The Chronic Treatment With 5-HT2A Receptor Agonists Affects the Behavior and the BDNF System in Mice

Indirect influence on the BDNF/TrkB receptor signaling pathway via GPCRs, an emerging strategy in the treatment of neurodegenerative disorders

Neuronal survival depends on neurotrophins and their receptors. There are two types of neurotrophin receptors: a nonenzymatic, trans-membrane protein of the tumor necrosis factor receptor (TNFR) family-p75 receptor and the tyrosine kinase receptors (TrkR) A, B, and C. Activation of the TrkBR by brain-derived neurotrophic factor (BDNF) or neurotrophin 4/5 (NT-4/5) promotes neuronal survival, differentiation, and synaptic function. It is shown that in the pathogenesis of several neurodegenerative conditions (Alzheimer's disease, Parkinson's disease, Huntington's disease) the BDNF/TrkBR signaling pathway is impaired. Since it is known that GPCRs and TrkR are regulating several cell functions by interacting with each other and generating a cross-communication in this review we have focused on the interaction between different GPCRs and their ligands on BDNF/TrkBR signaling pathway.

Psychedelics: A review of their effects on recalled aversive memories and fear/anxiety expression in rodents

Threatening events and stressful experiences can lead to maladaptive memories and related behaviors. Existing treatments often fail to address these issues linked to anxiety/stress-related disorders effectively. This review identifies dose ranges associated with specific actions across various psychedelics. We examined psilocybin/psilocin, lysergic acid diethylamide (LSD), N,N-dimethyltryptamine (DMT), mescaline, 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT), serotonin 2 A/2 C agonists (e.g., DOI) and 3,4-methylenedioxymethamphetamine (MDMA) on aversive memory extinction and reconsolidation, learned fear, anxiety, and locomotion in rodents. Nearly 400 studies published since 1957 were reviewed. Psychedelics often show biphasic effects on locomotion at doses that enhance extinction learning/retention, impair memory reconsolidation, or reduce learned fear and anxiety. Emerging evidence suggests a dissociation between their prospective benefits and locomotor effects. Under-explored aspects include sex differences, susceptibility to interference as memories age and generalize, repeated treatments, and immediate vs. delayed changes. Validating findings in traumatic-like memory and maladaptive fear/anxiety models is essential. Understanding how psychedelics modulate threat responses and post-retrieval memory processes in rodents may inform drug development and human studies, improving therapeutic approaches for related psychiatric conditions.

Mixed probiotics reduce the severity of stress-induced depressive-like behaviors

In recent years, the gut microbiome has gained significant attention in the spheres of research and public health. As a result, studies have increasingly explored the potential of probiotic dietary supplements as treatment interventions for conditions such as anxiety and depression. The present study examined the effect of mixed probiotics (Lacticaseibacillus rhamnosus and Enterococcus faecium) on inflammation, microbiome composition, and depressive-like behaviors in a macaque monkey model. The mixed probiotics effectively reduced the severity of depressive-like behaviors in macaque monkeys. Further, treatment with mixed probiotics gradually increased the abundance of beneficial bacteria in the gut, improving the balance of the gut microbiota. Additionally, macaques treated with the mixed probiotics showed decreased serum levels of inflammatory factors (P < 0.05), an increased rate of L-tryptophan metabolism (P < 0.05), and the restoration of 5-HT and 5-HTP levels (P < 0.05). Correlation analysis confirmed that Lacticaseibacillus and other beneficial bacteria exhibited a negative correlation with inflammation in the body (P < 0.05), and a positive correlation with tryptophan metabolism (P < 0.05). In conclusion, the mixed probiotics effectively restored intestinal homeostasis in macaques and enhanced tryptophan metabolism, ultimately alleviating inflammation and depressive-like behaviors.

