Rapid reorganization of serotonin projections and antidepressant response to 5-HT1A-biased agonist NLX-101 in fluoxetine-resistant cF1ko mice.

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) like fluoxetine remain a first-line treatment for major depression, but are effective in less than half of patients and can take 4-8 weeks to show results. In this study, we examined cF1ko mice with genetically induced upregulation of 5-HT1A autoreceptors that reduces 5-HT neuronal activity. These mice display anxiety- and depression-related behaviors that did not respond to chronic fluoxetine treatment. We examined treatment with NLX-101, a biased agonist that preferentially targets 5-HT1A heteroreceptors. By testing different doses of NLX-101, we found that a dose of 0.2 mg/kg was effective in reducing depression-related behavior in cF1ko mice without causing hypothermia, a 5-HT1A autoreceptor-mediated response. After 1 h, this dose activated dorsal raphe 5-HT neurons and cells in the medial prefrontal cortex (mPFC), increasing nuclear c-fos labelling in cF1ko mice. In cF1ko mice but not wild-type littermates, 0.2 mg/kg NLX-101 administered 1 h prior to each behavioral test for two weeks reduced depressive behavior in the forced swim test, but increased anxiety-related behaviors in the open field, elevated plus maze, and novelty suppressed feeding tests. During this treatment, NLX-101 induced widespread increases in the density of 5-HT axons, varicosities, and especially synaptic and triadic structures, particularly in depression-related brain regions including mPFC, hippocampal CA1 and CA2/3, amygdala and nucleus accumbens of cF1ko mice. Overall, NLX-101 was rapid and effective in reducing depressive behavior in SSRI-resistant mice, but also induced anxiety-related behaviors. The increase in serotonin innervation induced by intermittent NLX-101 may contribute to its behavioral actions.

Preclinical investigation of the effect of stress on the binding of [18F]F13640, a 5-HT1A radiopharmaceutical.

BACKGROUND: [18F]F13640 is a new PET radiopharmaceutical for brain molecular imaging of serotonin 5-HT1A receptors. Since we intend to use this radiopharmaceutical in psychiatric studies, it is crucial to establish possible sensitivity modification of 5-HT1A receptors availability during an acute stress exposure. In this study, we first assessed the cerebrometabolic effects of a new animal model of stress with [18F]FDG and then proceeded to test for effects of this model on the cerebral binding of [18F]F13640, a 5-HT1A receptors PET radiopharmaceutical. METHODS: Four groups of male Sprague-Dawley were used to identify the optimal model: "stressed group" (n = 10), "post-traumatic stress disorder (PTSD) group" (n = 9) and "restraint group" (n = 8), compared with a control group (n = 8). All rats performed neuroimaging [18F]FDG µPET-CT to decipher which model was the most appropriate to test effects of stress on radiotracer binding. Subsequently, a group of rats (n = 10) underwent two PET imaging acquisitions (baseline and PTSD condition) using the PET radiopharmaceutical [18F]F13640 to assess influence of stress on its binding. Voxel-based analysis was performed to assess [18F]FDG or [18F]F13640 changes. RESULTS: In [18F]FDG experiments, the PTSD group showed a pattern of cerebrometabolic activation in various brain regions previously implicated in stress (amygdala, perirhinal cortex, olfactory bulb and caudate). [18F]F13640 PET scans showed increased radiotracer binding in the PTSD condition in caudate nucleus and brainstem. CONCLUSIONS: The present study demonstrated stress-induced cerebrometabolic activation or inhibition of various brain regions involved in stress model. Applying this model to our radiotracer, [18F]F13640 showed few influence of stress on its binding. This will enable to rule out any confounding effect of stress during imaging studies.

Pharmacodynamic, pharmacokinetic and rat brain receptor occupancy profile of NLX-112, a highly selective 5-HT1A receptor biased agonist.

