this compound is very attractive to hallucinogenic substances users.

Methods

An exhaustive literature search was carried out in PubMed, Google Scholar and other biomedical data bases without limiting period, to identify relevant articles.

Results

Despite frequent recreational use, knowledge about the 25C-NBOMe action and toxic and fatal consequences is still very limited. Most data on this drug come from clinical reports, from cases of acute fatal and non-fatal intoxications. Some animal and in vitro studies indicated a route of metabolism of the drug in the body. The drug and its metabolites were also detected in human blood and urine using combinations of chromatographic separation and mass spectrometry detection.

Conclusions

Overall, findings show that 25C-NBOMe is a powerful hallucinogen. Easy online availability, low prize and the lack of knowledge of 25C-NBOMe makes this substance potentially very dangerous to its users. Thus, further investigation on the mechanism of action, chemical, pharmacological and toxicological properties is needed to evaluate 25C-NBOMe potential harmful effects.

NBOMes-Highly Potent and Toxic Alternatives of LSD

Recently, a new class of psychedelic compounds named NBOMe (or 25X-NBOMe) has appeared on the illegal drug market. NBOMes are analogs of the 2C family of phenethylamine drugs, originally synthesized by Alexander Shulgin, that contain a N-(2-methoxy)benzyl substituent. The most frequently reported drugs from this group are 25I-NBOMe, 25B-NBOMe, and 25C-NBOMe. NBOMe compounds are ultrapotent and highly efficacious agonists of serotonin 5-HT_2A and 5-HT_2C receptors (Ki values in low nanomolar range) with more than 1000-fold selectivity for 5-HT_2A compared with 5-HT_1A. They display higher affinity for 5-HT_2A receptors than their 2C counterparts and have markedly lower affinity, potency, and efficacy at the 5-HT_2B receptor compared to 5-HT_2A or 5-HT_2C. The drugs are sold as blotter papers, or in powder, liquid, or tablet form, and they are administered sublingually/buccally, intravenously, via nasal insufflations, or by smoking. Since their introduction in the early 2010s, numerous reports have been published on clinical intoxications and fatalities resulting from the consumption of NBOMe compounds. Commonly observed adverse effects include visual and auditory hallucinations, confusion, anxiety, panic and fear, agitation, uncontrollable violent behavior, seizures, excited delirium, and sympathomimetic signs such mydriasis, tachycardia, hypertension, hyperthermia, and diaphoresis. Rhabdomyolysis, disseminated intravascular coagulation, hypoglycemia, metabolic acidosis, and multiorgan failure were also reported. This survey provides an updated overview of the pharmacological properties, pattern of use, metabolism, and desired effects associated with NBOMe use. Special emphasis is given to cases of non-fatal and lethal intoxication involving these compounds. As the analysis of NBOMes in biological materials can be challenging even for laboratories applying modern sensitive techniques, this paper also presents the analytical methods most commonly used for detection and identification of NBOMes and their metabolites.

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'.

Neuronal and peripheral damages induced by synthetic psychoactive substances: an update of recent findings from human and animal studies

Preclinical and clinical studies indicate that synthetic psychoactive substances, in addition to having abuse potential, may elicit toxic effects of varying severity at the peripheral and central levels. Nowadays, toxicity induced by synthetic psychoactive substances poses a serious harm for health, since recreational use of these substances is on the rise among young and adult people. The present review summarizes recent findings on the peripheral and central toxicity elicited by “old” and “new” synthetic psychoactive substances in humans and experimental animals, focusing on amphetamine derivatives, hallucinogen and dissociative drugs and synthetic cannabinoids.

