Role of 5-HT3 Receptors in the Antidepressant Response

Randomized Controlled Trial of the Effects of High-Dose Ondansetron on Clinical Symptoms and Brain Connectivity in Obsessive-Compulsive and Tic Disorders

OBJECTIVE

Sensory phenomena (SP) are aversive sensations driving repetitive behaviors in obsessive-compulsive disorder (OCD) and Tourette's disorder that are not well addressed by standard treatments. SP are related to the functioning of an interoceptive-sensorimotor circuit that may be modulated by the 5-HT3 receptor antagonist ondansetron. The present study employed an experimental medicine approach to test the effects of 4 weeks of high-dose ondansetron compared to placebo on SP severity and brain connectivity in a cohort of individuals with OCD and/or Tourette's disorder.

METHODS

Of 51 participants who completed the study, 27 were assigned to receive 24 mg/day of ondansetron and 24 to receive placebo. Analyses examined changes in SP severity and, for participants with OCD, overall OCD severity from baseline to final visit. Functional MRI data were collected at both visits for analysis of intrinsic functional connectivity metrics characterizing global correlation (reflecting area "hubness") and local correlation (reflecting near-neighbor coherence).

RESULTS

There were no significant differences between ondansetron and placebo in the reduction of SP or overall OCD severity in the full sample. In a subsample of participants with OCD taking concomitant serotonin reuptake inhibitors (SRIs), ondansetron was associated with a significant decrease in overall OCD severity and global connectivity of the medial sensorimotor cortex compared with placebo. Longitudinal reductions in SP severity were related to decreases in right sensorimotor hubness in both groups, and to brainstem local coherence only in participants taking ondansetron.

CONCLUSIONS

There was no effect of high-dose ondansetron on SP. However, when used as an augmentation to SRIs, ondansetron reduced overall OCD severity, which may be related to changes in the "hubness" of the sensorimotor cortex. Ondansetron's ability to modulate brainstem connectivity may underlie its variable effectiveness in reducing SP.

Diffuse Noxious Inhibitory Controls in Chronic Pain States: Insights from Pre-Clinical Studies

Diffuse noxious inhibitory control (DNIC), also known as conditioned pain modulation (CPM) in humans, is a paradigm wherein the heterotopic application of a noxious stimulus results in the attenuation of another spatially distant noxious input. The pre-clinical and clinical studies show the involvement of several neurochemical systems in DNIC/CPM and point to a major contribution of the noradrenergic, serotonergic, and opioidergic systems. Here, we thoroughly review the latest data on the monoaminergic and opioidergic studies, focusing particularly on pre-clinical models of chronic pain. We also conduct an in-depth analysis of these systems by integrating the available data with the descending pain modulatory circuits and the neurochemical systems therein to bring light to the mechanisms involved in the regulation of DNIC. The most recent data suggest that DNIC may have a dual outcome encompassing not only analgesic effects but also hyperalgesic effects. This duality might be explained by the underlying circuitry and the receptor subtypes involved therein. Acknowledging this duality might contribute to validating the prognostic nature of the paradigm. Additionally, DNIC/CPM may serve as a robust paradigm with predictive value for guiding pain treatment through more effective targeting of descending pain modulation.

Concept article: Antidepressant-induced destabilization in bipolar illness mediated by serotonin 3 receptor (5HT3)

OBJECTIVES

Antidepressants used by patients with bipolar disorder have been associated with destabilization with an increase in mania, depression, and cycling. The most commonly proposed mechanism, that antidepressants 'overshoot' their antidepressant effect to create a manic or mixed state, is unlikely since antidepressants have actually been found to be ineffective in treating bipolar depression. Beginning with known bipolar-specific pathophysiologic abnormalities provides the greatest likelihood of insight.

METHODS

PubMed was queried with 'bipolar', 'sodium', 'intracellular sodium', 'serotonin 3', '5HT3', '5-hydroxytryptamine type 3 receptors', and 'antidepressant' either individually or in combination.

RESULTS

Pathologic mood states (both mania and depression) are associated with increased intracellular sodium (Na) concentrations that depolarize the resting membrane potential to increase cellular excitability (mania) or cause depolarization block (depression). Stimulation of the serotonin (5HT) receptors depolarizes the post-synaptic neuron. Stimulation of 5HT3 may be of particular importance since it is coupled to a cation channel that directly depolarizes the membrane. These effects directly impact the physiology of patients with bipolar disorder to alter neuronal excitability in a fashion that worsens both mania and depression.

PROPOSED CONCEPT

The most consistently observed biological abnormality in individuals going through mania or bipolar depression involves a decline in Na pump activity, with consequent elevation of intracellular Na levels. Antidepressant treatment potentiates this, particularly by activation of 5HT3. This hypothesis can be tested by coadministering a 5HT3 antagonist (e.g., vortioxetine or ondansetron) to achieve blockade of that receptor while treating bipolar depression with a serotoninergic antidepressant.

Vortioxetine as an alternative treatment for somatic symptom disorder: case report

Somatic symptom disorder (SSD) is characterized by persistent physical symptoms that cause significant distress and functional impairment. Despite the widespread use of serotonin reuptake inhibitors (SRIs) in treating SSD, some patients experience insufficient response, necessitating alternative therapeutic approaches. We report two cases of SSD that demonstrated significant improvement with vortioxetine, a novel antidepressant with multimodal serotonergic receptor activity. In Case 1, an 88-year-old female with throat discomfort and cough experienced an insufficient response to an SRI. After switching to vortioxetine, she achieved significant symptom relief within 10 days, with no relapse observed over the following four months. In Case 2, a 29-year-old female presenting with widespread somatic pain and palpitations, unresponsive to analgesics, achieved symptom resolution within two weeks with the initial use of vortioxetine. The therapeutic effects of vortioxetine were rapid and well-tolerated. These cases highlight the potential of vortioxetine for treating SSD, particularly in cases of insufficient response to SRIs, and suggest a possible overlap between SSD and obsessive-compulsive spectrum disorders through its action on serotonergic pathways.

Assessment of antiemetic activity of dihydrocoumarin: In vivo and in silico approaches on receptor binding affinity and modulatory effects

Dihydrocoumarin (DCN) is a natural compound widely used in the flavor industry and has antioxidant and anti-inflammatory properties. However, its potential antiemetic effects on gastrointestinal disturbances remain untested. This study emphasizes assessing the antiemetic properties of the natural aromatic compound DCN using copper sulfate (CuSO4.5H2O)-induced emetic model on chicks, and an in silico approach was also adopted to estimate the possible underlying mechanisms. Two doses (25 and 50 mg/kg b.w.) of DCN and several referral drugs considered positive controls (PCs), including domperidone (6 mg/kg), hyoscine (21 mg/kg), aprepitant (16 mg/kg), diphenhydramine (10 mg/kg), and ondansetron (5 mg/kg), were orally administered to chicks. The vehicle was provided as the control group. Co-treatments of DCN with referral drugs were also provided to chicks to evaluate the modulatory action of the test compound. According to the results, DCN delayed the emetic onset and decreased the frequency of retches in a dose-dependent manner compared to the vehicle group. DCN (50 mg/kg) represented a notable delayed latency period (61.17 ± 4.12 s) and a diminished number of retchings (17.67 ± 1.82 times) compared to the control group. Further, in the co-treatments, DCN increased the latency period and reduced the number of retches, except for domperidone. In the in silico investigation, DCN showed notable binding affinity toward the D2 (-7 kcal/mol), H1 (-7.5 kcal/mol), and M5 (-7 kcal/mol) receptors in the same binding site as the referral ligand. Our research indicates that DCN has mild antiemetic properties by interacting with the D2, H1, and M5 receptors. Therefore, several pre-clinical and clinical studies are necessary to assess the effectiveness and safety profile of this food ingredient.

pH-Sensitive In Situ Gel of Mirtazapine Invasomes for Rectal Drug Delivery: Protruded Bioavailability and Anti-Depressant Efficacy

The present research emphasizes fabrication alongside the assessment of an innovative nano-vesicular membranous system known as invasomes (NVMs) laden with Mirtazapine for rectal administration. This system could circumvent the confines of orally administered counterparts regarding dose schedules and bioavailability. Mirtazapine invasomes were tailored by amalgamating phospholipid, cineole, and ethanol through a thin-film hydration approach rooted in the Box-Behnken layout. Optimization of composition parameters used to fabricate desired NVMs' physicochemical attributes was undertaken using the Design-Expert® program. The optimal MRZ-NVMs were subsequently transformed to a pH-triggered in situ rectal gel followed by animal pharmacodynamic and pharmacokinetic investigations relative to rectal plain gel and oral suspension. The optimized NVMs revealed a diameter size of 201.3 nm, a z potential of -28.8 mV, an entrapment efficiency of 81.45%, a cumulative release within 12 h of 67.29%, and a cumulative daily permeated quantity of 468.68 µg/cm2. Compared to the oral suspension, pharmacokinetic studies revealed a 2.85- and 4.45-fold increase in calculated rectal bioavailability in circulation and brain, respectively. Pharmacodynamic and immunohistopathology evaluations exposed superior MRZ-NVMs attributed to the orally administered drug. Consequently, rectal MRZ-NVMs can potentially be regarded as a prospective nanoplatform with valuable pharmacokinetics and tolerability assets.

