5-HT1A Receptor Agonist Research Articles

Central dopaminergic, serotoninergic, as well as GABAergic systems mediate NMU-induced hypophagia in newborn chicken

Aim Dopaminergic, serotoninergic, and GABAergic systems influence feeding; however, it is unknown how these chemicals interact with neuromedin U (NMU)-induced feeding in birds. In the current study, ten trials were conducted to determine the links between the above-mentioned systems and NMU. Materials and Methods In the foremost experimentation, chickens were given intracerebroventricularly injections of NMU (0.1, 1, and 10 µg). NMU (10 µg), SCH23390 (5 nmol), a D1 receptor antagonist, and NMU + SCH23390 were administered in the second experiment. In subsequent experiments, instead of SCH23390, were applied AMI-193 (5 nmol D2 receptor antagonist), NGB2904 (6.4 nmol D3 receptor antagonist), L-741,742 (6 nmol D4 receptor antagonist), 6-OHDA (2.5 nmol dopamine inhibitor), SB242084 (5-HT2c receptor antagonist, 1.5 μg), 8-OH-DPAT (5-HT1A receptor agonist, 15.25 nmol), picrotoxin (GABAA receptor antagonist, 0.5 μg), and CGP54626 (GABAB receptor antagonist, 20 ng). Then, cumulative intake of food was recorded for 2 h. Results According to the results, NMU reduced feeding when compared to the control group (p < 0.05). The NMU-induced hypophagia was reduced with co-injection of NMU and SCH23390 (p < 0.05). Hypophagia was diminished with NMU and AMI-193 (p < 0.05). NMU + NGB2904 and NMU + L-741,742 co-injections had no influence (p > 0.05). 6-OHDA reduced the hypophagia (p < 0.05). NMU and SB242084 decreased the hypophagia (p < 0.05), whereas NMU and 8-OH-DPAT had no effect (p > 0.05). The effects were amplified with picrotoxin (p < 0.05). NMU with CGP54626 had no influence on the hypophagia (p > 0.05). Conclusion Thus, NMU-induced hypophagia is probably mediated by D1/D2, 5-HT2c, and GABAA receptors in neonatal chicks.

Therapeutic Effects of Quetiapine and 5-HT1A Receptor Agonism on Hyperactivity in Dopamine-Deficient Mice

Some diseases that are associated with dopamine deficiency are accompanied by psychiatric symptoms, including Parkinson’s disease. However, the mechanism by which this occurs has not been clarified. Previous studies found that dopamine-deficient (DD) mice exhibited hyperactivity in a novel environment. This hyperactivity is improved by clozapine and donepezil, which are used to treat psychiatric symptoms associated with dopamine deficiency (PSDD). We considered that DD mice could be used to study PSDD. In the present study, we sought to identify the pharmacological mechanism of PSDD. We conducted locomotor activity tests by administering quetiapine and drugs that have specific actions on serotonin (5-hydroxytryptamine [5-HT]) receptors and muscarinic receptors. Changes in neuronal activity that were induced by drug administration in DD mice were evaluated by examining Fos immunoreactivity. Quetiapine suppressed hyperactivity in DD mice while the 5-HT1A receptor antagonist WAY100635 inhibited this effect. The number of Fos-positive neurons in the median raphe nucleus increased in DD mice that exhibited hyperactivity and was decreased by treatment with quetiapine and 5-HT1A receptor agonists. In conclusion, hyperactivity in DD mice was ameliorated by quetiapine, likely through 5-HT1A receptor activation. These findings suggest that 5-HT1A receptors may play a role in PSDD, and 5-HT1A receptor-targeting drugs may help improve PSDD.

Ginsenoside Re attenuates 8-OH-DPAT-induced serotonergic behaviors in mice via interactive modulation between PKCδ gene and Nrf2

It has been recognized that serotonergic blocker showed serious side effects, and that ginsenoside modulated serotonergic system with the safety. However, the effects of ginsenoside on serotonergic impairments remain to be clarified. Thus, we investigated ginsenoside Re (GRe), a major bioactive component in the mountain-cultivated ginseng on (±)-8-hydroxy-dipropylaminotetralin (8-OH-DPAT), a 5-HT1A receptor agonist. In the present study, we observed that the treatment with GRe resulted in significant inhibition of protein kinase C δ (PKCδ) phosphorylation induced by the 5-HT1A receptor agonist (±)-8-hydroxy-dipropylaminotetralin (8-OH-DPAT) in the hypothalamus of the wild-type (WT) mice. The inhibition of GRe was comparable with that of the PKCδ inhibitor rottlerin or the 5-HT1A receptor antagonist WAY100635 (WAY). 8-OH-DPAT-induced significant reduction in nuclear factor erythroid-2-related factor 2 (Nrf2)-related system (i.e., Nrf2 DNA binding activity, γ-glutamylcysteine ligase modifier (GCLm) and γ-glutamylcysteine ligase catalytic (GCLc) mRNA expression, and glutathione (GSH)/oxidized glutathione (GSSG) ratio) was significantly attenuated by GRe, rottlerin, or WAY in WT mice. However, PKCδ gene knockout significantly protected the Nrf2-dependent system from 8-OH-DPAT insult in mice. Increases in 5-hydroxytryptophan (5-HT) turnover rate, overall serotonergic behavioral score, and hypothermia induced by 8-OH-DPAT were significantly attenuated by GRe, rottlerin, or WAY in WT mice. Consistently, PKCδ gene knockout significantly attenuated these parameters in mice. However, GRe or WAY did not provide any additional positive effects on the serotonergic protective potential mediated by PKCδ gene knockout in mice. Therefore, our results suggest that PKCδ is an important mediator for GRe-mediated protective activity against serotonergic impairments/oxidative burden caused by the 5-HT1A receptor.

