5-HT1A Receptor Agonist Research Articles

Psychedelic Psychiatry’s Brave New World

After a legally mandated, decades-long global arrest of research on psychedelic drugs, investigation of psychedelics in the context of psychiatric disorders is yielding exciting results. Outcomes of neuroscience and clinical research into 5-Hydroxytryptamine 2A (5-HT2A) receptor agonists, such as psilocybin, show promise for addressing a range of serious disorders, including depression and addiction.

Elucidating Anti‐Inflammatory SAR at the 5‐HT2A Receptor

IntroductionDysregulated or maladaptive inflammatory signaling is a major component of many modern human diseases, such as allergic asthma, coronary artery disease, inflammatory bowel disease, diabetes, neurodegenerative diseases, depression, and addiction. Current pharmacological therapies individually target specific enzymatic pathways involved in the synthesis of certain pro‐inflammatory mediators, cell‐cell immune signal propagation by sequestration of pro‐inflammatory mediators, or broad suppression of the immune response. Previously published data from our laboratory suggests including psychedelics, a class of serotonin (5‐hydroxytryptamine; 5‐HT) 2A (5‐HT2A) receptor agonists, as a new category of anti‐inflammatory drugs. Whereas whole organism models will provide insight into the physiological and behavioral response profile, the mechanism of action and structural basis mediating the anti‐inflammatory and behavioral activity of psychedelics have yet to be elucidated on a molecular level. This knowledge can be used to optimize the therapeutic response by informing structure‐activity relationship (SAR) studies and drug candidate selection matrices for development of novel, small molecule anti‐inflammatory compounds.ObjectivesWe sought to evaluate the relationship of in vitro functional selectivity at the 5‐HT2A receptor on the efficacy of an in vivo anti‐inflammatory response.MethodsWe utilized human embryonic kidney cells stably expressing the 5‐HT2A receptor to evaluate real‐time calcium mobilization as a proxy measure of Gαq pathway activation. Further, we evaluated Arrestin‐3 recruitment using the PRESTO‐Tango luciferase reporter gene assay. Concurrent studies in our laboratory measured in vivo anti‐inflammatory activity using an airways hyperresponsiveness assay in a rat model of acute allergic asthma. All assays were completed using a comprehensive panel of ligands comprising four chemical classes: tryptamines, ergolines, phenethylamines, and phenisopropylamines.ResultsWhile there are differential responses for each ligand to activate individual signaling pathways, results from examination of the canonical Gαq pathway and recruitment of the multi‐adaptor protein Arrestin‐3 exhibited no significant correlation between potency and efficacy for either pathway with in vivo measures of anti‐inflammatory activity.ConclusionThis data illustrates that small modifications on the molecular structure of recognized pharmacophores can impart unique conformational changes of the receptor protein, which will alter the interaction with downstream effectors. Ongoing studies are examining additional GPCR‐mediated signaling. With this data, the varying degree of effector pathway bias can be determined for each ligand which supports better understanding of adverse and favorable therapeutic activities, as well as informs structure‐activity studies and drug candidate selection matrices. The collective analysis of a comprehensive panel of 5HT2A receptor ligands has never been examined in this fashion; thus, we aim to elucidate the SAR to inform drug design for novel molecules that are biased to pathways targeting a biologically therapeutic response.Support or Funding InformationSupport from this work was provided by the Eleusis Public Benefit Corporation.

5‐HT2 Receptor Activation Differentially Modulates Linker Histone Kinetics and Histone Deacetylase Activity