NLX-112 (i.e., F13640, befiradol) exhibits nanomolar affinity, exceptional selectivity and full agonist efficacy at serotonin 5-HT1A receptors. NLX-112 shows efficacy in rat, marmoset and macaque models of L-DOPA induced dyskinesia (LID) in Parkinson's disease and has shown clinical efficacy in a Phase 2a proof-of-concept study for this indication. Here we investigated, in rats, its pharmacodynamic, pharmacokinetic (PK) and brain 5-HT1A receptor occupancy profiles, and its PK properties in the absence and presence of L-DOPA. Total and free NLX-112 exposure in plasma, CSF and striatal ECF was dose-proportional over the range tested (0.04, 0.16 and 0.63 mg/kg i.p.). NLX-112 exposure increased rapidly (Tmax 0.25-0.5h) and exhibited approximately threefold longer half-life in brain than in plasma (1.1 and 3.6h, respectively). At a pharmacologically relevant dose of 0.16 mg/kg i.p., previously shown to elicit anti-LID activity in parkinsonian rats, brain concentration of NLX-112 was 51-63 ng/g from 0.15 to 1h. In microPET imaging experiments, NLX-112 showed dose-dependent reduction of 18F-F13640 (i.e., 18F-NLX-112) brain 5-HT1A receptor labeling in cingulate cortex and striatum, regions associated with motor control and mood, with almost complete inhibition of labeling at the dose of 0.63 mg/kg i.p.. Co-administration of L-DOPA (6 mg/kg s.c., a dose used to elicit LID in parkinsonian rats) together with NLX-112 (0.16 mg/kg i.p.) did not modify PK parameters in rat plasma and brain of either NLX-112 or L-DOPA. Here, we demonstrate that NLX-112's profile is compatible with 'druggable' parameters for CNS indications, and the results provide measures of brain concentrations and 5-HT1A receptor binding parameters relevant to the anti-dyskinetic activity of the compound.

Association between 5-HT1A receptor C-1019G, 5-HTTLPR polymorphisms and panic disorder: a meta-analysis.

HTR1A C-1019G polymorphism (rs6295) and serotonin transporter promoter polymorphism (5-HTTLPR) have been linked with panic disorder (PD) in different ethnic backgrounds. Both these polymorphisms are in the promoter regions. However, results are inconsistent and contrasting evidence makes reliable conclusions even more challenging. A meta-analysis was conducted to test whether C-1019G polymorphism and 5-HTTLPR were involved in the etiology of PD. Articles researching the link between C-1019G, 5-HTTLPR polymorphisms, and PD were retrieved by database searching and systematically selected on the basis of selected inclusion parameters. 21 studies were included that examined the relationship of rs6295,5-HTTLPR polymorphisms with PD risk susceptibility (rs62957 polymorphism - 7 articles, and 5-HTTLPR polymorphism - 14 articles). A significant association was seen between the rs6295 polymorphism and PD pathogenesis, especially in Caucasian PD patients. No significant genetic linkage was found between the 5-HTTLPR polymorphism and PD. C-1019G polymorphism was involved in the etiology of PD in Caucasian patients. The 5-HTTLPR polymorphism was not a susceptibility factor of PD.

The 5-HT1A receptor biased agonists, NLX-204 and NLX-101, like ketamine, elicit rapid-acting antidepressant activity in the rat chronic mild stress model via cortical mechanisms.

BACKGROUND: The highly selective 5-HT1A serotonin receptor "biased" agonists NLX-101 and NLX-204 display, like ketamine, potent and efficacious rapid-acting antidepressant (RAAD) activity in the rat chronic mild stress (CMS) model with systemic (i.p.) administration. They rapidly (within 1 day) reverse anhedonia (i.e., CMS-induced sucrose consumption deficit), attenuate working memory deficit (novel object recognition: NOR), and decrease anxiety behavior in the elevated-plus maze (EPM). AIMS: Here, we sought to explore the contribution of prefrontal cortex (PFC) 5-HT1A receptor activation in the RAAD activity of NLX compounds. RESULTS/OUTCOMES: In male Wistar rats, unilateral PFC microinjections of NLX-204 and NLX-101 (16 µg), like ketamine (10 µg), reproduced the effects of their systemic administration: they reversed CMS-induced sucrose consumption deficit, attenuated anxiety (EPM), and reduced working memory deficits (NOR). In addition, unilateral PFC microinjections of the selective 5-HT1A antagonist, WAY-100,635 (2 µg), attenuated the beneficial effects of systemic NLX-204 and NLX-101 (0.16 mg/kg i.p.) in the sucrose intake and NOR models, indicating that these compounds exert their RAAD activity specifically through activation of PFC 5-HT1A receptors. CONCLUSIONS/INTERPRETATION: These data indicate that 5-HT1A receptor biased agonists share with ketamine a common neuroanatomical site for RAAD activity, which can be obtained not only by targeting glutamatergic/NMDA neurotransmission (ketamine's primary mechanism of action) but also by activating 5-HT1A receptors, as is the case for the NLX compounds. The present observations also reinforce the notion that biased agonism at 5-HT1A receptors constitutes a promising strategy to achieve RAAD effects, with additional benefits against cognitive deficits and anxiety in depressed patients, without ketamine's troublesome side effects.