Serotonin 5-HT1A and 5-HT1B receptor-mediated inhibition of glutamatergic transmission onto rat basal forebrain cholinergic neurones.

Cholinergic neurones in the basal forebrain (BF) project into various brain regions and receive excitatory inputs from the cortex and brain stem. These cholinergic neurones receive serotonergic fibres from the dorsal raphe nuclei. This study was aimed to elucidate serotonin (5-HT)-induced modulation of glutamatergic transmission onto rat BF cholinergic neurones identified with Cy3-192IgG. Excitatory postsynaptic currents (EPSCs) were evoked by focal stimulation. Bath application of either 5-HT, the 5-HT1A receptor agonist 8-OH-DPAT (DPAT), or the 5-HT1B receptor agonist CP93129 (CP), inhibited the amplitude of EPSCs. In the presence of both 5-HT1A and 5-HT1B receptor antagonists, the 5-HT-induced effect disappeared. The paired-pulse ratio (PPR) and coefficient of variation (CV) of the EPSCs were increased by CP, whereas DPAT had no effect on PPR or CV. DPAT inhibited the inward currents induced by puff application of l-glutamate, which were unaffected by CP. DPAT suppressed the amplitude of miniature EPSCs (mEPSCs) without affecting their frequency. CP decreased the frequency of mEPSCs in more than half of the neurones examined, whereas the amplitude was unaffected. DPAT or CP alone inhibited the NMDA receptor-mediated currents. 5-HT-induced inhibition of EPSCs was reduced in the presence of ω-agatoxin TK (Aga). Furthermore, CP-induced inhibition of EPSCs was eliminated in the presence of Aga. DPAT-induced inhibition of EPSCs was unchanged in the presence of Aga. These results suggest that activation of 5-HT1A receptors reduces the sensitivity of postsynaptic glutamate receptors to glutamate, whereas presynaptic activation of 5-HT1B receptors inhibits glutamate release by blocking P/Q-type calcium channels. KEY POINTS: We performed a patch-clamp study to investigate serotonin (5-HT)-induced modulation of glutamatergic transmission onto cholinergic neurones in the rat basal forebrain slices. Excitatory postsynaptic currents (EPSCs) were inhibited by 5-HT as well as agonists of 5-HT1A or 5-HT1B receptors. 5-HT-induced inhibition was antagonized by co-application of 5-HT1A and 5-HT1B receptor antagonists. The effects of 5-HT receptor agonists on the paired-pulse ratio, coefficient of variation of EPSCs, inward currents induced by puff application of l-glutamate as well as miniature EPSCs suggest that activation of 5-HT1A receptors decreases the sensitivity of postsynaptic glutamate receptors to glutamate, whereas 5-HT1B receptors presynaptically inhibit glutamate release. The 5-HT1B agonist-induced inhibition was eliminated in the presence of a P/Q-type calcium channel blocker, whereas the 5-HT1A agonist still inhibited the EPSCs even in the presence of the blocker. The present study reveals different pre- and postsynaptic mechanisms underlying 5-HT1A and 5-HT1B receptor-mediated modulation of excitatory transmission.

Cross state-dependent memory retrieval between cannabinoid CB1 and serotonergic 5-HT1A receptor agonists in the mouse dorsal hippocampus

Understanding the neurobiological mechanisms of drug-related learning and memory formation may help the treatment of cognitive disorders. Dysfunction of the cannabinoid and serotonergic systems has been demonstrated in learning and memory disorders.The present paper investigates the phenomenon called state-dependent memory (SDM) induced by ACPA (a selective cannabinoid CB1 receptor agonist) and 8-OH-DPAT (a nonselective 5-HT1A receptor agonist) with special focus on the role of the 5-HT1A receptor in the effects of both ACPA and 8-OH-DPAT SDM and cross state-dependent memory retrieval between ACPA and 8-OH-DPAT in a step-down inhibitory avoidance task.The dorsal hippocampal CA1 regions of adult male NMRI mice were bilaterally cannulated, and all drugs were microinjected into the intended injection sites. A single-trial step-down inhibitory avoidance task was used to assess memory retrieval and state-dependence.Post-training and/or pre-test microinjections of ACPA (1 and 2 ng/mouse) and 8-OH-DPAT (0.5 and 1 μg/mouse) dose-dependently induced amnesia. Pre-test administration of the same doses of ACPA and 8-OH-DPAT reversed the post-training ACPA- and 8-OH-DPAT-induced amnesia, respectively. This phenomenon has been named SDM. 8-OH-DPAT (1 μg/mouse) reversed the amnesia induced by ACPA (0.5, 1, and 2 ng/mouse) and induced ACPA SDM. ACPA (2 ng/mouse) reversed the amnesia induced by 8-OH-DPAT (0.25, 0.5, and 1 μg/mouse) and induced 8-OH-DPAT SDM. Pre-test administration of a 5-HT1A receptor antagonist, (S)-WAY 100,135 (0.25 and 0.5 μg/mouse), 5 min before ACPA and 8-OH-DPAT dose-dependently inhibited ACPA- and 8-OH-DPAT-induced SDM, respectively.The present study results demonstrated ACPA- and 8-OH-DPAT- induced SDM. Overall, the data revealed that dorsal hippocampal 5-HT1A receptor mechanisms play a pivotal role in modulating cross state-dependent memory retrieval between ACPA and 8-OH-DPAT.

