The hallucinogen 2,5-dimethoxy-4-iodoamphetamine hydrochloride activates neurotrophin receptors in a neuronal cell line and promotes neurites extension

Disentangling the acute subjective effects of classic psychedelics from their enduring therapeutic properties

Recent research with classic psychedelics suggests significant therapeutic potential, particularly for neuropsychiatric disorders. A mediating influence behind symptom resolution is thought to be the personal insight - at times, bordering on the mystical - one acquires during the acute phase of a psychedelic session. Indeed, current clinical trials have found strong correlations between the acute subjective effects (ASE) under the influence of psychedelics and their enduring therapeutic properties. However, with potential barriers to widespread clinical implementation, including the healthcare resource-intensive nature of psychedelic sessions and the exclusion of certain at-risk patient groups, there is an active search to determine whether ASE elimination can be accompanied by the retention of persisting therapeutic benefits of these class of compounds. Recognizing the aberrant underlying neural circuitry that characterizes a range of neuropsychiatric disorders, and that classic psychedelics promote neuroplastic changes that may correct abnormal circuitry, investigators are rushing to design and discover compounds with psychoplastogenic, but not hallucinogenic (i.e., ASE), therapeutic potential. These efforts have paved the discovery of 'non-psychedelic/subjective psychedelics', or compounds that lack hallucinogenic activity but with therapeutic efficacy in preclinical models. This review aims to distill the current evidence - both clinical and preclinical - surrounding the question: can the ASE of classic psychedelics be dissociated from their sustained therapeutic properties? Several plausible clinical scenarios are then proposed to offer clarity on and potentially answer this question.

Serotonergic Psychedelics in Neural Plasticity

Psychedelics, compounds that can induce dramatic changes in conscious experience, have been used by humans for centuries. Recent studies have shown that certain psychedelics can induce neural plasticity by promoting neurite growth and synapse formation. In this review, we focus on the role of classical serotonergic psychedelics in neural plasticity and discuss its implication for their therapeutic potentials.

Neuropsychological Functioning in Users of Serotonergic Psychedelics - A Systematic Review and Meta-Analysis

Background: Serotonergic psychedelics (SPs) like LSD, psilocybin, DMT, and mescaline are a heterogeneous group of substances that share agonism at 5-HT2a receptors. Besides the ability of these substances to facilitate profoundly altered states of consciousness, persisting psychological effects have been reported after single administrations, which outlast the acute psychedelic effects. In this review and meta-analysis, we investigated if repeated SP use associates with a characteristic neuropsychological profile indicating persisting effects on neuropsychological function. Methods: We conducted a systematic review of studies investigating the neuropsychological performance in SP users, searching studies in Medline, Web of Science, embase, ClinicalTrials.gov, and EudraCT. Studies were included if they reported at least one neuropsychological measurement in users of SPs. Studies comparing SP users and non-users that reported mean scores and standard deviations were included in an exploratory meta-analysis. Results: 13 studies (N = 539) published between 1969 and 2020 were included in this systematic review. Overall, we found that only three SPs were specifically investigated: ayahuasca (6 studies, n = 343), LSD (5 studies, n = 135), and peyote (1 study, n = 61). However, heterogeneity of the methodological quality was high across studies, with matching problems representing the most important limitation. Across all SPs, no uniform pattern of neuropsychological impairment was identified. Rather, the individual SPs seemed to be associated with distinct neuropsychological profiles. For instance, one study (n = 42) found LSD users to perform worse in trials A and B of the Trail-Making task, whereas meta-analytic assessment (5 studies, n = 352) of eleven individual neuropsychological measures indicated a better performance of ayahuasca users in the Stroop incongruent task (p = 0.03) and no differences in the others (all p > 0.05). Conclusion: The majority of the included studies were not completely successful in controlling for confounders such as differences in non-psychedelic substance use between SP-users and non-users. Our analysis suggests that LSD, ayahuasca and peyote may have different neuropsychological consequences associated with their use. While LSD users showed reduced executive functioning and peyote users showed no differences across domains, there is some evidence that ayahuasca use is associated with increased executive functioning.

Substances of abuse and the blood brain barrier: Interactions with physical exercise

Substance use disorders pose a common medical, social and financial problem. Among the pathomechanisms of substance use disorders, the disruption and increased permeability of the blood-brain barrier has been recently revealed. Physical exercise appears to be a relatively inexpensive and feasible way to implement behavioral therapy counteracting the blood-brain barrier impairment. Concomitantly, there are also studies supporting a potential protective role of selected substances of abuse in maintaining the blood-brain barrier integrity. In this review, we aim to provide a summary on the modulatory influence of physical exercise, a non-pharmacological intervention, on the blood-brain barrier alterations caused by substances of abuse. Further studies are needed to understand the precise mechanisms that underlie various effects of physical exercise in substance use disorders.