The antidepressant-like effect and proposed mechanism of action of TPN672MA, a novel serotonin-dopamine receptor modulator for the treatment of schizophrenia.

TPN672MA, an innovative antipsychotic drug candidate currently in clinical trials, acts as a dopamine D2/D3 receptor partial agonist, serotonin 5-HT1A receptor agonist, and serotonin 5-HT2A receptor antagonist. Preclinical investigations have demonstrated its potential in treating the core symptoms of schizophrenia. The present study highlights TPN672MA's significant antidepressant-like effects in classical behavioral models, such as the chronic social defeat stress paradigm. The pronounced 5-HT1A receptor agonism and D2/D3 receptor partial agonism of TPN672MA likely contribute to its therapeutic effects in depression. Additionally, TPN672MA's antidepressant-like efficacy may be linked to its ability to enhance the expression levels of brain-derived neurotrophic factor (BDNF) and postsynaptic density protein-95 (PSD95) in the hippocampus. Furthermore, TPN672MA displayed a more rapid onset of antidepressant-like action. In conclusion, TPN672MA represents a promising new drug candidate for the treatment of symptoms of schizophrenia and depression.

Comparison of Protective Effects of Antidepressants Mediated by Serotonin Receptor in Aß-Oligomer-Induced Neurotoxicity.

Amyloid ß-peptide (Aß) synthesis and deposition are the primary factors underlying the pathophysiology of Alzheimer's disease (AD). Aß oligomer (Aßo) exerts its neurotoxic effects by inducing oxidative stress and lesions by adhering to cellular membranes. Though several antidepressants have been investigated as neuroprotective agents in AD, a detailed comparison of their neuroprotection against Aßo-induced neurotoxicity is lacking. Here, we aimed to elucidate the neuroprotective effects of clinically prescribed selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, and noradrenergic and specific serotonergic antidepressants at the cellular level and establish the underlying mechanisms for their potential clinical applications. Therefore, we compared the neuroprotective effects of three antidepressants, fluoxetine (Flx), duloxetine (Dlx), and mirtazapine (Mir), by their ability to prevent oxidative stress-induced cell damage, using SH-SY5Y cells, by evaluating cell viability, generation of reactive oxygen species (ROS) and mitochondrial ROS, and peroxidation of cell membrane phospholipids. These antidepressants exhibited potent antioxidant activity (Dlx > Mir > Flx) and improved cell viability. Furthermore, pretreatment with a 5-hydroxytryptamine 1A (5-HT1A) antagonist suppressed their effects, suggesting that the 5-HT1A receptor is involved in the antioxidant mechanism of the antidepressants' neuroprotection. These findings suggest the beneficial effects of antidepressant treatment in AD through the prevention of Aß-induced oxidative stress.

Synthesis and biological evaluation of multimodal monoaminergic arylpiperazine derivatives with potential antidepressant profile.

Depression is a common psychiatric disorder with an estimated global prevalence of 4.4 %. Here, we designed a series of new multimodal monoaminergic arylpiperazine derivatives using a pharmacophore hybrid approach and synthesized them for the treatment of depression. Molecular docking was employed to elucidate the differences in activity and selectivity of the corresponding compounds on SERT, NET, and DAT. In vitro experiments demonstrated that compound A3 has a relatively balanced multi-target activity profile with SERT reuptake inhibition (IC50 = 12 nM), NET reuptake inhibition (IC50 = 78 nM), DAT reuptake inhibition (IC50 = 135 nM), and 5-HT1AR agonism (EC50 = 34 nM). Pharmacokinetic experiments revealed that A3 exhibited excellent bioavailability and low clearance in mice. Subsequent behavioral experiments further confirmed its significant antidepressant effects. These results further highlight the rationality of our design strategy.

5-hydroxytryptamine 2C/1A receptors modulate the biphasic dose response of the head twitch response and locomotor activity induced by DOM in mice.