1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI): From an Obscure to Pivotal Member of the DOX Family of Serotonergic Psychedelic Agents - A Review

1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI, or DOX where X = -I) was first synthesized in 1973 in a structure-activity study to explore the effect of various aryl substituents on the then newly identified, and subsequently controlled, hallucinogenic agent 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM, or DOX where X = -CH3). Over time, DOI was found to be a serotonin (5-HT) receptor agonist using various peripheral 5-HT receptor tissue assays and later, following the identification of multiple families of central 5-HT receptors, an agonist at 5-HT2 serotonin receptors in rat and, then, human brain. Today, classical hallucinogens, currently referred to as serotonergic psychedelic agents, are receiving considerable attention for their potential therapeutic application in various neuropsychiatric disorders including treatment-resistant depression. Here, we review, for the first time, the historical and current developments that led to DOI becoming a unique, perhaps a landmark, agent in 5-HT2 receptor research.

TrkB receptor interacts with mGlu2 receptor and mediates antipsychotic-like effects of mGlu2 receptor activation in the mouse

Metabotropic glutamate receptor 2 (mGlu2) attracts particular attention as a possible target for a new class of antipsychotics. However, the signaling pathways transducing the effects of mGlu2 in the brain remain poorly characterized. Here, we addressed this issue by identifying native mGlu2 interactome in mouse prefrontal cortex. Nanobody-based affinity purification and mass spectrometry identified 149 candidate mGlu2 partners, including the neurotrophin receptor TrkB. The later interaction was confirmed both in cultured cells and prefrontal cortex. mGlu2 activation triggers phosphorylation of TrkB on Tyr816 in primary cortical neurons and prefrontal cortex. Reciprocally, TrkB stimulation enhances mGlu2-operated Gi/o protein activation. Furthermore, TrkB inhibition prevents the rescue of behavioral deficits by glutamatergic antipsychotics in phencyclidine-treated mice. Collectively, these results reveal a cross-talk between TrkB and mGlu2, which is key to the behavioral response to glutamatergic antipsychotics.

The potential of psychedelics for the treatment of Alzheimer's disease and related dementias

Alzheimer's Disease (AD) is a currently incurable but increasingly prevalent fatal and progressive neurodegenerative disease, demanding consideration of therapeutically relevant natural products and their synthetic analogues. This paper reviews evidence for effectiveness of natural and synthetic psychedelics in the treatment of AD causes and symptoms. The plastogenic effects of serotonergic psychedelics illustrate that they have efficacy for addressing multiple facets of AD pathology. We review findings illustrating neuroplasticity mechanisms of classic (serotonergic) and non-classic psychedelics that indicate their potential as treatments for AD and related dementias. Classic psychedelics modulate glutamatergic neurotransmission and stimulate synaptic and network remodeling that facilitates synaptic, structural and behavioral plasticity. Up-regulation of neurotrophic factors enable psychedelics to promote neuronal survival and glutamate-driven neuroplasticity. Muscimol modulation of GABAAR reduces Aβ-induced neurotoxicity and psychedelic Sig-1R agonists provide protective roles in Aβ toxicity. Classic psychedelics also activate mTOR intracellular effector pathways in brain regions that show atrophy in AD. The potential of psychedelics to treat AD involves their ability to induce structural and functional neural plasticity in brain circuits and slow or reverse brain atrophy. Psychedelics stimulate neurotrophic pathways, increase neurogenesis and produce long-lasting neural changes through rewiring pathological neurocircuitry. Psychedelic effects on 5-HT receptor target genes and induction of synaptic, structural, and functional changes in neurons and networks enable them to promote and enhance brain functional connectivity and address diverse mechanisms underlying degenerative neurological disorders. These findings provide a rationale for immediate investigation of psychedelics as treatments for AD patients.

Neurotoxic effects of hallucinogenic drugs 25H-NBOMe and 25H-NBOH in organotypic hippocampal cultures

Introduction

NBOMes and NBOHs are psychoactive drugs derived from phenethylamines and have hallucinogenic effects due to their strong agonism to serotonin 5-HT_2A receptors. Although cases of toxicity associated with the recreational use of substituted phenethylamines are frequently reported, there is a lack of information on the possible neurotoxic effects of NBOMe and NBOH in the brain hippocampus, a major neurogenesis region.