Phytoconstituents Targeting the Serotonin 5-HT3 Receptor: Promising Therapeutic Strategies for Neurological Disorders

The 5-hydroxytryptamine-3 receptor (5-HT3R), a subtype of serotonin receptor, is a ligand-gated ion channel crucial in mediating fast synaptic transmission in the central and peripheral nervous systems. This receptor significantly influences various neurological activities, encompassing neurotransmission, mood regulation, and cognitive processing; hence, it may serve as an innovative target for neurological disorders. Multiple studies have revealed promising results regarding the beneficial effects of these phytoconstituents and extracts on conditions such as nausea, vomiting, neuropathic pain depression, anxiety, Alzheimer's disease, cognition, epilepsy, sleep, and dyskinesia via modulation of 5-HT3R in the pathophysiology of neurological disorder. The review delves into a detailed exploration of in silico, in vitro, and in vivo studies and clinical studies that discussed phytoconstituents acting on 5-HT3R and attenuates difficulties in neurological diseases. The diverse mechanisms by which plant-derived phytoconstituents influence 5-HT3R activity offer exciting avenues for developing innovative therapeutic interventions. Besides producing an agonistic or antagonistic effect, some phytoconstituents exert modulatory effects on 5-HT3R activity through multifaceted mechanisms. These include γ-aminobutyric acid and cholinergic neuronal pathways, interactions with neurokinin (NK)-1, NK2, serotonergic, and γ-aminobutyric acid(GABA)ergic systems, dopaminergic influences, and mediation of calcium ions release and inflammatory cascades. Notably, the phytoconstituent's capacity to reduce oxidative stress has also emerged as a significant factor contributing to their modulatory role. Despite the promising implications, there is currently a dearth of exploration needed to understand the effect of phytochemicals on the 5-HT3R. Comprehensive preclinical and clinical research is of the utmost importance to broaden our knowledge of the potential therapeutic benefits associated with these substances.

Structural basis for partial agonism in 5-HT3A receptors

Hyperactivity of serotonin 3 receptors (5-HT3R) underlies pathologies associated with irritable bowel syndrome and chemotherapy-induced nausea and vomiting. Setrons, a class of high-affinity competitive antagonists, are used in the treatment of these conditions. Although generally effective for chemotherapy-induced nausea and vomiting, the use of setrons for treating irritable bowel syndrome has been impaired by adverse side effects. Partial agonists are now being considered as an alternative strategy, with potentially less severe side effects than full antagonists. However, a structural understanding of how these ligands work is lacking. Here, we present high-resolution cryogenic electron microscopy structures of the mouse 5-HT3AR in complex with partial agonists (SMP-100 and ALB-148471) captured in pre-activated and open-like conformational states. Molecular dynamics simulations were used to assess the stability of drug-binding poses and interactions with the receptor over time. Together, these studies reveal mechanisms for the functional differences between orthosteric partial agonists, full agonists and antagonists of the 5-HT3AR.

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.

Antiemetic activity of abietic acid possibly through the 5HT3 and muscarinic receptors interaction pathways

The present study was designed to evaluate the antiemetic activity of abietic acid (AA) using in vivo and in silico studies. To assess the effect, doses of 50 mg/kg b.w. copper sulfate (CuSO4⋅5H2O) were given orally to 2-day-old chicks. The test compound (AA) was given orally at two doses of 20 and 40 mg/kg b.w. On the other hand, aprepitant (16 mg/kg), domperidone (6 mg/kg), diphenhydramine (10 mg/kg), hyoscine (21 mg/kg), and ondansetron (5 mg/kg) were administered orally as positive controls (PCs). The vehicle was used as a control group. Combination therapies with the referral drugs were also given to three separate groups of animals to see the synergistic and antagonizing activity of the test compound. Molecular docking and visualization of ligand-receptor interaction were performed using different computational tools against various emesis-inducing receptors (D2, D3, 5HT3, H1, and M1-M5). Furthermore, the pharmacokinetics and toxicity properties of the selected ligands were predicted by using the SwissADME and Protox-II online servers. Findings indicated that AA dose-dependently enhances the latency of emetic retching and reduces the number of retching compared to the vehicle group. Among the different treatments, animals treated with AA (40 mg/kg) exhibited the highest latency (98 ± 2.44 s) and reduced the number of retching (11.66 ± 2.52 times) compared to the control groups. Additionally, the molecular docking study indicated that AA exhibits the highest binding affinity (- 10.2 kcal/mol) toward the M4 receptors and an elevated binding affinity toward the receptors 5HT3 (- 8.1 kcal/mol), M1 (- 7.7 kcal/mol), M2 (- 8.7 kcal/mol), and H1 (- 8.5 kcal/mol) than the referral ligands. Taken together, our study suggests that AA has potent antiemetic effects by interacting with the 5TH3 and muscarinic receptor interaction pathways. However, additional extensive pre-clinical and clinical studies are required to evaluate the efficacy and toxicity of AA.

Possible role of exercise therapy on depression: Effector neurotransmitters as key players

About 280 million people suffer from depression as the most common neurological disorder and the most common cause of death worldwide. Exercise with serotonin released in the brain by the 5-HT3-IGF-1 mechanism can lead to antidepressant effects. Swimming exercise has antidepressant effects by increasing the sensitivity of serotonin 5-HT2 receptors and postsynaptic 5-HT1A receptors, increasing 5-HT and 5HIAA levels, increasing TPH and serotonin, and decreasing inflammatory levels of IFN-γ and TNF-α. Anaerobic and aerobic exercises increase beta-endorphin, enkephalin, and dynorphin and have antidepressant effects. Exercise by increasing dopamine, D1R, and D2R leads to the expression of BDNF and activation of TrkB and has antidepressant behavior. Exercise leads to a significant increase in GABAAR (γ2 and α2 subunits) and reduces neurodegenerative disorders caused by GABA imbalance through anti-inflammatory pathways. By increasing glutamate and PGC1α and reducing glutamatergic neurotoxicity, exercise enhances neurogenesis and synaptogenesis and prevents neurodegeneration and the onset of depression. Irisin release during exercise shows an important role in depression by increasing dopamine, BDNF, NGF, and IGF-1 and decreasing inflammatory mediators such as IL-6 and IL-1β. In addition, exercise-induced orexin and NPY can increase hippocampal neurogenesis and relieve depression. After exercise, the tryptophan to large neutral amino acids (TRP/LNAA) ratio and the tryptophan to branched-chain amino acids (BCAA) ratio increase, which may have antidepressant effects. The expression of M5 receptor and nAChR α7 increases after exercise and significantly increases dopamine and acetylcholine and ameliorates depression. It appears that during exercise, muscarinic receptors can reduce depression through dopamine in the absence of acetylcholine. Therefore, exercise can be used to reduce depression by affecting neurotransmitters, neuromodulators, cytokines, and/or neurotrophins.

Biomarkers of Affective Dysregulation Associated with In Utero Exposure to EtOH

INTRODUCTION

Children with fetal alcohol spectrum disorders (FASD) exhibit behavioral and affective dysregulation, including hyperactivity and depression. The mechanisms are not known, but they could conceivably be due to postnatal social or environmental factors. However, we postulate that, more likely, the affective dysregulation is associated with the effects of EtOH exposure on the development of fetal serotonergic (5-HT) and/or dopaminergic (DA) pathways, i.e., pathways that in postnatal life are believed to regulate mood. Many women who use alcohol (ethanol, EtOH) during pregnancy suffer from depression and take selective serotonin reuptake inhibitors (SSRIs), which might influence these monoaminergic pathways in the fetus. Alternatively, monoaminergic pathway abnormalities might reflect a direct effect of EtOH on the fetal brain. To distinguish between these possibilities, we measured their expressions in fetal brains and in fetal brain-derived exosomes (FB-Es) isolated from the mothers' blood. We hypothesized that maternal use of EtOH and/or SSRIs during pregnancy would be associated with impaired fetal neural development, detectable as abnormal levels of monoaminergic and apoptotic biomarkers in FB-Es.