RATIONALE: The phenylalkylamine hallucinogen (-)-2,5-dimethoxy-4-methylamphetamine (DOM) exhibits an inverted U-shaped dose-response curve for both head twitch response (HTR) and locomotor activity in mice. Accumulated studies suggest that HTR and locomotor hyperactivity induced by DOM are mainly caused by the activation of serotonin 5-hydroxytryptamine 2 A receptor (5-HT2A receptor). However, the mechanisms underlying the biphasic dose response of HTR and locomotor activity induced by DOM, particularly at high doses, remain unclear. OBJECTIVES: The primary objective of this study is to investigate the modulation of 5-HT2A/2C/1A receptors in HTR and locomotor activity, while also exploring the potential receptor mechanisms underlying the biphasic dose response of DOM. METHODS: In this study, we employed pharmacological methods to identify the specific 5-HT receptor subtypes responsible for mediating the biphasic dose-response effects of DOM on HTR and locomotor activity in C57BL/6J mice. RESULTS: The 5-HT2A receptor selective antagonist (R)-[2,3-di(methoxy)phenyl]-[1-[2-(4-fluorophenyl)ethyl]piperidin-4-yl]methanol (M100907) (500 µg/kg, i.p.) fully blocked the HTR at every dose of DOM (0.615-10 mg/kg, i.p.) in C57BL/6J mice. M100907 (50 µg/kg, i.p.) decreased the locomotor hyperactivity induced by a low dose of DOM (0.625, 1.25 mg/kg, i.p.), but had no effect on the locomotor hypoactivity induced by a high dose of DOM (10 mg/kg) in C57BL/6J mice. The 5-HT2C antagonist 6-chloro-5-methyl-1-[(2-[2-methylpyrid-3yloxy]pyrid-5yl)carbamoyl]indoline (SB242084) (0.3, 1 mg/kg, i.p.) reduced the HTR induced by a dose of 2.5 mg/kg DOM, but did not affect the response to other doses. SB242084 (1 mg/kg, i.p.) significantly increased the locomotor activity induced by DOM (0.615-10 mg/kg, i.p.) in mice. The 5-HT1A antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]N-(2-pyridinyl) cyclohexane carboxamide maleate (WAY100635) (1 mg/kg, i.p.) increased both HTR and locomotor activity induced by DOM in mice. The 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (1 mg/kg, i.p.) significantly reduced both the HTR and locomotor activity induced by DOM in mice. Additionally, pretreatment with the Gαi/o inhibitor PTX (0.25 µg/mouse, i.c.v.) enhanced the HTR induced by DOM and attenuated the effect of DOM on locomotor activity in mice. CONCLUSIONS: Receptor subtypes 5-HT2C and 5-HT1A are implicated in the inverted U-shaped dose-response curves of HTR and locomotor activity induced by DOM in mice. The biphasic dose-response function of HTR and locomotor activity induced by DOM has different mechanisms in mice.

CaMKIV-Mediated Phosphorylation Inactivates Freud-1/CC2D1A Repression for Calcium-Dependent 5-HT1A Receptor Gene Induction.

Calcium calmodulin-dependent protein kinase (CaMK) mediates calcium-induced neural gene activation. CaMK also inhibits the non-syndromic intellectual disability gene, Freud-1/CC2D1A, a transcriptional repressor of human serotonin-1A (5-HT1A) and dopamine-D2 receptor genes. The altered expression of these Freud-1-regulated genes is implicated in mental illnesses such as major depression and schizophrenia. We hypothesized that Freud-1 is blocked by CaMK-induced phosphorylation. The incubation of purified Freud-1 with either CaMKIIα or CaMKIV increased Freud-1 phosphorylation that was partly prevented in Freud-1-Ser644Ala and Freud-1-Thr780Ala CaMK site mutants. In human SK-N-SH neuroblastoma cells, active CaMKIV induced the serine and threonine phosphorylation of Freud-1, and specifically increased Freud-1-Thr780 phosphorylation in transfected HEK-293 cells. The activation of purified CaMKIIα or CaMKIV reduced Freud-1 binding to its DNA element on the 5-HT1A and dopamine-D2 receptor genes. In SK-N-SH cells, active CaMKIV but not CaMKIIα blocked the Freud-1 repressor activity, while Freud-1 Ser644Ala, Thr780Ala or dual mutants were resistant to inhibition by activated CaMKIV or calcium mobilization. These results indicate that the Freud-1 repressor activity is blocked by CaMKIV-induced phosphorylation at Thr780, resulting in the up-regulation of the target genes, such as the 5-HT1A receptor gene. The CaMKIV-mediated inhibition of Freud-1 provides a novel de-repression mechanism to induce 5-HT1A receptor expression for the regulation of cognitive development, behavior and antidepressant response.

