The role of serotonin 5-HT2A receptors in memory and cognition

Uncoupling serotonin (2C) and dopamine (D2) receptor heterodimers ameliorate PTSD-like behaviors

BACKGROUND

G-protein-coupled receptors (GPCRs), crucial for various physiological functions, can form complexes with themselves or other GPCRs, influencing their signaling and drug interactions. GPCR oligomerization remains an active area of research in neurological diseases, including Post-Traumatic Stress Disorder (PTSD). Here, we illuminated a novel serotonin and dopamine receptor heterodimerization that played an etiological role in fear conditioning behaviors associated with memory defects in the single prolonger stress (SPS) mice and reverting effects of receptors interaction interfering with peptide.

METHODS

To assess our projected goal, we prepared a single prolonged stress (SPS) mice model followed by peptide treatment, behavior assays, and biochemical analysis.

RESULTS

Our study revealed a direct interaction between dopamine D2 receptors (D2R) and serotonin 5-HT2C receptors (5-HT2CR) via the K226-L240 region in the brains of SPS mice. This D2R/5-HT2CR interaction modulated downstream PI3K-AKT signaling and contributed to cognitive deficits in a mouse model of SPS. An interfering peptide (TAT-D2R-KL) designed to disrupt D2R/5-HT2CR heterodimerization reduced the excitatory/inhibitory neuron firing frequency ratio, attenuated PI3K/AKT signaling impairment, and alleviated cognitive deficits in SPS mice. Furthermore, treatment with the PI3K inhibitor, Bisperoxovanadium Compound bpV (pic), reversed the effects of the peptide, confirming the critical role of PI3K/AKT signaling in D2R/5-HT2CR dimerization and the associated pathophysiology of SPS.

CONCLUSION

These findings revealed a causative role of D2R/5-HT2CR hetero-dimer in PTSD and could be reversed by TAT-D2R-KL treatment.

Peri-traumatic consumption of classic psychedelics is associated with lower anxiety and post-traumatic responses 3 weeks after exposure

Emerging evidence indicates the therapeutic potential of psychedelic compounds for post-traumatic stress, yet the mechanisms mediating their effects remain unclear. Delineating the effect of psychedelics on traumatic memory formation could shed light on target therapeutic mechanisms. Here, we report on 343 adult survivors of a single, large-scale terrorist attack taking place during a festival in which different psychedelic compounds were consumed, in whom levels of anxiety and post-traumatic symptoms were assessed 3 weeks following the attack. Findings indicated that those who were under the influence of classic psychedelics during the attack reported significantly lower levels of anxiety and post-traumatic responses compared to those who were under the influence of 3,4-methylenedioxymethamphetamine and those who consumed no psychedelics. Furthermore, the protective effects of classic psychedelics for post-traumatic responses manifested more strongly among participants who did not consume additional recreational substances alongside psychedelics. These findings suggest that pharmacologic targets of classic psychedelics may modulate the formation of enduring trauma memories and confer a protective effect against the development of post-traumatic stress and anxiety responses.

The evolution of N, N-Dimethyltryptamine: from metabolic pathways to brain connectivity

RATIONALE

N, N-Dimethyltryptamine (DMT), a potent serotonergic psychedelic, bridges ancient wisdom and modern science. The mechanisms underlying its powerful psychedelic effects and out-of-body experiences continue to intrigue scientists. The functional role of DMT remains ambiguous. This paper explores the endogenous presence of DMT in the human body and its diverse neuroregulatory functions, which influence hierarchical brain connectivity, and the mechanisms driving its psychedelic effects.

OBJECTIVE

This paper aims to analyze DMT-receptor binding, its effects on neuronal modulation, brain oscillations, and connectivity, and its influence on hallucinations, out-of-body experiences, and cognitive functions.

RESULTS

DMT administration induces significant changes in brain wave dynamics, including reduced alpha power, increased delta power, and heightened Lempel-Ziv complexity, reflecting enhanced neural signal diversity. Functional neuroimaging studies reveal that DMT enhances global functional connectivity (GFC), particularly in transmodal association cortices such as the salience network, frontoparietal network, and default mode network, correlating with ego dissolution. The receptor density-dependent effects of DMT were mapped to brain regions rich in serotonin 5-HT2A receptors, supporting its role in modulating consciousness and neuroplasticity.

CONCLUSION

This integrated analysis provides insights into the profound effects of DMT on human cognition, and consciousness, and its role in enhancing natural well-being. As we uncover the endogenous functions of DMT, it becomes clear that the study of its biology reveals a complex interplay between brain chemistry and consciousness.

Unscrambling the cellular and molecular threads of Neuroplasticity: Insights into Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is predominantly the most recurring and devastating neurological condition among the elderly population, characterized by the accumulation of amyloid-β (Aβ) and phosphorylated tau proteins, and is accompanied by progressive decline of learning and memory. Due to its complex and multifactorial etiology, a wide variety of therapeutic interventions have been developed. Despite constant advancements in the field, effective treatments that ameliorate the severity of Alzheimer's symptoms or cease their progression are still insufficient. Mounting evidence suggests that synaptic dysfunction could be an essential component of AD pathogenesis as synapse signaling is impaired in the aging brain, which contributes to synaptic decline. Therefore, improving neuroplasticity such as synaptic plasticity or neurogenesis could be a promising therapeutic approach for alleviating the effects of AD. This article reviews the cellular and molecular threads of neuroplasticity as well as targets that restore neuronal survival and plasticity to provide functional recoveries, including receptors, downstream signaling pathways, ion channels, transporters, enzymes, and neurotrophic factors.

Plasma tryptophan levels are linked to hippocampal integrity and cognitive function in individuals with mild cognitive impairment

Tryptophan has been shown to improve cognitive functions, but whether these benefits emanate from changes in hippocampal structure or other mechanisms like enhanced serotonin pathways remains unclear. This study aimed to examine the relationship between tryptophan levels and hippocampal volumes in individuals with mild cognitive impairment (MCI) and to determine if changes in hippocampal volume correlate with cognitive function. A total of 499 individuals with MCI were recruited based on ADNI's clinical criteria. Cognitive function was assessed using the ADAS-Cog scale, and hippocampal volumes were measured through MRI using semi-automated Medtronic Surgical Navigation Technologies (SNT). Tryptophan levels in plasma were analyzed using a nuclear magnetic resonance (NMR)-based assay. This study used two models: One unadjusted and another adjusted for covariates such as age, gender, handedness, and ApoE ɛ3 and ɛ4. In both models, higher tryptophan levels were significantly associated with increased bilateral hippocampal volumes, with a stronger effect in the left hippocampus. Furthermore, larger hippocampal volumes were linked to improved cognitive performance. Mediation analysis showed that hippocampal volumes mediated the relationship between plasma tryptophan levels and cognitive function. These findings suggested that elevated plasma tryptophan levels support cognitive health by maintaining hippocampal structural integrity, underscoring its potential role in preserving cognitive function in individuals with MCI.

[18F]R91150: Improved radiosynthesis and in vivo evaluation as imaging probe for 5-HT2A receptors

Serotonergic 5-HT2A receptors in the cortex and other forebrain structures have been linked to cognitive, emotional and memory processes. In addition, dysfunction or altered expression of these receptors is associated with neuropsychiatric and neurodegenerative disorders. [18F]R91150 is a candidate radiotracer for positron emission tomography (PET) imaging of 5-HT2A receptors, which showed promising properties in in vitro studies. However, existing methods for the production of [18F]R91150 are rather inefficient and its imaging properties have not been studied in vivo. In the present work, we describe improved protocols for preparation of [18F]R91150, the corresponding reference compound and two alternative boronate radiolabeling precursors. Furthermore, we present the results of an in vivo evaluation of the radioligand in rodents. [18F]R91150 was prepared in activity yields of 20 ± 5% (two-step radiosynthesis) or 12 ± 2% (one-step radiosynthesis) and with molar activities of >200 GBq/μmol. μPET measurements in mice revealed sufficient stability against in vivo defluorination and predominantly hepatobiliary excretion of the tracer, with high radioactivity uptake in gall bladder and intestines. μPET imaging in rats demonstrated specific tracer accumulation in the cortex and subcortical forebrain structures, which could be reduced by pretreatment or displacement with the 5-HT2A receptor ligands altanserin or ketanserin but was insensitive to pretreatment with the 5-HT2C receptor ligand SB242084. In addition, [18F]R91150 showed specific accumulation in the choroid plexus that was much less sensitive to displacement with ketanserin and unaffected by pretreatment with altanserin or SB242084. Taken together, our results indicate that [18F]R91150 may be a promising candidate for in vivo PET imaging of cortical 5-HT2A receptors, although further studies will be required to elucidate the mechanisms underlying tracer accumulation in the choroid plexus.

Long-term ayahuasca use is associated with preserved global cognitive function and improved memory: a cross-sectional study with ritual users

Although several studies have been conducted to elucidate the relationship between psychedelic consumption and cognition, few have focused on understanding the long-term use influence of these substances on these variables, especially in ritualistic contexts.  To verify the influence of ritualistic ayahuasca consumption on the cognition of experienced ayahuasca religious users (> 20 years) and beginners (< 3 years), which participated in rituals of the Centro Luz Divina (CLD), a Santo Daime church in Brazil. Observational, descriptive, and cross-sectional study was carried out in which 48 people participated divided into three groups: (a) experienced ayahuasca users (n = 16), (b) beginner ayahuasca users (n = 16) and (c) control group (n = 16). All groups were matched by sex, age, and education and contained 8 women and 8 men. Cognition was assessed with the WASI (intelligence quotient), Digit Span (verbal working memory), Corsi Block-Tapping Task (visuospatial-related and working memory), Rey-Osterrieth Complex Figure test (visual perception, immediate memory), and Wisconsin Card Sorting and Five Digit Test (executive functions). Groups were homogenous in terms of sociodemographic characteristics, with participants presenting average intellectual performance. There was no evidence of cognitive decline amongst ayahuasca users. The experienced group showed higher scores compared to the less experienced group in the Digit Span and Corsi Block-Tapping tasks, which assess working verbal and visuospatial memories respectively. We confirmed the botanical identities of Psychotria viridis and Banisteriopsis caapi and the presence of the alkaloids both in the plants and in the brew. Short and long-term ayahuasca consumption does not seem to alter human cognition, while long-term use seems to be associated with improvements in aspects of working memory when compared with short-term use.