Objectives

This study aimed at assessing the phenotypic and molecular effects of prolonged exposure of the hippocampus to the drugs 25H-NBOMe and 25H-NBOH.

Methods

The ex vivo organotypic culture model of hippocampal slices (OHC) was used to investigate, by immunofluorescence and confocal microscopy, and transcriptome analyses, the mechanisms associated with the neurotoxicity of 25H-NBOMe and 25H-NBOH.

Results

Reduction in the density of mature neurons in the OHCs occurred after two and seven days of exposure to 25H-NBOMe and 25H-NBOH, respectively. After the withdrawal of 25H-NBOMe, the density of mature neurons in the OHCs stabilized. In contrast, up to seven days after 25H-NBOH removal from the culture medium, progressive neuron loss was still observed in the OHCs. Interestingly, the exposure to 25H-NBOH induced progenitor cell differentiation, increasing the density of post-mitotic neurons in the OHCs. Corroborating these findings, the functional enrichment analysis of differentially expressed genes in the OHCs exposed to 25H-NBOH revealed the activation of WNT/Beta-catenin pathway components associated with neurogenesis. During and after the exposure to 25H-NBOMe or 25H-NBOH, gene expression patterns related to the activation of synaptic transmission and excitability of neurons were identified. Furthermore, activation of signaling pathways and biological processes related to addiction and oxidative stress and inhibition of the inflammatory response were observed after the period of drug exposure.

Conclusion

25H-NBOMe and 25H-NBOH disrupt the balance between neurogenesis and neuronal death in the hippocampus and, although chemically similar, have distinct neurotoxicity mechanisms.

Relationship between gene-environment interaction and obsessive-compulsive disorder: A systematic review

BACKGROUND

Gene-environment interaction (G × E) refers to the change of genetic effects under the participation of environmental factors resulting in differences in genetic expression. G × E has been studied in the occurrence and development of many neuropsychiatric disorders, including obsessive-compulsive disorder (OCD).

AIM

A systematic review was conducted to investigate the role of G × E plays in OCD. This review explored the relationship between G × E and the susceptibility to OCD occurrence, disease progression, and treatment response.

METHODS

This systematic literature search was performed using Web of Science, PubMed, Cochrane Library, and CNKI. Seven studies were selected, which included seven genes (BDNF, COMT, MAO, 5-HTT, SMAD4, PGRN, and SLC1A1) polymorphisms, polygenic risk score (PRS), and two environmental factors (childhood trauma and stressful life events).

RESULTS

Information from this systematic review indicated that G × E increased the susceptibility to OCD, played a crucial role in the clinical characteristics, and had an inconsistent impact on treatment response of OCD.

FUTURE DIRECTIONS

The multi-omics studies and the inclusion of G × E in future GWAS studies of OCD should be drawn more attention, which may contribute to a deeper understanding of the etiology of OCD as well as guide therapeutic interventions for the disease.

Effects of Chronic Combined Treatment with Ketanserin and Fluoxetine in B6.CBA-D13Mit76C Recombinant Mice with Abnormal 5-HT1A Receptor Functional Activity

The recombinant B6.CBA-D13Mit76C mouse strain is characterized by an altered sensitivity of 5-HT1A receptors and upregulated 5-HT1A gene transcription. Recently, we found that in B6.CBA-D13Mit76C mice, chronic fluoxetine treatment produced the pro-depressive effect in a forced swim test. Since 5-HT2A receptor blockade may be beneficial in treatment-resistant depression, we investigated the influence of chronic treatment (14 days, intraperitoneally) with selective 5-HT2A antagonist ketanserin (0.5 mg/kg), fluoxetine (20 mg/kg), or fluoxetine + ketanserin on the behavior, functional activity of 5-HT1A and 5-HT2A receptors, serotonin turnover, and transcription of principal genes of the serotonin system in the brain of B6.CBA-D13Mit76C mice. Ketanserin did not reverse the pro-depressive effect of fluoxetine, while fluoxetine, ketanserin, and fluoxetine + ketanserin decreased the functional activity of 5-HT1A receptors and Htr1a gene transcription in the midbrain and hippocampus. All tested drug regimens decreased the mRNA levels of Slc6a4 and Maoa in the midbrain. These changes were not accompanied by a significant shift in the levels of serotonin and its metabolite 5-HIAA. Notably, ketanserin upregulated enzymatic activity of tryptophan hydroxylase 2 (TPH2). Thus, despite some benefits (reduced Htr1a, Slc6a4, and Maoa transcription and increased TPH2 activity), prolonged blockade of 5-HT2A receptors failed to ameliorate the adverse effect of fluoxetine in the case of abnormal functioning of 5-HT1A receptors.