IntroductionAlterations to chromatin dynamics and histone modification represent crucial processes metazoan cells employ to influence regulation and gene expression. As such, modification to the mobility of the linker histone, the chief component of chromatin compaction and higher‐order chromatin architecture, significantly impacts downstream transcriptional regulation and cellular processing. At present, the contributions of serotonergic signaling to not only heritable epigenetic modification but also higher‐order chromatin structure are a matter of intense research focus. Through both in vitro and in vivo assays, our lab has shown that serotonin 5‐HT2A receptor agonists (psychedelics) exhibit differential efficacy and potency in their ability to prevent inflammatory pathway activation. Modulation to both overall chromatin structure and epigenetic signaling may represent a potential mechanism that psychedelics employ to promote their long‐lasting, therapeutic effects.ObjectivesWe sought to evaluate the impact of chromatin compaction and histone acetylation on 5‐HT2A functional selectivity in human embryonic kidney cells stably expressing the 5‐HT2A receptor.MethodsWe utilized fluorescence recovery after photobleaching (FRAP) to probe the kinetics of the linker histone H1c transiently transfected into the aforementioned HEKH2A cell line. We concurrently measured histone deacetylase (HDAC) activity following exposure to numerous 5‐HT2A agonists.Results5‐HT itself minimally impacts H1c mobility, whereas compounds such as psilocin and the highly selective 5‐HT2 agonist (R)‐2,5‐dimethoxy‐4‐iodoamphetamine [(R)‐DOI] significantly slow H1c kinetics. Interestingly, these changes to linker histone mobility do not correlate with putative epigenetic regulation, as 5‐HT2A compounds with anti‐inflammatory properties reduce histone deacetylase (HDAC) activity, whereas antagonism of the 5‐HT2A receptor induces HDAC activity.ConclusionTogether, this data illustrates that agonism of 5‐HT2A receptors induce unique changes to chromatin architecture and HDAC activity, a conceivable mechanism psychedelics might employ to promote their potent therapeutic properties. Translationally, while HDAC inhibitors have emerged as attractive agents in cancer therapy and asthma treatment, their utility is limited by off‐target toxicity. 5‐HT2A receptor activation represents a potentially more promising therapeutic strategy to modulate histone acetylation patterns for therapeutic effects.Support or Funding InformationSupport from this work was provided in part by the Eleusis Benefit Corporation and the LSU Foundation.

Pharmacological Studies on the Role of 5-HT1 A Receptors in Male Sexual Behavior of Wildtype and Serotonin Transporter Knockout Rats.

Brain serotonin (5-HT) neurotransmission plays an important role in male sexual behavior and it is well established that activating 5-HT1A receptors in rats facilitate ejaculatory behavior. However, the relative contribution of 5-HT1A somatodendritic autoreceptors and heteroreceptors in this pro-sexual behavior is unclear. Moreover, it is unclear whether the contribution of somatodendritic 5-HT1A autoreceptors and postsynaptic 5-HT1A heteroreceptors alter when extracellular 5-HT levels are chronically increased. Serotonin transporter knockout (SERT–/–) rats exhibit enhanced extracellular 5-HT levels and desensitized 5-HT1A receptors. These rats model neurochemical changes underlying chronic SSRI-induced sexual dysfunction. We want to determine the role of presynaptic versus postsynaptic 5-HT1A receptors in the pro-sexual effects of 5-HT1A receptor agonists in SERT+/+ and in SERT–/– rats. Therefore, acute effects of the biased 5-HT1A receptor agonists F-13714, a preferential 5-HT1A autoreceptor agonist, or F-15599, a preferential 5-HT1A heteroreceptor agonist, and S15535 a mixed 5-HT1A autoreceptor agonist/heteroreceptor antagonist, on male sexual behavior were assessed. A clear and stable genotype effect was found after training where SERT+/+ performed sexual behavior at a higher level than SERT–/– rats. Both F-15599 and F-13714 induced pro-sexual activity in SERT+/+ and SERT–/– animals. Compared to SERT+/+, the F13714-dose-response curve in SERT–/– rats was shifted to the right. SERT+/+ and SERT–/– rats responded similar to F15599. Within both SERT+/+ and SERT–/– rats the potency of F-13714 was much stronger compared to F-15599. S15535 had no effect on sexual behavior in either genotype. In SERT+/+ and SERT–/– rats that were selected on comparable low sexual activity (SERT+/+ 3 or less ejaculations and SERT–/– 5 or less ejaculations in 10 weeks) S15535 also did not influence sexual behavior. The two biased compounds with differential effects on 5-HT1A auto- and hetero-receptors, exerted pro-sexual activity in both SERT+/+ and SERT–/– rats. Applying these specific pharmacological tools has not solved whether pre- or post-synaptic 5-HT1A receptors are involved in pro-sexual activity. Moreover, the inactivity of S15535 in male sexual behavior in either genotype was unexpected. The question is whether the in vivo pharmacological profile of the different 5-HT1A receptor ligands used, is sufficient to differentiate pre- and/or post-synaptic 5-HT1A receptor contributions in male rat sexual behavior.