Effects of the serotonin 5-HT1B receptor agonist CP 94253 on the locomotor activity and body temperature of preweanling and adult male and female rats

Serotonin 5-HT1A receptor agonists increase locomotor activity of both preweanling and adult rodents. The part played by the 5-HT1B receptor in locomotion is less certain, with preliminary evidence suggesting that the actions of 5-HT1B receptor agonists are not uniform across ontogeny. To more fully examine the role of 5-HT1B receptors, locomotor activity and axillary temperatures of preweanling and adult male and female rats was assessed. In the first experiment, adult (PD 70) and preweanling (PD 10 and PD 15) male and female rats were injected with the 5-HT1B agonist CP 94253 (2.5–10 mg/kg) immediately before locomotor activity testing and 60 min before axillary temperatures were recorded. In the second experiment, specificity of drug action was determined in PD 10 rats by administering saline, WAY 100635 (a 5-HT1A antagonist), or GR 127935 (a 5-HT1B antagonist) 30 min before CP 94253 (10 mg/kg) treatment. CP 94253 significantly increased the locomotor activity of preweanling rats on PD 10, an effect that was fully attenuated by GR 127935. Conversely, CP 94253 significantly decreased the locomotor activity of male and female adult rats, while CP 94253 did not affect the locomotor activity of PD 15 rats. Regardless of age, CP 94253 (2.5–10 mg/kg) significantly reduced the axillary temperatures of preweanling and adult rats. When considered together, these results show that 5-HT1B receptor stimulation activates motor circuits in PD 10 rats; whereas, 5-HT1B receptor agonism reduces the overall locomotor activity of adult rats, perhaps by blunting exploratory tendencies.

Interactions between Fentanyl and 2,5‐dimethoxy‐4‐methylamphetamine (DOM), a 5‐HT2AReceptor Agonist, in Rhesus Monkeys Responding under a Food Versus Drug Choice Procedure

5‐HT2Areceptor agonists such as DOM enhance antinociceptive effects of opioids suggesting a 5‐HT2Areceptor agonist could be combined with an opioid to improve treatment of pain. However, it is unclear whether 5‐HT2A receptor agonists also enhance adverse effects of opioids, including positive reinforcing effects that contribute to abuse. This study examined whether DOM alters the reinforcing effects of fentanyl in rhesus monkeys (n=5) responding under a food versus drug choice procedure. Responding on one lever delivered sucrose pellets and responding on the other lever delivered intravenous infusions. Sessions comprised 4 blocks, each with 2 forced trials, during which only one option was available, followed by 6 choice trials, during which both options were available. The unit dose of fentanyl (0.0001‐0.0032 mg/kg/infusion) increased across blocks each session. In the first experiment, sessions were preceded by intravenous administration of DOM (0032‐0.32 mg/kg), naltrexone (0.032 mg/kg), or heroin (0.1 mg/kg). Then, fentanyl was available for self‐administration in combination with DOM in unit dose ratios (fentanyl to DOM) of 1:3, 1:10, or 1:30. Fentanyl increased choice of infusions from less than 10% of trials with the two smallest unit doses to over 80% of trials with the two larger unit doses. Naltrexone decreased choice of fentanyl, shifting the dose‐effect curve rightward, and heroin increased choice of the two smallest unit doses of fentanyl. When administered before the session, DOM reduced choice of fentanyl as well as the number of trials completed. However, DOM did not alter choice or the number of trials completed when available in combination with fentanyl. Attenuation of fentanyl choice by naltrexone and enhancement of fentanyl choice by heroin demonstrate sensitivity of responding to modulation by other drugs. DOM did not appear to enhance the reinforcing effects of fentanyl whether given as a pretreatment or made available in combination with fentanyl. Although pretreatment with DOM decreased choice of fentanyl, it did so at doses that reduced trials completed, suggesting effects of DOM might have been due, at least in part, to generalized rate‐decreasing effects. Taken together with previous studies, these results suggest that DOM enhances some (antinociceptive) but not other (reinforcing) effects of opioids and that combining a 5‐HT2A receptor agonist with an opioid to treat pain would not increase potential for abuse.

