Serotonin-2 Receptor Agonists Produce Anti-inflammatory Effects through Functionally Selective Mechanisms That Involve the Suppression of Disease-Induced Arginase 1 Expression

Functional selectivity in the context of serotonin 2A (5-HT2A) receptor agonists is often described as differences psychedelic compounds have in the activation of Gq vs β-arrestin signaling in the brain and how that may relate to inducing psychoactive and hallucinatory properties with respect to each other. However, the presence of 5-HT2A receptors throughout the body in several cell types, including endothelial, endocrine, and immune-related tissues, suggests that functional selectivity may exist in the periphery as well. Here, we examine functional selectivity between two 5-HT2A receptor agonists of the phenylalkylamine class: (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI] and (R)-2,5-dimethoxy-4-trifluoromethylamphetamine [(R)-DOTFM]. Despite comparable in vitro activity at the 5-HT2A receptor as well as similar behavioral potency, (R)-DOTFM does not exhibit an ability to prevent inflammation or elevated airway hyperresponsiveness (AHR) in an acute murine ovalbumin-induced asthma model as does (R)-DOI. Furthermore, there are distinct differences between protein expression and inflammatory-related gene expression in pulmonary tissues between the two compounds. Using (R)-DOI and (R)-DOTFM as tools, we further elucidated the anti-inflammatory mechanisms underlying the powerful anti-inflammatory effects of certain psychedelics and identified key mechanistic components of the anti-inflammatory effects of psychedelics, including suppression of arginase 1 expression.

Preclinical perspectives on the mechanisms underlying the therapeutic actions of psilocybin in psychiatric disorders

Psychedelic compounds have shown extraordinary potential in treating a wide range of neuropsychiatric disorders. Psilocybin, for example, has now been shown in several clinical trials to induce a rapid (within days) and persistent (3-12 months) improvement in human treatment-resistant depression and other neuropsychiatric conditions. Here we review the preclinical models and experimental approaches that have been used to study the neurobiological actions of psychedelic drugs. We further summarize the insights these studies have provided into the possible mechanisms underlying the induction of their therapeutic actions, including the receptors to which psychedelics bind and the second messenger signaling cascades that they activate. We also discuss potential biological processes that psychedelics may alter to produce the lasting amelioration of symptoms, including improvements in synaptic structure and function and suppression of inflammation. Improved mechanistic understanding of psychedelic drug actions will aid in the advancement of these promising new medicines.

Psychedelic drug abuse potential assessment research for new drug applications and Controlled Substances Act scheduling

New medicines containing classic hallucinogenic and entactogenic psychedelic substance are under development for various psychiatric and neurological disorders. Many of these, including psilocybin, lysergic acid diethylamide (LSD), and 3,4-methylenedioxymethamphetamine (MDMA) are Schedule I controlled substances of the United States Controlled Substances Act (US CSA), and similarly controlled globally. The implications of the CSA for research and medicines development, the path to approval of medicines, and their subsequent removal from Schedule I in the US are discussed. This entire process occurs within the framework of the CSA in the US and its counterparts internationally in accordance with international drug control treaties. Abuse potential related research in the US informs the eight factors of the CSA which provide the basis for rescheduling actions that must occur upon approval of a drug that contains a Schedule I substance. Abuse-related research also informs drug product labeling and the risk evaluation and mitigation strategies (REMS) will likely be required for approved medicines. Human abuse potential studies typically employed in CNS drug development may be problematic for substances with strong hallucinogenic effects such as psilocybin, and alternative strategies are discussed. Implications for research, medicinal development, and controlled substance scheduling are presented in the context of the US CSA and FDA requirements with implications for global regulation. We also discuss how abuse-related research can contribute to understanding mechanisms of action and therapeutic effects as well as the totality of the effects of the drugs on the brain, behavior, mood, and the constructs of spirituality and consciousness.

Preface to the special issue "Psychedelics and Neurochemistry"

Psychedelics are a relatively recent field of research that had not gained much support half a century ago, yet it developed into a much acknowledged, highly relevant field that extends to many people's lives. Psychedelics have demonstrated profound and durable therapeutic potential for the treatment of several psychiatric disorders including depression, anxiety, and substance use disorders, among others. In this special issue, basic science of psychedelics is reviewed with respect to fundamental cellular, molecular, and genetic mechanisms, all the way up to the human systems level with clinical reviews. We hope the articles, authored by leading scientists in their field, will help to understand better the role of the serotonin 5-HT_2A receptor in particular in healthy and diseased brain function.

Validation of the forced swim test in Drosophila, and its use to demonstrate psilocybin has long-lasting antidepressant-like effects in flies

Psilocybin has been shown to be a powerful, long-lasting antidepressant in human clinical trials and in rodent models. Although rodents have commonly been used to model psychiatric disorders, Drosophila have neurotransmitter systems similar to mammals and many comparable brain structures involved in similar behaviors. The forced swim test (FST), which has been used extensively to evaluate compounds for antidepressant efficacy, has recently been adapted for Drosophila. The fly FST has potential to be a cost-effective, high-throughput assay for evaluating potential antidepressants. For this study we pharmacologically validated the fly FST using methamphetamine, DL-α-methyltyrosine, and the antidepressant citalopram. While methamphetamine and DL-α-methyltyrosine altered overall locomotor activity in the Drosophila Activity Monitor System (DAMS), they had no significant impact on measures of immobility in the FST. Conversely, chronic citalopram decreased measures of immobility in the FST in both sexes without increasing DAMS activity. We used the validated FST to evaluate the antidepressant-like effects of high (3.5 mM) and low (0.03 mM) doses of psilocybin. Both doses of psilocybin significantly reduced measures of immobility in male flies, but not females. 0.03 mM had an effect size comparable to chronic citalopram, and 3.5 mM had an effect size approximately twice that of chronic citalopram.