METHODS

Fetal brain tissues and maternal blood were collected at 9-23 weeks of pregnancy. EtOH groups were compared with unexposed controls matched for gestational age (GA). The expression of 84 genes associated with the DA and 5-HT pathways was analyzed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) on microarrays. FB-Es also were assayed for serotonin transporter protein (SERT) and brain-derived neurotrophic factor (BDNF) by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Six EtOH-exposed human fetal brain samples were compared to SSRI- or polydrug-exposed samples and to unexposed controls. EtOH exposure was associated with significant upregulation of DA receptor D3 and 5-HT receptor HTR2C, while HTR3A was downregulated. Monoamine oxidase A (MAOA), MAOB, the serine/threonine kinase AKT3, and caspase-3 were upregulated, while mitogen-activated protein kinase 1 (MAPK1) and AKT2 were downregulated. ETOH was associated with significant upregulation of the DA transporter gene, while SERT was downregulated. There were significant correlations between EtOH exposure and (a) caspase-3 activation, (b) reduced SERT protein levels, and (c) reduced BDNF levels. SSRI exposure independently increased caspase-3 activity and downregulated SERT and BDNF. Early exposure to EtOH and SSRI together was associated synergistically with a significant upregulation of caspase-3 and a significant downregulation of SERT and BDNF. Reduced SERT and BDNF levels were strongly correlated with a reduction in eye diameter, a somatic manifestation of FASD.

CONCLUSIONS

Maternal use of EtOH and SSRI during pregnancy each was associated with changes in fetal brain monoamine pathways, consistent with potential mechanisms for the affective dysregulation associated with FASD.

Phenotypic distinctions in depression and anxiety: a comparative analysis of comorbid and isolated cases

BACKGROUND

Anxiety and depression are frequently comorbid yet phenotypically distinct. This study identifies differences in the clinically observable phenome across a wide variety of physical and mental disorders comparing patients with diagnoses of depression without anxiety, anxiety without depression, or both depression and anxiety.

METHODS

Using electronic health records for 14 994 participants with depression and/or anxiety in the Mayo Clinic Biobank, a phenotype-based phenome-wide association study (Phe2WAS) was performed to test for differences between these groups across a broad range of clinical diagnoses observed in the electronic health record. Additional analyses were performed to determine the temporal sequencing of diagnoses.

RESULTS

Compared to patients diagnosed only with anxiety, those diagnosed only with depression were more likely to have diagnoses of obesity (OR 1.75; p = 1 × 10-27), sleep apnea (OR 1.71; p = 1 × 10-22), and type II diabetes (OR 1.74; p = 9 × 10-18). Compared to those diagnosed only with depression, those diagnosed only with anxiety were more likely to have diagnoses of palpitations (OR 1.91; p = 2 × 10-25), benign skin neoplasms (OR 1.61; p = 2 × 10-17), and cardiac dysrhythmias (OR 1.45; p = 2 × 10-12). Patients with comorbid depression and anxiety were more likely to have diagnoses of other mental health disorders, substance use disorders, sleep problems, and gastroesophageal reflux relative to isolated depression.

CONCLUSIONS

While depression and anxiety are closely related, this study suggests that phenotypic distinctions exist between depression and anxiety. Improving phenotypic characterization within the broad categories of depression and anxiety could improve the clinical assessment of depression and anxiety.

Atypical antidepressant mirtazapine inhibits 5-hydroxytryptamine3 receptor currents in NCB-20 cells

Mirtazapine, an atypical antidepressant, is known to enhance serotonergic transmission by inhibiting the 5-hydroxytryptamine (5-HT)_1A, 5-HT_2C, and 5-HT₃ receptors. However, the mechanism of action on the 5-HT₃ receptor remains unclear. We investigated the inhibitory mechanisms of mirtazapine on 5-HT₃ receptors of NCB20 neuroblastoma cells using the whole-cell voltage-clamp method. Mirtazapine inhibited the 5-HT₃ receptor currents in a concentration-dependent manner, and the inhibitory effect was influenced by the concentration of 5-HT. When mirtazapine was co-applied to 5-HT, the maximal response of the 5-HT₃ receptor current was reduced and EC₅₀ was increased, suggesting that mirtazapine might act as a non-competitive inhibitor. Inhibition of 5-HT₃ current by mirtazapine was stronger in pre-application than in co-application, which suggests that mirtazapine might act as a closed state inhibitor. This finding was further supported by no use-dependency of the mirtazapine for 5-HT₃ receptor inhibition. Finally, mirtazapine accelerated the desensitization and deactivation process in a concentration-dependent manner. The difference in recovery time showed that mirtazapine drastically influences the desensitization process than the deactivation process. These mechanistic characteristics of mirtazapine support the understanding of the relationship between the 5-HT₃ receptor and atypical antidepressants.

Intranasal ondansetron microemulsion counteracting the adverse effects of cisplatin: animal study

BACKGROUND

Cisplatin is considered one of the most effective and commonly used chemotherapeutic drugs, but despite its high therapeutic effectiveness, most patients treated with cisplatin suffer from nausea and vomiting, neurotoxic side effects, and cerebral psychiatric disorders such as depression. Therefore, the aim of the current work was to explore whether a selective 5-HT₃ receptor antagonist (Ondansetron) administered via the oral route or intranasally in microemulsion form would alleviate cisplatin's adverse effects.

METHODS

The selected ondansetron microemulsion was characterized in vitro for particle size, polydispersity, zeta potential, morphology, and nasal permeation, and in vivo in terms of anti-emetic and antidepressant activity, with the assessment of biochemical markers in brain homogenates.

RESULTS

Results revealed that both orally administered ondansetron and intranasally administered microemulsion were able to counteract the pica effect by increasing food consumption, water intake, and decreasing kaolin intake. They were also able to increase BDNF, normalize IL-6, increase serotonin, and normalize NOx, MDA, GSSH/GSH as well as 8OHdG levels in rats' brain homogenates. The intranasal ondansetron microemulsion displayed superiority compared to oral conventional ondansetron in terms of increasing food intake, reduction of stomach content, and normalization of serotonin turnover.

CONCLUSION

Ondansetron microemulsion can be administered by an alternative route of administration (intranasal) rather than oral, for patients on cisplatin chemotherapy.

Serotonin Type 3 Receptor Is Potentially Involved in Cellular Stress Induced by Hydrogen Peroxide

Depression is a disease with several molecular mechanisms involved, such as problems in the serotonergic pathway. This disease is very complex and prevalent, and thus important to deeply study and aim to overcome high rates of relapse and therapeutic failure. In this study, two cellular lines were used (HT-22 and SH-SY5Y cells) to gain insight about the role of the serotonin type 3 (5-HT3) receptor in cellular stress induced by hydrogen peroxide and/or corticosterone. In research, these compounds are known to mimic the high levels of oxidative stress and dysfunction of the hypothalamus–hypophysis–adrenal axis by the action of glucocorticoids, usually present in depressed individuals. The receptor 5-HT3 is also known to be involved in depression, previously demonstrated in studies that highlight the role of these receptors as promising targets for antidepressant therapy. Indeed, the drugs used in this work (mirtazapine, scopolamine, and lamotrigine) interact with this serotonergic receptor. Thus, by using cell morphology, cell viability (neutral red and MTT), and HPLC assays, this work aimed to understand the role of these drugs in the stress induced by H₂O₂/corticosterone to HT-22 and SH-SY5Y cell lines. We concluded that the antagonism of the 5-HT3 receptor by these drugs may be important in the attenuation of H₂O₂-induced oxidative stress to the cells, but not in the corticosterone-induced stress.