The Selective 5HT2A Receptor Agonist, 25CN-NBOH Exerts Excitatory and Inhibitory Cellular Actions on Mouse Medial Prefrontal Cortical Neurons

Psychedelic compounds have gained renewed interest due to their rapid and long-lasting therapeutic effects on stress-related disorders. While the underlying mechanisms of therapeutic actions of psychedelic compounds are still unclear, these drugs are thought to modulate the activity of the serotonergic system, primarily through activating serotonin type 2A receptor (5-HT2AR) and studies have focused on these actions in the medial prefrontal cortex (mPFC). 25CN-NBOH, a synthetic psychedelic compound with a high binding affinity for 5-HT2ARs and anti-anxiety actions, has emerged as a valuable tool for investigating the physiological functions mediated by this receptor. This study aimed to investigate the electrophysiological effects of 25CN-NBOH on pyramidal mPFC neurons using whole-cell patch clamp recordings in mouse brain slices. We recorded synaptic events and action potential rates during acute and long-term exposure to two concentrations of 25CN-NBOH. Acute application of 10 µM 25CN-NBOH increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) that was reliant on activation of 5-HT2AR, and which was not seen upon chronic exposure. A similar effect of 200 nM 25CN-NBOH was not noted. Surprisingly, both 10 µM and 200 nM 25CN-NBOH significantly suppressed the firing rate following acute as well as a longer-term exposure of 1 h. This suppression was independent of 5-HT2AR activation but was mediated by M-current channels, as evidenced by the reversal of suppression with the M-current blocker XE-991. Our data suggest a complicated dual action of 25CN-NBOH in enhancing excitatory transmission while also reducing excitability. Our data contribute to knowledge regarding the cellular consequence of 5-HT2AR agonism and contribute to widening our understanding of the potential mechanisms underlying the therapeutic actions of serotonergic psychedelics.

Reduction of Prostate Cancer Risk: Role of Frequent Ejaculation-Associated Mechanisms

Prostate cancer (PCa) accounts for roughly 15% of diagnosed cancers among men, with disease incidence increasing worldwide. Age, family history and ethnicity, diet, physical activity, and chemoprevention all play a role in reducing PCa risk. The prostate is an exocrine gland that is characterized by its multi-functionality, being involved in reproductive aspects such as male ejaculation and orgasmic ecstasy, as well as playing key roles in the regulation of local and systemic concentrations of 5α-dihydrotestosterone. The increase in androgen receptors at the ventral prostate is the first elevated response induced by copulation. The regulation of prostate growth and function is mediated by an androgen-dependent mechanism. Binding 5-DHT to androgen receptors (AR) results in the formation of a 5α-DHT:AR complex. The interaction of the 5α-DHT:AR complex with the specific DNA enhancer element of androgen-regulated genes leads to the regulation of androgen-specific target genes to maintain prostate homeostasis. Consequently, ejaculation may play a significant role in the reduction of PCa risk. Thus, frequent ejaculation in the absence of risky sexual behavior is a possible approach for the prevention of PCa. In this review, we provide an insight into possible mechanisms regulating the impact of frequent ejaculation on reducing PCa risk.

Psychedelics and Suicide-Related Outcomes: A Systematic Review

Background/Objectives: Suicide accounts for 1.4% of global deaths, and the slow-acting nature of traditional treatments for suicide risk underscores the need for alternatives. Psychedelic therapies may rapidly reduce suicide risk. This systematic review evaluates impact of psychedelic therapies on suicide-related outcomes. Methods: A systematic search of MEDLINE, Embase, PsycINFO, and ClinicalTrials.gov was conducted up to November 2024. Results: Four randomized controlled trials (RCTs) evaluated suicidality as a secondary outcome or safety measure, showing significant reductions in suicidal ideation with psilocybin (three studies) and MDMA-assisted therapy (MDMA-AT; one study). Effect sizes, measured by Cohen's d, ranged from =0.52 to 1.25 (p = 0.01 to 0.005), with no safety issues reported. Five additional RCTs assessed suicidality as a safety measure, showing reductions in suicidal ideation with psilocybin (two studies) and MDMA-AT (three studies; p = 0.02 to 0.04). Among 24 non-randomized and cross-sectional studies, results were mixed. Psilocybin (three studies) reduced suicidal ideation, with odds ratios (OR) of 0.40-0.75. MDMA-AT (five studies in PTSD patients) had a pooled effect size of d = 0.61 (95% CI: 0.32-0.89). LSD (six studies) showed increased odds of suicidality, with odds ratios ranging from 1.15 to 2.08. Studies involving DMT (two studies) and multiple psychedelics (three studies) showed mixed results, with DMT studies not showing significant effects on suicidality and studies involving multiple psychedelics showing varying outcomes, some reporting reductions in suicidal ideation and others showing no significant change. Conclusions: The effect of psychedelic therapies on suicide-related outcomes remains inconclusive, highlighting the need for further trials to clarify safety and therapeutic mechanisms.

Agitation: Neurobiology and current management guidelines

There have been important updates in the guidelines for the management of agitation in emergency room settings, including psychiatric emergency services. This manuscript provides a synthesis of current recommendations, combined with a detailed breakdown of the neurobiology of agitation, linking these neuroscientific dimensions with the pharmacological profiles of the drugs recommended by practice guidelines (as well as the profiles of other important agents). Since Project BETA (Best Practices in Evaluation and Treatment of Agitation) guidelines were published in 2012 (by the American Association for Emergency Psychiatry), there have been several developments in the standard of care, including an increase in use of ketamine and droperidol. Recommended treatment strategies for clinicians will be presented, including consideration of how to address specific causes of agitation.

Mushrooms, Microdosing, and Mental Illness: The Effect of Psilocybin on Neurotransmitters, Neuroinflammation, and Neuroplasticity

The incidence of mental health disorders is increasing worldwide. While there are multiple factors contributing to this problem, neuroinflammation underlies a significant subset of psychiatric conditions, particularly major depressive and anxiety disorders. Anti-inflammatory interventions have demonstrated benefit in these conditions. Psilocin, the active ingredient of mushrooms in the Psilocybe genus, is both a potent serotonin agonist and anti-inflammatory agent, increases neuroplasticity, and decreases overactivity in the default mode network. Studies using hallucinogenic doses of psilocin under the supervision of a therapist/guide have consistently demonstrated benefits to individuals with depression and end-of-life anxiety. Microdosing psilocybin in sub-hallucinogenic doses has also demonstrated benefit in mood disorders, and may offer a safe, less expensive, and more available alternative to full doses of psilocybin for mood disorders, as well as for other medical conditions in which inflammation is the principal pathophysiology.

Antidopaminergic medications in Huntington's disease

Huntington's disease (HD) is a progressive neurodegenerative disorder marked by motor, cognitive, and behavioral impairments. Antidopaminergic medications (ADMs), such as VMAT2 inhibitors and antipsychotics, are commonly used to manage HD motor disturbances and behavioral disorders. For patients and caregivers, ADMs are an important tool for managing symptoms that negatively affect daily life. However, the impact of ADM use in HD is not firmly understood due to a lack of robust, systematic studies that assessed their overall effect on HD disease. A mounting body of evidence suggests these medications may be associated with worse clinical measures of cognitive function and functional impairment. While regulatory guidelines highlight adverse effects like sedation, cognitive dysfunction, and extrapyramidal symptoms, it is unclear whether ADMs directly impact disease progression or if the side effects mimic or exacerbate measures of HD symptoms in clinical trials. Given ADM effects on the central nervous system and biological uncertainty within HD outcomes, clinical trial designs should recognize the impact of ADMs on key outcomes, as measured by acceptable scales including Total Functional Capacity, Stoop Word Reading, Symbol Digit Modality Test, and the composite Unified Huntington's Disease Rating Scale. The development of novel HD interventions requires consideration of concomitant ADM use that may influence measures of disease presentation. In this review, we highlight the role of ADMs in HD management, their symptomatic benefits and potential risks, especially with high dose associated side effects, interactions with CYP2D6 inhibitors, and the individualized need for careful dose monitoring for clinical care and trial design.

Functional connectivity gradients and neurotransmitter maps among patients with mild cognitive impairment and depression symptoms

BACKGROUND

Both depressive symptoms and neurotransmitter changes affect the characteristics of functional brain networks in clinical patients. We sought to explore how brain functional grading is organized among patients with mild cognitive impairment and depressive symptoms (D-MCI) and whether changes in brain organization are related to neurotransmitter distribution.

METHODS

Using 3 T magnetic resonance imaging (MRI) we acquired functional MRI (fMRI) data from patients with D-MCI, patients with mild cognitive impairment without depression (nD-MCI), and healthy controls. We used resting-state fMRI and diffusion embedding to examine the pattern of functional connectivity gradients. We used analysis of covariance and post hoc t tests to compare the difference in functional connectivity gradients among the 3 groups. We examined the correlation between variations in functional connectivity gradients and neurotransmitter maps using the JuSpace toolbox.