Neurochemical and Behavioral Profiling in Male and Female Rats of the Psychedelic Agent 25I-NBOMe

4-Iodo-2,5-dimethoxy-N-(2-methoxybenzyl)phenethylamine (25I-NBOMe), commonly called “N-Bomb,” is a synthetic phenethylamine with psychedelic and entactogenic effects; it was available on the Internet both as a legal alternative to lysergic acid diethylamide (LSD) and as a surrogate of 3,4-methylenedioxy-methamphetamine (MDMA), but now it has been scheduled among controlled substances. 25I-NBOMe acts as full agonist on serotonergic 5-HT2A receptors. Users are often unaware of ingesting fake LSD, and several cases of intoxication and fatalities have been reported. In humans, overdoses of “N-Bomb” can cause tachycardia, hypertension, seizures, and agitation. Preclinical studies have not yet widely investigated the rewarding properties and behavioral effects of this compound in both sexes. Therefore, by in vivo microdialysis, we evaluated the effects of 25I-NBOMe on dopaminergic (DA) and serotonergic (5-HT) transmissions in the nucleus accumbens (NAc) shell and core, and the medial prefrontal cortex (mPFC) of male and female rats. Moreover, we investigated the effect of 25I-NBOMe on sensorimotor modifications as well as body temperature, nociception, and startle/prepulse inhibition (PPI). We showed that administration of 25I-NBOMe affects DA transmission in the NAc shell in both sexes, although showing different patterns; moreover, this compound causes impaired visual responses in both sexes, whereas core temperature is heavily affected in females, and the highest dose tested exerts an analgesic effect prominent in male rats. Indeed, this drug is able to impair the startle amplitude with the same extent in both sexes and inhibits the PPI in male and female rats. Our study fills the gap of knowledge on the behavioral effects of 25I-NBOMe and the risks associated with its ingestion; it focuses the attention on sex differences that might be useful to understand the trend of consumption as well as to recognize and treat intoxication and overdose symptoms.

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.

Serotonergic Psychedelics: Experimental Approaches for Assessing Mechanisms of Action

Recent, well-controlled - albeit small-scale - clinical trials show that serotonergic psychedelics, including psilocybin and lysergic acid diethylamide, possess great promise for treating psychiatric disorders, including treatment-resistant depression. Additionally, fresh results from a deluge of clinical neuroimaging studies are unveiling the dynamic effects of serotonergic psychedelics on functional activity within, and connectivity across, discrete neural systems. These observations have led to testable hypotheses regarding neural processing mechanisms that contribute to psychedelic effects and therapeutic benefits. Despite these advances and a plethora of preclinical and clinical observations supporting a central role for brain serotonin 5-HT2A receptors in producing serotonergic psychedelic effects, lingering and new questions about mechanisms abound. These chiefly pertain to molecular neuropharmacology. This chapter is devoted to illuminating and discussing such questions in the context of preclinical experimental approaches for studying mechanisms of action of serotonergic psychedelics, classic and new.

Hallucinogen-Like Action of the Novel Designer Drug 25I-NBOMe and Its Effect on Cortical Neurotransmitters in Rats

NBOMes are N-benzylmethoxy derivatives of the 2C family hallucinogens. 4-Iodo-2,5-dimethoxy-N-(2-methoxybenzyl)phenethylamine (25I-NBOMe) is one of the commonly used illicit drugs. It exhibits high binding affinity for 5-HT_2A/C and 5-HT_1A serotonin receptors. Activation of 5-HT_2A receptor induces head-twitch response (HTR) in rodents, a behavioral marker of hallucinogen effect in humans. There is not much data on neurochemical properties of NBOMes. Therefore, we aimed to investigate the effect of 25I-NBOMe on extracellular level of dopamine (DA), serotonin (5-HT), and glutamate (GLU) in the rat frontal cortex, tissue contents of monoamines, and hallucinogenic activity in rats. The extracellular levels of DA, 5-HT, and GLU were studied using microdialysis in freely moving animals. The tissue contents of DA, 5-HT and their metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were determined in the rat frontal cortex. We also tested a drug-elicited HTR. 25I-NBOMe at doses 1, 3, and 10 mg/kg (sc) increased extracellular DA, 5-HT, and GLU levels, enhanced tissue content of 5-HT and 5-HIAA, but did not affect tissue level of DA and its metabolites. The compound exhibited an inverted U-shaped dose-response curve with respect to the effect on extracellular DA and 5-HT levels, but a U-shaped dose-response curve was observed for its effect on GLU release and HTR. The data from our study suggest that hallucinogenic activity of 25I-NBOMe seems to be related with the increase in extracellular GLU level-mediated via cortical 5-HT_2A receptors. The influence of 25I-NBOMe on 5-HT_2C and 5-HT_1A receptors may modulate its effect on neurotransmitters and HTR.

