Effect of Bulky N-Dibenzofuranylmethyl Substitution on the 5-HT2 Receptor Affinity and Efficacy of a Psychedelic Phenethylamine.

The introduction of arylmethyl substituents on the amine nitrogen atom of phenethylamines and tryptamines often results in profound increases in their affinity and functional activity at 5-HT2 serotonin receptors. To probe the sensitivity of this effect to substantially larger N-substituents, ten derivatives of the well-characterized psychedelic phenethylamine 2C-B were prepared by appending different dibenzo[b,d]furylmethyl (DBFM) moieties to the basic nitrogen. The DBFM group attached to the amino group through its 1-, -2-, or 3-position decreased affinity and agonist activity at the 5-HT2A/2C receptors. Substitution through the 4-position usually favored affinity for all three 5-HT2 receptor subtypes with compound 5 exhibiting 10- and 40-fold higher affinities at the 5-HT2A and 5-HT2C receptors, respectively, but less than fourfold selectivity among the three receptor subtypes. Nevertheless, all were relatively weak partial 5-HT2AR agonists, mostly in the low micromolar range, but full or nearly full agonists at the 5-HT2C subtype as determined in a calcium mobilization assay. Molecular docking simulations suggested that the dibenzofuryl portion dives more deeply into the orthosteric binding site of the 5-HT2A than the 5-HT2C receptor, interacting with the Trp3366.48 toggle switch associated with its activation, while the phenylamine moiety lies close to the extracellular side of the receptor. In conclusion, a very bulky N-substituent on a phenethylamine 5-HT2 receptor agonist is tolerated and may increase affinity if its orientation is appropriate. However, the Gq protein-mediated potencies are generally low, with low efficacy (relative to 5-HT) at the 5-HT2A receptor, somewhat higher efficacy at the 5-HT2B subtype, and full or nearly full efficacy at the 5-HT2C subtype.

LSD and language: Decreased structural connectivity, increased semantic similarity, changed vocabulary in healthy individuals.

Language has been explored as a window into the mind. Psychedelics, known to affect perception and cognition, seem to change language, but a systematic, time-dependent exploration is lacking. Therefore, we aimed at mapping the psychedelic effects on language over the time course of the acute and sub-acute effects in an explorative manner. For this, 24 healthy volunteers (age [mean±SD, range]: 35±11, 25-61 years; 33% women) received 50 µg lysergic acid diethylamide (LSD) or inactive placebo in a randomized, double-blind, placebo-controlled, crossover study. We assessed different language productions (experience reporting, storytelling), components (structure, semantics, vocabulary) and time points (+0 h to +24 h). Language productions included 5-min experience reporting (+1.5 h, +6.5 h) and 1-min storytelling (+0 h, +2 h, +4 h, +6 h, +24 h). Language structure was assessed by computing speech topology (SpeechGraphs), semantics by semantic distances (FastText), vocabulary by word categories (LIWC). LSD, compared to placebo, changed language structure, including decreased verbosity, lexicon, global and local connectivity (+1.5 h to +4 h); decreased semantic distances between neighbouring words and overall words (+2 h to +24 h); and changed vocabulary related to grammar, persons, time, space and biological processes (+1.5 h to +24 h). In conclusion, low to moderate LSD doses changed language over diverse production types, components and time points. While simpler and disconnected structure and semantic similarity might reflect cognitive impairments, changed vocabulary might reflect subjective perceptions. Therefore, language under LSD might provide a window into the psychedelic mind and automated language quantifications should be better explored as valuable tools to yield more unconstrained insights into psychedelic perception and cognition.

5-HT and α-m-5-HT attenuate excitatory synaptic transmissions onto the lateral amygdala principal neurons via presynaptic 5-HT1B receptors.

Accumulating evidence suggests that the serotonergic (5-HT) system in the amygdala has significant effects on affective states. Dysregulation of the 5-HT system in the basolateral amygdaloid complex causes affective disorders. To search for therapeutic targets, subtype specification of 5-HT receptors is crucial. The present study was undertaken to identify the 5-HT receptor subtype responsible for the 5-HT-mediated suppression of excitatory transmission to principal neurons (PNs) in the lateral amygdala (LA). Whole-cell recordings were performed to record excitatory post synaptic currents (EPSCs) in acute rat brain slices. We confirmed that 5-HT and α-m-5-HT, a broad 5-HT2 receptor agonist, attenuated EPSCs in LA PNs. The extent of suppressions by 5-HT and α-m-5-HT remained unchanged in the presence of ritanserin, a broad 5-HT2 receptor antagonist. In the presence of NAS-181, a selective 5-HT1B receptor antagonist, the extent of EPSC suppressions by 5-HT and α-m-5-HT was diminished. CP93129, a selective 5-HT1B receptor agonist, attenuated EPSCs in LA PNs, and this effect was abolished in the presence of NAS-181. Additionally, the paired-pulse ratio of EPSCs was increased by CP93129. Thus, our results indicate that 5-HT and α-m-5-HT attenuate excitatory transmissions to LA PNs via presynaptic 5-HT1B receptors.

Forced Remyelination Promotes Axon Regeneration in a Rat Model of Spinal Cord Injury.