SR 57227A, a serotonin type-3 receptor agonist, as a candidate analgesic agent targeting nociplastic pain

Pain is influenced by various factors, such as fear, anxiety, and memory. We previously reported that pain-like behaviors in mice can be induced by environmental cues in which a pain stimulus was previously presented, and that pain was reduced using fentanyl (an opioid). Although opioid analgesics are currently used to treat persistent pain, their inappropriate use causes a significant number of deaths in the United States. Thus, alternative medicines to opioids are needed. Here, we reported that SR 57227A, a serotonin type-3 receptor agonist, significantly reduced pain-like behaviors. The number of c-Fos positive cells increased by environmental cues in PFC was decreased by SR 57227A. Moreover, SR 57227A reduced pain-like behaviors of the formalin test, and restored reductions in paw withdrawal thresholds by acidic saline intramuscular injection and sciatic nerve ligation. Unlike opioids, SR 57227A induced no preference behaviors as measured by the conditioned place preference test. These data suggested that SR 57227A is an effective alternative pain reliever to opioids that targets chronic pain.

Serotonin Receptor HTR3A Gene Polymorphisms rs1985242 and rs1062613, E-Cigarette Use and Personality

We nowadays record growing numbers of e-cigarette users. The development of nicotine dependence is a result of many factors, including genetics and personality. In this study we analyzed two polymorphisms—rs1985242 and rs1062613—in the serotonin receptor HTR3A gene in a group of e-cigarette users (n = 135) and controls (n = 106). Personality traits were measured using the NEO Five-Factor Inventory. The comparison of e-cigarette users with the control group indicates that the former showed significantly higher scores on the neuroticism scale and lower scores on the scales of extraversion and conscientiousness of the NEO-FFI. Homozygote variants of rs1985242 were more frequent in the study group. The results of the 2 × 3 factorial ANOVA for e-cigarette users and the control group as well as interaction between the HTR3A rs1985242 variants were found for the NEO-FFI conscientiousness scale. These results allow us to conclude that the combination of psychological factors and genetic data creates a possibility for making more complete models of substance use disorders.

The interplay between 5-HT2C and 5-HT3A receptors in the dorsal periaqueductal gray mediates anxiety-like behavior in mice

The monoamine neurotransmitter serotonin (5-HT) modulates anxiety by its activity on 5-HT_2C receptors (5-HT_2CR) expressed in the dorsal periaqueductal gray (dPAG). Here, we investigated the presence of 5-HT_3A receptors (5-HT_3AR) in the dPAG, and the interplay between 5-HT_2CR and 5-HT_3AR in the dPAG in mediating anxiety-like behavior in mice. We found that 5-HT_3AR is expressed in the dPAG and the blockade of these receptors using intra-dPAG infusion of ondansetron (5-HT_3AR antagonist; 3.0 nmol) induced an anxiogenic-like effect. The activation of 5-HT_3ABR by the infusion of mCPBG [1-(m-Chlorophenyl)-biguanide; 5-HT₃R agonist] did not alter anxiety-like behaviors. In addition, blockade of 5-HT_3AR (1.0 nmol) prevented the anxiolytic-like effect induced by the infusion of the 5-HT_2CR agonist mCPP (1-(3-chlorophenyl) piperazine; 0.03 nmol). None of the treatment effects on anxiety-like behaviors altered the locomotor activity levels. The present results suggest that the anxiolytic-like effect exerted by serotonin activity on 5-HT_2CR in the dPAG is modulated by 5-HT_3AR expressed in same region.

Something Old, Something New: Ion Channel Blockers as Potential Anti-Tuberculosis Agents

Tuberculosis (TB) remains a challenging global health concern and claims more than a million lives every year. We lack an effective vaccine and understanding of what constitutes protective immunity against TB to inform rational vaccine design. Moreover, treatment of TB requires prolonged use of multi-drug regimens and is complicated by problems of compliance and drug resistance. While most Mycobacterium tuberculosis (Mtb) bacilli are quickly killed by the drugs, the prolonged course of treatment is required to clear persistent drug-tolerant subpopulations. Mtb's differential sensitivity to drugs is, at least in part, determined by the interaction between the bacilli and different host macrophage populations. Therefore, to design better treatment regimens for TB, we need to understand and modulate the heterogeneity and divergent responses that Mtb bacilli exhibit within macrophages. However, developing drugs de-novo is a long and expensive process. An alternative approach to expedite the development of new TB treatments is to repurpose existing drugs that were developed for other therapeutic purposes if they also possess anti-tuberculosis activity. There is growing interest in the use of immune modulators to supplement current anti-TB drugs by enhancing the host's antimycobacterial responses. Ion channel blocking agents are among the most promising of the host-directed therapeutics. Some ion channel blockers also interfere with the activity of mycobacterial efflux pumps. In this review, we discuss some of the ion channel blockers that have shown promise as potential anti-TB agents.

Exercise and fluoxetine treatment during adolescence protect against early life stress-induced behavioral abnormalities in adult rats

Depression is a psychiatric disorder with several comorbidities that has a complicated pathophysiology. Multiple mechanisms such as abnormal hypothalamic-pituitary adrenal (HPA) axis activity, neurotransmission (namely serotonin), and immune-inflammatory responses are involved in the pathophysiology of disease. In this study, we hypothesized that applying exercise (running wheel (RW) and treadmill (TM)) or fluoxetine (FLX) during adolescence could protect adult rats against the negative impact of early-life stress. To do this, we applied maternal separation stress (MS) to neonatal rats from postnatal day (PND) 2 to 14 and at PND 28, rats were divided into 8 experimental groups and were subjected to TM or RW or FLX treatment. After four weeks of physical activity or FLX treatment, at PND 64, behaviors were assessed by applying forced swimming test, sucrose preference test, open-field test, and elevated plus maze test. Serum cortiscosterone (CORT) levels and expression of genes associated with inflammatory factors (Il1β, Hmgb1, and Il6) and serotonergic systems (5-ht2c and 5-ht3a) were studies in the hippocampus (HIPP) and prefrontal cortex (PFC). Our results revealed that RW and FLX treatment during adolescence are capable of attenuating MS-induced depressive- and anxiety-like disorders in adult male rats. These effects were accompanied by the normalization of both serum CORT and the expression of genes in the HIPP and PFC. TM exercise in adolescence showed anxiolytic effects but failed to produce antidepressant-like effects. Results of this study suggest that voluntary physical activity during adolescence can reduce the negative effects of early-life stress through different mechanisms.

Leite L, da S. Tavares-Henriques M, Lopes LAF, Oliveira LGR, Silva-Filho SE, da Silveira APS, Cuman RKN, de S. Silva-Comar FM, Comar JF, do A. Brasileiro L, dos Santos JN, de Freitas WR, Leão KV, da Silva JG, Klein RC, Klein MHF, da S. Ramos BH, Fernandes CKC, de L. Ribas DG, Oesterreich SA. Modulation of the Serotonergic Receptosome in the Treatment of Anxiety and Depression: A Narrative Review of the Experimental Evidence

Serotonin (5-HT) receptors are found throughout central and peripheral nervous systems, mainly in brain regions involved in the neurobiology of anxiety and depression. 5-HT receptors are currently promising targets for discovering new drugs for treating disorders ranging from migraine to neuropsychiatric upsets, such as anxiety and depression. It is well described in the current literature that the brain expresses seven types of 5-HT receptors comprising eighteen distinct subtypes. In this article, we comprehensively reviewed 5-HT1-7 receptors. Of the eighteen 5-HT receptors known today, thirteen are G protein-coupled receptors (GPCRs) and represent targets for approximately 40% of drugs used in humans. Signaling pathways related to these receptors play a crucial role in neurodevelopment and can be modulated to develop effective therapies to treat anxiety and depression. This review presents the experimental evidence of the modulation of the “serotonergic receptosome” in the treatment of anxiety and depression, as well as demonstrating state-of-the-art research related to phytochemicals and these disorders. In addition, detailed aspects of the pharmacological mechanism of action of all currently known 5-HT receptor families were reviewed. From this review, it will be possible to direct the rational design of drugs towards new therapies that involve signaling via 5-HT receptors.

Role of central serotonin and noradrenaline interactions in the antidepressants' action: Electrophysiological and neurochemical evidence

The development of antidepressant drugs, in the last 6 decades, has been associated with theories based on a deficiency of serotonin (5-HT) and/or noradrenaline (NA) systems. Although the pathophysiology of major depression (MD) is not fully understood, numerous investigations have suggested that treatments with various classes of antidepressant drugs may lead to an enhanced 5-HT and/or adapted NA neurotransmissions. In this review, particular morpho-physiological aspects of these systems are first considered. Second, principal features of central 5-HT/NA interactions are examined. In this regard, the effects of the acute and sustained antidepressant administrations on these systems are discussed. Finally, future directions including novel therapeutic strategies are proposed.