Herpes Simplex Virus-1 Induced Serotonin-Associated Metabolic Pathways Correlate With Severity of Virus- and Inflammation-Associated Ocular Disease

Herpes simplex virus-associated diseases are a complex interaction between cytolytic viral replication and inflammation. Within the normally avascular and immunoprivileged cornea, HSV ocular infection can result in vision-threatening immune-mediated herpetic keratitis, the leading infectious cause of corneal blindness in the industrialized world. Viral replicative processes are entirely dependent upon numerous cellular biosynthetic and metabolic pathways. Consistent with this premise, HSV infection was shown to profoundly alter gene expression associated with cellular amino acid biosynthetic pathways, including key tryptophan metabolism genes. The essential amino acid tryptophan is crucial for pathogen replication, the generation of host immune responses, and the synthesis of neurotransmitters, such as serotonin. Intriguingly, Tryptophan hydroxylase 2 (TPH2), the neuronal specific rate-limiting enzyme for serotonin synthesis, was the most significantly upregulated gene by HSV in an amino acid metabolism PCR array. Despite the well-defined effects of serotonin in the nervous system, the association of peripheral serotonin in disease-promoting inflammation has only recently begun to be elucidated. Likewise, the impact of serotonin on viral replication and ocular disease is also largely unknown. We therefore examined the effect of HSV-induced serotonin-associated synthesis and transport pathways on HSV-1 replication, as well as the correlation between HSV-induced ocular serotonin levels and disease severity. HSV infection induced expression of the critical serotonin synthesis enzymes TPH-1, TPH-2, and DOPA decarboxylase (DDC), as well as the serotonin transporter, SERT. Concordantly, HSV-infected cells upregulated serotonin synthesis and its intracellular uptake. Increased serotonin synthesis and uptake was shown to influence HSV replication. Exogenous addition of serotonin increased HSV-1 yield, while both TPH-1/2 and SERT pharmacological inhibition reduced viral yield. Congruent with these in vitro findings, rabbits intraocularly infected with HSV-1 exhibited significantly higher aqueous humor serotonin concentrations that positively and strongly correlated with viral load and ocular disease severity. Collectively, our findings indicate that HSV-1 promotes serotonin synthesis and cellular uptake to facilitate viral replication and consequently, serotonin's proinflammatory effects may enhance the development of ocular disease.

Psychedelics and Anti-inflammatory Activity in Animal Models

The serotonin (5-hydroxytryptamine, 5-HT) 2A receptor is most well known as the common target for classic psychedelic compounds. Interestingly, the 5-HT_2A receptor is the most widely expressed mammalian serotonin receptor and is found in nearly every examined tissue type including neural, endocrine, endothelial, immune, and muscle, suggesting it could be a novel and pharmacological target for several types of disorders. Despite this, the bulk of research on the 5-HT_2A receptor is focused on its role in the central nervous system (CNS). Recently, activation of 5-HT_2A receptors has emerged as a new anti-inflammatory strategy. This review will describe recent findings regarding psychedelics as anti-inflammatory compounds, as well as parse out differences in functional selectivity and immune regulation that exist between a number of well-known hallucinogenic compounds.

Lysergic acid diethylamide induces increased signalling entropy in rats' prefrontal cortex

Psychedelic drugs are gaining attention from the scientific community as potential new compounds for the treatment of psychiatric diseases such as mood and substance use disorders. The 5‐HT_2A receptor has been identified as the main molecular target, and early studies pointed to an effect on the expression of neuroplasticity genes. Analysing RNA‐seq data from the prefrontal cortex of rats chronically treated with lysergic acid diethylamide (LSD), we describe the psychedelic‐induced rewiring of gene co‐expression networks, which become less centralised but more complex, with an overall increase in signalling entropy typical of highly plastic systems. Intriguingly, signalling entropy mirrors, at the molecular level, the increased brain entropy reported through neuroimaging studies in human, suggesting the underlying mechanisms of higher‐order phenomena. Moreover, from the analysis of network topology, we identify potential transcriptional regulators and propose the involvement of different cell types in psychedelics’ activity.

Serotonin 5-HT2A receptor activity mediates adipocyte differentiation through control of adipogenic gene expression

Serotonin 5-HT2 receptors are expressed in many tissues and play important roles in biological processes. Although the 5-HT2A receptor is primarily known for its role in central nervous system, it is also expressed in peripheral tissues. We have found that 5-HT2A receptor antagonists inhibit human subcutaneous primary adipocyte differentiation. We also show that siRNA knockdown of the 5-HT2A receptor blocks differentiation. Using gene expression analysis in combination with receptor antagonists we found that activity of 5-HT2A receptors is necessary very early in the differentiation process to mediate expression of adipogenic genes, including peroxisome proliferator-activated receptor gamma (ppar-γ), adipocyte protein 2 (aP2), adiponectin, and serine/threonine-protein kinase 1 (sgk1). We show here for the first time that 5-HT2A receptor activity is necessary for differentiation of human primary subcutaneous preadipocytes to adipocytes, and that 5-HT2A receptor activity mediates key genes related to adipogenesis during this process. Importantly, this work contributes to a greater understanding of the adipocyte differentiation process, as well as to the role of 5-HT2A receptors in peripheral tissues, and may be relevant to the development of novel therapeutic strategies targeting this receptor for the treatment of obesity related diseases.