The laryngeal adductor reflex (LAR) is modulated by the serotonin 5‐HT1A agonist 8‐OH‐DPAT

Airway protection is maintained through a constellation of behaviors. The laryngeal adductor reflex (LAR) responds to mechanical or chemical stimulation of the laryngeal orifice with rapid adduction of the vocal folds. While there are abundant serotonin receptors on laryngeal motoneurons, the effects of serotonin agents on the LAR have not been investigated. To this end, a dose response protocol of 8‐OH‐DPAT (5HT1A receptor agonist) was performed on adult cats (n = 2). Animals were anesthetized using an intravenous dose of sodium pentobarbital and then tracheostomized. Electromyogram (EMG) activity of laryngeal muscles was recorded and LARs were induced by infusing water into the larynx during both normocapnia (0% CO2) and hypercapnia (10% CO2) conditions. A series of six cumulative doses (1 – 300 μg/kg) were delivered intra‐venously. 8‐OH‐DPAT is thought to activate the serotonergic raphe neuron autoreceptors at lower doses and the post‐synaptic receptors on target neurons at higher doses. LAR occurred as a response to water stimulus in 50±23% of control trials. LAR occurrence was modulated by 8‐OH‐DPAT in a dose‐dependent manner: LAR frequency at lower doses may have decreased but this was variable, and LAR frequency appeared to be increased at higher doses (LAR occurred in 13±18%, 17±23%, 50±70%, 57±9%, 84±7%, and 60±4% of stimulus trials at 1, 3, 10, 30, 100, and 300 μg/kg doses, respectively). LAR can be used as a strong clinical predictor of swallow impairment; while other airway protective behaviors require activity across multiple cranial nerves, the LAR is regulated by only laryngeal branches of the vagus nerve. Thus, the LAR is a promising biomarker for testing novel therapeutic agents. These results suggest that pharmacological interventions may be capable of facilitating laryngeal function in patients suffering from dysphagia.

The 5‐HT1A Agonist 8‐OH‐DPAT Enhances Submental Laryngeal Elevator EMG Amplitude During Swallow

Swallow is a critical behavior for sustaining life, important for both for the ingestion of nutrients and for protecting the airways. To produce an effective swallow, neural circuits must coordinate over 20 muscles across multiple cranial/spinal nerves to produce a rostral‐caudal pressure gradient to move the bolus from the mouth to the stomach. The medullary raphe nuclei are the main source of serotonin in the brainstem, and this region has been implicated in modulation of swallow and other airway protective behaviors. In order to explore the role of serotonin in swallow, we conducted experiments in adult cats (n = 6). Animals were anesthetized with intravenous sodium pentobarbital and tracheostomized. Fine wire intramuscular electromyograms (EMGs) were recorded from swallow and respiratory related muscles. The 5‐HT1A receptor agonist 8‐OH‐DPAT was delivered either intravenously through the femoral artery (n = 3) or intra‐arterially through the vertebral artery (n = 3) as a series of six cumulative doses (0.1‐30 ug/kg i.v.; 1‐300 ug/kg i.a.). Swallow was elicited by oral infusion water (3 ml) via syringe and was confirmed by the presence coordinated activity on swallow‐related EMGs. EMG amplitude was normalized prior to analysis. Administration of 8‐OH‐DPAT demonstrated a significant effect on the two primary submental muscles responsible for hyolaryngeal elevation necessary for full occlusion of the airway by the epiglottis. Mylohyoid amplitude increased by 45% (p = 0.006) and geniohyoid amplitude increased by 64% (p = 0.04) at the highest dose when compared to control. This is evidence of the raphe and its serotonergic network coordinating distributed aspects of the swallow control network as these two muscles are innervated via separate cranial nerves: the trigeminal for the mylohyoid and hypoglossal for the geniohyoid. Disordered hyolaryngeal function is a leading cause of aspiration across a multitude of neuro‐ degenerative and ‐traumatic diseases, and pharmacologic intervention with serotonergic agonists represents a promising agent for therapeutic interventions.

Basal and Hypoxic Respiratory Behaviors in Aged 6‐OHDA‐Induced SN Lesion PD Rat Model: Effects of the 5‐HT1A Receptor Agonist Buspirone