Discovery of aryl-piperidine derivatives as potential antipsychotic agents using molecular hybridization strategy

Schizophrenia is a chronic, disabling mental disorder that affects about one percent of world’s population. Drugs acting on multiple targets have been demonstrated to provide superior efficacy in schizophrenia than agents acting on single target. In this study, based on FW01, a selective potent 5-HT1A receptor agonist discovered via dynamic pharmacophore-based virtual screening, molecular hybridization strategy was employed to optimize its in vitro activity over D2 and 5-HT2A receptors. The optimized compound 9f was found to show dual potent D2 and 5-HT2A receptors antagonistic activity. In addition, compound 9f showed good in vivo metabolic stability with t1/2 of 2 h in ICR mice and good capability to penetrate the blood-brain barrier with Kp value of 4.03. These results demonstrated that the dual D2 and 5-HT1A receptor antagonist 9f could serve as a promising lead compound to discover potent antipsychotic agents.

Trace Amine-Associated Receptor 5 Provides Olfactory Input Into Limbic Brain Areas and Modulates Emotional Behaviors and Serotonin Transmission.

Trace amine-associated receptors (TAARs) are a class of G-protein-coupled receptors found in mammals. While TAAR1 is expressed in several brain regions, all the other TAARs have been described mainly in the olfactory epithelium and the glomerular layer of the olfactory bulb and are believed to serve as a new class of olfactory receptors sensing innate odors. However, there is evidence that TAAR5 could play a role also in the central nervous system. In this study, we characterized a mouse line lacking TAAR5 (TAAR5 knockout, TAAR5-KO) expressing beta-galactosidase mapping TAAR5 expression. We found that TAAR5 is expressed not only in the glomerular layer in the olfactory bulb but also in deeper layers projecting to the limbic brain olfactory circuitry with prominent expression in numerous limbic brain regions, such as the anterior olfactory nucleus, the olfactory tubercle, the orbitofrontal cortex (OFC), the amygdala, the hippocampus, the piriform cortex, the entorhinal cortex, the nucleus accumbens, and the thalamic and hypothalamic nuclei. TAAR5-KO mice did not show gross developmental abnormalities but demonstrated less anxiety- and depressive-like behavior in several behavioral tests. TAAR5-KO mice also showed significant decreases in the tissue levels of serotonin and its metabolite in several brain areas and were more sensitive to the hypothermic action of serotonin 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propilamino)tetralin (8-OH-DPAT). These observations indicate that TAAR5 is not just innate odor-sensing olfactory receptor but also serves to provide olfactory input into limbic brain areas to regulate emotional behaviors likely via modulation of the serotonin system. Thus, anxiolytic and/or antidepressant action of future TAAR5 antagonists could be predicted. In general, “olfactory” TAAR-mediated brain circuitry may represent a previously unappreciated neurotransmitter system involved in the transmission of innate odors into emotional behavioral responses.

2-(4-Iodo-2,5-dimethoxyphenyl)-N-[(2-methoxyphenyl)methyl]ethanamine (25I-NBOME): A Harmful Hallucinogen Review

NBOMes are N-benzylmethoxy derivatives of the 2C family compounds with N-2-methoxybenzyl moiety substituted by the methoxy group at the 2- and 5-position and the halogen group at the 4-position of the phenyl ring. These substances are a new class of potent serotonin 5-HT2A receptor agonist hallucinogens with potential harmful effects. The substitution with halogen of the already psychoactive phenethylamine produces a derivative (2C-I) with increased hallucinogenic effects. This class of hallucinogens has chemical structures very similar to natural hallucinogenic alkaloid mescaline and these are sold mainly via internet as a 'legal' alternative to other hallucinogenic drug-lysergic acid diethylamide (LSD). 25I-NBOMe is the first synthesized and one of the most common compound from NBOMes. Knowledge of pharmacological properties of 25I-NBOMe is very limited so far. There are only a few in vivo and in vitro so far published studies. The behavioral experiments are mainly related with the hallucinogenic effect of 25I-NBOMe while the in vitro studies concerning mainly the affinity for 5-HT2A receptors. The 25I-NBOMe Critical Review 2016 reported 51 non-fatal intoxications and 21 deaths associated with 25I-NBOMe across Europe. Case reports describe various toxic effects of 25I-NBOMe usage including tachycardia, hypertension, hallucinations, rhabdomyolysis, acute kidney injury and death. The growing number of fatal and non-fatal intoxication cases indicates that 25I-NBOMe should be considered as a serious danger to public health. This review aims to present the current state of knowledge on pharmacological effects and chemical properties of 25I-NBOMe and to describe reported clinical cases and analytical methods available for identification of this agent in biological material.