Effects of Subchronic Buspirone Treatment on Depressive Profile in Socially Isolated Rats: Implication of Early Life Experience on 5-HT1A Receptor-Related Depression.

The heterogeneity of etiology may serve as a crucial factor in the challenges of treatment, including the low response rate and the delay in establishing therapeutic effect. In the present study, we examined whether social experience since early life is one of the etiologies, with the involvement of the 5-HT1A receptors, and explored the potentially therapeutic action of the subchronic administration of buspirone, a partial 5-HT1A agonist. Rats were isolation reared (IR) since their weaning, and the depressive profile indexed by the forced-swim test (FST) was examined in adulthood. Nonspecific locomotor activity was used for the IR validation. Buspirone administration (1 mg/kg/day) was introduced for 14 days (week 9-11). The immobility score of the FST was examined before and after the buspirone administration. Tissue levels of serotonin (5-HT) and its metabolite 5-HIAA were measured in the hippocampus, the amygdala, and the prefrontal cortex. Efflux levels of 5-HT, dopamine (DA), and norepinephrine (NE) were detected in the hippocampus by brain dialysis. Finally, the full 5-HT1A agonist 8-OH-DPAT (0.5 mg/kg) was acutely administered in both behavioral testing and the dialysis experiment. Our results showed (i) increased immobility time in the FST for the IR rats as compared to the social controls, which could not be reversed by the buspirone administration; (ii) IR-induced FST immobility in rats receiving buspirone was corrected by the 8-OH-DPAT; and (iii) IR-induced reduction in hippocampal 5-HT levels can be reversed by the buspirone administration. Our data indicated the 5-HT1A receptor-linked early life social experience as one of the mechanisms of later life depressive mood.

Effects of an external static EF on the conformational transition of 5-HT1A receptor: A molecular dynamics simulation study.

The serotonin receptor subtype 1A (5-HT1AR), one of the G-protein-coupled receptor (GPCR) family, has been implicated in several neurological conditions. Understanding the activation and inactivation mechanism of 5-HT1AR at the molecular level is critical for discovering novel therapeutics in many diseases. Recently there has been a growing appreciation for the role of external electric fields (EFs) in influencing the structure and activity of biomolecules. In this study, we used molecular dynamics (MD) simulations to examine conformational features of active states of 5-HT1AR and investigate the effect of an external static EF with 0.02 V/nm applied on the active state of 5-HT1AR. Our results showed that the active state of 5-HT1AR maintained the native structure, while the EF led to structural modifications in 5-HT1AR, particularly inducing the inward movement of transmembrane helix 6 (TM6). Furthermore, it disturbed the conformational switches associated with activation in the CWxP, DRY, PIF, and NPxxY motifs, consequently predisposing an inclination towards the inactive-like conformation. We also found that the EF led to an overall increase in the dipole moment of 5-HT1AR, encompassing TM6 and pivotal amino acids. The analyses of conformational properties of TM6 showed that the changed secondary structure and decreased solvent exposure occurred upon the EF condition. The interaction of 5-HT1AR with the membrane lipid bilayer was also altered under the EF. Our findings reveal the molecular mechanism underlying the transition of 5-HT1AR conformation induced by external EFs, which offer potential novel insights into the prospect of employing structure-based EF applications for GPCRs.

Advances in drug design and therapeutic potential of selective or multitarget 5-HT1A receptor ligands.

5-HT1A receptor (5-HT1A-R) is a serotoninergic G-protein coupled receptor subtype which contributes to several physiological processes in both central nervous system and periphery. Despite being the first 5-HT-R identified, cloned and studied, it still represents a very attractive target in drug discovery and continues to be the focus of a myriad of drug discovery campaigns due to its involvement in numerous neuropsychiatric disorders. The structure-activity relationship studies (SAR) performed over the last years have been devoted to three main goals: (i) design and synthesis of 5-HT1A-R selective/preferential ligands; (ii) identification of 5-HT1A-R biased agonists, differentiating pre- versus post-synaptic agonism and signaling cellular mechanisms; (iii) development of multitarget compounds endowed with well-defined poly-pharmacological profiles targeting 5-HT1A-R along with other serotonin receptors, serotonin transporter (SERT), D2-like receptors and/or enzymes, such as acetylcholinesterase and phosphodiesterase, as a promising strategy for the management of complex psychiatric and neurodegenerative disorders. In this review, medicinal chemistry aspects of ligands acting as selective/preferential or multitarget 5-HT1A-R agonists and antagonists belonging to different chemotypes and developed in the last 7 years (2017-2023) have been discussed. The development of chemical and pharmacological 5-HT1A-R tools for molecular imaging have also been described. Finally, the pharmacological interest of 5-HT1A-R and the therapeutic potential of ligands targeting this receptor have been considered.