Preferential Modulatory Action of 5-HT2A Receptors on the Dynamic Regulation of Basal Ganglia Circuits

In rodents, cortical information is transferred to the substantia nigra pars reticulata (SNr) through motor and medial prefrontal (mPF) basal ganglia (BG) circuits implicated in motor and cognitive/motivational behaviors, respectively. The serotonergic 5-HT_2A receptors are located in both of these neuronal networks, displaying topographical differences with a high expression in the associative/limbic territories, and a very low expression in the subthalamic nucleus. This study investigated whether the stimulation of 5-HT_2A receptors could have a specific signature on the dynamic regulation of BG circuits, preferentially modulating the mPF information processing through trans-striatal pathways. We performed in vivo single-unit extracellular recordings to assess the effect of the 5-HT_2A agonist TCB-2 on the spontaneous and cortically evoked activity of lateral and medial SNr neurons in male rats (involved in motor and mPF circuits, respectively). TCB-2 (50-200 µg/kg, i.v.) increased the basal firing rate and enhanced the cortically evoked inhibitory response of medial SNr neurons (transmission through the direct striato-nigral pathway). A prior administration of the preferential 5-HT_2A receptor antagonist MDL11939 (200 µg/kg, i.v.) did not modify any electrophysiological parameter, but occluded TCB-2-induced effects. In animals treated with the 5-HT synthesis inhibitor pCPA (4-chloro-dl-phenylalanine methyl ester hydrochloride), TCB-2 failed to induce the above-mentioned effects, thus suggesting the contribution of endogenous 5-HT. However, the mobilization of 5-HT induced by the acute administration of fluoxetine (10 mg/kg, i.p.) did not mimic the effects triggered by TCB-2. Overall, these data suggest that 5-HT_2A receptors have a preferential modulatory action on the dynamic regulation of BG circuitry.SIGNIFICANCE STATEMENT Motor and medial prefrontal (mPF) basal ganglia (BG) circuits play an important role in integrative brain functions like movement control or cognitive/motivational behavior, respectively. Although these neuronal networks express 5-HT_2A receptors, the expression is higher in associative/limbic structures than in the motor ones. We show a topographical-dependent dissociation in the effects triggered by the 5HT_2A agonist TCB-2, which specifically increases the medial substantia nigra pars reticulata neuron activity and has a preferential action on mPF information processing through the striato-nigral direct pathway. These are very likely to be 5-HT_2A receptor-mediated effects that require mobilization of the endogenous 5-HT system. These findings provide evidence about the specific signature of 5-HT_2A receptors on the dynamic regulation of BG circuits.

On Associations between Fear-Induced Aggression, Bdnf Transcripts, and Serotonin Receptors in the Brains of Norway Rats: An Influence of Antiaggressive Drug TC-2153