The Influence of Perinatal Stress and Antidepressants on Different Types of Adaptive Behavior and Cognitive Abilities of Prepubertal Female Rats

We investigated the influence of repeated peripheral inflammatory nociceptive stimulation of neonate female rats born to mothers exposed during pregnancy to chronic stress and the effect of an antidepressant drug fluoxetine, a selective serotonin (5-HT) reuptake inhibitor, and an anxiolytic drug buspirone, a 5-HT1A receptor agonist, on adaptive behavior and cognitive abilities of the offspring during the prepubertal period. The data on the effect of maternal stress exposure during the critical perinatal period of individual development on adaptive behavior and spatial learning abilities of the offspring provide support for the hypothesis on the possible beneficial effect of moderate stressful events experienced at an early age on stress tolerance in subsequent ontogenesis. The corrective effect of the above drugs on adaptive behavior and cognitive abilities of the prenatally stressed prepubertal female offspring exposed to repeated peripheral inflammatory pain at the neonatal stage is characterized.

NBOMes–Highly Potent and Toxic Alternatives of LSD

Recently, a new class of psychedelic compounds named NBOMe (or 25X-NBOMe) has appeared on the illegal drug market. NBOMes are analogs of the 2C family of phenethylamine drugs, originally synthesized by Alexander Shulgin, that contain a N-(2-methoxy)benzyl substituent. The most frequently reported drugs from this group are 25I-NBOMe, 25B-NBOMe, and 25C-NBOMe. NBOMe compounds are ultrapotent and highly efficacious agonists of serotonin 5-HT2A and 5-HT2C receptors (Ki values in low nanomolar range) with more than 1000-fold selectivity for 5-HT2A compared with 5-HT1A. They display higher affinity for 5-HT2A receptors than their 2C counterparts and have markedly lower affinity, potency, and efficacy at the 5-HT2B receptor compared to 5-HT2A or 5-HT2C. The drugs are sold as blotter papers, or in powder, liquid, or tablet form, and they are administered sublingually/buccally, intravenously, via nasal insufflations, or by smoking. Since their introduction in the early 2010s, numerous reports have been published on clinical intoxications and fatalities resulting from the consumption of NBOMe compounds. Commonly observed adverse effects include visual and auditory hallucinations, confusion, anxiety, panic and fear, agitation, uncontrollable violent behavior, seizures, excited delirium, and sympathomimetic signs such mydriasis, tachycardia, hypertension, hyperthermia, and diaphoresis. Rhabdomyolysis, disseminated intravascular coagulation, hypoglycemia, metabolic acidosis, and multiorgan failure were also reported. This survey provides an updated overview of the pharmacological properties, pattern of use, metabolism, and desired effects associated with NBOMe use. Special emphasis is given to cases of non-fatal and lethal intoxication involving these compounds. As the analysis of NBOMes in biological materials can be challenging even for laboratories applying modern sensitive techniques, this paper also presents the analytical methods most commonly used for detection and identification of NBOMes and their metabolites.

The selective 5-HT1A receptor agonist, NLX-112, exerts anti-dyskinetic and anti-parkinsonian-like effects in MPTP-treated marmosets