Improving dietary patterns in obese mice: Effects on body weight, adiposity, anhedonia-like behavior, pro-BDNF expression and 5-HT system.

INTRODUCTION: The excessive fat accumulation in obesity, resulting from an unbalanced diet, can lead to metabolic and neurological disorders and increase the risk of developing anxiety and depression. AIM: Assess the impact of dietary intervention (DI) on the serotonergic system, brain-derived neurotrophic factor (BDNF) expression and behaviors of obese mice. METHODS: Male C57BL/6 mice, 5 weeks old, received a high-fat diet (HFD) for 10 weeks for the induction of obesity. After this period, for 8 weeks, half of these animals received a control diet (CD), group obese (OB) + control diet (OB + CD, n = 10), and another half continued being fed HFD, group obese + HFD (OB + HFD, n = 10). At the end of the eighth week of intervention, behavioral tests were performed (sucrose preference test, open field, novel object recognition, elevated plus maze and tail suspension). Body weight and food intake were assessed weekly. Visceral adiposity, the hippocampal and hypothalamic protein expression of BDNF, 5-HT1A (5-HT1A serotonin receptor) and TPH2 (key enzyme in serotonin synthesis), were evaluated after euthanasia. RESULTS: The dietary intervention involved changing from a HFD to a CD over an 8-week period, effectively reduced body weight gain, adiposity, and anhedonia-like behavior. In the OB + HFD group, we saw a lower sucrose preference and shorter traveled distance in the open field, along with increased pro-BDNF expression in the hypothalamus compared to the OB + CD mice. However, the levels of TPH2 and 5-HT1A remained unchanged. CONCLUSION: The HFD model induced both obesity and anhedonia, but the dietary intervention successfully improved these conditions.

5-HT1A and 5-HT2A receptor effects on recognition memory, motor/exploratory behaviors, emotionality and regional dopamine transporter binding in the rat.

Both dopamine (DA) and serotonin (5-HT) play key roles in numerous functions including motor control, stress response and learning. So far, there is scarce or conflicting evidence about the effects of 5-HT1A and 5-HT2A receptor (R) agonists and antagonists on recognition memory in the rat. This also holds for their effect on cerebral DA as well as 5-HT release. In the present study, we assessed the effects of the 5-HT1AR agonist 8-OH-DPAT and antagonist WAY100,635 and the 5-HT2AR agonist DOI and antagonist altanserin (ALT) on rat behaviors. Moreover, we investigated their impact on monoamine efflux by measuring monoamine transporter binding in various regions of the rat brain. After injection of either 8-OH-DPAT (3 mg/kg), WAY100,635 (0.4 mg/kg), DOI (0.1 mg/kg), ALT (1 mg/kg) or the respective vehicle (saline, DMSO), rats underwent an object and place recognition memory test in the open field. Upon the assessment of object exploration, motor/exploratory parameters and feces excretion, rats were administered the monoamine transporter radioligand N-o-fluoropropyl-2b-carbomethoxy-3b-(4-[123I]iodophenyl)-nortropane ([123I]-FP-CIT; 8.9 ± 2.6 MBq) into the tail vein. Regional radioactivity accumulations in the rat brain were determined post mortem. Compared vehicle, administration of 8-OH-DPAT impaired memory for place, decreased rearing behavior, and increased ambulation as well as head-shoulder movements. DOI administration led to a reduction in rearing behavior but an increase in head-shoulder motility relative to vehicle. Feces excretion was diminished after ALT relative to vehicle. Dopamine transporter (DAT) binding was increased in the caudateputamen (CP), but decreased in the nucleus accumbens (NAC) after 8-OH-DPAT relative to vehicle. Moreover, DAT binding was decreased in the NAC after ALT relative to vehicle. Findings indicate that 5-HT1AR inhibition and 5-HT2AR activation may impair memory for place. Furthermore, results imply associations not only between recognition memory, motor/exploratory behavior and emotionality but also between the respective parameters and the levels of available DA in CP and NAC.