Safety, tolerability, pharmacokinetics, and pharmacodynamics of low dose lysergic acid diethylamide (LSD) in healthy older volunteers

Research has shown that psychedelics, such as lysergic acid diethylamide (LSD), have profound anti-inflammatory properties mediated by 5-HT2A receptor signaling, supporting their evaluation as a therapeutic for neuroinflammation associated with neurodegenerative disease.

OBJECTIVE

This study evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of orally repeated administration of 5 μg, 10 μg, and 20 μg LSD in older healthy individuals. In the current paper, we present safety, tolerability, pharmacokinetics, and pharmacodynamic measures that relate to safety, tolerability, and dose response.

METHODS

This was a phase 1 double-blind, placebo-controlled, randomized study. Volunteers were randomly assigned to 1 of 4 dose groups (5 μg, 10 μg, 20 μg LSD, and placebo), and received their assigned dose on six occasions (i.e., every 4 days).

RESULTS

Forty-eight older healthy volunteers (mean age = 62.9 years) received placebo (n = 12), 5 μg (n = 12), 10 μg (n = 12), or 20 μg (n = 12) LSD. LSD plasma levels were undetectable for the 5 μg group and peak blood plasma levels for the 10 μg and 20 μg groups occurred at 30 min. LSD was well tolerated, and the frequency of adverse events was no higher than for placebo. Assessments of cognition, balance, and proprioception revealed no impairment.

CONCLUSIONS

Our results suggest safety and tolerability of orally administered 5 μg, 10 μg, and 20 μg LSD every fourth day over a 21-day period and support further clinical development of LSD for the treatment and prevention of Alzheimer's disease (AD).

[Neurotrophic mechanisms of psychedelic therapy]

Psychedelic drugs, often referred to as hallucinogens, are quite distinct from other classes of psychotropic drugs. Although the subjective and behavioral effects they induce are quite dramatic, they possess little addictive potential when compared to nicotine, alcohol or opiates. Since the discovery of ketamine antidepressant effects, there has been growing interest for these molecules. Serotonergic psychedelics such as psilocybin and lysergic acid diethylamide (LSD) are gaining attention as potential treatments for depression and addiction, similarly to 3,4-methylenedioxymethamphetamine (MDMA) for post-traumatic stress disorder (PTSD), and ibogaine for addiction. Although they possess distinct pharmacological profiles, their kinetics of action are quite similar: the therapeutic effects are felt within the hours following administration, and last well beyond drug elimination by the organism. This strongly suggests the induction of neurogenic and plastic mechanisms, including the involvement of trophic factors. This review will explore the literature dealing with the effects of psychedelics on neurotrophins, as well as the plastic adaptations that they induce, in an attempt to understand their surprising therapeutic potential. We will show that although ketamine and serotonergic psychedelics have affinity for very different receptors (NMDA, 5-HT2A), they ultimately initiate similar plastic adaptations in the prefrontal cortex through the involvement of the brain-derived neurotrophic factor (BDNF). We will see that although MDMA uses the same receptors as serotonergic psychedelics to alleviate PTSD symptoms, its effect on BDNF levels seem paradoxical and quite different. Finally, we show how ibogaine could exert its anti-addictive properties through a completely different neurotrophic factor than other psychedelic drugs, the glial cell line-derived neurotrophic factor (GDNF). While the current literature concerning the psychiatric applications of psychedelic therapy is encouraging, it remains to be determined whether their benefits could be obtained without their psychotomimetic effects, or concerns over potential toxicity.

Psychedelics Promote Structural and Functional Neural Plasticity

Atrophy of neurons in the prefrontal cortex (PFC) plays a key role in the pathophysiology of depression and related disorders. The ability to promote both structural and functional plasticity in the PFC has been hypothesized to underlie the fast-acting antidepressant properties of the dissociative anesthetic ketamine. Here, we report that, like ketamine, serotonergic psychedelics are capable of robustly increasing neuritogenesis and/or spinogenesis both in vitro and in vivo. These changes in neuronal structure are accompanied by increased synapse number and function, as measured by fluorescence microscopy and electrophysiology. The structural changes induced by psychedelics appear to result from stimulation of the TrkB, mTOR, and 5-HT2A signaling pathways and could possibly explain the clinical effectiveness of these compounds. Our results underscore the therapeutic potential of psychedelics and, importantly, identify several lead scaffolds for medicinal chemistry efforts focused on developing plasticity-promoting compounds as safe, effective, and fast-acting treatments for depression and related disorders.