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.

Neurochemical pharmacology of psychoactive substituted N-benzylphenethylamines: High potency agonists at 5-HT2A receptors

The use of new psychoactive substituted 2,5-dimethoxy-N-benzylphenethylamines is associated with abuse and toxicity in the United States and elsewhere and their pharmacology is not well known. This study compares the mechanisms of action of 2-(2,5-dimethoxy-4-methylphenyl)-N-(2-methoxybenzyl)ethanamine (25D-NBOMe), 2-(4-ethyl-2,5-dimethoxyphenyl)-N-(2-methoxybenzyl)ethanamine (25E-NBOMe), 2-(2,5-dimethoxyphenyl)-N-(2-methoxybenzyl)ethanamine (25H-NBOMe), 2-(((4-iodo-2,5-dimethoxyphenethyl)amino)methyl)phenol (25I-NBOH); and 2-(2,5-dimethoxy-4-nitrophenyl)-N-(2-methoxybenzyl)ethanamine) (25N-NBOMe) with hallucinogens and stimulants. Mammalian cells heterologously expressing 5-HT1A, 5-HT2A, 5-HT2B or 5-HT2C receptors, or dopamine, serotonin or norepinephrine transporters (DAT, SERT and NET, respectively) were used to assess drug affinities at radioligand binding sites. Potencies and efficacies were determined using [35S]GTPγS binding assays (5-HT1A), inositol-phosphate accumulation assays (5-HT2A, 5-HT2B and 5-HT2C), and uptake and release assays (transporters). The substituted phenethylamines were very low potency and low efficacy agonists at the 5-HT1A receptor. 25D-NBOMe, 25E-NBOMe, 25H-NBOMe, 25I-NBOH and 25N-NBOMe had very high affinity for, and full efficacy at, 5-HT2A and 5-HT2C receptors. In the 5-HT2A receptor functional assay, 25D-NBOMe, 25E-NBOMe, 25I-NBOH and 25N-NBOMe had subnanomolar to low nanomolar potencies similar to (+)lysergic acid diethylamide (LSD) while 25H-NBOMe had lower potency, similar to serotonin. At the 5-HT2C receptor, four had very high potencies, similar to LSD and serotonin, while 25H-NBOMe had lower potency. At the 5-HT2B receptor, the compounds had lower affinity, potency and efficacy compared to 5-HT2A or 5-HT2C. The phenethylamines had low to mid micromolar affinities and potencies at the transporters. These results demonstrate that these -NBOMe and -NBOH substituted phenethylamines have a biochemical pharmacology consistent with hallucinogenic activity, with little psychostimulant activity.

Comparative neuropharmacology of N-(2-methoxybenzyl)-2,5-dimethoxyphenethylamine (NBOMe) hallucinogens and their 2C counterparts in male rats