The Bdnf (brain-derived neurotrophic factor) gene contains eight regulatory exons (I-VIII) alternatively spliced to the protein-coding exon IX. Only exons I, II, IV, and VI are relatively well studied. The BDNF system and brain serotonergic system are tightly interconnected and associated with aggression. The benzopentathiepine TC-2153 affects both systems and exerts antiaggressive action. Our aim was to evaluate the effects of TC-2153 on the Bdnf exons I-IX's expressions and serotonin receptors' mRNA levels in the brain of rats featuring high aggression toward humans (aggressive) or its absence (tame). Aggressive and tame adult male rats were treated once with vehicle or 10 or 20 mg/kg of TC-2153. mRNA was quantified in the cortex, hippocampus, hypothalamus, and midbrain with real-time PCR. Selective breeding for high aggression or its absence affected the serotonin receptors' and Bdnf exons' transcripts differentially, depending on the genotype (strain) and brain region. TC-2153 had comprehensive effects on the Bdnf exons' expressions. The main trend was downregulation in the hypothalamus and midbrain. TC-2153 increased 5-HT_1B receptor hypothalamusc mRNA expression. For the first time, an influence of TC-2153 on the expressions of Bdnf regulatory exons and the 5-HT_1B receptor was shown, as was an association between Bdnf regulatory exons and fear-induced aggression involving genetic predisposition.

Lopez S, Amodeo DA. Impact of specific serotonin receptor modulation on restricted repetitive behaviors

Restricted, repetitive behaviors (RRBs) are commonly divided into two behavioral categories, lower-order and higher-order RRBs. Individuals displaying lower-order motoric RRBs may express repetitive hand flapping behaviors, body rocking back and forth movements, and continuous body spinning. Higher-order RRBs most commonly cover the behavior inflexibility and cognitive rigidity commonly found in disorders such as autism spectrum disorder and obsessive-compulsive disorder. Various neuropsychiatric disorders are plagued by RRBs yet no FDA-approved treatments have been identified. In rodents, lower-order RRBs are commonly measured through various tasks, such as repetitive self-grooming, marble burying, and stereotypic motor behaviors. This review focuses on the effects that modulation of specific serotonin receptors have on lower-order RRBs. Although there is research examining how changes in 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2B, 5-HT2C, 5-HT3, 5-HT6, and 5-HT7 receptor modulation, more research has focused on the 5-HT1A, 5-HT2A, and 5-HT2C receptors. The accumulating data suggest that increasing 5-HT1A activation decreases RRBs while blocking 5-HT1A activation has no effect on RRBs. While there are mixed findings regarding the impact of 5-HT2A modulation on RRBs, the general trend shows mixed effects of 5-HT2A receptor activation RRB expression, whereas blockade generally decreases RRBs. 5-HT2C receptor activation can modulate RRBs in either direction depending on the 5-HT2C drug used, blocking 5-HT2C activation only seems to show therapeutic properties when 5-HT2C activation is already elevated. The other 5-HT receptors have been explored far less but show promise as potential targets for regulating RRBs. Although it is less clear due to the involvement of 5-HT1D, 5-HT1A activation increases RRBs, and blocking 5-HT1A tends to decrease RRBs. 5-HT2B activation could reduce RRBs, while inhibiting 5-HT2B does not impact RRBs. Increasing 5-HT3 has not been shown to affect RRBs. Yet, increases in RRBs have been observed in Htr3a KO mice. 5-HT6 receptor activation can increase RRBs, while blocking 5-HT6 activity tends to decrease RRBs. Lastly, neither increasing or blocking 5-HT7 activity can reduce RRBs. In sum, there is no uniform pattern in whether all specific 5-HT receptors affect RRBs in either direction, instead, there is evidence suggesting that different 5-HT receptors can modulate RRBs in different directions. Further researching the less explored receptors and aiming to understand why these receptors can differently modulate RRBs, may play a key role in developing therapeutics that treat RRBs.