RESULTS

We included 105 participants, including 31 patients with D-MCI, 40 patients with nD-MCI, and 34 healthy controls. Compared with healthy controls, both the nD-MCI and D-MCI groups showed abnormalities in the principal unimodal-transmodal gradient pattern. Compared with controls, the D-MCI group showed an increased secondary gradient in the default mode network. Differences in the functional connectivity gradients between the D-MCI and nD-MCI groups were significantly correlated with the distribution of 5-hydroxytryptamine receptor subtype 1A.

LIMITATIONS

The small sample size affects the generalizability of the results, and the neurotransmitter template is based on healthy participants, not patients.

CONCLUSION

Our results suggest that depressive symptoms cause abnormalities in the hierarchical segregation of functional brain organization among patients with MCI. Such abnormal changes may be related to the distribution of neurotransmitters.

Pharmaceutical-mediated neuroimmune modulation in psychiatric/psychological adverse events

The therapeutic use of many pharmaceuticals, including small molecules and biological therapies, has been associated with the onset of psychiatric and psychological adverse events (PPAEs), posing substantial concerns to patients' health and safety. These events, which encompass mood (e.g., depression, schizophrenia, suicidal ideation) and cognitive changes (e.g., learning and memory impairment, dementia) often remain undetected until advanced stages of clinical trials or pharmacovigilance, mostly because the mechanisms underlying the onset of PPAEs remain poorly understood. In recent years, the role of neuroimmune modulation (comprising an intricate interplay between various cell types and signaling pathways) in PPAEs has garnered substantial interest. Indeed, understanding these complex interactions would substantially contribute to increase the ability to predict the potential onset of PPAEs during preclinical stages of a new drug's R&D. This review provides a comprehensive summary of the most recent advances in neuroimmune modulation-related mechanisms contributing to the onset of PPAEs and their association with specific pharmaceuticals. Reported data strongly support an association between neuroimmune modulation and the onset of PPAEs. Pharmaceuticals may target specific molecular pathways and pathway elements (e.g., cholinergic and serotonergic systems), which in turn may directly or indirectly impact the inflammatory status and the homeostasis of the brain, regulating inflammation and neuronal function. Also, modulation of the peripheral immune system by pharmaceuticals that do not permeate the blood-brain barrier (e.g., monoclonal antibodies) may alter the neuroimmunomodulatory status of the brain, leading to PPAEs. In summary, this review underscores the diverse pathways through which drugs can influence brain inflammation, shedding light on potential targeted interventions.

Serotonin enhances neurogenesis biomarkers, hippocampal volumes, and cognitive functions in Alzheimer's disease

Research on serotonin reveals a lack of consensus regarding its role in brain volume, especially concerning biomarkers linked to neurogenesis and neuroplasticity, such as ciliary neurotrophic factor (CNTF), fibroblast growth factor 4 (FGF-4), bone morphogenetic protein 6 (BMP-6), and matrix metalloproteinase-1 (MMP-1) in Alzheimer's disease (AD). This study aimed to investigate the influence of serotonin on brain structure and hippocampal volumes in relation to cognitive functions in AD, as well as its link with biomarkers like CNTF, FGF-4, BMP-6, and MMP-1. Data from 133 ADNI participants with AD included cognitive assessments (CDR-SB), serotonin measurements (Biocrates AbsoluteIDQ p180 kit, UPLC-MS/MS), and neurotrophic factors quantified via multiplex proteomics. Gray matter volume changes were analyzed using Voxel-Based Morphometry (VBM) with MRI. Statistical analyses employed Pearson correlation, bootstrap methods, and FDR-adjusted p-values (< 0.05 or < 0.01) via the Benjamini-Hochberg procedure, alongside nonparametric methods. The analysis found a positive correlation between serotonin levels and total brain (r = 0.229, p = 0.023) and hippocampal volumes (right: r = 0.186, p = 0.032; left: r = 0.210, p = 0.023), even after FDR adjustment. Higher serotonin levels were linked to better cognitive function (negative correlation with CDR-SB, r = -0.230, p = 0.024). Notably, serotonin levels were positively correlated with BMP-6 (r = 0.173, p = 0.047), CNTF (r = 0.216, p = 0.013), FGF-4 (r = 0.176, p = 0.043), and MMP-1 (r = 0.202, p = 0.019), suggesting a link between serotonin and neurogenesis and neuroplasticity. However, after adjusting for multiple comparisons and controlling for confounding factors such as age, gender, education, and APOE genotypes (APOE3 and APOE4), none of the correlations of biomarkers remained statistically significant. In conclusion, increased serotonin levels are associated with improved cognitive function and increased brain volume. However, associations with CNTF, FGF-4, BMP-6, and MMP-1 were not statistically significant after adjustments, highlighting the complexity of serotonin's role in AD and the need for further research.

The Role of the Serotonergic System in Time Perception: A Systematic Review

Time perception is a fundamental cognitive function essential for adaptive behavior and shared across species. The neural mechanisms underlying time perception, particularly its neuromodulation, remain debated. In this review, we examined the role of the serotonergic system in time perception (at the scale of seconds and minutes), building a translational bridge between human and non-human animal studies. The literature search was conducted according to the PRISMA statement in PubMed, APA PsycINFO, and APA PsycARTICLES. Sixty papers were selected for full-text review, encompassing both human (n = 10) and animal studies (n = 50). Summarizing the reviewed literature, we revealed consistent evidence for the role of serotonin in timing behavior, highlighting its complex involvement across retrospective, immediate, and prospective timing paradigms. Increased serotonergic activation appears to accelerate internal time speed, which we interpret through the dual klepsydra model as accelerated discharge of the temporal accumulator. However, some findings challenge this framework. Additionally, we link impulsivity-associated with decreased serotonergic functioning in our review-to a slower internal time speed. Variability in prospective timing tasks underscores the need for further research into how serotonin modulates reward-based temporal decisions, using novel approaches to disentangle internal time speed, response inhibition, and other factors.

Dissecting the antidepressant effect of troxerutin: modulation of neuroinflammatory and oxidative stress biomarkers in lipopolysaccharide-treated mice

The role of neuroinflammation in the pathogenesis of depression has prompted the search for new antidepressants. Troxerutin, a bioflavonoid with anti-inflammatory and antioxidant properties, has shown promise, but its impact on neurobehavioral functions remains poorly understood. This study aimed to investigate the antidepressant potential of troxerutin and its effect on the neuroinflammatory response. Here, we exposed male Swiss mice (n = 5/group) to various treatments, including naive and negative controls receiving distilled water, troxerutin-treated groups administered at different doses (10, 20, 40 mg/kg, i.p.), and an imipramine-treated group (25 mg/kg, i.p.). After seven days of treatment, with the exception of the naive group, mice were administered a single dose of lipopolysaccharide (LPS, 0.83 mg/kg). Behavioral evaluations, consisting of the novelty-suppressed feeding (NSF) test, forced swim test (FST), and open field test (OFT), were conducted. Additionally, brain samples were collected for biochemical and immunohistochemical analyses. Troxerutin significantly reduced immobility time in the FST and mitigated behavioral deficits in the NSF test. Additionally, troxerutin increased glutathione (GSH) and superoxide dismutase (SOD) levels while reducing nitrite, malondialdehyde (MDA), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interferon-gamma (IFN-γ) levels compared to the negative control. Immunohistochemistry analysis revealed decreased expression of inducible nitric oxide synthase (iNOS) and nuclear factor-kappa B (NF-κB) in troxerutin-treated mice. Overall, these findings suggest that troxerutin exerts significant antidepressive-like effects, likely mediated by its anti-inflammatory and antioxidant mechanisms. The reduction in neuroinflammatory and oxidative stress biomarkers, along with the improvement in behavioral outcomes, underscores troxerutin's potential as a therapeutic agent for depression.

Impact of psilocybin on cognitive function: A systematic review

Psilocybin is a classic psychedelic with demonstrated preliminary clinical efficacy in a range of psychiatric disorders. Evaluating the impact of psilocybin on cognitive function is essential to unravel its potential benefits and risks. In this systematic review, we assessed psilocybin's effect on cognitive function through a comprehensive search of electronic databases from inception to January 2024, identifying 20 articles involving 2,959 participants. While 85% of studies were conducted in healthy volunteers, most of these studies (85%) used macrodoses, ranging from 45 μg/kg to 30 mg/70 kg. Various cognitive aspects were evaluated and yielded mixed results. Global cognitive function, and processing speed remained mostly unchanged in healthy individuals; However, a limited number of studies reported improvements in certain areas such as sustained attention, working memory, and executive function especially in patients with treatment-resistant depression (TRD). Emotional processing was positively modified, particularly in TRD patients. Psilocybin was observed to enhance emotional empathy without significantly altering cognitive empathy and social cognition. Cognitive flexibility and creative cognition were noted to initially decline but could potentially improve over time. Additionally, with respect to learning and memory skills, psilocybin showed promise in improving specific memory types such as semantic associations and associative learning, while its effects on episodic and verbal memory have been less pronounced compared to other cognitive enhancers. The observed mixed findings underscore the complexity of psilocybin's cognitive influence. Further research is essential to provide a clearer understanding of psilocybin's impact on cognitive domains and to guide the development of safe and effective interventions.

Combining machine learning, molecular dynamics, and free energy analysis for (5HT)-2A receptor modulator classification

The 5-Hydroxytryptamine (5HT)-2A receptor, a key target in psychoactive drug development, presents significant challenges in the design of selective compounds. Here, we describe the construction, evaluation and validation of two machine learning (ML) models for the classification of bioactivity mechanisms against the (5HT)-2A receptor. Employing neural networks and XGBoost models, we achieved an overall accuracy of around 87 %, which was further enhanced through molecular modelling (MM) (e.g. molecular dynamics simulations) and binding free energy analysis. This ML-MM integration provided insights into the mechanisms of direct modulators and prodrugs. A significant outcome of the current study is the development of a 'binding free energy fingerprint' specific to (5HT)-2A modulators, offering a novel metric for evaluating drug efficacy against this target. Our study demonstrates the prospective of employing a successful workflow combining AI with structural biology, offering a powerful tool for advancing psychoactive drug discovery.