Structure-Activity Relationship Analysis of Psychedelics in a Rat Model of Asthma Reveals the Anti-Inflammatory Pharmacophore

Psychedelic drugs can exert potent anti-inflammatory effects. However, anti-inflammatory effects do not appear to correlate with behavioral activity, suggesting different underlying mechanisms. We hypothesized that the distinct structural features of psychedelics underlie functionally selective mechanisms at the target 5-HT2A receptor to elicit maximal anti-inflammatory effects. In order to test this hypothesis, we developed a new rat-based screening platform for allergic asthma. Next, we investigated 21 agonists at the 5-HT2A receptor from the three primary chemotypes (phenylalkylamine, ergoline, and tryptamine) for their ability to prevent airways hyperresponsiveness as a measure of pulmonary inflammation. Furthermore, we assessed each drug for in vitro activation of the canonical signaling pathway, calcium mobilization, from the 5-HT2A receptor. We find that the drug 2,5-dimethoxyphenethylamine (2C-H) represents the pharmacophore for anti-inflammatory activity and identify structural modifications that are either permissive or detrimental to anti-inflammatory activity. Additionally, there is no correlation between the ability of a particular psychedelic to activate intracellular calcium mobilization and to prevent the symptoms of asthma or with behavioral potencies. Our results support the notions that specific structural features mediate functional selectivity underlying anti-inflammatory activity and that relevant receptor activated pathways necessary for anti-inflammatory activity are different from canonical signaling pathways. Our results inform on the nature of interactions between ligands at the 5-HT2A receptor as they relate to anti-inflammatory activity and are crucial for the development of new 5-HT2A receptor agonists for anti-inflammatory therapeutics in the clinic that may be devoid of behavioral activity.

Psychedelics, but Not Ketamine, Produce Persistent Antidepressant-like Effects in a Rodent Experimental System for the Study of Depression

Psilocybin shows efficacy to alleviate depression in human clinical trials for six or more months after only one or two treatments. Another hallucinogenic drug, esketamine, has recently been U.S. Food and Drug Administration (FDA)-approved as a rapid-acting antidepressant. The mechanistic basis for the antidepressant effects of psilocybin and ketamine appear to be conserved. The efficacy of these two medications has not, however, been directly compared either clinically or preclinically. Further, whether or not a profound subjective existential experience is necessary for psilocybin to have antidepressant effects is unknown. To address these questions, we tested psilocybin, lysergic acid diethylamide (LSD), and ketamine in a rat model for depression. As in humans, a single administration of psilocybin or LSD produced persistent antidepressant-like effects in our model. In contrast, ketamine produced only a transient antidepressant-like effect. Our results indicate that classic psychedelics may have therapeutic efficacy that is more persistent than that of ketamine, and also suggest that a subjective existential experience may not be necessary for therapeutic effects.

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).

5-HT2 receptor activation alleviates airway inflammation and structural remodeling in a chronic mouse asthma model

AIMS

Although the bulk of research into the biology of serotonin 5-HT_2A receptors has focused on its role in the CNS, selective activation of these receptors in peripheral tissues can produce profound anti-inflammatory effects. We previously demonstrated that the small molecule 5-HT₂ receptor agonist (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI] inhibits TNF-α-mediated proinflammatory signaling cascades and inflammation via 5-HT_2A receptor activation and prevents the development of, and inflammation associated with, acute allergic asthma in a mouse ovalbumin (OVA) model. Here, we investigated the ability of (R)-DOI to reverse inflammation and symptoms associated with established asthma in a newly developed model of chronic asthma.

METHODS

An 18-week ovalbumin challenge period was performed to generate persistent, chronic asthma in BALB/c mice. Four once daily intranasal treatments of (R)-DOI were administered one week after allergen cessation, with respiratory parameters being measured by whole-body plethysmography (WBP). Cytokine and chemokine levels were measured by quantitative real-time polymerase chain reaction (qRT-PCR) in homogenized lung tissue, bronchoalveolar (BALF) fluid was analyzed for chemokine modulation by multiplex assays, and Periodic Acid-Schiff and Masson's Trichrome staining was performed to determine goblet cell infiltration and overall changes to lung morphology.

KEY FINDINGS

5-HT₂ activation via (R)-DOI attenuates elevated airway hyperresponsiveness to methacholine, reduces pulmonary inflammation and mucus production, and reduces airway structural remodeling and collagen deposition by nearly 70%.

SIGNIFICANCE

Overall, these data provide support for the therapeutic potential of (R)-DOI and 5-HT₂ receptor activation for the treatment of asthma, and identifies (R)-DOI as a novel therapeutic compound against pulmonary fibrosis.

Activation of 5-HT2 Receptors Reduces Inflammation in Vascular Tissue and Cholesterol Levels in High-Fat Diet-Fed Apolipoprotein E Knockout Mice

Coronary artery disease (CAD) is a progressive cardiovascular syndrome characterized by cholesterol-induced focal arterial lesions that impair oxygen delivery to the heart. As both innate and adaptive immune cells play critical roles in the formation and progression of arterial plaques and endothelial cell dysfunction, CAD is commonly viewed as a chronic inflammatory disorder. Our lab has previously discovered that 5-HT_2A receptor activation with the 5-HT₂ receptor selective agonist (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI] has potent anti-inflammatory activity in both cell culture and whole animal models. Here we have examined the putative therapeutic effects of (R)-DOI in the ApoE^−/− high fat model of cardiovascular disease. Subcutaneously implanted osmotic minipumps were used to infuse sustained low rates (0.15 μg / hr) of (R)-DOI∙HCl to mice fed a high-fat “Western” diet. (R)-DOI treated mice had significant reductions in expression levels of mRNA for inflammatory markers like Il6 in vascular tissue, normalized glucose homeostasis, and reduced circulating cholesterol levels. As cardiovascular disease is a leading cause of death both globally and in the Western world, activation of 5-HT_2A receptors at sub-behavioral levels may represent a new strategy to treat inflammation-based cardiovascular disease.

Microdosing psychedelics: More questions than answers? An overview and suggestions for future research

BACKGROUND

In the past few years, the issue of 'microdosing' psychedelics has been openly discussed in the public arena where claims have been made about their positive effect on mood state and cognitive processes such as concentration. However, there are very few scientific studies that have specifically addressed this issue, and there is no agreed scientific consensus on what microdosing is.

AIM

This critique paper is designed to address questions that need to be answered by future scientific studies and to offer guidelines for these studies.

APPROACH

Owing to its proximity for a possible approval in clinical use and short-lasting pharmacokinetics, our focus is predominantly on psilocybin. Psilocybin is allegedly, next to lysergic acid diethylamide (LSD), one of the two most frequently used psychedelics to microdose. Where relevant and available, data for other psychedelic drugs are also mentioned.