Parkinson’s disease (PD) is progressive neurodegenerative disease, with the diagnosis of idiopathic PD occurring in humans at ~60 years of age. Most studies, however, use young adult (≤3 month old) rats to investigate PD‐related abnormalities in various physiological systems, with the most commonly used experimental rat PD model being generated by unilateral injection of the neurotoxin 6‐hydroxydopamine (6‐OHDA) into specific regions of the nigrostriatal pathway. While this model results in the loss of dopaminergic neurons and the subsequent changes in downstream neurotransmitter signaling that are characteristic of PD, it does not consider potential contributions of physical changes to the brain and neurotransmitter signaling that are part of normal aging on the progression of PD. To better understand age‐related influences and potential contributions of PD‐related abnormalities in serotonergic (5‐HT) neurotransmission on respiratory dysfunction (which is a common non‐motor symptom) in PD, we investigated basal and hypoxic (12% O2; 90s) respiratory behaviors before and after acute administration of the frequently prescribed anxiolytic 5‐HT1A receptor agonist buspirone (BUS; 0.5 mg/kg, iv) in an aged (~9 month old) female Sprague‐Dawley PD rat model produced by unilateral 6‐OHDA injection into the substantia nigra (SN). For these experiments, diaphragm EMG activity was recorded and quantified from spontaneously breathing urethane‐anesthetized rats at 2‐weeks after SN 6‐OHDA or vehicle (control) injections. We found that 6‐OHDA‐injected rats have a lower basal breathing frequency (P&lt;0.05) due to shorter expiratory duration (TE; P&lt;0.05) than vehicle‐injected rats, but both 6‐OHDA‐ and vehicle‐injected rats exhibit significant increases in breathing frequency (P≤0.001) and EMG amplitude (P≤0.023) during hypoxia; the magnitude of the peak frequency increase in 6‐OHDA‐injected rats was slightly greater (P=0.083). Both 6‐OHDA‐ and vehicle‐injected rats also showed similar post‐hypoxic frequency decline (P≤0.003), but only vehicle‐injected rats displayed a slight and sustained post‐hypoxic amplitude depression (P&lt;0.1). In vehicle‐injected rats, acute BUS injection produced a progressive decrease in basal EMG amplitude (P=0.066) and a persistent increase in breathing frequency (P=0.064) by decreasing inspiratory duration (TI; P&lt;0.001) while in 6‐OHDA‐injected rats, a transient initial increase in EMG amplitude (P=0.043) and a persistent decrease in TI (P=0.005) and TE (P=0.089) were noted. In both 6‐OHDA‐ and vehicle‐injected rats, BUS injection also slightly exaggerated the initial hypoxic frequency increase, but blunted the amplitude increase with amplitude progressively declining to near pre‐hypoxic levels before the end of the hypoxic exposure. BUS injection also shortened the duration of post‐hypoxic EMG amplitude depression in vehicle‐injected rats. These data demonstrate that some differences in basal and hypoxic respiratory behaviors exist between older 6‐OHDA‐ and vehicle‐injected rats, and that some respiratory behaviors of these rat models are differentially impacted by BUS‐induced effects on respiratory control. We suggest that this older PD rat model be further evaluated.

Differential Regulation of Inflammatory Responses Following 5‐HT2 Receptor Activation in Pulmonary Tissues

IntroductionThe concept of functional selectivity and psychedelics is often regarded as the ability of different 5‐HT2A receptor agonist compounds to exert varying degrees of psychoactivity in the central nervous system. However, the distribution and expression of the 5‐HT2A receptor, the primary pharmacological target for psychedelics, in peripheral and immune‐related tissue suggests selective signaling may occur here as well. Using an ovalbumin (OVA)‐induced model of rodent acute asthma, our lab has previously shown that subtle changes to the 2,5‐dimethoxy‐phenethylamine pharmacophore structure can profoundly impact the ability of these compounds to prevent asthmatic exacerbations. Here, through both in vitroand in vivoassays, we interrogate elements of functional selectivity in peripheral tissues following exposure to the 5‐HT2 receptor selective agonists (R)‐2,5‐dimethoxy‐4‐iodoamphetamine [(R)‐DOI] and 2,5‐dimethoxy‐4‐trifluoromethylamphetamine (DOTFM). (R)‐DOI is a full and potent anti‐inflammatory compound, whereas DOTFM has no measurable anti‐inflammatory activity. We find that elements of selective signaling combined with modulation to overall chromatin structure and downstream protein expression provide mechanistic clues regarding how psychedelics may elicit their long‐lasting, therapeutic effects.ObjectiveTo elucidate mechanistic variations between anti‐inflammatory and non‐anti‐inflammatory 5‐HT2 receptor agonists.MethodsWe utilized fluorescence recovery after photobleaching (FRAP) to probe the kinetics of the linker histone H1c transiently transfected into a HEK293 cell line stably expressing the human 5‐HT2A receptor, and calcium mobilization assays in the same cell line to determine differences in signaling between (R)‐DOI and DOTFM. For in vivoassays we measured enhanced pause (PenH) values for BALB/c mice challenged with OVA and treated with either (R)‐DOI or DOTFM, using PenH values as a proxy measure for pulmonary inflammation. Lungs were removed en bloc,processed, and analyzed by qPCR and quantitative proteomics using tandem tag mass spectrometry (TMT).ResultsIn vitro assays indicate modest differences irrespective of phenethylamine compound, whereas whole‐body plethysmography (WBP), qPRC, and proteomic analysis reveal significant differential regulation of proteins relevant for both asthmatic initiation and chromatin compaction dependent upon 5‐HT2A agonist.ConclusionAs 5‐HT2‐mediated expression of asthma‐relevant proteins are differentially regulated by either (R)‐DOI and DOTFM, the downregulation of inflammatory pathways via activation of the 5‐HT2 receptor likely requires an accessible, non‐sterically hindered subunit at the 4‐position of the standard 2,5‐dimethoxy‐ampetamine structure to maximally induce anti‐inflammatory effects. Changes to both linker histone mobility and the expression of proteins relevant to chromatin architecture suggest that modulation to the overall chromatin structure combined with downstream epigenetic regulation is a potential mechanism by which certain 5‐HT2A agonists can exert their therapeutic effects.