Caveolae with serotonin and NMDA receptors as promising targets for the treatment of Alzheimer's disease

Alzheimer's disease is the most general type of cognitive impairments. Until recently, strategies that prevent its clinical progression have remained more elusive. Consequently, research direction should be for finding effective neuroprotective agents. It has been suggested oxidative stress, mitochondrial injury, and inflammation level might lead to brain cell death in many neurological disorders. Therefore, several autophagy-targeted bioactive compounds may be promising candidate therapeutics for the prevention of brain cell damage. Interestingly, some risk genes to Alzheimer's disease are expressed within brain cells, which may be linked to cholesterol metabolism, lipid transport, endocytosis, exocytosis and/or caveolae formation, suggesting that caveolae may be a fruitful therapeutic target to improve cognitive impairments. This review would highlight the latest advances in therapeutic technologies to improve the treatment of Alzheimer's disease. In particular, a paradigm that serotonin and N-methyl-d-aspartate (NMDA) receptors agonist/antagonist within caveolae structure might possibly improve the cognitive impairment. Consequently, cellular membrane biophysics should improve our understanding of the pathology of the cognitive dysfunction associated with Alzheimer's disease. Here, this research direction for the purpose of therapy may open the potential to move a clinical care toward disease-modifying treatment strategies with certain benefits for patients.

GABALAGEN Facilitates Pentobarbital-Induced Sleep by Modulating the Serotonergic System in Rats

Gamma-aminobutyric acid (GABA) is one of the inhibitory neurotransmitters with beneficial effects including sedative properties. However, despite various clinical trials, scientific evidence regarding the impact on sleep of orally ingested GABA, whether natural or synthesized through biological pathways, is not clear. GABALAGEN (GBL) is the product of fermented collagen by Lactobacillus brevis BJ20 (L. brevis BJ20) and Lactobacillus plantarum BJ21 (L. plantarum BJ21), enriched with GABA and characterized by low molecular weight. The aim of this study was to investigate the effect of GBL on sleep improvement via a receptor binding assay in a pentobarbital-induced sleep-related rat model. We utilized a pentobarbital-induced sleep-related rat model to conduct this research. The present study investigated the sedative effects of GBL through electroencephalography (EEG) analysis in the pentobarbital-induced sleep animal model. Exploration of the neural basis of these positive effects involved evaluating orexin in the brain via immunohistochemical methods and 5-HT in the serum using an enzyme-linked immunosorbent assay (ELISA). Furthermore, we conducted a binding assay for 5-HT2C receptors, as these are considered pivotal targets in the mechanism of action for sleep aids. Diazepam (DZP) was used as a positive control to compare the efficacy of GBL. Results: In the binding assay, GBL displayed binding affinity to the 5-HT2C receptor (IC50 value, 5.911 µg/mL). Administration of a low dose of GBL (GBL_L; 100 mg/kg) increased non-rapid eye movement sleep time and decreased wake time based on EEG data in pentobarbital-induced rats. Administration of a high dose of GBL (GBL_H; 250 mg/kg) increased non-rapid eye movement sleep time. Additionally, GBL groups significantly increased concentration of the 5-HT level in the serum. GBL_H decreased orexin expression in the lateral hypothalamus. Conclusion: Overall, the sedative effect of GBL may be linked to the activation of serotonergic systems, as indicated by the heightened affinity of the 5-HT2C receptor binding and elevated levels of 5-HT observed in the serum. This suggests that GBL holds promise as a novel compound for inducing sleep in natural products.

Mechanisms of psilocybin on the treatment of posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is a condition that can develop after a traumatic event, causing distressing symptoms, including intrusive re-experiencing symptoms, alterations in mood and cognition, and changes in arousal and reactivity. Few treatment options exist for patients who find conventional psychotherapy and pharmacotherapy to be inaccessible, ineffective, or intolerable. We explore psilocybin as a potential treatment option for PTSD by examining the neurobiology of PTSD as well as psilocybin's mechanism of action. Based on both pharmacodynamic and psychoanalytic principles, psilocybin may be an underexplored treatment option for patients with PTSD, though further research is required.

Serotonergic neuromodulation of synaptic plasticity

Synaptic plasticity constitutes a fundamental process in the reorganization of neural networks that underlie memory, cognition, emotional responses, and behavioral planning. At the core of this phenomenon lie Hebbian mechanisms, wherein frequent synaptic stimulation induces long-term potentiation (LTP), while less activation leads to long-term depression (LTD). The synaptic reorganization of neuronal networks is regulated by serotonin (5-HT), a neuromodulator capable of modify synaptic plasticity to appropriately respond to mental and behavioral states, such as alertness, attention, concentration, motivation, and mood. Lately, understanding the serotonergic Neuromodulation of synaptic plasticity has become imperative for unraveling its impact on cognitive, emotional, and behavioral functions. Through a comparative analysis across three main forebrain structures-the hippocampus, amygdala, and prefrontal cortex, this review discusses the actions of 5-HT on synaptic plasticity, offering insights into its role as a neuromodulator involved in emotional and cognitive functions. By distinguishing between plastic and metaplastic effects, we provide a comprehensive overview about the mechanisms of 5-HT neuromodulation of synaptic plasticity and associated functions across different brain regions.

Experience-dependent serotonergic signaling in glia regulates targeted synapse elimination

The optimization of brain circuit connectivity based on initial environmental input occurs during critical periods characterized by sensory experience-dependent, temporally restricted, and transiently reversible synapse elimination. This precise, targeted synaptic pruning mechanism is mediated by glial phagocytosis. Serotonin signaling has prominent, foundational roles in the brain, but functions in glia, or in experience-dependent brain circuit synaptic connectivity remodeling, have been relatively unknown. Here, we discover that serotonergic signaling between glia is essential for olfactory experience-dependent synaptic glomerulus pruning restricted to a well-defined Drosophila critical period. We find that experience-dependent serotonin signaling is restricted to the critical period, with both (1) serotonin production and (2) 5-HT2A receptors specifically in glia, but not neurons, absolutely required for targeted synaptic glomerulus pruning. We discover that glial 5-HT2A receptor signaling limits the experience-dependent synaptic connectivity pruning in the critical period and that conditional reexpression of 5-HT2A receptors within adult glia reestablishes "critical period-like" experience-dependent synaptic glomerulus pruning at maturity. These results reveal an essential requirement for glial serotonergic signaling mediated by 5-HT2A receptors for experience-dependent synapse elimination.

Desloratadine ameliorates paclitaxel-induced peripheral neuropathy and hypersensitivity reactions in mice

Paclitaxel (PTX) serves as a primary chemotherapy agent against diverse solid tumors including breast cancer, lung cancer, head and neck cancer and ovarian cancer, having severe adverse effects including PTX-induced peripheral neuropathy (PIPN) and hypersensitivity reactions (HSR). A recommended anti-allergic agent diphenhydramine (DIP) has been used to alleviate PTX-induced HSR. Desloratadine (DLT) is a third generation of histamine H1 receptor antagonist, but also acted as a selective antagonist of 5HTR2A. In this study we investigated whether DLT ameliorated PIPN-like symptoms in mice and the underlying mechanisms. PIPN was induced in male mice by injection of PTX (4 mg/kg, i.p.) every other day for 4 times. The mice exhibited 50% reduction in mechanical threshold, paw thermal response latency and paw cold response latency compared with control mice. PIPN mice were treated with DLT (10, 20 mg/kg, i.p.) 30 min before each PTX administration in the phase of establishing PIPN mice model and then administered daily for 4 weeks after the model was established. We showed that DLT administration dose-dependently elevated the mechanical, thermal and cold pain thresholds in PIPN mice, whereas administration of DIP (10 mg/kg, i.p.) had no ameliorative effects on PIPN-like symptoms. We found that the expression of 5HTR2A was selectively elevated in the activated spinal astrocytes of PIPN mice. Spinal cord-specific 5HTR2A knockdown by intrathecal injection of AAV9-5Htr2a-shRNA significantly alleviated the mechanical hyperalgesia, thermal and cold hypersensitivity in PIPN mice, while administration of DLT (20 mg/kg) did not further ameliorate PIPN-like symptoms. We demonstrated that DLT administration alleviated dorsal root ganglion neuronal damage and suppressed sciatic nerve destruction, spinal neuron apoptosis and neuroinflammation in the spinal cord of PIPN mice. Furthermore, we revealed that DLT administration suppressed astrocytic neuroinflammation via the 5HTR2A/c-Fos/NLRP3 pathway and blocked astrocyte-neuron crosstalk by targeting 5HTR2A. We conclude that spinal 5HTR2A inhibition holds promise as a therapeutic approach for PIPN and we emphasize the potential of DLT as a dual-functional agent in ameliorating PTX-induced both PIPN and HSR in chemotherapy. In summary, we determined that spinal 5HTR2A was selectively activated in PIPN mice and DLT could ameliorate the PTX-induced both PIPN- and HSR-like pathologies in mice. DLT alleviated the damages of DRG neurons and sciatic nerves, while restrained spinal neuronal apoptosis and CGRP release in PIPN mice. The underlying mechanisms were intensively investigated by assay against the PIPN mice with 5HTR2A-specific knockdown in the spinal cord by injection of adeno-associated virus 9 (AAV9)-5Htr2a-shRNA. DLT inhibited astrocytic NLRP3 inflammasome activation-mediated spinal neuronal damage through 5HTR2A/c-FOS pathway. Our findings have supported that spinal 5HTR2A inhibition shows promise as a therapeutic strategy for PIPN and highlighted the potential advantage of DLT as a dual-functional agent in preventing against PTX-induced both PIPN and HSR effects in anticancer chemotherapy.