Changes in Induced-Antipredation Defense Traits and Transcriptome Regulations of Daphnia magna in Response to 5-HT1A Receptor Antagonist.

The serotonin signaling system plays a crucial role in regulating the ontogeny of crustaceans. Here, we describe the effects of different concentrations of the 5-hydroxytryptamine 1A receptor antagonist (WAY-100635) on the induced antipredation (Rhodeus ocellatus as the predator), morphological, behavioral, and life-history defenses of Daphnia magna and use transcriptomics to analyze the underlying molecular mechanisms. Our results indicate that exposure to WAY-100635 leads to changes in the expression of different defensive traits in D. magna when faced with fish predation risks. Specifically, as the length of exposure to WAY-100635 increases, high concentrations of WAY-100635 inhibit defensive responses associated with morphological and reproductive activities but promote the immediate negative phototactic behavioral defense of D. magna. This change is related to the underlying mechanism through which WAY-100635 interferes with gene expression of G-protein-coupled GABA receptors by affecting GABBR1 but promotes serotonin receptor signaling and ecdysteroid signaling pathways. In addition, we also find for the first time that fish kairomone can significantly activate the HIF-1α signaling pathway, which may lead to an increase in the rate of immediate movement. These results can help assess the potential impacts of serotonin-disrupting psychotropic drugs on zooplankton in aquatic ecosystems.

Activating SRC/MAPK signaling via 5-HT1A receptor contributes to the effect of vilazodone on improving thrombocytopenia.

Thrombocytopenia caused by long-term radiotherapy and chemotherapy exists in cancer treatment. Previous research demonstrates that 5-Hydroxtrayptamine (5-HT) and its receptors induce the formation of megakaryocytes (MKs) and platelets. However, the relationships between 5-HT1A receptor (5-HTR1A) and MKs is unclear so far. We screened and investigated the mechanism of vilazodone as a 5-HTR1A partial agonist in promoting MK differentiation and evaluated its therapeutic effect in thrombocytopenia. We employed a drug screening model based on machine learning (ML) to screen the megakaryocytopoiesis activity of Vilazodone (VLZ). The effects of VLZ on megakaryocytopoiesis were verified in HEL and Meg-01 cells. Tg (itga2b: eGFP) zebrafish was performed to analyze the alterations in thrombopoiesis. Moreover, we established a thrombocytopenia mice model to investigate how VLZ administration accelerates platelet recovery and function. We carried out network pharmacology, Western blot, and immunofluorescence to demonstrate the potential targets and pathway of VLZ. VLZ has been predicted to have a potential biological action. Meanwhile, VLZ administration promotes MK differentiation and thrombopoiesis in cells and zebrafish models. Progressive experiments showed that VLZ has a potential therapeutic effect on radiation-induced thrombocytopenia in vivo. The network pharmacology and associated mechanism study indicated that SRC and MAPK signaling are both involved in the processes of megakaryopoiesis facilitated by VLZ. Furthermore, the expression of 5-HTR1A during megakaryocyte differentiation is closely related to the activation of SRC and MAPK. Our findings demonstrated that the expression of 5-HTR1A on MK, VLZ could bind to the 5-HTR1A receptor and further regulate the SRC/MAPK signaling pathway to facilitate megakaryocyte differentiation and platelet production, which provides new insights into the alternative therapeutic options for thrombocytopenia.

Cannabidiol exhibits anxiolytic-like effects and antipsychotic-like effects in mice models.

Cannabidiol (CBD), a non-psychoactive compound derived from the cannabis plant, has been confirmed to induce anxiolytic-like and antipsychotic-like effects. However, the exact mechanisms remain unclear. This study substantiated CBD's interaction with the 5-HT1A receptor (5-HT1AR) in vitro (CHO cells expressing human 5-HT1AR) and in vivo (rat lower lip retraction test, LLR test). We then assessed the impact of CBD in mice using the stress-induced hyperthermia (SIH) model and the phencyclidine (PCP)-induced negative symptoms of schizophrenia model, respectively. Concurrently, we investigated whether WAY-100635, a typical 5-HT1AR antagonist, could attenuate these effects. Furthermore, the neurotransmitter changes through high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) were studied. Results revealed that CBD exhibits selective 5-HT1AR agonists-mediated effects in the rat lower lip retraction test, aligning with the robust agonistic (EC50 = 1.75 µM) profile observed in CHO cells. CBD at 3 mg/kg significantly reduced SIH (ΔT), a response that WAY-100635 abolished. Chronic administration of CBD at 100 mg/kg mitigated the increase in PCP-induced immobility time in the forced swim test (FST) and tail suspension test (TST). Moreover, it induced significant alterations in gamma-aminobutyric acid (GABA) and norepinephrine (NE) levels within the hippocampus (HPC). Thus, we concluded that the 5-HT1AR mediates CBD's anxiolytic-like effects. Additionally, CBD's effects on the negative symptoms of schizophrenia may be linked to changes in GABA and NE levels in the hippocampus. These findings offer novel insights for advancing the exploration of CBD's anxiolytic-like and antipsychotic-like effects.