CONCLUSION

It is concluded that while most anecdotal reports focus on the positive experiences with microdosing, future research should also focus on potential risks of (multiple) administrations of a psychedelic in low doses. To that end, (pre)clinical studies including biological (e.g. heart rate, receptor turnover and occupancy) as well as cognitive (e.g. memory, attention) parameters have to be conducted and will shed light on the potential negative consequences microdosing could have.

Population Survey Data Informing the Therapeutic Potential of Classic and Novel Phenethylamine, Tryptamine, and Lysergamide Psychedelics

INTRODUCTION

The majority of contemporary psychedelic research has focused on ayahuasca, lysergic acid diethylamide, and psilocybin, though there are hundreds of novel psychedelic compounds that may have clinical utility. The purpose of the present study was to evaluate the therapeutic potential of classic and novel phenethylamine, tryptamine, and lysergamide psychedelics via a large, nationally representative population-based survey.

METHODS

We tested the unique associations of lifetime classic and novel phenethylamine, tryptamine, and lysergamide psychedelics with past month psychological distress and past year suicidality among respondents pooled from years 2008-2017 of the National Survey on Drug Use and Health (weighted N = 260,964,827).

RESULTS

Lifetime classic tryptamine use was associated with a decreased odds of past month psychological distress [aOR = 0.76; (0.69-0.83)] and past year suicidal thinking [aOR = 0.79; (0.72-0.87)]. Lifetime novel phenethylamine use, on the other hand, was associated with an increased odds of past year suicidal thinking [aOR = 1.44; (1.06-1.95)] and past year suicidal planning [aOR = 1.60; (1.06-2.41)]. No other significant associations were found.

DISCUSSION AND CONCLUSIONS

These findings, which may be driven by differences in pharmacodynamics, suggest that classic tryptamines may hold the greatest therapeutic potential of the psychedelics, whereas novel phenethylamines may pose risk for harm. The present findings thus support continued research on the clinical application of classic tryptamines. Though the current results caution against the clinical utility of novel phenethylamines, further study of these and other novel psychedelic substances is nonetheless warranted to better understand their potential application.

Psychedelics as anti-inflammatory agents

Serotonin (5-hydroxytryptamine, 5-HT)_2A receptor agonists have recently emerged as promising new treatment options for a variety of disorders. The recent success of these agonists, also known as psychedelics, like psilocybin for the treatment of anxiety, depression, obsessive-compulsive disorder (OCD), and addiction, has ushered in a renaissance in the way these compounds are perceived in the medical community and populace at large. One emerging therapeutic area that holds significant promise is their use as anti-inflammatory agents. Activation of 5-HT_2A receptors produces potent anti-inflammatory effects in animal models of human inflammatory disorders at sub-behavioural levels. This review discusses the role of the 5-HT_2A receptor in the inflammatory response, as well as highlight studies using the 5-HT_2A agonist (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI] to treat inflammation in cellular and animal models. It also examines potential mechanisms by which 5-HT_2A agonists produce their therapeutic effects. Overall, psychedelics regulate inflammatory pathways via novel mechanisms, and may represent a new and exciting treatment strategy for several inflammatory disorders.

Neurocytometry: Flow Cytometric Sorting of Specific Neuronal Populations from Human and Rodent Brain

Flow cytometry has the potential to facilitate understanding of the heterogeneous responses of diverse brain cell populations to a variety of stimuli. However, existing methods of applying flow cytometry to brain tissues are each limited in certain ways. They either require genetically labeled cells to achieve separation of specific populations, are not applicable to previously fixed tissue, or are not compatible with downstream mRNA analysis. Here, we describe a group of related methods that overcome many previous limitations and allow robust sorting and downstream molecular analysis of highly enriched populations of specific neuronal and non-neuronal cells from any mammalian brain. We illustrate these techniques, which are compatible with antibodies for both nuclear and non-nuclear epitopes and do not require transgenic animals, with three examples. First, we describe the separation and downstream mRNA analysis of four types of cortical interneurons (somatostatin, parvalbumin, calretinin, and calbindin) from paraformaldehyde-fixed rat brain sections. Second, we demonstrate separation of neurons and non-neurons from zinc-fixed mouse brain cortical sections followed by analysis of enzymatic activity (ACE2 activity) and mRNA expression. Third, we show that routinely fixed post-mortem human brain can be analyzed by isolating parvalbumin-containing neurons from cortical samples that were fixed for periods of up to 8 weeks in formalin. In each case, sorted cell identity was confirmed with mRNA analysis. The neurocytometry methodology described here has the potential to significantly expand studies to analyze the effects of drugs, environmental manipulations, and disease states on the nucleic acid and protein content of specific brain cell populations.

Psychedelics as Medicines: An Emerging New Paradigm

Scientific interest in serotonergic psychedelics (e.g., psilocybin and LSD; 5-HT_2A receptor agonists) has dramatically increased within the last decade. Clinical studies administering psychedelics with psychotherapy have shown preliminary evidence of robust efficacy in treating anxiety and depression, as well as addiction to tobacco and alcohol. Moreover, recent research has suggested that these compounds have potential efficacy against inflammatory diseases through novel mechanisms, with potential advantages over existing antiinflammatory agents. We propose that psychedelics exert therapeutic effects for psychiatric disorders by acutely destabilizing local brain network hubs and global network connectivity via amplification of neuronal avalanches, providing the occasion for brain network "resetting" after the acute effects have resolved. Antiinflammatory effects may hold promise for efficacy in treatment of inflammation-related nonpsychiatric as well as potentially for psychiatric disorders. Serotonergic psychedelics operate through unique mechanisms that show promising effects for a variety of intractable, debilitating, and lethal disorders, and should be rigorously researched.