Decoding the genetic landscape of autism: A comprehensive review

BACKGROUND

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by heterogeneous symptoms and genetic underpinnings. Recent advancements in genetic and epigenetic research have provided insights into the intricate mechanisms contributing to ASD, influencing both diagnosis and therapeutic strategies.

AIM

To explore the genetic architecture of ASD, elucidate mechanistic insights into genetic mutations, and examine gene-environment interactions.

METHODS

A comprehensive systematic review was conducted, integrating findings from studies on genetic variations, epigenetic mechanisms (such as DNA methylation and histone modifications), and emerging technologies [including Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 and single-cell RNA sequencing]. Relevant articles were identified through systematic searches of databases such as PubMed and Google Scholar.

RESULTS

Genetic studies have identified numerous risk genes and mutations associated with ASD, yet many cases remain unexplained by known factors, suggesting undiscovered genetic components. Mechanistic insights into how these genetic mutations impact neural development and brain connectivity are still evolving. Epigenetic modifications, particularly DNA methylation and non-coding RNAs, also play significant roles in ASD pathogenesis. Emerging technologies like CRISPR-Cas9 and advanced bioinformatics are advancing our understanding by enabling precise genetic editing and analysis of complex genomic data.

CONCLUSION

Continued research into the genetic and epigenetic underpinnings of ASD is crucial for developing personalized and effective treatments. Collaborative efforts integrating multidisciplinary expertise and international collaborations are essential to address the complexity of ASD and translate genetic discoveries into clinical practice. Addressing unresolved questions and ethical considerations surrounding genetic research will pave the way for improved diagnostic tools and targeted therapies, ultimately enhancing outcomes for individuals affected by ASD.

Epigenetic mechanisms of rapid-acting antidepressants

BACKGROUND

Rapid-acting antidepressants (RAADs), including dissociative anesthetics, psychedelics, and empathogens, elicit rapid and sustained therapeutic improvements in psychiatric disorders by purportedly modulating neuroplasticity, neurotransmission, and immunity. These outcomes may be mediated by, or result in, an acute and/or sustained entrainment of epigenetic processes, which remodel chromatin structure and alter DNA accessibility to regulate gene expression.

METHODS

In this perspective, we present an overview of the known mechanisms, knowledge gaps, and future directions surrounding the epigenetic effects of RAADs, with a focus on the regulation of stress-responsive DNA and brain regions, and on the comparison with conventional antidepressants.

MAIN BODY

Preliminary correlative evidence indicates that administration of RAADs is accompanied by epigenetic effects which are similar to those elicited by conventional antidepressants. These include changes in DNA methylation, post-translational modifications of histones, and differential regulation of non-coding RNAs in stress-responsive chromatin areas involved in neurotrophism, neurotransmission, and immunomodulation, in stress-responsive brain regions. Whether these epigenetic changes causally contribute to the therapeutic effects of RAADs, are a consequence thereof, or are unrelated, remains unknown. Moreover, the potential cell type-specificity and mechanisms involved are yet to be fully elucidated. Candidate mechanisms include neuronal activity- and serotonin and Tropomyosine Receptor Kinase B (TRKB) signaling-mediated epigenetic changes, and direct interaction with DNA, histones, or chromatin remodeling complexes.

CONCLUSION

Correlative evidence suggests that epigenetic changes induced by RAADs accompany therapeutic and side effects, although causation, mechanisms, and cell type-specificity remain largely unknown. Addressing these research gaps may lead to the development of novel neuroepigenetics-based precision therapeutics.

Visual mismatch negativity in Parkinson's psychosis and potential for testing treatment mechanisms

Psychosis and visual hallucinations are a prevalent non-motor symptom of Parkinson's disease, negatively affecting patients' quality of life and constituting a greater risk for dementia. Understanding neural mechanisms associated to these symptoms is instrumental for treatment development. The mismatch negativity is an event-related potential evoked by a violation in a sequence of sensory events. It is widely considered an index of sensory change-detection. Reduced mismatch negativity response is one of the most replicated results in schizophrenia and has been suggested to be a superior psychosis marker. To understand whether this event-related potential component could be a similarly robust marker for Parkinson's psychosis, we used electroencephalography with a change-detection task to study the mismatch negativity in the visual modality in 20 participants with Parkinson's and visual hallucinations and 18 matched Parkinson's participants without hallucinations. We find that visual mismatch negativity is clearly present in participants with Parkinson's disease without hallucinations at both parieto-occipital and frontal sites, whereas participants with Parkinson's and visual hallucinations show reduced or no differences in the two waveforms, confirming the sensitivity of mismatch negativity to psychosis, even within the same diagnostic group. We also explored the relationship between hallucination severity and visual mismatch negativity amplitude, finding a negative correlation between visual hallucinations severity scores and visual mismatch negativity amplitude at a central frontal and a parieto-occipital electrodes, whereby the more severe or complex (illusions, formed visual hallucinations) the symptoms the smaller the amplitude. We have also tested the potential role of the serotonergic 5-HT2A cascade in visual hallucinations in Parkinson's with these symptoms, following the receptor trafficking hypothesis. We did so with a pilot study in healthy controls (N = 18) providing support for the role of the Gi/o-dependent pathway in the psychedelic effect and a case series in participants with Parkinson's and visual hallucinations (N = 5) using a double-blind crossover design. Positive results on psychosis scores and mismatch amplitude add further to the potential role of serotonergic modulation of visual hallucinations in Parkinson's disease.

Serotonin effects on human iPSC-derived neural cell functions: from mitochondria to depression

Depression's link to serotonin dysregulation is well-known. The monoamine theory posits that depression results from impaired serotonin activity, leading to the development of antidepressants targeting serotonin levels. However, their limited efficacy suggests a more complex cause. Recent studies highlight mitochondria as key players in depression's pathophysiology. Mounting evidence indicates that mitochondrial dysfunction significantly correlates with major depressive disorder (MDD), underscoring its pivotal role in depression. Exploring the serotonin-mitochondrial connection, our study investigated the effects of chronic serotonin treatment on induced-pluripotent stem cell-derived astrocytes and neurons from healthy controls and two case study patients. One was a patient with antidepressant non-responding MDD ("Non-R") and another had a non-genetic mitochondrial disorder ("Mito"). The results revealed that serotonin altered the expression of genes related to mitochondrial function and dynamics in neurons and had an equalizing effect on calcium homeostasis in astrocytes, while ATP levels seemed increased. Serotonin significantly decreased cytosolic and mitochondrial calcium in neurons. Electrophysiological measurements evidenced that serotonin depolarized the resting membrane potential, increased both sodium and potassium current density and ultimately improved the overall excitability of neurons. Specifically, neurons from the Non-R patient appeared responsive to serotonin in vitro, which seemed to improve neurotransmission. While it is unclear how this translates to the systemic level and AD resistance mechanisms are not fully elucidated, our observations show that despite his treatment resistance, this patient's cortical neurons are responsive to serotonergic signals. In the Mito patient, evidence suggested that serotonin, by increasing excitability, exacerbated an existing hyperexcitability highlighting the importance of considering mitochondrial disorders in patients with MDD, and avoiding serotonin-increasing medication. Taken together, our findings suggested that serotonin positively affects calcium homeostasis in astrocytes and increases neuronal excitability. The latter effect must be considered carefully, as it could have beneficial or detrimental implications based on individual pathologies.

Physical activity promotes brain development through serotonin during early childhood

Early childhood serves as a critical period for neural development and skill acquisition when children are extremely susceptible to the external environment and experience. As a crucial experiential stimulus, physical activity is believed to produce a series of positive effects on brain development, such as cognitive function, social-emotional abilities, and psychological well-being. The World Health Organization recommends that children engage in sufficient daily physical activity, which has already been strongly advocated in the practice of preschool education. However, the mechanisms by which physical activity promotes brain development are still unclear. The role of neurotransmitters, especially serotonin, in promoting brain development through physical activity has received increasing attention. Physical activity has been shown to stimulate the secretion of serotonin by increasing the bioavailability of free tryptophan and enriching the diversity of gut microbiota. Due to its important role in modulating neuronal proliferation, differentiation, synaptic morphogenesis, and synaptic transmission, serotonin can regulate children's explicit cognitive and social interaction behavior in the early stages of life. Therefore, we hypothesized that serotonin emerges as a pivotal transmitter that mediates the relationship between physical activity and brain development during early childhood. Further systematic reviews and meta-analyses are needed to specifically explore whether the type, intensity, dosage, duration, and degree of voluntariness of PA may affect the role of serotonin in the relationship between physical activity and brain function. This review not only helps us understand the impact of exercise on development but also provides a solid theoretical basis for increasing physical activity during early childhood.

Therapeutic modulation of the kynurenine pathway in severe mental illness and comorbidities: A potential role for serotonergic psychedelics

Mounting evidence points towards a crucial role of the kynurenine pathway (KP) in the altered gut-brain axis (GBA) balance in severe mental illness (SMI, namely depression, bipolar disorder, and schizophrenia) and cardiometabolic comorbidities. Preliminary evidence shows that serotonergic psychedelics and their analogues may hold therapeutic potential in addressing the altered KP in the dysregulated GBA in SMI and comorbidities. In fact, aside from their effects on mood, psychedelics elicit therapeutic improvement in preclinical models of obesity, metabolic syndrome, and vascular inflammation, which are highly comorbid with SMI. Here, we review the literature on the therapeutic modulation of the KP in the dysregulated GBA in SMI and comorbidities, and the potential application of psychedelics to address the altered KP in the brain and systemic dysfunction underlying SMI and comorbidities. Psychedelics might therapeutically modulate the KP in the altered GBA in SMI and comorbidities either directly, via altering the metabolic pathway by influencing the rate-limiting enzymes of the KP and affecting the levels of available tryptophan, or indirectly, by affecting the gut microbiome, gut metabolome, metabolism, and the immune system. Despite promising preliminary evidence, the mechanisms and outcomes of the KP modulation with psychedelics in SMI and systemic comorbidities remain largely unknown and require further investigation. Several concerns are discussed surrounding the potential side effects of this approach in specific cohorts of individuals with SMI and systemic comorbidities.

