Phencyclidine-like in vivo effects of methoxetamine in mice and rats

Phencyclidine-Like Abuse Liability and Psychosis-Like Neurocognitive Effects of Novel Arylcyclohexylamine Drugs of Abuse in Rodents

Abuse of novel arylcyclohexylamines (ACX) poses risks for toxicities, including adverse neurocognitive effects. In vivo effects of ring-substituted analogs of phencyclidine (PCP), eticyclidine (PCE), and ketamine are understudied. Adult male National Institutes of Health Swiss mice were used to assess locomotor effects of PCP and its 3-OH, 3-MeO, 3-Cl, and 4-MeO analogs, PCE and its 3-OH and 3-MeO analogs, and ketamine and its deschloro and 2F-deschloro analogs, in comparison with those of methamphetamine (METH), 3,4-methylenedioxymethamphetamine (MDMA), and two benzofuran analogs of MDMA. PCP-like interoceptive effects for all of these ACXs were determined using a food-reinforced drug discrimination procedure in adult male Sprague Dawley rats. A novel operant assay of rule-governed behavior incorporating aspects of attentional set-shifting was used to profile psychosis-like neurocognitive effects of PCP and 3-Cl-PCP in rats, in comparison with cocaine and morphine. PCP-like ACXs were more effective locomotor stimulants than the amphetamines, PCE-like ACXs were as effective as the amphetamines, and ketamine-like ACXs were less effective than the amphetamines. Addition of -Cl, -OH, or -OMe at the 3-position on the aromatic ring did not impact locomotor effectiveness, but addition of -OMe at the 4-position reduced locomotor effectiveness. Lethal effects were induced by drugs with -OH at the 3-position or -OMe at the 3- or 4-position. All novel ACXs substituted at least partially for PCP, and PCP and 3-Cl-PCP elicited dose-dependent psychosis-like neurocognitive deficits in the rule-governed behavior task not observed with cocaine or morphine. Novel ACXs exhibit substantial abuse liability and toxicities not necessarily observed with their parent drugs. SIGNIFICANCE STATEMENT: Novel arylcyclohexylamine analogs of PCP, PCE, and ketamine are appearing on the illicit market, and abuse of these drugs poses risks for toxicities, including adverse neurocognitive effects. These studies demonstrate that the novel ACXs exhibit PCP-like abuse liability in the drug discrimination assay, elicit varied locomotor stimulant and lethal effects in mice, and induce psychosis-like neurocognitive effects in rats.

New insights into methoxetamine mechanisms of action: Focus on serotonergic 5-HT2 receptors in pharmacological and behavioral effects in the rat

Methoxetamine (MXE) is a dissociative substance of the arylcyclohexylamine class that has been present on the designer drug market as a ketamine-substitute since 2010. We have previously shown that MXE (i) possesses ketamine-like discriminative and positive rewarding effects in rats, (ii) affects brain processing involved in cognition and emotional responses, (iii) causes long-lasting behavioral abnormalities and neurotoxicity in rats and (iv) induces neurological, sensorimotor and cardiorespiratory alterations in mice. To shed light on the mechanisms through which MXE exerts its effects, we conducted a multidisciplinary study to evaluate the various neurotransmitter systems presumably involved in its actions on the brain. In vivo microdialysis study first showed that a single administration of MXE (0.25 and 0.5 mg/kg, i.v.) is able to significantly alter serotonin levels in the rat medial prefrontal cortex (mPFC) and nucleus accumbens. Then, we observed that blockade of the serotonin 5-HT₂ receptors through two selective antagonists, ketanserin (0.1 mg/kg, i.p.) and MDL 100907 (0.03 mg/kg, i.p.), at doses not affecting animals behavior per se, attenuated the facilitatory motor effect and the inhibition on visual sensory responses induced by MXE (3 mg/kg, i.p.) and ketamine (3 mg/kg, i.p.), and prevented MXE-induced reduction of the prepulse inhibition in rats, pointing to the 5-HT₂ receptors as a key target for the recently described MXE-induced sensorimotor effects. Finally, in-vitro electrophysiological studies revealed that the GABAergic and glutamatergic systems are also likely involved in the mechanisms through which MXE exerts its central effects since MXE inhibits, in a concentration-dependent manner, NMDA-mediated field postsynaptic potentials and GABA-mediated spontaneous currents. Conversely, MXE failed to alter both the AMPA component of field potentials and presynaptic glutamate release, and seems not to interfere with the endocannabinoid-mediated effects on mPFC GABAergic synapses. Altogether, our results support the notion of MXE as a NMDA receptor antagonist and shed further lights into the central mechanisms of action of this ketamine-substitute by pointing to serotonin 5-HT₂ receptors as crucial players in the expression of its sensorimotor altering effects and to the NMDA and GABA receptors as potential further important targets of action.