Psychedelics Recruit Multiple Cellular Types and Produce Complex Transcriptional Responses Within the Brain

There has recently been a resurgence of interest in psychedelics, substances that profoundly alter perception and cognition and have recently demonstrated therapeutic efficacy to treat anxiety, depression, and addiction in the clinic. The receptor mechanisms that drive their molecular and behavioral effects involve activation of cortical serotonin 5-HT_2A receptors, but the responses of specific cellular populations remain unknown. Here, we provide evidence that a small subset of 5-HT_2A-expressing excitatory neurons is directly activated by psychedelics and subsequently recruits other select cell types including subpopulations of inhibitory somatostatin and parvalbumin GABAergic interneurons, as well as astrocytes, to produce distinct and regional responses. To gather data regarding the response of specific neuronal populations, we developed methodology for fluorescence-activated cell sorting (FACS) to segregate and enrich specific cellular subtypes in the brain. These methods allow for robust neuronal sorting based on cytoplasmic epitopes followed by downstream nucleic acid analysis, expanding the utility of FACS in neuroscience research.

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Psychedelics activate distinct transcription across cell types, including excitatory neurons, inhibitory neurons, and astrocytes

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Psychedelics induce internalization of 5-HT_2A receptors throughout the cortex and claustrum

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FACS can separate neuronal subpopulations that require non-nuclear markers

Psychedelic drugs are known to act through the 5-HT_2A receptor to produce many of their effects, however, the precise cellular populations in the brain which respond to this class of drugs remain unknown. We use flow cytometric analyses, immunohistochemistry, and gene expression analyses to identify small populations of specific cells in the brain that are activated by the psychedelic drug, (R)-DOI. The methodology used in these studies will be useful to determine the molecular effects of any manipulation or disease on particular brain cells.

Serotonin 5-HT₂ receptor activation prevents allergic asthma in a mouse model

Asthma is an inflammatory disease of the lung characterized by airways hyper-responsiveness (AHR), inflammation, and mucus hyperproduction. Current mainstream therapies include bronchodilators that relieve bronchoconstriction and inhaled glucocorticoids to reduce inflammation. The small molecule hormone and neurotransmitter serotonin has long been known to be involved in inflammatory processes; however, its precise role in asthma is unknown. We have previously established that activation of serotonin 5-hydroxytryptamine (5-HT)(2A) receptors has potent anti-inflammatory activity in primary cultures of vascular tissues and in the whole animal in vasculature and gut tissues. The 5-HT(2A) receptor agonist, (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI] is especially potent. In this work, we have examined the effect of (R)-DOI in an established mouse model of allergic asthma. In the ovalbumin mouse model of allergic inflammation, we demonstrate that inhalation of (R)-DOI prevents the development of many key features of allergic asthma, including AHR, mucus hyperproduction, airways inflammation, and pulmonary eosinophil recruitment. Our results highlight a likely role of the 5-HT2 receptors in allergic airways disease and suggest that 5-HT2 receptor agonists may represent an effective and novel small molecule-based therapy for asthma.

Chronic LSD alters gene expression profiles in the mPFC relevant to schizophrenia

Chronic administration of lysergic acid diethylamide (LSD) every other day to rats results in a variety of abnormal behaviors. These build over the 90 day course of treatment and can persist at full strength for at least several months after cessation of treatment. The behaviors are consistent with those observed in animal models of schizophrenia and include hyperactivity, reduced sucrose-preference, and decreased social interaction. In order to elucidate molecular changes that underlie these aberrant behaviors, we chronically treated rats with LSD and performed RNA-sequencing on the medial prefrontal cortex (mPFC), an area highly associated with both the actions of LSD and the pathophysiology of schizophrenia and other psychiatric illnesses. We observed widespread changes in the neurogenetic state of treated animals four weeks after cessation of LSD treatment. QPCR was used to validate a subset of gene expression changes observed with RNA-Seq, and confirmed a significant correlation between the two methods. Functional clustering analysis indicates differentially expressed genes are enriched in pathways involving neurotransmission (Drd2, Gabrb1), synaptic plasticity (Nr2a, Krox20), energy metabolism (Atp5d, Ndufa1) and neuropeptide signaling (Npy, Bdnf), among others. Many processes identified as altered by chronic LSD are also implicated in the pathogenesis of schizophrenia, and genes affected by LSD are enriched with putative schizophrenia genes. Our results provide a relatively comprehensive analysis of mPFC transcriptional regulation in response to chronic LSD, and indicate that the long-term effects of LSD may bear relevance to psychiatric illnesses, including schizophrenia.

5-HT stimulation of heart rate in Drosophila does not act through cAMP as revealed by pharmacogenetics

The fruit fly, Drosophila melanogaster, is a good experimental organism to study the underlying mechanism of heart rate (HR) regulation. It is already known that many neuromodulators (serotonin, dopamine, octopamine, acetylcholine) change the HR in Drosophila melanogaster larvae. In this study, we investigated the role of cAMP-PKA signaling pathway in HR regulation and 5-HT positive chronotropic action. In order to obtain insight into the 5-HT mechanism of action in larvae cardiomyocytes, genetic and pharmacological approaches were used. We used transgenic flies that expressed the hM4Di receptor [designer receptors exclusively activated by designer drugs (DREADDs)] as one tool. Our previous results showed that activation of hM4Di receptors (modified muscarinic acetylcholine receptors) decreases or arrests the heart from beating. In this study, it was hypothesized that the positive chronotropic effect of serotonin [5-hydroxytryptamine (5-HT)] are mediated by serotonin receptors coupled to the adenylyl cyclase pathway and downstream cAMP and PKA activity. Activation of hM4Di by clozapine-N-oxide (CNO) was predicted to block the effects of serotonin by inhibiting adenylyl cyclase activity through Gαi pathway activation. Interestingly, we found here that manipulation of adenylyl cyclase activity and cAMP levels had no significant effect on HR. The ability of hM4Di receptor activation to slow or stop the heart is therefore likely mediated by activation of GIRK channels to produce hyperpolarization of cardiomyocytes, and not through inhibition of adenylyl cyclase.