Cannabinoids and monoaminergic system: implications for learning and memory

Cannabinoids and the endocannabinoid system (ECS) have been intensively studied for their neuroregulatory roles in the central nervous system (CNS), especially in regulating learning and memory. However, many experimental and clinical studies obtained conflicting results indicating a complex network of interaction underlying the regulation of learning and memory by different cannabinoids and the ECS. The ECS influences neuronal synaptic communications, and therefore may exert different regulation via their different impact on other neurotransmitters. The monoaminergic system includes a variety of neurotransmitters, such as dopamine, norepinephrine, and serotonin, which play important roles in regulating mood, cognition, and reward. The interaction among cannabinoids, ECS and the monoaminergic system has drawn particular attention, especially their contributions to learning and memory. In this review, we summarized the current understanding of how cannabinoids, ECS and the monoaminergic system contribute to the process of learning and memory, and discussed the influences of monoaminergic neurotransmission by cannabinoids and ECS during this process.

Influence of Genetic Polymorphisms on Cognitive Function According to Dietary Exposure to Bisphenols in a Sample of Spanish Schoolchildren

BACKGROUND

Neurodevelopmental disorders (NDDs) like intellectual disability (ID) are highly heritable, but the environment plays an important role. For example, endocrine disrupting chemicals (EDCs), including bisphenol A (BPA) and its analogues, have been termed neuroendocrine disruptors. This study aimed to evaluate the influence of different genetic polymorphisms (SNPs) on cognitive function in Spanish schoolchildren according to dietary bisphenol exposure.

METHODS

A total of 102 children aged 6-12 years old were included. Ten SNPs in genes involved in brain development, synaptic plasticity, and neurotransmission (BDNF, NTRK2, HTR2A, MTHFR, OXTR, SLC6A2, and SNAP25) were genotyped. Then, dietary exposure to bisphenols (BPA plus BPS) was estimated and cognitive functions were assessed using the WISC-V Spanish form.

RESULTS

BDNF rs11030101-T and SNAP25 rs363039-A allele carriers scored better on the fluid reasoning domain, except for those inheriting the BDNF rs6265-A allele, who had lower scores. Secondly, relevant SNP-bisphenol interactions existed in verbal comprehension (NTRK2 rs10868235 (p-int = 0.043)), working memory (HTR2A rs7997012 (p-int = 0.002), MTHFR rs1801133 (p-int = 0.026), and OXTR rs53576 (p-int = 0.030)) and fluid reasoning (SLC6A2 rs998424 (p-int = 0.004)).

CONCLUSIONS

Our findings provide the first proof that exploring the synergistic or additive effects between genetic variability and bisphenol exposure on cognitive function could lead to a better understanding of the multifactorial and polygenic aetiology of NDDs.

Early biomarkers in the presymptomatic phase of cognitive impairment: changes in the endocannabinoidome and serotonergic pathways in Alzheimer's-prone mice after mTBI

BACKGROUND

Despite extensive studies on the neurobiological correlates of traumatic brain injury (TBI), little is known about its molecular determinants on long-term consequences, such as dementia and Alzheimer's disease (AD).

METHODS

Here, we carried out behavioural studies and an extensive biomolecular analysis, including inflammatory cytokines, gene expression and the combination of LC-HRMS and MALDI-MS Imaging to elucidate the targeted metabolomics and lipidomics spatiotemporal alterations of brains from wild-type and APP-SWE mice, a genetic model of AD, at the presymptomatic stage, subjected to mild TBI.

RESULTS

We found that brain injury does not affect cognitive performance in APP-SWE mice. However, we detected an increase of key hallmarks of AD, including Aβ1-42 levels and BACE1 expression, in the cortices of traumatized transgenic mice. Moreover, significant changes in the expanded endocannabinoid (eCB) system, or endocannabinoidome (eCBome), occurred, including increased levels of the endocannabinoid 2-AG in APP-SWE mice in both the cortex and hippocampus, and N-acylserotonins, detected for the first time in the brain. The gene expression of enzymes for the biosynthesis and inactivation of eCBs and eCB-like mediators, and some of their main molecular targets, also underwent significant changes. We also identified the formation of heteromers between cannabinoid 1 (CB1) and serotonergic 2A (5HT2A) receptors, whose levels increased in the cortex of APP-SWE mTBI mice, possibly contributing to the exacerbated pathophysiology of AD induced by the trauma.

CONCLUSIONS

Mild TBI induces biochemical changes in AD genetically predisposed mice and the eCBome may play a role in the pathogenetic link between brain injury and neurodegenerative disorders also by interacting with the serotonergic system.

The effects of psilocybin on cognition and emotional processing in healthy adults and adults with depression: a systematic literature review

INTRODUCTION

Psilocybin, a naturally occurring serotonergic agonist in some mushroom species, has shown promise as a novel, fast-acting pharmacotherapy seeking to overcome the limitations of conventional first-line antidepressants. Studying psilocybin effects on cognition and emotional processing may help to clarify the mechanisms underlying the therapeutic potential of psilocybin and may also support studies with people suffering from depression. Thus, this review aims to provide a comprehensive overview of the current literature regarding the effects of psilocybin on these two key areas in both healthy and depressed populations.

METHOD

A systematic search was performed on 29 January 2024, in the PubMed, EBSCOhost, Web of Science and SCOPUS databases. After duplicates removal, study selection was conducted considering pre-specified criteria. Data extraction was then performed. The quality assessment of the studies was carried out using the Cochrane Collaboration tools for randomized (RoB 2.0) and non-randomized (ROBINS-I) controlled trials.

RESULTS

Twenty articles were included, with 18 targeting healthy adults and two adults with depression. Results point to impairments within attentional and inhibitory processes, and improvements in the domains of creativity and social cognition in healthy individuals. In the population with depression, only cognitive flexibility and emotional recognition were affected, both being enhanced. The comparison of outcomes from both populations proved limited.

CONCLUSIONS

Psilocybin acutely alters several cognitive domains, with a localized rather than global focus, in a dose- and time-dependent manner. However, the significant methodological constraints call for further research, in the context of depression and with standardized protocols, with longitudinal studies also imperative.

Psilocybin for dementia prevention? The potential role of psilocybin to alter mechanisms associated with major depression and neurodegenerative diseases

Major depression is an established risk factor for subsequent dementia, and depression in late life may also represent a prodromal state of dementia. Considering current challenges in the clinical development of disease modifying therapies for dementia, the focus of research is shifting towards prevention and modification of risk factors to alter the neurodegenerative disease trajectory. Understanding mechanistic commonalities underlying affective symptoms and cognitive decline may reveal biomarkers to aid early identification of those at risk of progressing to dementia during the preclinical phase of disease, thus allowing for timely intervention. Adult hippocampal neurogenesis (AHN) is a phenomenon that describes the birth of new neurons in the dentate gyrus throughout life and it is associated with spatial learning, memory and mood regulation. Microglia are innate immune system macrophages in the central nervous system that carefully regulate AHN via multiple mechanisms. Disruption in AHN is associated with both dementia and major depression and microgliosis is a hallmark of several neurodegenerative diseases. Emerging evidence suggests that psychedelics promote neuroplasticity, including neurogenesis, and may also be immunomodulatory. In this context, psilocybin, a serotonergic agonist with rapid-acting antidepressant properties has the potential to ameliorate intersecting pathophysiological processes relevant for both major depression and neurodegenerative diseases. In this narrative review, we focus on the evidence base for the effects of psilocybin on adult hippocampal neurogenesis and microglial form and function; which may suggest that psilocybin has the potential to modulate multiple mechanisms of action, and may have implications in altering the progression from major depression to dementia in those at risk.

Effects of a Serotonin Receptor Peptide on Behavioral Pattern Separation in Sham- vs. Mild Traumatic Brain Injured Rats

Aims

Behavioral pattern separation is a hippocampal-dependent component of episodic memory and a sensitive marker of early cognitive decline. Here we tested whether mild traumatic injury causes loss of pattern separation in the rat and for its prevention by a novel neuroprotective peptide fragment of the human serotonin 2A receptor (SN..8).

Methods

Lateral fluid percussion was used to induce mild traumatic brain injury in male Sprague- Dawley rats. Rats were trained to distinguish between a stable vs unstable swim platform separated by increasing distances (4.5 vs 3.0 vs 1.5 feet) in a modification to the classic Morris water maze. Peptide SN..8 vs scrambled version of same amino acids (2 mg/kg) was administered via intraperitoneal route (1-, 3- and 5-days) after lateral fluid percussion or sham injury. Rats received three weeks of training and two weeks of testing before injury and were tested again at 2 and 5-weeks after injury.

Results

There was a gradient of decreasing incorrect responses to the choice between (stable vs unstable platform) as the platform separation distance was increased from 1.5 to 3.0 to 4.5 feet consistent with behavioral pattern separation. Systemic administration of SN..8 peptide (vs scrambled) peptide was associated with statistically significant lower rate of incorrect responses (at both 4.5 feet and 3.0 feet platform separation) in traumatic brain-injured rats (but not in sham-injured rats) tested at 2-weeks post-injury. Five weeks after injury, the rats had largely recovered and exhibited a much lower overall rate of incorrect responses across both drug and injury subgroups.