Light cycle phase advance as a model for jet lag reprograms the circadian rhythms of murine extraorbital lacrimal glands

PURPOSE

Jet lag causes a disruption in physiological rhythms in humans. This study aims to explore the extent to which jet lag affects the circadian rhythmicity in the lacrimal glands.

METHODS

C57BL/6J mice were subjected to a 12-h light/12-h dark (LD) cycle and an 8-h advanced LD schedule as a model for jet lag. On day 5 after the LD advance, the extraorbital lacrimal glands (ELGs) were collected at 3-h intervals during a 24-h cycle. Total mRNA was extracted from normal and advanced LD-treated ELGs and assayed using high-throughput RNA sequencing. The rhythmic transcripts were identified, analyzed, and visualized by bioinformatics techniques. Finally, (i) animal behavior; (ii) the mass, cell size, and secretion response of ELGs; and (iii) circadian migration of immune cells to ELGs were also assayed.

RESULTS

Jet lag treatment drastically altered the phase and composition of the rhythmic transcripts compared to that of normal ELGs. The key biological processes, signaling pathways, and protein-protein association networks were also dramatically altered in a spatiotemporal pattern. Furthermore, the circadian migration of neutrophils, T cells, B cells, and macrophages to the ELGs increased and shifted later by 6-h. Finally, the circadian rhythms of the ELGs with respect to mass, cell size, and secretion response were also impaired in jet lag-treated animals.

CONCLUSIONS

Jet lag impairs the circadian rhythm of the transcriptomic profile, structure, and secretion function of the lacrimal glands. This information provides novel insight into the negative effects of jet lag on ELGs.

The rise of new psychoactive substances and psychiatric implications: A wide-ranging, multifaceted challenge that needs far-reaching common legislative strategies

The ever-growing number of novel psychoactive substances (NPS) that have been surfacing globally, as well as related changes in drug abuse trends, undoubtedly constitute a difficult and multifaceted challenge for psychiatry. The intake and abuse of such substances has been linked to a risk of psychopathological disturbances, which stem from imbalances of a range of neurotransmitter pathways and receptors. Through an analysis of relevant research articles and reviews (particularly those outlining NPS neurological and cerebral mechanisms of action and psychopathological consequences arising from NPS abuse; research papers more closely focused on chemical/pharmacological aspects have been ruled out), through a systematic analysis of Pubmed, Medline, PsycLIT and EMBASE literature, as well as data released by health care institutions and drug enforcement agencies (among which the World Health Organization, the United Nations Office on Drugs and Crime, the European Monitoring Centre for Drugs and Drug Addiction, Eurojust, the Novel Psychoactive Treatment UK Network, the Court of Justice of the European Union), the authors aimed to elaborate on the most relevant data relative to NPS-related psychiatric effects, focusing on the conceptual and definition-related complexities inherent to NPS, clinical management and motivations for NPS use; moreover, an effort has been made to highlight the possible measures in order to tackle the unremitting rise of such elusive and potentially harmful substances.