Serotonin 5-HT2A receptor activation blocks TNF-α mediated inflammation in vivo

Tumor necrosis factor alpha (TNF-α) plays a key role in inflammation, and its production and signaling contribute to many inflammatory related diseases. Recently, we discovered that selective activation of serotonin 5-HT2A receptors with the agonist (R)-DOI produces a super-potent blockade of proinflammatory markers in primary rat aortic smooth muscle cells. Here, we demonstrate that systemic administration of (R)-DOI can block the systemic effects of TNF-α in whole animal, with potent anti-inflammatory effects in the aortic arch and small intestine. This includes blockade of TNF-α-induced expression of pro-inflammatory cell adhesion (Icam-1, Vcam-1), cytokine (Il-6, IL-1b), and chemokine (Mcp-1, Cx3cl1) genes, and expression of VCAM-1 protein in the intestine. Further, systemic (R)-DOI also prevents the TNF-α-induced increase of circulating IL-6. Importantly, utilizing receptor selective antagonists, we have demonstrated that the mechanism underlying the systemic anti-inflammatory effects of (R)-DOI is activation of serotonin 5-HT2A receptors. Our results highlight a powerful new role for the serotonin 5-HT2A receptor in inflammatory processes, and indicate that agonism of serotonin receptors may represent an effective and novel approach to develop powerful small molecule therapeutics for inflammatory diseases and conditions such as atherosclerosis and inflammatory bowel disease.

DREADDs in Drosophila: a pharmacogenetic approach for controlling behavior, neuronal signaling, and physiology in the fly

We have translated a powerful genetic tool, designer receptors exclusively activated by designer drugs (DREADDs), from mammalian systems to Drosophila melanogaster to selectively, rapidly, reversibly, and dose-dependently control behaviors and physiological processes in the fly. DREADDs are muscarinic acetylcholine G protein-coupled receptors evolved for loss of affinity to acetylcholine and for the ability to be fully activated by an otherwise biologically inert chemical, clozapine-N-oxide. We demonstrate its ability to control a variety of behaviors and processes in larvae and adults, including heart rate, sensory processing, diurnal behavior, learning and memory, and courtship. The advantages of this particular technology include the dose-responsive control of behaviors, the lack of a need for specialized equipment, and the capacity to remotely control signaling in essentially all neuronal and nonneuronal fly tissues.

RNA-binding ability of FUS regulates neurodegeneration, cytoplasmic mislocalization and incorporation into stress granules associated with FUS carrying ALS-linked mutations

Amyotrophic lateral sclerosis (ALS) is an uncommon neurodegenerative disease caused by degeneration of upper and lower motor neurons. Several genes, including SOD1, TDP-43, FUS, Ubiquilin 2, C9orf72 and Profilin 1, have been linked with the sporadic and familiar forms of ALS. FUS is a DNA/RNA-binding protein (RBP) that forms cytoplasmic inclusions in ALS and frontotemporal lobular degeneration (FTLD) patients' brains and spinal cords. However, it is unknown whether the RNA-binding ability of FUS is required for causing ALS pathogenesis. Here, we exploited a Drosophila model of ALS and neuronal cell lines to elucidate the role of the RNA-binding ability of FUS in regulating FUS-mediated toxicity, cytoplasmic mislocalization and incorporation into stress granules (SGs). To determine the role of the RNA-binding ability of FUS in ALS, we mutated FUS RNA-binding sites (F305L, F341L, F359L, F368L) and generated RNA-binding-incompetent FUS mutants with and without ALS-causing mutations (R518K or R521C). We found that mutating the aforementioned four phenylalanine (F) amino acids to leucines (L) (4F-L) eliminates FUS RNA binding. We observed that these RNA-binding mutations block neurodegenerative phenotypes seen in the fly brains, eyes and motor neurons compared with the expression of RNA-binding-competent FUS carrying ALS-causing mutations. Interestingly, RNA-binding-deficient FUS strongly localized to the nucleus of Drosophila motor neurons and mammalian neuronal cells, whereas FUS carrying ALS-linked mutations was distributed to the nucleus and cytoplasm. Importantly, we determined that incorporation of mutant FUS into the SG compartment is dependent on the RNA-binding ability of FUS. In summary, we demonstrate that the RNA-binding ability of FUS is essential for the neurodegenerative phenotype in vivo of mutant FUS (either through direct contact with RNA or through interactions with other RBPs).

A triple arg motif mediates α(2B)-adrenergic receptor interaction with Sec24C/D and export

Recent studies have demonstrated that cargo exit from the endoplasmic reticulum (ER) may be directed by ER export motifs recognized by components of the coat protein II (COPII) vesicles. However, little is known about ER export motifs and vesicle targeting of the G protein-coupled receptor (GPCR) superfamily. Here, we have demonstrated that a triple Arg (3R) motif in the third intracellular loop functions as a novel ER export signal for α(2B)-adrenergic receptor (α(2B)-AR). The 3R motif mediates α(2B)-AR interaction with Sec24C/D and modulates ER exit, cell surface transport and function of α(2B)-AR. Furthermore, export function of the 3R motif is independent of its position within α(2B)-AR and can be conferred to CD8 glycoprotein. These data provide the first evidence implicating that export of GPCRs is controlled by code-directed interactions with selective components of the COPII transport machinery.