2,5-Dimethoxyphenethylamines (2C compounds) are 5-HT2A/2C receptor agonists that induce hallucinogenic effects. N-methoxybenzylation of 2C compounds markedly increases their affinity for 5-HT2A receptors, and two such analogs, 2-(4-chloro-2,5-dimethoxyphenyl)-N-[(2-methoxyphenyl)methyl]ethanamine (25C-NBOMe) and 2-(4-iodo-2,5-dimethoxyphenyl)-N-[(2-methoxyphenyl)methyl]ethanamine (25I-NBOMe), have emerged in recreational drug markets. Here, we investigated the neuropharmacology of 25C-NBOMe and 25I-NBOMe in rats, as compared to their 2C analogs and the prototypical 5-HT2A/2C agonist 1-(4-iodo-2,5-dimethoxyphenyl)propan-2-amine (DOI). Compounds were tested in vitro using 5-HT2A receptor binding and calcium mobilization assays. For in vivo experiments, 25C-NBOMe (0.01-0.3 mg/kg), 25I-NBOMe (0.01-0.3 mg/kg), 2-(4-chloro-2,5-dimethoxyphenyl)ethanamine (2C-C) (0.1-3.0 mg/kg), 2-(4-iodo-2,5-dimethoxyphenyl)ethanamine (2C-I) (0.1-3.0 mg/kg) and DOI (0.03-1.0 mg/kg) were administered subcutaneously (sc) to male rats, and 5-HT2A-mediated behaviors were assessed. NBOMes displayed higher affinity for 5-HT2A receptors than their 2C counterparts but were substantially weaker in functional assays. 25C-NBOMe and 25I-NBOMe were much more potent at inducing wet dog shakes (WDS) and back muscle contractions (BMC) when compared to 2C-C and 2C-I. Pretreatment with the selective 5-HT2A antagonist (R)-(2,3-dimethoxyphenyl){1-[2-(4-fluorophenyl)ethyl]-4-piperidinyl}methanol (M100907) reversed behaviors produced by all agonists. Interestingly, binding affinities at the 5-HT2A receptor were significantly correlated with potencies to induce BMC but not WDS. Our findings show that NBOMes are highly potent 5-HT2A agonists in rats, similar to effects in mice, and consistent with the reported hallucinogenic effects in human users. This article is part of the Special Issue entitled 'Psychedelics: New Doors, Altered Perceptions'.

Receptor binding profiles and behavioral pharmacology of ring-substituted N,N-diallyltryptamine analogs

Substantial effort has been devoted toward understanding the psychopharmacological effects of tryptamine hallucinogens, which are thought to be mediated by activation of 5-HT_2A and 5-HT_1A receptors. Recently, several psychoactive tryptamines based on the N,N-diallyltryptamine (DALT) scaffold have been encountered as recreational drugs. Despite the apparent widespread use of DALT derivatives in humans, little is known about their pharmacological properties. We compared the binding affinities of DALT and its 2-phenyl-, 4-acetoxy-, 4-hydroxy-, 5-methoxy-, 5-methoxy-2-methyl-, 5-fluoro-, 5-fluoro-2-methyl-, 5-bromo-, and 7-ethyl-derivatives at 45 receptor and transporter binding sites. Additionally, studies in C57BL/6 J mice examined whether these substances induce the head twitch response (HTR), a 5-HT_2A receptor-mediated response that is widely used as a behavioral proxy for hallucinogen effects in humans. Most of the test drugs bound to serotonin receptors, σ sites, α₂-adrenoceptors, dopaminergic D₃ receptors, histaminergic H₁ receptors, and the serotonin transporter. DALT and several of the ring-substituted derivatives were active in the HTR assay with the following rank order of potency: 4-acetoxy-DALT > 5-fluoro-DALT > 5-methoxy-DALT > 4-hydroxy-DALT > DALT > 5-bromo-DALT. 2-Phenyl-DALT, 5-methoxy-2-methyl-DALT, 5-fluoro-2-methyl-DALT, and 7-ethyl-DALT did not induce the HTR. HTR potency was not correlated with either 5-HT_1A or 5-HT_2A receptor binding affinity, but a multiple regression analysis indicated that 5-HT_2A and 5-HT_1A receptors make positive and negative contributions, respectively, to HTR potency (R² = 0.8729). In addition to supporting the established role of 5-HT_2A receptors in the HTR, these findings are consistent with evidence that 5-HT_1A activation by tryptamine hallucinogens buffers their effects on HTR. This article is part of the Special Issue entitled 'Psychedelics: New Doors, Altered Perceptions'.