Conclusions

Introduction of an unstable platform (choice phase of the Morris water maze) at varying distances from the stable platform resulted in behavior having the hallmark of pattern separation. Our data are the first to suggest that systemic administration of (2 mg/kg) SN..8 peptide immediately after mild traumatic brain injury (lateral fluid percussion) appeared to protect against loss of behavioral pattern separation in the rat.

G protein-specific mechanisms in the serotonin 5-HT2A receptor regulate psychosis-related effects and memory deficits

G protein-coupled receptors (GPCRs) are sophisticated signaling machines able to simultaneously elicit multiple intracellular signaling pathways upon activation. Complete (in)activation of all pathways can be counterproductive for specific therapeutic applications. This is the case for the serotonin 2 A receptor (5-HT2AR), a prominent target for the treatment of schizophrenia. In this study, we elucidate the complex 5-HT2AR coupling signature in response to different signaling probes, and its physiological consequences by combining computational modeling, in vitro and in vivo experiments with human postmortem brain studies. We show how chemical modification of the endogenous agonist serotonin dramatically impacts the G protein coupling profile of the 5-HT2AR and the associated behavioral responses. Importantly, among these responses, we demonstrate that memory deficits are regulated by Gαq protein activation, whereas psychosis-related behavior is modulated through Gαi1 stimulation. These findings emphasize the complexity of GPCR pharmacology and physiology and open the path to designing improved therapeutics for the treatment of stchizophrenia.

Chronic Behavioral and Neurochemical Effects of Four Novel N-Benzyl-2-phenylethylamine Derivatives Recently Identified as "Psychoactive" in Adult Zebrafish Screens

Potently affecting human and animal brain and behavior, hallucinogenic drugs have recently emerged as potentially promising agents in psychopharmacotherapy. Complementing laboratory rodents, the zebrafish (Danio rerio) is a powerful model organism for screening neuroactive drugs, including hallucinogens. Here, we tested four novel N-benzyl-2-phenylethylamine (NBPEA) derivatives with 2,4- and 3,4-dimethoxy substitutions in the phenethylamine moiety and the -F, -Cl, and -OCF3 substitutions in the ortho position of the phenyl ring of the N-benzyl moiety (34H-NBF, 34H-NBCl, 24H-NBOMe(F), and 34H-NBOMe(F)), assessing their behavioral and neurochemical effects following chronic 14 day treatment in adult zebrafish. While the novel tank test behavioral data indicate anxiolytic-like effects of 24H-NBOMe(F) and 34H-NBOMe(F), neurochemical analyses reveal reduced brain norepinephrine by all four drugs, and (except 34H-NBCl) - reduced dopamine and serotonin levels. We also found reduced turnover rates for all three brain monoamines but unaltered levels of their respective metabolites. Collectively, these findings further our understanding of complex central behavioral and neurochemical effects of chronically administered novel NBPEAs and highlight the potential of zebrafish as a model for preclinical screening of small psychoactive molecules.

DReAmocracy: A Method to Capitalise on Prior Drug Discovery Efforts to Highlight Candidate Drugs for Repurposing

In the area of drug research, several computational drug repurposing studies have highlighted candidate repurposed drugs, as well as clinical trial studies that have tested/are testing drugs in different phases. To the best of our knowledge, the aggregation of the proposed lists of drugs by previous studies has not been extensively exploited towards generating a dynamic reference matrix with enhanced resolution. To fill this knowledge gap, we performed weight-modulated majority voting of the modes of action, initial indications and targeted pathways of the drugs in a well-known repository, namely the Drug Repurposing Hub. Our method, DReAmocracy, exploits this pile of information and creates frequency tables and, finally, a disease suitability score for each drug from the selected library. As a testbed, we applied this method to a group of neurodegenerative diseases (Alzheimer's, Parkinson's, Huntington's disease and Multiple Sclerosis). A super-reference table with drug suitability scores has been created for all four neurodegenerative diseases and can be queried for any drug candidate against them. Top-scored drugs for Alzheimer's Disease include agomelatine, mirtazapine and vortioxetine; for Parkinson's Disease, they include apomorphine, pramipexole and lisuride; for Huntington's, they include chlorpromazine, fluphenazine and perphenazine; and for Multiple Sclerosis, they include zonisamide, disopyramide and priralfimide. Overall, DReAmocracy is a methodology that focuses on leveraging the existing drug-related experimental and/or computational knowledge rather than a predictive model for drug repurposing, offering a quantified aggregation of existing drug discovery results to (1) reveal trends in selected tracks of drug discovery research with increased resolution that includes modes of action, targeted pathways and initial indications for the investigated drugs and (2) score new candidate drugs for repurposing against a selected disease.

Insights into the development of 99mTc-radioligands for serotonergic receptors imaging: Synthesis, labeling, In vitro, and In vivo studies

Serotonergic (5-hydroxytryptamine; 5-HT) receptors play critical roles in neurological and psychological disorders such as schizophrenia, anxiety, depression, and Alzheimer's diseases. Therefore, it is particularly important to develop novel radioligands or modify the existing ones to identify the serotonergic receptors involved in psychiatric disorders. Among the 16 subtypes of serotonergic systems, only technetium-99m based radiopharmaceuticals have been evaluated for serotonin-1A (5-HT1A), serotonin-2A (5-HT2A), 5-HT1A/7 heterodimers and serotonin receptor neurotransmitter (SERT). This review focuses on recent efforts in the design, synthesis and evaluation of 99mTc-radioligands used for single photon emission computerized tomography (SPECT) imaging of serotonergic (5-HT) receptors. Additionally, the discussion will cover aspects such as chemical structure, in vitro/vivo stability, affinity toward serotonin receptors, blood-brain barrier permeation (BBB), and biodistribution study.

The 5-HT2A, 5-HT5A, and 5-HT6 serotonergic receptors in the medial prefrontal cortex behave differently in extinction learning: Does social support play a role?

Studies on the social modulation of fear have revealed that in social species, individuals in a distressed state show better recovery from aversive experiences when accompanied - referred to as social buffering. However, the underlying mechanisms remain unknown, hindering the understanding of such an approach. Our previous data showed that the presence of a conspecific during the extinction task inhibited the retrieval of fear memory without affecting the extinction memory in the retention test. Here, we investigate the role of serotonergic receptors (5-HTRs), specifically 5-HT2A, 5-HT5A, and 5-HT6 in the medial prefrontal cortex (mPFC), In the retention of extinction after the extinction task, in the absence or presence of social support. Extinction training was conducted on 60-day-old male Wistar rats either alone or with a conspecific (a familiar cagemate, non-fearful). The antagonists for these receptors were administered directly into the mPFC immediately after the extinction training. The results indicate that blocking 5-HT5A (SB-699551-10 μg/side) and 5-HT6 (SB-271046A - 10 μg/side) receptors in the mPFC impairs the consolidation of CFC in the social support group. Interestingly, blocking 5-HT2A receptors (R65777 - 4 μg/side) in the mPFC led to impaired CFC specifically in the group undergoing extinction training alone. These findings contribute to a better understanding of brain mechanisms and neuromodulation associated with social support during an extinction protocol. They are consistent with previously published research, suggesting that the extinction of contextual fear conditioning with social support involves distinct neuromodulatory processes compared to when extinction training is conducted alone.

Synthesis, molecular docking, ADMET, and evaluation of the anxiolytic effect in adult zebrafish of synthetic chalcone (E)-3-(4-(dimethylamino)phenyl)-1-(2-hydroxyphenyl)prop-2-en-1-one: An in vivo and in silico approach

BACKGROUND

Anxiety disorders represent the complex interaction between biological, psychological, temperamental, and environmental factors; drugs available to treat anxiety such as benzodiazepines (BZDs) are associated with several unwanted side effects. Although there are useful treatments, there is still a need for more effective anxiolytics with better safety profiles than BZDs. Chalcones or 1,3-diphenyl-2-proper-1-ones can be an alternative since this class of compounds has shown therapeutic potential mainly due to interactions with GABAA receptors and serotonergic system.

OBJECTIVES

This study evaluated the anxiolytic potential of chalcone (E)-3-(4-(dimethylamino)phenyl)-1-(2-hydroxyphenyl)prop-2-en-1-one (C2OHPDA) in adult zebrafish (Danio rerio) (ZFa).

METHODS

Each animal (n = 6/group) was treated intraperitoneally (i.p.; 20 μL) with the chalcone (4, 20, and 40 mg/kg) and with the vehicle (DMSO 3%; 20 μL), being submitted to the tests of locomotor activity and 96-h acute toxicity. The light/dark test was also performed, and the serotonergic mechanism (5-HT) was evaluated through the antagonists of the 5-HTR1 , 5-HTR2A/2C , and 5-HTR3A/3B receptors. It was investigated the prediction of the chalcone's position and preferential orientation concerning its receptor, as well as the pharmacokinetic parameters (ADMET) involved in the process after administration.

RESULTS

As a result, C2OHPDA was not toxic and reduced the locomotor activity of ZFa. Furthermore, chalcone demonstrated an anxiolytic effect on the central nervous system (CNS), mediated by the serotonergic system, with action on 5-HT2A and 5-HTR3A/3B receptors. The interaction of C2OHPDA with 5-HT2A R and 5-HT3A receptors was confirmed by molecular docking study, the affinity energy observed was -8.7 and -9.1 kcal/mol, respectively.

CONCLUSION

Thus, this study adds new evidence and highlights that chalcone can potentially be used to develop compounds with anxiolytic properties.