Methods to assay Drosophila behavior

Drosophila melanogaster, the fruit fly, has been used to study molecular mechanisms of a wide range of human diseases such as cancer, cardiovascular disease and various neurological diseases(1). We have optimized simple and robust behavioral assays for determining larval locomotion, adult climbing ability (RING assay), and courtship behaviors of Drosophila. These behavioral assays are widely applicable for studying the role of genetic and environmental factors on fly behavior. Larval crawling ability can be reliably used for determining early stage changes in the crawling abilities of Drosophila larvae and also for examining effect of drugs or human disease genes (in transgenic flies) on their locomotion. The larval crawling assay becomes more applicable if expression or abolition of a gene causes lethality in pupal or adult stages, as these flies do not survive to adulthood where they otherwise could be assessed. This basic assay can also be used in conjunction with bright light or stress to examine additional behavioral responses in Drosophila larvae. Courtship behavior has been widely used to investigate genetic basis of sexual behavior, and can also be used to examine activity and coordination, as well as learning and memory. Drosophila courtship behavior involves the exchange of various sensory stimuli including visual, auditory, and chemosensory signals between males and females that lead to a complex series of well characterized motor behaviors culminating in successful copulation. Traditional adult climbing assays (negative geotaxis) are tedious, labor intensive, and time consuming, with significant variation between different trials(2-4). The rapid iterative negative geotaxis (RING) assay(5) has many advantages over more widely employed protocols, providing a reproducible, sensitive, and high throughput approach to quantify adult locomotor and negative geotaxis behaviors. In the RING assay, several genotypes or drug treatments can be tested simultaneously using large number of animals, with the high-throughput approach making it more amenable for screening experiments.

Insulin-producing cells in the brain of adult Drosophila are regulated by the serotonin 5-HT1A receptor

Insulin signaling regulates lifespan, reproduction, metabolic homeostasis, and resistance to stress in the adult organism. In Drosophila, there are seven insulin-like peptides (DILP1-7). Three of these (DILP2, 3 and 5) are produced in median neurosecretory cells of the brain, designated IPCs. Previous work has suggested that production or release of DILPs in IPCs can be regulated by a factor secreted from the fat body as well as by neuronal GABA or short neuropeptide F. There is also evidence that serotonergic neurons may regulate IPCs. Here, we investigated mechanisms by which serotonin may regulate the IPCs. We show that the IPCs in adult flies express the 5-HT(1A), but not the 5-HT(1B) or 5-HT(7) receptors, and that processes of serotonergic neurons impinge on the IPC branches. Knockdown of 5-HT(1A) in IPCs by targeted RNA interference (RNAi) leads to increased sensitivity to heat, prolonged recovery after cold knockdown and decreased resistance to starvation. Lipid metabolism is also affected, but no effect on growth was seen. Furthermore, we show that DILP2-immunolevels in IPCs increase after 5-HT(1A) knockdown; this is accentuated by starvation. Heterozygous 5-HT(1A) mutant flies display the same phenotype in all assays, as seen after targeted 5-HT(1A) RNAi, and flies fed the 5-HT(1A) antagonist WAY100635 display reduced lifespan at starvation. Our findings suggest that serotonin acts on brain IPCs via the 5-HT(1A) receptor, thereby affecting their activity and probably insulin signaling. Thus, we have identified a second inhibitory pathway regulating IPC activity in the Drosophila brain.

Serotonin receptor activity is necessary for olfactory learning and memory in Drosophila melanogaster

Learning and memory in the fruit fly, Drosophila melanogaster, is a complex behavior with many parallels to mammalian learning and memory. Although many neurotransmitters including acetylcholine, dopamine, glutamate, and GABA have previously been demonstrated to be involved in aversive olfactory learning and memory, the role of serotonin has not been well defined. Here, we present the first evidence of the involvement of individual serotonin receptors in olfactory learning and memory in the fly. We initially followed a pharmacological approach, utilizing serotonin receptor agonists and antagonists to demonstrate that all serotonin receptor families present in the fly are necessary for short-term learning and memory. Isobolographic analysis utilizing combinations of drugs revealed functional interactions are occurring between 5-HT(1A)-like and 5-HT(2), and 5-HT(2) and 5-HT(7) receptor circuits in mediating short-term learning and memory. Examination of long-term memory suggests that 5-HT(1A)-like receptors are necessary for consolidation and important for recall, 5-HT(2) receptors are important for consolidation and recall, and 5-HT(7) receptors are involved in all three phases. Importantly, we have validated our pharmacological results with genetic experiments and showed that hypomorph strains for 5-HT(2)Dro and 5-HT(1B)Dro receptors, as well as knockdown of 5-HT(7)Dro mRNA, significantly impair performance in short-term memory. Our data highlight the importance of the serotonin system and individual serotonin receptors to influence olfactory learning and memory in the fly, and position the fly as a model system to study the role of serotonin in cognitive processes relevant to mammalian CNS function.

The serotonin 5-HT7Dro receptor is expressed in the brain of Drosophila, and is essential for normal courtship and mating

The 5-HT(7) receptor remains one of the less well characterized serotonin receptors. Although it has been demonstrated to be involved in the regulation of mood, sleep, and circadian rhythms, as well as relaxation of vascular smooth muscles in mammals, the precise mechanisms underlying these functions remain largely unknown. The fruit fly, Drosophila melanogaster, is an attractive model organism to study neuropharmacological, molecular, and behavioral processes that are largely conserved with mammals. Drosophila express a homolog of the mammalian 5-HT(7) receptor, as well as homologs for the mammalian 5-HT(1A), and 5-HT(2), receptors. Each fly receptor couples to the same effector pathway as their mammalian counterpart and have been demonstrated to mediate similar behavioral responses. Here, we report on the expression and function of the 5-HT(7)Dro receptor in Drosophila. In the larval central nervous system, expression is detected postsynaptically in discreet cells and neuronal circuits. In the adult brain there is strong expression in all large-field R neurons that innervate the ellipsoid body, as well as in a small group of cells that cluster with the PDF-positive LNvs neurons that mediate circadian activity. Following both pharmacological and genetic approaches, we have found that 5-HT(7)Dro activity is essential for normal courtship and mating behaviors in the fly, where it appears to mediate levels of interest in both males and females. This is the first reported evidence of direct involvement of a particular serotonin receptor subtype in courtship and mating in the fly.