Prevention of MK-801-induced amnestic effect with combined activation of 5-HT1A and muscarinic receptors in mice.

BACKGROUND: Muscarinic or 5-HT1A receptors are crucial in learning and memory processes, and their expression is evident in the brain areas involved in cognition. The administration of the activators of these receptors prevents the development of cognitive dysfunctions in animal models of schizophrenia induced by MK-801 (N-methyl-d-aspartate receptor antagonist) administration. GABAergic dysfunction is considered as one of the most important causes of MK-801-induced spatial learning deficits. METHODS: Novel object recognition (NOR) and Morris water maze (MWM) tests were used to study the anti-amnestic effect of the biased 5-HT1A receptor agonist (F15599) alone or in combinations with VU0357017 (M1 receptor allosteric agonist), VU0152100 (M4 receptor positive allosteric modulator), and VU0238429 (M5 receptor positive allosteric modulator) on MK-801-induced dysfunctions. The compounds were administered for 5 consecutive days. Animals tested with the MWM underwent 5-day training. Western blotting was used to study the expressions of 5-HT1A receptors and the level of GAD65 in the frontal cortices (FCs) and hippocampi of the animals. RESULTS: F15599 prevented the amnestic effect induced by MK-801 in the MWM at a dose of 0.1 mg/kg. The co-administration of the compound with muscarinic receptors activators had no synergistic effect. The additive effect of the combinations was evident in the prevention of declarative memory dysfunctions investigated in NOR. The administration of MK-801 impaired 5-HT1A expression in the hippocampi and decreased GAD65 levels in both the FCs and hippocampi. The administration of muscarinic ligands prevented these MK-801-induced deficits only in the hippocampi of MWM-trained animals. No effects of the compounds were observed in untrained mice. CONCLUSION: Our results indicate that F15599 prevents schizophrenia-related spatial learning deficits in the MWM; however, the activity of the compound is not intensified with muscarinic receptors activators. In contrast, the combined administration of the ligands is effective in the NOR model of declarative memory. The muscarinic receptors activators reversed MK-801-induced 5-HT1A and GAD65 dysfunctions in the hippocampi of MWM-trained mice, but not in untrained mice.

Cannabidiol Exerts Anticonvulsant Effects Alone and in Combination with Δ9-THC through the 5-HT1A Receptor in the Neocortex of Mice.

Cannabinoids have shown potential in drug-resistant epilepsy treatment; however, we lack knowledge on which cannabinoid(s) to use, dosing, and their pharmacological targets. This study investigated (i) the anticonvulsant effect of Cannabidiol (CBD) alone and (ii) in combination with Delta-9 Tetrahydrocannabinol (Δ9-THC), as well as (iii) the serotonin (5-HT)1A receptor's role in CBD's mechanism of action. Seizure activity, induced by 4-aminopyridine, was measured by extracellular field recordings in cortex layer 2/3 of mouse brain slices. The anticonvulsant effect of 10, 30, and 100 µM CBD alone and combined with Δ9-THC was evaluated. To examine CBD's mechanism of action, slices were pre-treated with a 5-HT1A receptor antagonist before CBD's effect was evaluated. An amount of ≥30 µM CBD alone exerted significant anticonvulsant effects while 10 µM CBD did not. However, 10 µM CBD combined with low-dose Δ9-THC (20:3 ratio) displayed significantly greater anticonvulsant effects than either phytocannabinoid alone. Furthermore, blocking 5-HT1A receptors before CBD application significantly abolished CBD's effects. Thus, our results demonstrate the efficacy of low-dose CBD and Δ9-THC combined and that CBD exerts its effects, at least in part, through 5-HT1A receptors. These results could address drug-resistance while providing insight into CBD's mechanism of action, laying the groundwork for further testing of cannabinoids as anticonvulsants.