High-resolution structures of multiple 5-HT3AR-setron complexes reveal a novel mechanism of competitive inhibition

Serotonin receptors (5-HT3AR) play a crucial role in regulating gut movement, and are the principal target of setrons, a class of high-affinity competitive antagonists, used in the management of nausea and vomiting associated with radiation and chemotherapies. Structural insights into setron-binding poses and their inhibitory mechanisms are just beginning to emerge. Here, we present high-resolution cryo-EM structures of full-length 5-HT3AR in complex with palonosetron, ondansetron, and alosetron. Molecular dynamic simulations of these structures embedded in a fully-hydrated lipid environment assessed the stability of ligand-binding poses and drug-target interactions over time. Together with simulation results of apo- and serotonin-bound 5-HT3AR, the study reveals a distinct interaction fingerprint between the various setrons and binding-pocket residues that may underlie their diverse affinities. In addition, varying degrees of conformational change in the setron-5-HT3AR structures, throughout the channel and particularly along the channel activation pathway, suggests a novel mechanism of competitive inhibition.

Protective Effects of Spirulina platensis, Voluntary Exercise and Environmental Interventions Against Adolescent Stress-Induced Anxiety and Depressive-Like Symptoms, Oxidative Stress and Alterations of BDNF and 5HT-3 Receptors of the Prefrontal Cortex in Female Rats

BACKGROUND AND PURPOSE

Ample evidence indicates that chronic adolescence stress is associated with an increased risk of developing neuropsychiatric disorders in adulthood. Given the importance of the effective therapeutic ways to overcome adolescent stress-related deficits, the present study investigated the effects of Spirulina platensis (SP), environmental enrichment (EE), and voluntary exercise (EX) and their combination on anxiety or depression-like behaviors, oxidative stress, and alterations of BDNF and 5HT-3 receptors in the prefrontal cortex (PFC) induced by adolescent stress in adult female rats.

METHODS

During the adolescent period (PNDs30-40), rats were subjected to restraint stress. Then, the animals were subjected to SP treatment (200 mg/kg/day), EX, EE, and the combined treatments (SP+EX, and SP+EE) for 15 days between PNDs41-55. Subsequently, anxiety or depression-like behaviors, BDNF levels, oxidative stress markers and mRNA expression of BDNF and 5HT₃ in the PFC were assessed.

RESULTS

Stressed rats demonstrated enhanced anxiety levels and depression-like behaviors in adulthood. Regarding the oxidative stress markers, stressed rats exhibited significantly higher levels of malondialdehyde, a lipid peroxidation product, higher activities of antioxidant enzymes (glutathione peroxidase and superoxide dismutase) and significantly lower total antioxidant reactivity capacity in the PFC. Additionally, adolescent stress significantly increased 5HT3 receptor mRNA expression and decreased BDNF content and its mRNA expression in the PFC. Treatments with SP, EX, EE, and the combined interventions alleviated these deficits.

CONCLUSION

Our findings indicate that appropriate interventions during the adolescent period can protect against adolescent stress-induced behavioral, and biochemical defects and oxidative stress damage in adulthood.

Bupropion Inhibits Serotonin Type 3AB Heteromeric Channels at Clinically Relevant Concentrations

Bupropion, a Food and Drug Administration–approved antidepressant and smoking cessation aid, blocks dopamine and norepinephrine reuptake transporters and noncompetitively inhibits nicotinic acetylcholine and serotonin (5-HT) type 3A receptors (5-HT_3ARs). 5-HT₃ receptors are pentameric ligand-gated ion channels that regulate synaptic activity in the central and peripheral nervous system, presynaptically and postsynaptically. In the present study, we examined and compared the effect of bupropion and its active metabolite hydroxybupropion on mouse homomeric 5-HT_3A and heteromeric 5-HT_3AB receptors expressed in Xenopus laevis oocytes using two-electrode voltage clamp experiments. Coapplication of bupropion or hydroxybupropion with 5-HT dose dependently inhibited 5-HT–induced currents in heteromeric 5-HT type 3AB receptors (5-HT_3ABRs) (IC₅₀ = 840 and 526 μM, respectively). The corresponding IC₅₀s for bupropion and hydroxybupropion for homomeric 5-HT_3ARs were 10- and 5-fold lower, respectively (87 and 113 μM). The inhibition of 5-HT_3ARs and 5-HT_3ABRs was non–use dependent and voltage independent, suggesting bupropion is not an open channel blocker. The inhibition by bupropion was reversible and time-dependent. Of note, preincubation with a low concentration of bupropion that mimics therapeutic drug conditions inhibits 5-HT–induced currents in 5-HT_3A and 5-HT_3AB receptors considerably. In summary, we demonstrate that bupropion inhibits heteromeric 5-HT_3ABRs as well as homomeric 5-HT_3ARs. This inhibition occurs at clinically relevant concentrations and may contribute to bupropion’s clinical effects.

5-HT3 Receptor Antagonists in Neurologic and Neuropsychiatric Disorders: The Iceberg Still Lies beneath the Surface

5-HT₃ receptor antagonists, first introduced to the market in the mid-1980s, are proven efficient agents to counteract chemotherapy-induced emesis. Nonetheless, recent investigations have shed light on unappreciated dimensions of this class of compounds in conditions with an immunoinflammatory component as well as in neurologic and psychiatric disorders. The promising findings from multiple studies have unveiled several beneficial effects of these compounds in multiple sclerosis, stroke, Alzheimer disease, and Parkinson disease. Reports continue to uncover important roles for 5-HT₃ receptors in the physiopathology of neuropsychiatric disorders, including depression, anxiety, drug abuse, and schizophrenia. This review addresses the potential of 5-HT₃ receptor antagonists in neurology- and neuropsychiatry-related disorders. The broad therapeutic window and high compliance observed with these agents position them as suitable prototypes for the development of novel pharmacotherapeutics with higher efficacy and fewer adverse effects.

Theoretical and Experimental Approaches Aimed at Drug Design Targeting Neurodegenerative Diseases

In recent years, green chemistry has been strengthening, showing how basic and applied sciences advance globally, protecting the environment and human health. A clear example of this evolution is the synergy that now exists between theoretical and computational methods to design new drugs in the most efficient possible way, using the minimum of reagents and obtaining the maximum yield. The development of compounds with potential therapeutic activity against multiple targets associated with neurodegenerative diseases/disorders (NDD) such as Alzheimer’s disease is a hot topic in medical chemistry, where different scientists from various disciplines collaborate to find safe, active, and effective drugs. NDD are a public health problem, affecting mainly the population over 60 years old. To generate significant progress in the pharmacological treatment of NDD, it is necessary to employ different experimental strategies of green chemistry, medical chemistry, and molecular biology, coupled with computational and theoretical approaches such as molecular simulations and chemoinformatics, all framed in the rational drug design targeting NDD. Here, we review how green chemistry and computational approaches have been used to develop new compounds with the potential application against NDD, as well as the challenges and new directions of the drug development multidisciplinary process.

Molecular mechanism of setron-mediated inhibition of full-length 5-HT3A receptor

Serotonin receptor (5-HT_3AR) is the most common therapeutic target to manage the nausea and vomiting during cancer therapies and in the treatment of irritable bowel syndrome. Setrons, a class of competitive antagonists, cause functional inhibition of 5-HT_3AR in the gastrointestinal tract and brainstem, acting as effective anti-emetic agents. Despite their prevalent use, the molecular mechanisms underlying setron binding and inhibition of 5-HT_3AR are not fully understood. Here, we present the structure of granisetron-bound full-length 5-HT_3AR solved by single-particle cryo-electron microscopy to 2.92 Å resolution. The reconstruction reveals the orientation of granisetron in the orthosteric site with unambiguous density for interacting sidechains. Molecular dynamics simulations and electrophysiology confirm the granisetron binding orientation and the residues central for ligand recognition. Comparison of granisetron-bound 5-HT_3AR with the apo and serotonin-bound structures, reveals key insights into the mechanism underlying 5-HT_3AR inhibition.

Multi-modal antidepressant-like action of 6- and 7-chloro-2-aminodihydroquinazolines in the mouse tail suspension test

RATIONALE

2-Amino-6-chloro-3,4-dihydroquinazoline (e.g., A6CDQ) represents a novel putative antidepressant originally thought to act through a 5-HT₃ serotonin receptor antagonist mechanism. Here, we investigated this further by examining a positional isomer of A6CDQ (i.e., A7CDQ).