Selective Targeting of Serotonin 5-HT1a and 5-HT3 Receptors Attenuates Acute and Long-Term Hypersensitivity Associated With Neonatal Procedural Pain.

Neonatal painful procedures causes acute pain and trigger long-term changes in nociceptive processing and anxiety behavior, highlighting the need for adequate analgesia during this critical time. Spinal serotonergic receptors 5-HT1a and 5-HT3 play an important role in modulating incoming nociceptive signals in neonates. The current study aims to attenuate acute and long-term hypersensitivity associated with neonatal procedural pain using ondansetron (a 5-HT3 antagonist) and buspirone (a 5-HT1a agonist) in a well-established rat model of repetitive needle pricking. Sprague-Dawley rat pups of both sexes received ondansetron (3 mg/kg), buspirone (3 mg/kg) or saline prior to repetitive needle pricks into the left hind-paw from postnatal day 0–7. Control animals received tactile stimulation or were left undisturbed. Acute, long-term, and post-operative mechanical sensitivity as well as adult anxiety were assessed. Neonatal 5-HT1a receptor agonism completely reverses acute hypersensitivity from P0-7. The increased duration of postoperative hypersensitivity after re-injury in adulthood is abolished by 5-HT3 receptor antagonism during neonatal repetitive needle pricking, without affecting baseline sensitivity. Moreover, 5-HT1a and 5-HT3 receptor modulation decreases adult state anxiety. Altogether, our data suggests that targeted pharmacological treatment based on the modulation of spinal serotonergic network via the 5-HT1a and 5-HT3 receptors in neonates may be of use in treatment of neonatal procedural pain and its long-term consequences. This may result in a new mechanism-based therapeutic venue in treatment of procedural pain in human neonates.

Effects of a psychedelic 5-HT2A receptor agonist on anxiety-related behavior and fear processing in mice.

Psychedelic-assisted psychotherapy gained considerable interest as a novel treatment strategy for fear-related mental disorders but the underlying mechanism remains poorly understood. The serotonin 2A (5-HT2A) receptor is a key target underlying the effects of psychedelics on emotional arousal but its role in fear processing remains controversial. Using the psychedelic 5-HT2A/5-HT2C receptor agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) and 5-HT2A receptor knockout (KO) mice we investigated the effect of 5-HT2A receptor activation on emotional processing. We show that DOI administration did not impair performance in a spontaneous alternation task but reduced anxiety-like avoidance behavior in the elevated plus maze and elevated zero maze tasks. Moreover, we found that DOI did not block memory recall but diminished fear expression in a passive avoidance task. Likewise, DOI administration reduced fear expression in an auditory fear conditioning paradigm, while it did not affect retention of fear extinction when administered prior to extinction learning. The effect of DOI on fear expression was abolished in 5-HT2A receptor KO mice. Administration of DOI induced a significant increase of c-Fos expression in specific amygdalar nuclei. Moreover, local infusion of the 5-HT2A receptor antagonist M100907 into the amygdala reversed the effect of systemic administration of DOI on fear expression while local administration of DOI into the amygdala was sufficient to suppress fear expression. Our data demonstrate that activation of 5-HT2A receptors in the amygdala suppresses fear expression but provide no evidence for an effect on retention of fear extinction.

Spinal 5-HT2A receptor is involved in electroacupuncture inhibition of chronic pain.

Knee osteoarthritis (KOA) is a highly prevalent, chronic joint disorder, and it is a typical disease which can develop chronic pain. Our previous study has proved that endocannabinoid (2-AG)-CB1R-GABA-5-HT pathway is involved in electroacupuncture (EA) mediated inhibition of chronic pain. However, it is still unclear which among the 5-HT receptor subtype is involved in EA evoked 5-HT mediated inhibition of chronic pain in the dorsal spinal cord. 5-HT2A is a G protein-coupled receptor and it is involved in 5-HT descending pain modulation system. We found that EA treatment at frequency of 2 Hz +1 mA significantly increased the expression of 5-HT2A receptor in the dorsal spinal cord and intrathecal injection of 5-HT2A receptor antagonist or agonist reversed or mimicked the analgesic effect of EA in each case respectively. Intrathecal injection of a selective GABAA receptor antagonist Bicuculline also reversed the EA effect on pain hypersensitivity. Additionally, EA treatment reversed the reduced expression of GABAA receptor and KCC2 in the dorsal spinal cord of KOA mice. Furthermore, we demonstrated that intrathecal 5-HT2A receptor antagonist/agonist reversed or mimicked the effect of EA up-regulate of KCC2 expression, respectively. Similarly, intrathecal injection of PLC and PKC inhibitors prevented both anti-allodynic effect and up-regulation of KCC2 expression by EA treatment. Our data suggest that EA treatment up-regulated KCC2 expression through activating 5-HT2A-Gq-PLC-PKC pathway and enhanced the inhibitory function of GABAA receptor, thereby inhibiting chronic pain in a mouse model of KOA.