Use of new and uncommon synthetic psychoactive drugs among a nationally representative sample in the United States, 2005-2017

OBJECTIVES

This study aims to examine patterns and first mentions of reported use of new or uncommon drugs across 13 years, among nationally representative samples in the United States.

METHODS

Participants (ages ≥12) in the National Surveys on Drug Use and Health (2005-2017, N = 730,418) were provided opportunities to type in names of new or uncommon drugs they had ever used that were not specifically queried. We examined self-reported use across survey years and determined years of first mentions.

RESULTS

From 2005 to 2017, there were 2,343 type-in responses for use of 79 new or uncommon synthetic drugs, and 54 were first-ever mentions of these drugs. The majority (65.8%) of mentions were phenethylamines (e.g., 2C-x, NBOMe), which were also the plurality of new drug mentions (n = 22; 40.7%). Mentions of 2C-x drugs in particular increased from 30 mentions in 2005 to 147 mentions in 2013. We estimate an upward trend in use of new or uncommon drugs between 2005 and 2017 (p < 0.001).

CONCLUSION

Although type-in responses on surveys are limited and underestimate prevalence of use, such responses can help inform researchers when new compounds are used. Continued surveillance of use of new and uncommon drugs is needed to inform adequate public health response.

Methoxetamine: A foe or friend?

Methoxetamine (MXE) is an N-methyl-D-aspartate (NMDA) receptor antagonist that is chemically and pharmacologically similar to other dissociative substances, such as ketamine and phencyclidine. There are reports on the misuse of MXE, which sometimes resulted in adverse consequences and death. Studies have also shown that MXE has abuse liability and stimulates dopamine neurotransmission in the mesolimbic reward pathway in the brain. These findings have contributed to the negative impression on MXE. However, recent preclinical studies have identified the antidepressant properties of MXE, which are attributed to its ability to affect the glutamatergic and serotonergic systems. MXE is also reported to have analgesic effects. These findings show some of the "redeeming qualities" of MXE and indicate its possible therapeutic uses. In this paper, we have reviewed the findings that provide insights into the adverse and potential therapeutic effects of MXE. We compiled studies on the toxicity, psychotomimetic effects, and abuse liability of MXE, as well as its promising antidepressant and analgesic properties. We also have discussed the mechanism of action that might mediate the somewhat paradoxical effects observed. Importantly, this review provides valuable information on MXE for future research and will enable a better understanding of its psychopharmacological properties and the mechanisms responsible for its unique effects.

Neurological, sensorimotor and cardiorespiratory alterations induced by methoxetamine, ketamine and phencyclidine in mice

Novel psychoactive substances are intoxicating compounds developed to mimic the effects of well-established drugs of abuse. They are not controlled by the United Nations drug convention and pose serious health concerns worldwide. Among them, the dissociative drug methoxetamine (MXE) is structurally similar to ketamine (KET) and phencyclidine (PCP) and was created to purposely mimic the psychotropic effects of its "parent" compounds. Recent animal studies show that MXE is able to stimulate the mesolimbic dopaminergic transmission and to induce KET-like discriminative and rewarding effects. In light of the renewed interest in KET and PCP analogs, we decided to deepen the investigation of MXE-induced effects by a battery of behavioral tests widely used in studies of "safety-pharmacology" for the preclinical characterization of new molecules. To this purpose, the acute effects of MXE on neurological and sensorimotor functions in mice, including visual, acoustic and tactile responses, thermal and mechanical pain, motor activity and acoustic startle reactivity were evaluated in comparisons with KET and PCP to better appreciate its specificity of action. Cardiorespiratory parameters and blood pressure were also monitored in awake and freely moving animals. Acute systemic administrations of MXE, KET and PCP (0.01-30 mg/kg i.p.) differentially alter neurological and sensorimotor functions in mice depending in a dose-dependent manner specific for each parameter examined. MXE and KET (1 and 30 mg/kg i.p.) and PCP (1 and 10 mg/kg i.p.) also affect significantly cardiorespiratory parameters, systolic and diastolic blood pressure in mice.