l-DOPA is the gold-standard pharmacotherapy for treatment of Parkinson's disease (PD) but can lead to the appearance of troubling dyskinesia which are attributable to ‘false neurotransmitter’ release of dopamine by serotonergic neurons. Reducing the activity of these neurons diminishes l-DOPA-induced dyskinesia (LID), but there are currently no clinically approved selective, high efficacy 5-HT1A receptor agonists. Here we describe the effects of NLX-112, a highly selective and efficacious 5-HT1A receptor agonist, on LID in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated marmosets, a non-human primate model of PD.NLX-112 exhibited modest plasma half-life (~2h) and marked plasma protein binding (96%). When administered to parkinsonian marmosets with l-DOPA (7 mg/kg p.o.), NLX-112 (0.025, 0.1 and 0.4 mg/kg p.o.) reduced LID scores at early time-points after administration, whilst only minimally interfering with the l-DOPA-induced reversal of motor disability. In contrast, the prototypical 5-HT1A receptor agonist, (+)8-OH-DPAT (0.6 and 2 mg/kg p. o.), reduced LID but also abolished l-DOPA's anti-disability activity.Administered by itself, NLX-112 (0.1, 0.2 mg/kg p.o.) produced very little dyskinesia or locomotor activity, but reduced motor disability scores by about half the extent elicited by l-DOPA, suggesting that it may have motor facilitation effects of its own. Both NLX-112 and (+)8-OH-DPAT induced unusual and dose-limiting behaviors in marmoset that resembled ‘serotonin behavioral syndrome’ observed previously in rat.Overall, the present study showed that NLX-112 has anti-LID activity at the doses tested as well as reducing motor disability. The data suggest that additional investigation of NLX-112 is desirable to explore its potential as a treatment for PD and PD-LID.

Endocannabinoids mediate long-lasting behavioural and physiological changes in male rats induced by the repeated activation of the mesolimbic system by copulation to satiety

Sexually satiated male rats exhibit long-lasting physiological changes, suggestive of brain plasticity, the most conspicuous of which are a sexual behaviour inhibition and a generalised drug hypersensitivity. Copulation activates the mesolimbic circuit increasing dopamine (DA) release in the nucleus accumbens (NAcc) and, enhanced midbrain DA neuron activity promotes endocannabinoid (eCB) release in the ventral tegmental area (VTA). The objective of this work was to explore the possible participation of DA and/or eCB transmission in the induction of these two long-lasting phenomena. To this aim we analysed the effect of blocking DA or CB1 receptors during the process of copulation to exhaustion, on the expression 24 h later, of the sexual inhibitory state and the hypersensitivity to two different drugs: 8-OH-DPAT, a 5-HT1A receptor agonist, and yohimbine, an α2-adrenoceptor antagonist. Blockade of DA receptors failed to prevent these phenomena, while blockade of CB1 receptors interfered with the appearance of the sexual inhibition and the hypersensitivity to both drugs in the sexually satiated animals. Specific blockade of CB1 receptors in the VTA during copulation to satiety mimicked these results, suggesting that both eCB-mediated effects were exerted in this brain region. It is concluded that eCBs play a role in the induction of behavioural and physiological changes, triggered by copulation to satiety, by acting at the VTA, while increased NAcc DA levels appear not to contribute to the changes induced by intense copulation. Results pose sexual satiety as a useful model for the study of brain plasticity phenomena induced by natural rewards.

Spaced Training Enhances Contextual Fear Memory via Activating Hippocampal 5-HT2A Receptors.

Spaced training is robustly superior to massed training, which is a well-documented phenomenon in humans and animals. However, the mechanisms underlying the spacing effect still remain unclear. We have reported previously that spacing training exerts memory-enhancing effects by inhibiting forgetting via decreasing hippocampal Rac1 activity. Here, using contextual fear conditioning in rat, we found that spaced but not massed training increased hippocampal 5-HT2A receptors’ expression. Furthermore, hippocampal administration of 5-HT2A receptor antagonist MDL11939 before spaced training blocked the enhanced memory, while hippocampal administration of 5-HT2A receptor agonist TCB-2 before massed training promoted the memory. Moreover, MDL11939 activated hippocampal Rac1, while TCB-2 decreased hippocampal Rac1 activity in naïve rats. These results indicated the possibility of interaction between 5-HT2A receptors and Rac1, which was demonstrated by co-immunoprecipitation experiments. Our study first demonstrates that activation of hippocampal 5-HT2A is a mechanism underlying the spacing effect, and forgetting related molecular Rac1 is engaged in this process through interacting with 5-HT2A receptors, which suggest a promising strategy to modulate abnormal learning in cognitive disorders.