Serotonin 1A Receptor Pharmacotherapy and Neuroplasticity in Spinal Cord Injury.

Spinal cord injury is associated with damage in descending and ascending pathways between brainstem/cortex and spinal neurons, leading to loss in sensory-motor functions. This leads not only to locomotor reduction but also to important respiratory impairments, both reducing cardiorespiratory engagement, and increasing cardiovascular risk and mortality. Moreover, individuals with high-level injuries suffer from sleep-disordered breathing in a greater proportion than the general population. Although no current treatments exist to restore motor function in spinal cord injury (SCI), serotoninergic (5-HT) 1A receptor agonists appear as pharmacologic neuromodulators that could be important players in inducing functional improvements by increasing the activation of spared motoneurons. Indeed, single therapies of serotoninergic 1A (5-HT1A) agonists allow for acute and temporary recovery of locomotor function. Moreover, the 5-HT1A agonist could be even more promising when combined with other pharmacotherapies, exercise training, and/or spinal stimulation, rather than administered alone. In this review, we discuss previous and emerging evidence showing the value of the 5HT1A receptor agonist therapies for motor and respiratory limitations in SCI. Moreover, we provide mechanistic hypotheses and clinical impact for the potential benefit of 5-HT1A agonist pharmacology in inducing neuroplasticity and improving locomotor and respiratory functions in SCI.

Design, Synthesis, and Characterization of a Novel Fluoroprobe for Live Human Islet Cell Imaging of Serotonin 5-HT1A Receptor.

Mounting evidence suggests that the serotonin system serves in signal transmission to regulate insulin secretion in pancreatic islets of Langerhans. Among the 5-HT receptor subtype found in pancreatic islets, serotonin receptor 1A (5-HT1A ) demonstrates a unique ability to inhibit β-cell insulin secretion. We report the design, synthesis, and characterization of two novel fluorescent probes for the 5-HT1A receptor. The compounds were prepared by conjugating the scaffold of the 5-HT1A receptor agonist 8-OH-DPAT with two fluorophores suitable for live-cell imaging. Compound 5a {5-(dimethylamino)-N-[5-[(8-hydroxy-1,2,3,4-tetrahydronaphthalen-2-yl)(propyl)amino]pentyl]naphtalen-1-sulfonammide} showed high affinity for the 5-HT1A receptor (Ki =1.8 nM). Fluoroprobe 5a was able to label the 5-HT1A receptor in pancreatic islet cell cultures in a selective manner, as the fluorescence emission was significantly attenuated by co-administration of the 5-HT1A receptor antagonist WAY-100635. Thus, fluoroprobe 5a showed useful properties to further characterize this unique receptor's role.

The role of serotonin neurotransmission in rapid antidepressant actions.

Ketamine has rapid antidepressant effects that represent a significant advance in treating depression, but its poor safety and tolerability limit its clinical utility. Accreting evidence suggests that serotonergic neurotransmission participates in the rapid antidepressant effects of ketamine and hallucinogens. Thus, understanding how serotonin contributes to these effects may allow identification of novel rapid antidepressant mechanisms with improved tolerability. The goal of this paper is to understand how serotonergic mechanisms participate in rapid antidepressant mechanisms. We review the relevance of serotonergic neurotransmission for rapid antidepressant effects and evaluate the role of 5-HT1A, 5-HT1B, 5-HT2A, and 5-HT4 receptors in synaptic plasticity, BDNF signaling, and GSK-3β activity. Subsequently, we develop hypotheses on the relationship of these receptor systems to rapid antidepressant effects. We found that 5-HT1A and 5-HT1B receptors may participate in ketamine's rapid antidepressant mechanisms, while agonists at 5-HT2A and 5-HT4 receptors may independently behave as rapid antidepressants. 5-HT1A, 5-HT2A, and 5-HT4 receptors increase synaptic plasticity in the cortex or hippocampus but do not consistently increase BDNF signaling. We found that 5-HT1A and 5-HT1B receptors may participate in rapid antidepressant mechanisms as a consequence of increased BDNF signaling, rather than a cause. 5-HT2A and 5-HT4 receptor agonists may increase BDNF signaling, but these relationships are tenuous and need more study. Finally, we found that ketamine and several serotonergic receptor systems may mechanistically converge on reduced GSK-3β activity. We find it plausible that serotonergic neurotransmission participates in rapid antidepressant mechanisms by increasing synaptic plasticity, perhaps through GSK-3β inhibition.

The effects of Vilazodone, YL-0919 and Vortioxetine in hemiparkinsonian rats.