Animal Behavior in Psychedelic Research

Psychedelic-assisted psychotherapy holds great promise in the treatment of mental health disorders. Research into 5-hydroxytryptamine 2A receptor (5-HT_2AR) agonist psychedelic compounds has increased dramatically over the past two decades. In humans, these compounds produce drastic effects on consciousness, and their therapeutic potential relates to changes in the processing of emotional, social, and self-referential information. The use of animal behavior to study psychedelics is under debate, and this review provides a critical perspective on the translational value of animal behavior studies in psychedelic research. Acute activation of 5-HT_2ARs produces head twitches and unique discriminative cues, disrupts sensorimotor gating, and stimulates motor activity while inhibiting exploration in rodents. The acute treatment with psychedelics shows discrepant results in conventional rodent tests of depression-like behaviors but generally induces anxiolytic-like effects and inhibits repetitive behavior in rodents. Psychedelics impair waiting impulsivity but show discrepant effects in other tests of cognitive function. Tests of social interaction also show conflicting results. Effects on measures of time perception depend on the experimental schedule. Lasting or delayed effects of psychedelics in rodent tests related to different behavioral domains appear to be rather sensitive to changes in experimental protocols. Studying the effects of psychedelics on animal behaviors of relevance to effects on psychiatric symptoms in humans, assessing lasting effects, publishing negative findings, and relating behaviors in rodents and humans to other more translatable readouts, such as neuroplastic changes, will improve the translational value of animal behavioral studies in psychedelic research. SIGNIFICANCE STATEMENT: Psychedelics like LSD and psilocybin have received immense interest as potential new treatments of psychiatric disorders. Psychedelics change high-order consciousness in humans, and there is debate about the use of animal behavior studies to investigate these compounds. This review provides an overview of the behavioral effects of 5-HT_2AR agonist psychedelics in laboratory animals and discusses the translatability of the effects in animals to effects in humans. Possible ways to improve the utility of animal behavior in psychedelic research are discussed.

Serotonin Receptor 5-HT2A Regulates TrkB Receptor Function in Heteroreceptor Complexes

Serotonin receptor 5-HT_2A and tropomyosin receptor kinase B (TrkB) strongly contribute to neuroplasticity regulation and are implicated in numerous neuronal disorders. Here, we demonstrate a physical interaction between 5-HT_2A and TrkB in vitro and in vivo using co-immunoprecipitation and biophysical and biochemical approaches. Heterodimerization decreased TrkB autophosphorylation, preventing its activation with agonist 7,8-DHF, even with low 5-HT_2A receptor expression. A blockade of 5-HT_2A receptor with the preferential antagonist ketanserin prevented the receptor-mediated downregulation of TrkB phosphorylation without restoring the TrkB response to its agonist 7,8-DHF in vitro. In adult mice, intraperitoneal ketanserin injection increased basal TrkB phosphorylation in the frontal cortex and hippocampus, which is in accordance with our findings demonstrating the prevalence of 5-HT_2A–TrkB heteroreceptor complexes in these brain regions. An expression analysis revealed strong developmental regulation of 5-HT_2A and TrkB expressions in the cortex, hippocampus, and especially the striatum, demonstrating that the balance between TrkB and 5-HT_2A may shift in certain brain regions during postnatal development. Our data reveal the functional role of 5-HT_2A–TrkB receptor heterodimerization and suggest that the regulated expression of 5-HT_2A and TrkB is a molecular mechanism for the brain-region-specific modulation of TrkB functions during development and under pathophysiological conditions.

Gs signaling pathway distinguishes hallucinogenic and nonhallucinogenic 5-HT2AR agonists induced head twitch response in mice

5- HT2A receptor is a member of the family A G-protein-coupled receptor. It is involved in many psychiatric disorders, such as depression, addiction and Parkinson's disease. 5-HT2AR targeted drugs play an important role in regulating cognition, memory, emotion and other physiological function by coupling G proteins, and their most notable function is stimulating the serotonergic hallucination. However, not all 5-HT2AR agonists exhibit hallucinogenic activity, such as lisuride. Molecular mechanisms of these different effects are not well illustrated. This study suggested that 5-HT2AR coupled both Gs and Gq protein under hallucinogenic agonists DOM and 25CN-NBOH stimulation, but nonhallucinogenic agonist lisuride and TBG only activates Gq signaling. Moreover, in head twitch response (HTR) model, we found that cAMP analogs 8-Bromo-cAMP and PDE4 inhibitor Rolipram could increase HTR, while Gs protein inhibitor Melittin could reduce HTR. Collectively, these results revealed that Gs signaling is a key signaling pathway that may distinguish hallucinogenic agonists and nonhallucinogenic agonists.