Role of the treatment environment in the effects of aripiprazole on ethanol-induced behavioral sensitization and conditioned place preference in female mice

BackgroundEvidence suggests that aripiprazole, a partial dopamine D2 and serotonin 5-HT1A receptor agonist and 5-HT2A receptor antagonist, show significant efficacy in reducing alcohol use. We have previously demonstrated that treatment with aripiprazole blocked the reinstatement of cocaine-induced behavioral sensitization in a context-dependent manner, suggesting that the treatment environment may modulate the therapeutic effects of aripiprazole. The present study aimed to evaluate the effects of treatment with aripiprazole on ethanol-induced behavioral sensitization and conditioned place preference in female mice, and the role of the treatment environment in those effects. MethodsAdult female mice were either sensitized with ethanol injections in the open-field apparatus, or conditioned with ethanol in the conditioned place preference (CPP) apparatus. Animals were then treated with vehicle or 0.1 mg/kg aripiprazole paired to the test environment (open-field or CPP apparatus) or not (home-cage treatments) for 4 alternate days, and the subsequent expression of behavioral sensitization or CPP to ethanol was evaluated during or following an ethanol re-exposure, respectively. ResultsRepeated treatment with aripiprazole attenuated the expression of ethanol-induced behavioral sensitization regardless of the treatment environment. Treatment with aripiprazole was only effective at preventing the reinstatement of ethanol-induced CPP when paired with the ethanol-associated environment, but not when administered in the home-cage. ConclusionsThe present findings corroborate previous studies suggesting the effectiveness of aripiprazole for the treatment of alcohol use disorder. Our results also point to an important role of the treatment environment in the therapeutic effects of aripiprazole in rodent models of ethanol abuse.

Design, Synthesis, and Structure-Activity Relationship Studies of Novel Indolyalkylpiperazine Derivatives as Selective 5-HT1A Receptor Agonists.

5-HT1A receptor (5-HT1AR) agonists have been implicated in the treatment of a variety of central nervous system (CNS) diseases such as depression and anxiety, et al. Based on our previously found compound FW01 (Ki = 51 ± 16 nM) obtained by virtual screening, a series of FW01 derivatives were designed and synthesized by the modification of the amide tail group as well as indole headgroup of FW01. SAR exploration found that amide tail group and indole headgroup play pivotal roles in determining the binding affinity and selectivity on dopamine and serotonin receptor subtypes. Among all tested compounds, 9_24 has a Ki value of 5 ± 0.6 nM with a good selectivity toward 5-HT1AR. The [35S] GTPγS assay showed that 9_24 is a full agonist toward 5-HT1AR with an EC50 value of 0.059 nM, which shows 266.2 and 146.4-fold selectivity to 5-HT2A and D3 respectively. Molecular dynamics simulations and molecular docking studies with 5-HT1AR-9_24 were performed to disclose the mechanism of its high activity and selectivity. Finally, a detailed stepwise 9_24 induced signal transduction mechanism of 5-HT1AR is proposed.

Role of 5-HT<sub>1A</sub> receptor in myelin damage caused by maladaptation to stress in mice

Recent studies reported that human psychiatric disorders display oligodendroglial abnormalities and alterations in oligodendrocyte structure. Our previous studies suggested that 5-HT1A receptor in the hippocampus may be involved in the protection of myelin loss induced by unadaptable excessive stress. In oligodendrocytes, adenomatous polyposis coli (APC) appears at maturation and the onset of myelination. In the present study, we investigated whether 5-HT1A receptor regulate remyelination in unadaptable stress-induced myelin damage. A single exposure to restraint stress for 60 min induced a decrease in head-dipping behavior in the hole-board test. This stress response disappeared in mice that had been exposed to repeated restraint stress for 60 min/day for 14 days. In contrast, repeated exposure to restraint stress for 240 min/day for 14 days did not develop stress adaptation, and still showed a decrease in head-dipping behaviors. Immunohistochemistry analysis revealed that the expression level of APC was decreased in the dentate gyrus of the hippocampus of stress-maladaptive mice. These behavioral and biochemical changes were inhibited by chronic treatment with flesinoxan, a 5-HT1A receptor agonist. The present findings indicate that activation of 5-HT1A receptor may promote remyelination in stress-induced myelin damage.

Citalopram reduces glutamatergic synaptic transmission in the auditory cortex via activation of 5-HT1A receptors.