MATERIALS AND METHODS

5-HT₃ receptor and transporter activity (uptake-1 and uptake-2) were investigated using a variety of in vitro assays and the in vivo mouse tail suspension test (TST).

RESULTS

Although A7CDQ binds at 5-HT₃ receptors with low affinity (K_i = 1975 nM) compared to A6CDQ (K_i = 80 nM), it retained 5-HT₃ receptor antagonist action (IC₅₀ = 5.77 and 0.26 μM, respectively). In the mouse TST A7CDQ produced antidepressant-like actions (ED₅₀ = 0.09 mg/kg) comparable to that of A6CDQ. In addition, A6CDQ was found to be a 5-HT releasing agent (K_m = 2.8 μM) at hSERT and a reuptake inhibitor (IC₅₀ = 1.8 μM) at hNET, whereas A7CDQ was a weak reuptake inhibitor (K_m = 43.6 μM) at SERT but a releasing agent (EC₅₀ = 3.3 μM) at hNET. Moreover, A6CDQ and A7CDQ were potent inhibitors of uptake-2 (e.g.; OCT3 IC₅₀ = 3.9 and 5.9 μM, respectively).

CONCLUSIONS

A simple shift of a substituent in a common quinazoline scaffold from one position to another (i.e., a chloro group from the 6- to the 7-position) resulted in a common action in the TST but via a somewhat different mechanism. A6CDQ and A7CDQ might represent the first members of a new class of potential antidepressants with a unique multi-modal mechanism of action.

Treating depressive episodes or symptoms in patients with schizophrenia

Depressive episodes or symptoms occur frequently in patients with schizophrenia and may have far-reaching consequences. Despite the high prevalence rate and clinical relevance of this comorbidity, knowledge about treatment options is still limited. The aim of this review is to provide an overview of the literature concerning treatment options for depressive episodes or symptoms in schizophrenia. Based on the current evidence, we present a stepwise treatment approach. The first step is to evaluate the current antipsychotic treatment of psychotic symptoms and consider lowering the dosage, since increased blockade of the dopamine D2 receptors may be associated with a worse subjective sense of well-being and dysphoria. A second step is to consider switching antipsychotics, since there are indications that some antipsychotics (including sulpiride, clozapine, olanzapine, aripiprazole, quetiapine, lurasidone, or amisulpride) are slightly more effective in reducing depressive symptoms compared to other antipsychotics or placebo. In the case of a persistent depressive episode, additional therapeutic interventions are indicated. However, the evidence is indecisive regarding the treatment of choice: either starting cognitive-behavioral therapy or adding an antidepressant. A limited number of studies examined the use of antidepressants in depressed patients with schizophrenia showing modest effectiveness. Overall, additional research is needed to determine the most effective treatment approach for patients with schizophrenia and depressive episodes.

Potential roles of 5-HT3 receptor (5-HT3R) antagonists in modulating the effects of nicotine

5-HT₃R antagonists such as ondansetron, granisetron and tropisetron have been clinically used to treat nausea and vomiting in chemotherapy patients. However, current study and research revealed novel potentials of these ligands in other diseases like inflammation, Alzheimer's, and drug abuse. Towards utilising these drugs as anti-smoking agents to treat nicotine dependence problem, there are conflicting reports regarding the potential of these ligands in modulating the effects of nicotine in both human and animal behavioural studies. This is complicated by the heterogeneity of 5-HT₃R itself, cross regulation between nicotinic acetylcholinergic receptor (nAChR) and distinct pharmacological profiles of 5-HT₃R antagonists. This review gathered existing studies conducted investigating the potential of "-setron" class of 5-HT₃R antagonists in modulating nicotine effects. We proposed that the mechanism where 5-HT₃R antagonists mediate the effects of nicotine could be attributed by both direct at 5-HT₃R and indirect mechanism in nicotine addiction downstream regulation. The indirect mechanism mediated by the 5-HT₃R antagonist could be through α7 nAChR, 5-HT_1B receptor (5-HT_1BR), 5-HT_1C receptor (5-HT_1CR), calcineurin activity, p38 MAPK level, PPAR-γ and NF-κβ. Our review suggested that future studies should focus on newer 5-HT₃R antagonist with superior pharmacological profile or the one with multitarget action rather than high selectivity at single receptor.

Molecular aspects of depression: A review from neurobiology to treatment

Major depressive disorder (MDD), also known as unipolar depression, is one of the leading causes of disability and disease worldwide. The signs and symptoms are low self‑esteem, anhedonia, feeling of worthlessness, sense of rejection and guilt, suicidal thoughts, among others. This review focuses on studies with molecular-based approaches involving MDD to obtain an integrated, more detailed and comprehensive view of the brain changes produced by this disorder and its treatment and how the Central Nervous System (CNS) produces neuroplasticity to orchestrate adaptive defensive behaviors. This article integrates affective neuroscience, psychopharmacology, neuroanatomy and molecular biology data. In addition, there are two problems with current MDD treatments, namely: 1) Low rates of responsiveness to antidepressants and too slow onset of therapeutic effect; 2) Increased stress vulnerability and autonomy, which reduces the responses of currently available treatments. In the present review, we encourage the prospection of new bioactive agents for the development of treatments with post-transduction mechanisms, neurogenesis and pharmacogenetics inducers that bring greater benefits, with reduced risks and maximized access to patients, stimulating the field of research on mood disorders in order to use the potential of preclinical studies. For this purpose, improved animal models that incorporate the molecular and anatomical tools currently available can be applied. Besides, we encourage the study of drugs that do not present "classical application" as antidepressants, (e.g., the dissociative anesthetic ketamine and dextromethorphan) and drugs that have dual action mechanisms since they represent potential targets for novel drug development more useful for the treatment of MDD.

Mapping the Orthosteric Binding Site of the Human 5-HT3 Receptor Using Photo-cross-linking Antagonists

The serotonin-gated 5-HT₃ receptor is a ligand-gated ion channel. Its location at the synapse in the central and peripheral nervous system has rendered it a prime pharmacological target, for example, for antiemetic drugs that bind with high affinity to the neurotransmitter binding site and prevent the opening of the channel. Advances in structural biology techniques have led to a surge of disclosed three-dimensional receptor structures; however, solving ligand-bound high-resolution 5-HT₃ receptor structures has not been achieved to date. Ligand binding poses in the orthosteric binding site have been largely predicted from mutagenesis and docking studies. We report the synthesis of a series of photo-cross-linking compounds whose structures are based on the clinically used antiemetic drug granisetron (Kytril). These displaced [³H]granisetron from the orthosteric binding site with low nanomolar affinities and showed specific photo-cross-linking with the human 5-HT₃ receptor. Detailed analysis by protein-MS/MS identified a residue (Met-228) near the tip of binding loop C as the covalent modification site.

SR 57227A is a partial agonist/partial antagonist of 5-HT3 receptor and inhibits subsequent 5-HT- or SR 57227A-induced 5-HT3 receptor current

The serotonin (5-hydroxytryptamine) type 3 (5-HT₃) receptors are transmembrane ligand-gated ion channels. Although several 5-HT₃ receptor agonists have been used as preclinical tools, SR 57227A is the most commonly used 5-HT₃ receptor agonist with the ability to cross the blood brain barrier. However, the precise pharmacological profile of SR 57227A remains unclear. Therefore, we examined the pharmacological profile of SR 57227A at the 5-HT₃A and 5-HT₃AB receptors. We microinjected Xenopus laevis oocytes with human 5-HT₃A complementary RNA (cRNA) or a combination of human 5-HT₃A and human 5-HT₃AB cRNA and performed two electrode voltage clamp recordings of 5-HT₃A and 5-HT₃AB receptor current in the presence of SR 57227A. Results showed that SR 57227A acts as partial agonist/partial antagonist at the 5-HT₃ receptor. Interestingly, SR 57227A specifically reduced subsequent current amplitudes induced by 5-HT or SR 57227A. Based on its 5-HT₃ receptor partial agonist/partial antagonist properties, we predict that SR 57227A functions as a serotonin stabilizer.

Ondansetron - a promising adjunctive treatment for persistent schizophrenia

BACKGROUND

Ondansetron is a serotonin 3 receptor antagonist widely used to prevent nausea and vomiting in pregnancy and in patients receiving chemotherapy. There is growing evidence that adjunctive ondansetron treatment improves symptomatology associated with schizophrenia, particularly with respect to the positive, negative and cognitive symptoms. Further studies that are applicable to real world practice are required to assess the efficacy and effectiveness of this treatment, which could be readily and rapidly translated into clinical practice.