3-Acetyl coumarin alleviate neuroinflammatory responses and oxidative stress in aluminum chloride-induced Alzheimer's disease rat model

Alzheimer's disease (AD) is a neurodegenerative disorder that impairs mental ability and interrupts cognitive function. Heavy metal exposure like aluminum chloride is associated with neurotoxicity linked to neuro-inflammation, oxidative stress, accumulation of amyloid plaques, phosphorylation of tau proteins associated with AD like symptoms. The objective of the present investigation was to assess the effect 3-acetyl coumarin (3AC) in a rat model of AD. Preliminary screening was performed with SWISS ADME to check for the bioavailability of 3-AC and likeness score which proved favorable. 3-AC docked against Caspase 3, NF-κβ and tau protein kinase I exhibited good binding energies. Male rats were divided into six groups (n = 5). AlCl3 (100 mg/kg BW) was administered for 28 days before starting treatment to induce AD. Normal control rats received vehicle. Treatment groups received 10, 20 and 30 mg/kg 3-AC for 28 days. Rivastigmine (2 mg/kg) was the standard. Behavioral tests (EPM, MWM) were performed at 7-day intervals throughout study period. Rats showed improved spatial memory and learning in treatment groups during behavioral tests. Rats were euthanized on day 28. Inflammatory markers (IL-1β, IL-16 and TNFα) exhibited significant improvement (p < 0.001) in treated rats. Oxidative stress enzymes (SOD, CAT, GSH, MDA) were restored. Caspase3 and NF-κβ quantified through qRT-PCR also decreased significantly (p < 0.001) when compared to disease control group. Levels of acetyl cholinesterase, dopamine and noradrenaline were also restored in treated rats significantly (p < 0.001). 3-AC treatment restored neuroprotection probably because of anti-inflammatory, anti-oxidant and anti-cholinesterase potential; hence, this can be considered a promising therapeutic potential alternative.

Skeletons in the closet? Using a bibliometric lens to visualise phytochemical and pharmacological activities linked to Sceletium, a mood enhancer

Plants from the Sceletium genus (Aizoaceae) have been traditionally used for millennia by the Khoe and Khoen people in southern Africa, as an appetite suppressant as well as a mood elevator. In more recent times, this mood-elevating activity has been commercialised in the South African natural products industry for the treatment of anxiety and depression, with several products available both locally and abroad. Research on this species has seen rapid growth with advancements in analytical and pharmacological tools, in an effort to understand the composition and biological activity. The Web of Science (WoS) database was searched for articles related to 'Sceletium' and 'Mesembrine'. These data were additionally analysed by bibliometric software (VOSviewer) to generate term maps and author associations. The thematic areas with the most citations were South African Traditional Medicine for mental health (110) and anxiolytic agents (75). Pioneer studies in the genus focused on chemical structural isolation, purification, and characterisation and techniques such as thin layer chromatography, liquid chromatography (HPLC, UPLC, and more recently, LC-MS), gas chromatography mass spectrometry (GC-MS), and nuclear magnetic resonance (NMR) to study mesembrine alkaloids. Different laboratories have used a diverse range of extraction and preanalytical methods that became routinely favoured in the analysis of the main metabolites (mesembrine, mesembranol, mesembranone, and Sceletium A4) in their respective experimental settings. In contrast with previous reviews, this paper identified gaps in the research field, being a lack of toxicology assays, a deficit of clinical assessments, too few bioavailability studies, and little to no investigation into the minor alkaloid groups found in Sceletium. Future studies are likely to see innovations in analytical techniques like leaf spray mass spectrometry and direct analysis in real-time ionisation coupled with high-resolution time-of-flight mass spectrometry (DART-HR-TOF-MS) for rapid alkaloid identification and quality control purposes. While S. tortuosum has been the primary focus, studying other Sceletium species may aid in establishing chemotaxonomic relationships and addressing challenges with species misidentification. This research can benefit the nutraceutical industry and conservation efforts for the entire genus. At present, little to no pharmacological information is available in terms of the molecular physiological effects of mesembrine alkaloids in medical clinical settings. Research in these fields is expected to increase due to the growing interest in S. tortuosum as a herbal supplement and the potential development of mesembrine alkaloids into pharmaceutical drugs.

Intranasal delivery of shRNA to knockdown the 5HT-2A receptor enhances memory and alleviates anxiety

Short-hairpin RNAs (shRNA), targeting knockdown of specific genes, hold enormous promise for precision-based therapeutics to treat numerous neurodegenerative disorders. However, whether shRNA constructed molecules can modify neuronal circuits underlying certain behaviors has not been explored. We designed shRNA to knockdown the human HTR2A gene in vitro using iPSC-differentiated neurons. Multi-electrode array (MEA) results showed that the knockdown of the 5HT-2A mRNA and receptor protein led to a decrease in spontaneous electrical activity. In vivo, intranasal delivery of AAV9 vectors containing shRNA resulted in a decrease in anxiety-like behavior in mice and a significant improvement in memory in both mice (104%) and rats (92%) compared to vehicle-treated animals. Our demonstration of a non-invasive shRNA delivery platform that can bypass the blood-brain barrier has broad implications for treating numerous neurological mental disorders. Specifically, targeting the HTR2A gene presents a novel therapeutic approach for treating chronic anxiety and age-related cognitive decline.

Neurochemical mechanisms underlying serotonergic modulation of neuroplasticity in humans

BACKGROUND

Studies in animals and humans have shown that cortical neuroplasticity can be modulated by increasing serotonin levels by administering selective serotonin reuptake inhibitors (SSRI). However, little is known about the mechanistic background, especially the contribution of intracortical inhibition and facilitation, which depend on gamma-aminobutyric acid (GABA) and glutamate.

OBJECTIVE

We aimed to explore the relevance of drivers of plasticity (glutamate- and GABA-dependent processes) for the effects of serotonin enhancement on tDCS-induced plasticity in healthy humans.

METHODS

A crossover, partially double-blinded, randomized, and sham-controlled study was conducted in 21 healthy right-handed individuals. In each of the 7 sessions, plasticity was induced via transcranial direct current stimulation (tDCS). Anodal, cathodal, and sham tDCS were applied to the left motor cortex under SSRI (20 mg/40 mg citalopram) or placebo. Short-interval cortical inhibition (SICI) and intracortical facilitation (ICF) were monitored by paired-pulse transcranial magnetic stimulation for 5-6 h after intervention.

RESULTS

Under placebo, anodal tDCS-induced LTP-like plasticity decreased SICI and increased ICF. In contrast, cathodal tDCS-elicited LTD-like plasticity induced the opposite effect. Under 20 mg and 40 mg citalopram, anodal tDCS did not affect SICI largely, while ICF was enhanced and prolonged. For cathodal tDCS, citalopram converted the increase of SICI and decrease of ICF into antagonistic effects, and this effect was dosage-dependent since it lasted longer under 40 mg when compared to 20 mg.

CONCLUSION

We speculate that the main effects of acute serotonergic enhancement on tDCS-induced plasticity, the increase and prolongation of LTP-like plasticity effects, involves mainly the glutamatergic system.

Drug targeting in psychiatric disorders - how to overcome the loss in translation?

In spite of major efforts and investment in development of psychiatric drugs, many clinical trials have failed in recent decades, and clinicians still prescribe drugs that were discovered many years ago. Although multiple reasons have been discussed for the drug development deadlock, we focus here on one of the major possible biological reasons: differences between the characteristics of drug targets in preclinical models and the corresponding targets in patients. Importantly, based on technological advances in single-cell analysis, we propose here a framework for the use of available and newly emerging knowledge from single-cell and spatial omics studies to evaluate and potentially improve the translational predictivity of preclinical models before commencing preclinical and, in particular, clinical studies. We believe that these recommendations will improve preclinical models and the ability to assess drugs in clinical trials, reducing failure rates in expensive late-stage trials and ultimately benefitting psychiatric drug discovery and development.

Serotonergic neurotransmission mediated cognitive dysfunction in two mouse models of sepsis-associated encephalopathy

BACKGROUND

Patients with sepsis-associated encephalopathy (SAE) often exhibit cognitive impairments. Despite this, the underlying mechanisms of SAE remain largely unexplored. Here, we explored the role of serotonergic neurotransmission in cognitive dysfunction of two mouse models of SAE.

METHODS

The mouse models of SAE were established by injection of lipopolysaccharide (LPS, 10 mg/kg, intraperitoneal) and cecal ligation puncture (CLP) respectively. Barnes maze, new object recognition test and open field test were used to evaluate the effects of fluoxetine (selective serotonin reuptake inhibitor) and cyproheptadine (nonselective 5-HT2 receptor antagonist) on cognition and motor activity of mice. Additionally, WAY100635 (5-HT1A receptor antagonist) was co-administered with fluoxetine to explore the mechanism underlying effect of fluoxetine on cognitive impairments of SAE. Enzyme-linked immunosorbent assay (ELISA) was performed to determine 5-HT levels in hippocampus, brainstem and frontal lobe of experimental groups.

RESULTS

Both LPS-induced sepsis and CLP induced sepsis resulted in a notable learning deficit. Fluoxetine ameliorated, while cyproheptadine aggravated, cognitive impairment in two classic mouse models of SAE. The cognition-enhancing effect of fluoxetine is reversed by WAY100635. Decreased 5-HT levels in hippocampus, brainstem and frontal lobe were observed in LPS septic model and CLP septic model. Notably, both fluoxetine and cyproheptadine significantly increased 5-HT levels in those brain regions in LPS septic model. Additionally, fluoxetine significantly increased 5-HT levels in frontal lobe of CLP septic model.

CONCLUSIONS

Our study demonstrated that serotonergic neurotransmission plays a significant role in mechanisms underlying cognitive impairment in SAE. These findings contribute to identification of novel targets to prevent and arrest cognitive impairment in SAE.