Human disease models in Drosophila melanogaster and the role of the fly in therapeutic drug discovery

The common fruit fly, Drosophila melanogaster, is a well studied and highly tractable genetic model organism for understanding molecular mechanisms of human diseases. Many basic biological, physiological, and neurological properties are conserved between mammals and D. melanogaster, and nearly 75% of human disease-causing genes are believed to have a functional homolog in the fly. In the discovery process for therapeutics, traditional approaches employ high-throughput screening for small molecules that is based primarily on in vitro cell culture, enzymatic assays, or receptor binding assays. The majority of positive hits identified through these types of in vitro screens, unfortunately, are found to be ineffective and/or toxic in subsequent validation experiments in whole-animal models. New tools and platforms are needed in the discovery arena to overcome these limitations. The incorporation of D. melanogaster into the therapeutic discovery process holds tremendous promise for an enhanced rate of discovery of higher quality leads. D. melanogaster models of human diseases provide several unique features such as powerful genetics, highly conserved disease pathways, and very low comparative costs. The fly can effectively be used for low- to high-throughput drug screens as well as in target discovery. Here, we review the basic biology of the fly and discuss models of human diseases and opportunities for therapeutic discovery for central nervous system disorders, inflammatory disorders, cardiovascular disease, cancer, and diabetes. We also provide information and resources for those interested in pursuing fly models of human disease, as well as those interested in using D. melanogaster in the drug discovery process.

An animal model of schizophrenia based on chronic LSD administration: old idea, new results

Many people who take LSD experience a second temporal phase of LSD intoxication that is qualitatively different, and was described by Daniel Freedman as "clearly a paranoid state." We have previously shown that the discriminative stimulus effects of LSD in rats also occur in two temporal phases, with initial effects mediated by activation of 5-HT(2A) receptors (LSD30), and the later temporal phase mediated by dopamine D2-like receptors (LSD90). Surprisingly, we have now found that non-competitive NMDA antagonists produced full substitution in LSD90 rats, but only in older animals, whereas in LSD30, or in younger animals, these drugs did not mimic LSD. Chronic administration of low doses of LSD (>3 months, 0.16 mg/kg every other day) induces a behavioral state characterized by hyperactivity and hyperirritability, increased locomotor activity, anhedonia, and impairment in social interaction that persists at the same magnitude for at least three months after cessation of LSD treatment. These behaviors, which closely resemble those associated with psychosis in humans, are not induced by withdrawal from LSD; rather, they are the result of neuroadaptive changes occurring in the brain during the chronic administration of LSD. These persistent behaviors are transiently reversed by haloperidol and olanzapine, but are insensitive to MDL-100907. Gene expression analysis data show that chronic LSD treatment produced significant changes in multiple neurotransmitter system-related genes, including those for serotonin and dopamine. Thus, we propose that chronic treatment of rats with low doses of LSD can serve as a new animal model of psychosis that may mimic the development and progression of schizophrenia, as well as model the established disease better than current acute drug administration models utilizing amphetamine or NMDA antagonists such as PCP.

Engineered G-protein Coupled Receptors are Powerful Tools to Investigate Biological Processes and Behaviors

Understanding how discreet tissues and neuronal circuits function in relation to the whole organism to regulate physiological processes and behaviors is a fundamental goal of modern biological science. Powerful and important new tools in this discovery process are modified G-protein coupled receptors (GPCRs) known as ‘Receptors Activated Solely by Synthetic Ligands (RASSLs),’ and ‘Designer Receptors Exclusively Activated by a Designer Drug (DREADDs).’ Collectively, these are GPCRs modified either through rational design or directed molecular evolution, that do not respond to native ligand, but functionally respond only to synthetic ligands. Importantly, the utility of these receptors is not limited to examination of the role of GPCR-coupled effector signal transduction pathways. Due to the near ubiquitous expression of GPCRs throughout an organism, this technology, combined with whole animal transgenics to selectively target expression, has the ability to regulate activity of discreet tissues and neuronal circuits through effector pathway modulation to study function and behavior throughout the organism. Advantages over other systems currently used to modify in vivo function include the ability to rapidly, selectively and reversibly manipulate defined signal transduction pathways both in short term and long term studies, and no need for specialized equipment due to convenient systemic treatment with activating ligand.

Anterograde trafficking of G protein-coupled receptors: function of the C-terminal F(X)6LL motif in export from the endoplasmic reticulum

We have reported previously that the F(X)(6)LL motif in the C termini is essential for export of alpha(2B)-adrenergic (alpha(2B)-AR) and angiotensin II type 1 receptors (AT1Rs) from the endoplasmic reticulum (ER). Here, we further demonstrate that mutation of the F(X)(6)LL motif similarly abolished the cell-surface expression of alpha(2B)-AR, AT1R, alpha(1B)-AR, and beta(2)-AR, suggesting that the F(X)(6)LL motif plays a general role in ER export of G protein-coupled receptors (GPCRs). Mutation of Phe to Val, Leu, Trp, and Tyr, and mutation of LL to FF and VV, markedly inhibited alpha(2B)-AR transport, indicating that the F(X)(6)LL function cannot be fully substituted by other hydrophobic residues. The structural analysis revealed that the Phe residue in the F(X)(6)LL motif is buried in the transmembrane domains and possibly interacts with Ile58 in beta(2)-AR and Val42 in alpha(2B)-AR, whereas the LL motif is exposed to the cytosolic space. Indeed, mutation of Ile58 in beta(2)-AR and Val42 in alpha(2B)-AR markedly disrupted cell surface transport of the receptors. It is noteworthy that the Val and Ile residues are highly conserved among the GPCRs carrying the F(X)(6)LL motif. Furthermore, the Phe mutant exhibited a stronger interaction with ER chaperones and was more potently rescued by physical and chemical treatments than the LL mutant. These data suggest that the Phe residue is probably involved in folding of alpha(2B)-AR and beta(2)-AR, possibly through interaction with other hydrophobic residues in neighboring domains. These data also provide the first evidence implying crucial roles of the C termini possibly through modulating multiple events in anterograde trafficking of GPCRs.