AIMS

This randomized control trial compared adjunctive (8 mg/daily) ondansetron or placebo to commonly prescribed atypical antipsychotics for people suffering with chronic schizophrenia ( ClinicalTrials.gov NCT01121042).

METHODS

The study involved 85 outpatients aged 18-65 years with a diagnosis of schizophrenia or schizoaffective disorder who participated in a two-arm randomized control trial.

RESULTS

Longitudinal analyses revealed adjunctive ondansetron provided significant improvement in the cognitive domain ( p<0.05) as measured by the Positive and Negative Syndrome Scale between baseline and week 12. The analysis of "Combination" showed ondansetron effect on Total Positive and Negative Syndrome Scale, approaching significance by week 12 ( p=0.06). No group differences were obtained in the Montgomery-Asberg Depression Rating Scale or Positive and Negative Syndrome Scale subscales.

CONCLUSION

This treatment trial provides some support for adjunctive ondansetron medication as a treatment for the cognitive disorganization symptoms of schizophrenia.

Effect of a 5-HT1D receptor agonist on the reinstatement phase of the conditioned place preference test and hippocampal long-term potentiation in methamphetamine-treated rats

Methamphetamine (METH)-seeking relapse is associated with memory and synaptic plasticity changes. Serotonin is a key neuromodulator in this process. While there is a known distribution of 5-HT_1D receptors in reward and memory areas, such as the hippocampus, its physiological function is currently unknown. Here, we evaluated effect of a 5-HT_1D receptor agonist, PNU142633, on the reinstatement of METH-seeking behavior and long-term potentiation. Rats were implanted with a cannula into lateral ventricle, then treated with saline or METH (5 mg/kg) during the acquisition phase of the conditioned place preference (CPP) test. On day 13 of the extinction phase, METH groups were divided into four groups: METH (0: saline, 1, or 2.5 (priming METH) mg/kg; i.p.) + vehicle (5 µl/rat) or a priming dose of METH (2.5 mg/kg; i.p.) + PNU (2 µg/5 µl; i.c.v.) and their preference scores were calculated on reinstatement day (day 14). Immediately following this, electrophysiology was performed to assay the field excitatory postsynaptic potential (fEPSP) slope and population spike (PS) amplitude between groups. The results showed that CPP induction by METH gradually declined to extinction on days 12 and 13. A priming METH treatment significantly increased preference for the METH-paired chamber when compared with other groups, but pre-treatment with PNU significantly attenuated this effect. PS amplitude and fEPSP slopes in vehicle + priming METH rats were greater when compared with other groups. Furthermore, PNU attenuated the priming METH-induced increase in PS amplitude. These findings suggest that PNU can decrease synaptic transmission and prevent METH reinstatement in rats.

Neuropharmacological and neurochemical evaluation of N-n-propyl-3-ethoxyquinoxaline-2-carboxamide (6n): a novel serotonergic 5-HT3 receptor antagonist for co-morbid antidepressant- and anxiolytic-like potential using traumatic brain injury model in rats

BACKGROUND

Several preclinical studies have shown that serotonergic 5-HT3 receptor antagonists play an important role in the management of neuropsychiatric disorders, such as depression and anxiety. In the present study the compound "6n" (N-n-propyl-3-ethoxyquinoxaline-2-carboxamide), a novel 5-HT3 receptor antagonist with an optimal log P (2.52) and pA2 (7.6) value was screened for its neuro-pharmacological potential in chronic rodent models of depression and anxiety named traumatic brain injury (TBI).

METHODS

In this model, a 1 cm midline scalp incision was made, and the muscles were retracted to expose the skull. A stainless steel disc (10 mm in diameter and 3 mm in depth) was placed centrally between the lambda and bregma regions. The injury was induced using the impact acceleration model of TBI. Specifically, a 400 g metal weight was dropped from a height of 1 m guided by a straight pipe, onto the metal disc placed over the rat's skull.

RESULTS

The behavioral anomalies of the TBI rats were attenuated by the chronic treatment of compound 6n (1 and 2 mg/kg, p.o.; 14 days) as observed by the modified open field test (ambulation, rearing, and fecal pellet), sucrose consumption test (% sucrose consumption), elevated plus maze [% open arm entries [OAE] and % time spent in open arm (TSOA)], and marble burying test (numbers). In addition, 6n also increased the levels of neurotransmitters (norepinephrine and serotonin) and brain derived neurotrophic factor (BDNF) in TBI rats.

CONCLUSIONS

The result suggests that compound 6n exhibited antidepressant- and anxiolytic-like effects in rodent models of depression and anxiety.

Increased levels of 5HT2A receptor mRNA expression in peripheral blood mononuclear cells of patients with major depression: correlations with severity and duration of illness

BACKGROUND

Neuroimaging, immunologic, and pharmacologic studies have emphasized the role of 5-HT2A and 5-HT3A serotonin receptors in the pathophysiology of major depression.

AIM

The aim of this study was to measure the relative expression of 5-HT2A and 5-HT3A receptor mRNA in peripheral blood mononuclear cells (PBMCs) of patients with major depressive disorder (MDD).

METHOD

5-HT2A and 5-HT3A receptor mRNA expressions were examined in PBMCs of 25 medication-naïve-patients with MDD, 25 medication-free MDD patients, and 25 healthy controls. 5-HT2A and 5-HT3A receptor mRNA expressions were measured using real-time quantitative PCR. This study evaluated patients' clinical symptoms using the Hamilton Depression Rating Scale-17 items (HDRS) and the Beck Depression Inventory (BDI).

RESULTS

Relative 5-HTR2A mRNA expression was significantly higher in PBMCs of all MDD patients when compared with healthy controls (Z = -3.875, p < 0.05). However, there was no significant difference in the relative levels of 5-HTR3A mRNA expression in PBMCs of all MDD patients when compared with healthy controls (Z = -1.328, p > 0.05). MDD patients showed significant correlations between 5-HTR2A mRNA expression and HDRS scores (rs = 0.902, p < 0.001) and BDI scores (rs = 0.878, p < 0.001).

CONCLUSION

This study showed that depressed patients, irrespective of treatment, have higher 5-HTR2A mRNA levels in PBMCs than healthy subjects. It also provided evidence that 5-HTR2A mRNA levels in PBMCs of MDD patients could be associated with the severity of depression and the duration of the illness.

Novel 5-HT3 receptor antagonist QCM-4 attenuates depressive-like phenotype associated with obesity in high-fat-diet-fed mice

RATIONALE

Depression associated with obesity remains an interesting area to study the biological mechanisms and novel therapeutic intervention.

OBJECTIVES

The present study investigates the effect of a novel 5-HT₃ receptor antagonist 3-methoxy-N-p-tolylquinoxalin-2-carboxamide (QCM-4) on several pathogenic markers of depression associated with obesity such as plasma insulin resistance, hippocampal cyclic adenosine monophosphate (cAMP), brain-derived neurotrophic factor (BDNF), serotonin (5-HT) concentrations, hippocampal neuronal damage, and p53 protein expression in high-fat-diet (HFD)-fed mice.

METHODS

Obesity was experimentally induced in mice by feeding with HFD for 14 weeks followed by administration of QCM-4 (1 and 2 mg/kg, p.o.)/standard escitalopram (ESC) (10 mg/kg, p.o.)/vehicle (10 ml/kg, p.o.) for 28 days. Behavioral assays such as sucrose preference test (SPT); forced swim test (FST); elevated plus maze (EPM); biochemical assays including oral glucose tolerance tests (OGTT), insulin, cAMP, BDNF, and 5-HT concentrations; and molecular assays mainly histology and immunohistochemistry (IHC) of p53 protein in the dentate gyrus (DG), CA1, and CA3 regions of hippocampus in HFD fed mice were performed.

RESULTS

Chronic treatment with QCM-4 in HFD-fed mice reversed the behavioral alterations in SPT, FST, and EPM. QCM-4 showed poor sensitivity for plasma glucose, improved insulin sensitivity, increased hippocampal cAMP, BDNF, and 5-HT concentrations. In the hippocampal DG, CA1, and CA3 regions, QCM-4 treatment improved the neuronal morphology in the histopathology and inhibited p53 protein expression in IHC assay in HFD-fed mice.

CONCLUSION

QCM-4 attenuated the depressive-like phenotype in HFD-fed mice by improving behavioral, biochemical, and molecular alterations through serotonergic neuromodulation.