Serotonin modulates cognitive processes and is related to various psychiatric disorders, including major depression. Administration of citalopram reduces the amplitude of auditory evoked potentials in depressed people and animal models, suggesting that 5-HT has an inhibitory role. Here, we characterize the modulation of excitatory post-synaptic currents by application of either 5-HT or agonists of 5-HT1A and 5-HT2 receptors, or by endogenous 5-HT evoked by citalopram on pyramidal neurons from layer II/III of rat auditory cortex. We found that application of 5-HT concentration-dependently reduces excitatory post-synaptic currents amplitude without changing the paired-pulse ratio, suggesting a post-synaptic modulation. We observed that selective agonists of 5-HT1A and 5-HT2 receptors [8-OH-DPAT (10 µM) and DOI (10 µM), respectively] mimic the effect of 5-HT on the excitatory post-synaptic currents. Effect of 5-HT was entirely blocked by co-application of the antagonists NAN-190 (1 µM) and ritanserin (200 nM). Similarly, citalopram application (1 μM) reduced the amplitude of the evoked excitatory post-synaptic currents. Reduction in the magnitude of the excitatory post-synaptic currents by endogenous 5-HT was interpolated in the dose-response curve elicited by exogenous 5-HT, yielding that citalopram raised the extracellular 5-HT concentration to 823 nM. Effect of citalopram was blocked by the previous application of NAN-190 but not ritanserin, indicating that citalopram reduces glutamatergic synaptic transmission via 5-HT1A receptors in layer II/III of the auditory cortex. These results suggest that the local activity of 5-HT contributes to decrease in the basal excitability of the auditory cortex for enhancing the detection of external relevant acoustic signals.

Serotonin release measured in the human brain: a PET study with [11C]CIMBI-36 and d-amphetamine challenge.

Positron emission tomography (PET) enables non-invasive estimation of neurotransmitter fluctuations in the living human brain. While these methods have been applied to dopamine and some other transmitters, estimation of 5-hydroxytryptamine (5-HT; Serotonin) release has proved to be challenging. Here we demonstrate the utility of the novel 5-HT2A receptor agonist radioligand, [11C]CIMBI-36, and a d-amphetamine challenge to evaluate synaptic 5-HT changes in the living human brain. Seventeen healthy male volunteers received [11C]CIMBI-36 PET scans before and 3 h after an oral dose of d-amphetamine (0.5 mg/kg). Dynamic PET data were acquired over 90 min, and the total volume of distribution (VT) in the frontal cortex and the cerebellum derived from a kinetic analysis using MA1. The frontal cortex binding potential (BPNDfrontal) was calculated as (VTfrontal/VTcerebellum) - 1. ∆BPNDfrontal = 1 - (BPNDfrontal post-dose/BPNDfrontal baseline) was used as an index of 5-HT release. Statistical inference was tested by means of a paired Students t-test evaluating a reduction in post-amphetamine [11C]CIMBI-36 BPNDfrontal. Following d-amphetamine administration, [11C]CIMBI-36 BPNDfrontal was reduced by 14 ± 13% (p = 0.002). Similar effects were observed in other cortical regions examined in an exploratory analysis. [11C]CIMBI-36 binding is sensitive to synaptic serotonin release in the human brain, and when combined with a d-amphetamine challenge, the evaluation of the human brain serotonin system in neuropsychiatric disorders, such as major depression and Parkinson's disease is enabled.

Systemic serotonin inhibits brown adipose tissue sympathetic nerve activity via a GABA input to the dorsomedial hypothalamus, not via 5HT1A receptor activation in raphe pallidus.