Parkinson's disease is a neurodegenerative disease often characterized by motor deficits and most commonly treated with dopamine replacement therapy. Despite its benefits, chronic use of L-DOPA results in abnormal involuntary movements known as L-DOPA-induced dyskinesia. Growing evidence shows that with burgeoning dopamine cell loss, neuroplasticity in the serotonin system leads to the development of L-DOPA-induced dyskinesia through the unregulated uptake, conversion, and release of L-DOPA-derived dopamine into the striatum. Previous studies have shown that coincident 5-HT1A agonism and serotonin transporter inhibition may have anti-dyskinetic potential. Despite this, few studies have explicitly focused on targeting both 5-HT1A and the serotonin transporter. The present study compares the 5-HT compounds Vilazodone, YL-0919, and Vortioxetine which purportedly work as simultaneous 5-HT1A receptor agonists and SERT blockers. To do so, adult female Sprague Dawley rats were rendered hemiparkinsonian and treated daily for two weeks with L-DOPA to produce stable dyskinesia. The abnormal involuntary movements and forehand adjusting step tests were utilized as measurements for L-DOPA-induced dyskinesia and motor performance in a within-subjects design. Lesion efficacy was determined by analysis of striatal monoamines via high-performance liquid chromatography. Compounds selective for 5-HT1A/SERT target sites including Vilazodone and Vortioxetine significantly reduced L-DOPA-induced dyskinesia without compromising L-DOPA pro-motor efficacy. In contrast, YL-0919 failed to reduce L-DOPA-induced dyskinesia, with no effects on L-DOPA-related improvements. Collectively, this work supports pharmacological targeting of 5-HT1A/SERT to reduce L-DOPA-induced dyskinesia. Additionally, this further provides evidence for Vilazodone and Vortioxetine, FDA-approved compounds, as potential adjunct therapeutics for L-DOPA-induced dyskinesia management in Parkinson's patients.

Biased 5-HT1A receptor agonists F13714 and NLX-101 differentially affect pattern separation and neuronal plasticity in rats after acute and chronic treatment

Pattern separation is a hippocampal process in which highly similar stimuli are recognized as separate representations, and deficits could lead to memory impairments in neuropsychiatric disorders such as schizophrenia. The 5-HT1A receptor (5-HT1AR) is believed to be involved in these hippocampal pattern separation processes. However, in the dorsal raphe nucleus (DRN), the 5-HT1AR is expressed as a somatodendritic autoreceptor, negatively regulates serotonergic signaling, and could thereby counteract the effects of hippocampal postsynaptic 5-HT1A receptors. Therefore, this study aims to identify how pre- and post-synaptic 5-HT1AR activity affects pattern separation. Object pattern separation (OPS) performance was measured in male Wistar rats after both acute and chronic treatment (i.p.) with 5-HT1AR biased agonists F13714 (0.0025 mg/kg acutely, 0.02 mg/kg/day chronically) or NLX-101 (0.08 mg/kg acutely, 0.32 mg/kg/day chronically), which preferentially activate autoreceptors or postsynaptic receptors respectively, for 14 days. Body temperature - a functional correlate of hypothalamic 5-HT1AR stimulation - was measured daily. Additionally, 5-HT1AR density (DRN) and plasticity markers (hippocampus) were assessed. Acute treatment with F13714 impaired OPS performance, whereas chronic treatment normalized this, and a drop in body temperature was found from day 4 onwards. NLX-101 enhanced OPS performance acutely and chronically, and caused an acute drop in body temperature. Chronic NLX-101 treatment increased doublecortin positive neurons in the dorsal hippocampus, while chronic treatment with F13714 resulted in a downregulation of 5-HT1A autoreceptors, which likely reversed the acute impairment in OPS performance. Chronic treatment with NLX-101 appears to have therapeutic potential to improve brain plasticity and OPS performance.

Role of 5-HT2A receptors in the effects of ayahuasca on ethanol self-administration using a two-bottle choice paradigm in male mice.

Ayahuasca has been proposed as a potential treatment of alcohol (ethanol) use disorder (AUD). The serotonin 5-HT2A receptor agonist N,N-dimethyltryptamine (DMT) is the main psychoactive component of ayahuasca, suggesting that its therapeutic effects may be mediated by 5-HT2A receptors. The aim of the present study was to investigate the effects of ayahuasca on the expression of ethanol self-administration using a two-bottle choice procedure and the role of 5-HT2A receptors in those effects. Male mice had intermittent access to ethanol (10% v/v) in a two-bottle choice procedure for 30days. Animals were then submitted to 3 treatment phases, each followed by ethanol re-exposure tests. During the treatment phase, every 3days, animals received i.p. injections of either vehicle or the 5-HT2A receptor antagonist M100907 (M100, 1mg/kg) followed by an i.g. (gavage) administration of vehicle or ayahuasca (100mg/kg) and were exposed to the self-administration apparatus with no ethanol availability. During re-exposure tests, animals were submitted to the same conditions as during acquisition, with no treatments prior to those sessions. Treatment with ayahuasca blocked the expression of ethanol self-administration, decreasing ethanol intake and preference during re-exposure tests. Pretreatment with M100 blocked the effects of ayahuasca on ethanol drinking without significantly attenuating ethanol self-administration. Treatment with ayahuasca during alcohol abstinence blocked the expression of alcohol self-administration in mice, and 5-HT2A receptor activation is critical for those effects to emerge. Our findings support a potential for ayahuasca and other 5-HT2A receptor agonists as adjunctive pharmacotherapies for the treatment of AUD.