Efficacy of Risperidone Augmentation with Ondansetron in the Treatment of Negative and Depressive Symptoms in Schizophrenia: A Randomized Clinical Trial

BACKGROUND

Given the potential role of the 5-hydroxytryptamine-3 receptor in the pathogenesis of schizophrenia, this study was performed to determine whether ondansetron plus risperidone could reduce the negative and depressive symptoms in patients with treatment-resistant schizophrenia.

METHODS

In a double-blinded, placebo-controlled, randomized trial (IRCT registration # 201112125280N7), in 2012-2013 in Mashhad, Iran, 38 patients with treatment-resistant schizophrenia received risperidone either combined with a fixed dose (4-8 mg/d) of ondansetron (n=18) or with a placebo (n=20) for 12 weeks. The patients were evaluated using the Positive and Negative Syndrome Scale (PANSS), Wechsler's Adult Intelligence Scale-Revised (WAIS-R), and Hamilton's Rating Scale for Depression (HRSD) at baseline and 12 weeks later. Changes in the inventories were used to evaluate the efficacy of the treatment. The t test, Chi-square test, and SPSS (version 16) were used to analyze the data. The statistical significance was set atP<0.05.

RESULTS

Ondansetron plus risperidone was associated with a significantly larger improvement in the PANSS overall scale and subscales for negative symptoms and cognition than was risperidone plus placebo (P<0.001). The WAIS-R scale results indicated significant differences between the 2 groups before and after administrating the medicine and the placebo. The administration of ondansetron significantly improved visual memory based on the subtests of the WAIS (P<0.05). Ondansetron had no positive effects on depressive symptoms (effect size=0.13).

CONCLUSION

This study confirmed that ondansetron, as an adjunct treatment, reduces negative symptoms in patients with schizophrenia and can be used as a potential adjunctive strategy particularly for negative symptoms and cognitive impairments. Trial Registration Number: IRCT201112125280N7.

Synthesis and Pharmacological Evaluation of [11C]Granisetron and [18F]Fluoropalonosetron as PET Probes for 5-HT3 Receptor Imaging

Serotonin-gated ionotropic 5-HT₃ receptors are the major pharmacological targets for antiemetic compounds. Furthermore, they have become a focus for the treatment of irritable bowel syndrome (IBS) and there is some evidence that pharmacological modulation of 5-HT₃ receptors might alleviate symptoms of other neurological disorders. Highly selective, high-affinity antagonists, such as granisetron (Kytril) and palonosetron (Aloxi), belong to a family of drugs (the "setrons") that are well established for clinical use. To enable us to better understand the actions of these drugs in vivo, we report the synthesis of 8-fluoropalonosetron (15) that has a binding affinity (K_i = 0.26 ± 0.05 nM) similar to the parent drug (K_i = 0.21 ± 0.03 nM). We radiolabeled 15 by nucleophilic ¹⁸F-fluorination of an unsymmetrical diaryliodonium palonosetron precursor and achieved the radiosynthesis of 1-(methyl-¹¹C)-N-granisetron ([¹¹C]2) through N-alkylation with [¹¹C]CH₃I, respectively. Both compounds [¹⁸F]15 (chemical and radiochemical purity >95%, specific activity 41 GBq/μmol) and [¹¹C]2 (chemical and radiochemical purity ≥99%, specific activity 170 GBq/μmol) were evaluated for their utility as positron emission tomography (PET) probes. Using mouse and rat brain slices, in vitro autoradiography with both [¹⁸F]15 and [¹¹C]2 revealed a heterogeneous and displaceable binding in cortical and hippocampal regions that are known to express 5-HT₃ receptors at significant levels. Subsequent PET experiments suggested that [¹⁸F]15 and [¹¹C]2 are of limited utility for the PET imaging of brain 5-HT₃ receptors in vivo.

The muscarinic antagonists scopolamine and atropine are competitive antagonists at 5-HT3 receptors

Scopolamine is a high affinity muscarinic antagonist that is used for the prevention of post-operative nausea and vomiting. 5-HT3 receptor antagonists are used for the same purpose and are structurally related to scopolamine. To examine whether 5-HT3 receptors are affected by scopolamine we examined the effects of this drug on the electrophysiological and ligand binding properties of 5-HT3A receptors expressed in Xenopus oocytes and HEK293 cells, respectively. 5-HT3 receptor-responses were reversibly inhibited by scopolamine with an IC50 of 2.09 μM. Competitive antagonism was shown by Schild plot (pA2 = 5.02) and by competition with the 5-HT3 receptor antagonists [(3)H]granisetron (Ki = 6.76 μM) and G-FL (Ki = 4.90 μM). The related molecule, atropine, similarly inhibited 5-HT evoked responses in oocytes with an IC50 of 1.74 μM, and competed with G-FL with a Ki of 7.94 μM. The reverse experiment revealed that granisetron also competitively bound to muscarinic receptors (Ki = 6.5 μM). In behavioural studies scopolamine is used to block muscarinic receptors and induce a cognitive deficit, and centrally administered concentrations can exceed the IC50 values found here. It is therefore possible that 5-HT3 receptors are also inhibited. Studies that utilise higher concentrations of scopolamine should be mindful of these potential off-target effects.

5HT3 receptors: Target for new antidepressant drugs

5HT3 receptors (5HT3Rs) have long been identified as a potential target for antidepressants. Several studies have reported that antagonism of 5HT3Rs produces antidepressant-like effects. However, the exact role of 5HT3Rs and the mode of antidepressant action of 5HT3R antagonists still remain a mystery. Here, we provide a comprehensive overview of 5HT3Rs: (a) regional and subcellular distribution of 5HT3Rs in discrete brain regions, (b) preclinical and clinical evidence supporting the antidepressant effect of 5HT3R antagonists, and (c) neurochemical, biological and neurocellular signaling pathways associated with the antidepressant action of 5HT3R antagonists. 5HT3Rs located on the serotonergic and other neurotransmitter interneuronal projections control their release and affect mood and emotional behavior; however, new evidence suggests that apart from modulating the neurotransmitter functions, 5HT3R antagonists have protective effects in the pathogenic events including hypothalamic-pituitary-adrenal-axis hyperactivity, brain oxidative stress and impaired neuronal plasticity, pointing to hereby unknown and novel mechanisms of their antidepressant action. Nonetheless, further investigations are warranted to establish the exact role of 5HT3Rs in depression and antidepressant action of 5HT3R antagonists.

Differentiated effects of the multimodal antidepressant vortioxetine on sleep architecture: Part 2, pharmacological interactions in rodents suggest a role of serotonin-3 receptor antagonism

Antidepressants often disrupt sleep. Vortioxetine, a multimodal antidepressant acting through serotonin (5-HT) transporter (SERT) inhibition, 5-HT3, 5-HT7 and 5-HT1D receptor antagonism, 5-HT1B receptor partial agonism, and 5-HT1A receptor agonism, had fewer incidences of sleep-related adverse events reported in depressed patients. In the accompanying paper a polysomnographic electroencephalography (sleep-EEG) study of vortioxetine and paroxetine in healthy subjects indicated that at low/intermediate levels of SERT occupancy, vortioxetine affected rapid eye movement (REM) sleep differently than paroxetine. Here we investigated clinically meaningful doses (80-90% SERT occupancy) of vortioxetine and paroxetine on sleep-EEG in rats to further elucidate the serotoninergic receptor mechanisms mediating this difference. Cortical EEG, electromyography (EMG), and locomotion were recorded telemetrically for 10 days, following an acute dose, from rats receiving vortioxetine-infused chow or paroxetine-infused water and respective controls. Sleep stages were manually scored into active wake, quiet wake, and non-REM or REM sleep. Acute paroxetine or vortioxetine delayed REM onset latency (ROL) and decreased REM episodes. After repeated administration, vortioxetine yielded normal sleep-wake rhythms while paroxetine continued to suppress REM. Paroxetine, unlike vortioxetine, increased transitions from non-REM to wake, suggesting fragmented sleep. Next, we investigated the role of 5-HT3 receptors in eliciting these differences. The 5-HT3 receptor antagonist ondansetron significantly reduced paroxetine's acute effects on ROL, while the 5-HT3 receptor agonist SR57227A significantly increased vortioxetine's acute effect on ROL. Overall, our data are consistent with the clinical findings that vortioxetine impacts REM sleep differently than paroxetine, and suggests a role for 5-HT3 receptor antagonism in mitigating these differences.