Psychedelic-inspired approaches for treating neurodegenerative disorders

Psychedelics are increasingly being recognized for their potential to treat a wide range of brain disorders including depression, post-traumatic stress disorder (PTSD), and substance use disorder. Their broad therapeutic potential might result from an ability to rescue cortical atrophy common to many neuropsychiatric and neurodegenerative diseases by impacting neurotrophic factor gene expression, activating neuronal growth and survival mechanisms, and modulating the immune system. While the therapeutic potential of psychedelics has not yet been extended to neurodegenerative disorders, we provide evidence suggesting that approaches based on psychedelic science might prove useful for treating these diseases. The primary target of psychedelics, the 5-HT_2A receptor, plays key roles in cortical neuron health and is dysregulated in Alzheimer's disease. Moreover, evidence suggests that psychedelics and related compounds could prove useful for treating the behavioral and psychological symptoms of dementia (BPSD). While more research is needed to probe the effects of psychedelics in models of neurodegenerative diseases, the robust effects of these compounds on structural and functional neuroplasticity and inflammation clearly warrant further investigation.

Psychedelics as Novel Therapeutics in Alzheimer's Disease: Rationale and Potential Mechanisms

Serotonin 2A receptor (5-HT_2AR) agonist "classic psychedelics" are drawing increasing interest as potential mental health treatments. Recent work suggests psychedelics can exert persisting anxiolytic and antidepressant effects lasting up to several months after a single administration. Data indicate acute subjective drug effects as important psychological factors involved in observed therapeutic benefits. Additionally, animal models have shown an important role for 5-HT_2AR agonists in modulating learning and memory function with relevance for Alzheimer's Disease (AD) and related dementias. A number of biological mechanisms of action are under investigation to elucidate 5-HT_2AR agonists' therapeutic potential, including enhanced neuroplasticity, anti-inflammatory effects, and alterations in brain functional connectivity. These diverse lines of research are reviewed here along with a discussion of AD pathophysiology and neuropsychiatric symptoms to highlight classic psychedelics as potential novel pharmacotherapies for patients with AD. Human clinical research suggests a possible role for high-dose psychedelic administration in symptomatic treatment of depressed mood and anxiety in early-stage AD. Preclinical data indicate a potential for low- or high-dose psychedelic treatment regimens to slow or reverse brain atrophy, enhance cognitive function, and slow progression of AD. In conclusion, rationale and potential approaches for preliminary research with psychedelics in patients with AD are presented, and ramifications of this line of investigation for development of novel AD treatments are discussed.

Serotonin 2A receptor function and depression-like behavior in rats model of hypothyroidism

Hypothyroidism causes somatic, psychosocial and affective psychosis, including depression-like behaviors. In this study, (hypothyroidism group; HP group) adult male Sprague Dawley (SD) rats were induced to hypothyroidism after 5 weeks of exposure to 0.05% propylthiouracil (PTU) in potable water, control animals (CON group) were given the same amount of water. The following behavioral experiments were conducted, respectively: open-field test (OFT), forced swimming test (FST), tail suspension test (TST). TT[Formula: see text] and TT[Formula: see text] levels were measured after the behavior tests and the expression levels of 5-HT[Formula: see text] receptor and 5-HT[Formula: see text] receptor proteins were analyzed in the hippocampus and prefrontal cortex. The level of TT[Formula: see text] and TT[Formula: see text] in the HP group rats was much lower than that in the CON group. The hypothyroid rats also showed weight loss, much longer immobility time in tail suspension test and forced swimming test. Besides, 5 weeks of PTU administration was associated with significantly decreased expression levels of 5-HT[Formula: see text] receptor and 5-HT[Formula: see text] receptor proteins compared with control group, which were significantly negatively correlated with immobility time in FST and TST. In conclusion, our results suggest that hypothyroidism induces depressive behaviors through the influence of the serotonin system, and the decreased expression of the 5-HT[Formula: see text] receptor is an important cause of the depressive behaviors in hypothyroidism.