Serotonin (5-hydroxytryptamine, 5-HT), an important neurotransmitter and hormone, modulates many physiological functions including body temperature. We investigated neural mechanisms involved in the inhibition of brown adipose tissue (BAT) sympathetic nerve activity (SNA) and BAT thermogenesis evoked by 5-HT. Electrophysiological recordings, intravenous (iv) injections and nanoinjections in the brains of anaesthetized rats. Cooling-evoked increases in BAT SNA were inhibited by the intra-rostral raphé pallidus (rRPa) and the iv administration of the 5-HT1A receptor agonist, 8-OH-DPAT or 5-HT. The intra-rRPa 5-HT, the intra-rRPa and the iv 8-OH-DPAT, but not the iv 5-HT-induced inhibition of BAT SNA were prevented by nanoinjection of a 5-HT1A receptor antagonist in the rRPa. The increase in BAT SNA evoked by nanoinjection of NMDA in the rRPa was not inhibited by iv 5-HT, indicating that iv 5-HT does not inhibit BAT SNA by acting in the rRPa or in the sympathetic pathway distal to the rRPa. In contrast, under a warm condition, blockade of 5HT1A receptors in the rRPa increased BAT SNA and BAT thermogenesis, suggesting that endogenous 5-HT in the rRPa contributes to the suppression of BAT SNA and BAT thermogenesis. The increases in BAT SNA and BAT thermogenesis evoked by nanoinjection of NMDA in the dorsomedial hypothalamus (DMH) were inhibited by iv 5-HT, but those following bicuculline nanoinjection in the DMH were not inhibited. The systemic 5-HT-induced inhibition of BAT SNA requires a GABAergic inhibition of BAT sympathoexcitatory neurones in the DMH. In addition, during warming, 5-HT released endogenously in rRPa inhibits BAT SNA.

DARK Classics in Chemical Neuroscience: NBOMes.

N-Benzylphenethylamines, commonly known as NBOMes, are synthetic psychedelic compounds derived from the phenethylamine class of psychedelics (2C-X compounds), which originally have been derived from the naturally occurring alkaloid mescaline. Analogously to their parent compounds and other classical psychedelics, such as psilocybin and lysergic acid diethylamide (LSD), NBOMes are believed to exert their main pharmacological effects through activation of serotonin 2A (5-HT2A) receptors. Since their introduction as New Psychoactive Substances (NPSs) in 2010, NBOMes have been widely used for recreational purposes; this has resulted in numerous cases of acute toxicity, sometimes with lethal outcomes, leading to the classification of several NBOMes as Schedule I substances in 2013. However, in addition to their recreational use, the NBOMe class has yielded several important biochemical tools, including [11C]Cimbi-36, which is now being used in positron emission tomography (PET) studies of the 5-HT2A and 5-HT2C receptors in the mammalian brain, and 25CN-NBOH, one of the most selective 5-HT2A receptor agonists developed to date. In this Review, the history, chemistry, structure-activity relationships, ADME (absorption, distribution, metabolism, and excretion) properties, and safety profiles of NBOMes will be outlined and discussed.

Serotonergic modulation of sacral dorsal root stimulation-induced locomotor output in newborn rat

Descending neuromodulators from the brainstem play a major role in the development and regulation of spinal sensorimotor functions. Here, the contribution of serotonergic signaling in the lumbar spinal cord was investigated in the context of the generation of locomotor activity. Experiments were performed on in vitro spinal cord preparations from newborn rats (0–5 days). Rhythmic locomotor episodes (fictive locomotion) triggered by tonic electrical stimulations (2Hz, 30s) of a single sacral dorsal root were recorded from bilateral flexor-dominated (L2) and extensor-dominated (L5) ventral roots. We found that the activity pattern induced by sacral stimulation evolves over the 5 post-natal (P) day period. Although alternating rhythmic flexor-like motor bursts were expressed at all ages, the locomotor pattern of extensor-like bursting was progressively lost from P1 to P5. At later stages, serotonin (5-HT) and quipazine (5-HT2A receptor agonist) at concentrations sub-threshold for direct locomotor network activation promoted sacral stimulation-induced fictive locomotion. The 5-HT2A receptor antagonist ketanserin could reverse the agonist's action but was ineffective when fictive locomotion was already expressed in the absence of 5-HT (mainly before P2). Although inhibiting 5-HT7 receptors with SB266990 did not affect locomotor pattern organization, activating 5-HT1A receptors with 8-OH-DPAT specifically deteriorated extensor phase motor burst activity. We conclude that during the first 5 post-natal days in rat, serotonergic signaling in the lumbar cord becomes increasingly critical for the expression of fictive locomotion. Our findings therefore further underline the importance of both descending serotonergic and sensory afferent pathways in shaping locomotor activity during postnatal development.This article is part of the special issue entitled ‘Serotonin Research: Crossing Scales and Boundaries’.