Spinal cord injuries result in the loss of motor and sensory functions controlled by neurons located at the site of the lesion and below. We hypothesized that experimentally enhanced remyelination supports axon preservation and/or growth in the total spinal cord transection in rats. Multifocal demyelination was induced by injection of ethidium bromide (EB), either at the time of transection or twice during transection and at 5 days post-injury. We demonstrated that the number of oligodendrocyte progenitor cells (OPCs) significantly increased 14 days after demyelination. Most OPCs differentiated into mature oligodendrocytes by 60-90 dpi in double-EB-injected rats; however, most axons were remyelinated by Schwann cells. A significant number of axons passed the injury epicenter and entered the distant segments of the spinal cord in the double-EB-injected rats. Moreover, some serotoninergic fibers, not detected in control animals, grew caudally through the injury site. Behavioral tests performed at 60-90 dpi revealed significant improvement in locomotor function recovery in double-EB-injected rats, which was impaired by the blockade of serotonin receptors, confirming the important role of restored serotonergic fibers in functional recovery. Our findings indicate that enhanced remyelination per se, without substantial inhibition of glial scar formation, is an important component of spinal cord injury regeneration.

New insights into methoxetamine mechanisms of action: Focus on serotonergic 5-HT2 receptors in pharmacological and behavioral effects in the rat.

Methoxetamine (MXE) is a dissociative substance of the arylcyclohexylamine class that has been present on the designer drug market as a ketamine-substitute since 2010. We have previously shown that MXE (i) possesses ketamine-like discriminative and positive rewarding effects in rats, (ii) affects brain processing involved in cognition and emotional responses, (iii) causes long-lasting behavioral abnormalities and neurotoxicity in rats and (iv) induces neurological, sensorimotor and cardiorespiratory alterations in mice. To shed light on the mechanisms through which MXE exerts its effects, we conducted a multidisciplinary study to evaluate the various neurotransmitter systems presumably involved in its actions on the brain. In vivo microdialysis study first showed that a single administration of MXE (0.25 and 0.5 mg/kg, i.v.) is able to significantly alter serotonin levels in the rat medial prefrontal cortex (mPFC) and nucleus accumbens. Then, we observed that blockade of the serotonin 5-HT2 receptors through two selective antagonists, ketanserin (0.1 mg/kg, i.p.) and MDL 100907 (0.03 mg/kg, i.p.), at doses not affecting animals behavior per se, attenuated the facilitatory motor effect and the inhibition on visual sensory responses induced by MXE (3 mg/kg, i.p.) and ketamine (3 mg/kg, i.p.), and prevented MXE-induced reduction of the prepulse inhibition in rats, pointing to the 5-HT2 receptors as a key target for the recently described MXE-induced sensorimotor effects. Finally, in-vitro electrophysiological studies revealed that the GABAergic and glutamatergic systems are also likely involved in the mechanisms through which MXE exerts its central effects since MXE inhibits, in a concentration-dependent manner, NMDA-mediated field postsynaptic potentials and GABA-mediated spontaneous currents. Conversely, MXE failed to alter both the AMPA component of field potentials and presynaptic glutamate release, and seems not to interfere with the endocannabinoid-mediated effects on mPFC GABAergic synapses. Altogether, our results support the notion of MXE as a NMDA receptor antagonist and shed further lights into the central mechanisms of action of this ketamine-substitute by pointing to serotonin 5-HT2 receptors as crucial players in the expression of its sensorimotor altering effects and to the NMDA and GABA receptors as potential further important targets of action.

Serotonergic signals enhanced hamster sperm hyperactivation.

In the present study, we investigated the regulatory mechanisms underlying sperm hyperactivation enhanced by 5-hydroxytryptamine (5-HT) in hamsters. First, we examined the types of 5-HT receptors that regulate hyperactivation. Hyperactivation was significantly enhanced by 5-HT2A and 5-HT4 receptor agonists. Moreover, the results of the motility assay revealed that 5-HT2A, 5-HT3, and 5-HT4 receptor agonists significantly decreased the velocity and/or amplitude of sperm. Under 5-HT2 receptor stimulation, hyperactivation was associated with phospholipase C (PLC), inositol 1,4,5-trisphosphate (IP3) receptor, soluble adenylate cyclase (sAC), and protein kinase A (PKA). In contrast, under 5-HT4 receptor stimulation, hyperactivation was associated with transmembrane adenylate cyclase (tmAC), sAC, PKA, and CatSper channels. Accordingly, under the condition that sperm are hyperactivated, 5-HT likely stimulates PLC/IP3 receptor signals via the 5-HT2A receptor and tmAC/PKA/CatSper channel signals via the 5-HT4 receptor. After sAC and PKA are activated by these stimulations, sperm hyperactivation is enhanced.

Acupuncture ameliorates not only atopic dermatitis-like skin inflammation but also acute and chronic serotonergic itch possibly through blockade of 5-HT2 and 5-HT7 receptors in mice.

Acupuncture has been known to be effective for atopic dermatitis, especially ameliorating itch; however, its mechanisms are still unclear. The aim of this study was to test the anti-itch effects of acupuncture and to investigate its possible mechanisms. Acupuncture was performed at Gok-Ji (LI11) acupoints just before the injection of pruritogens in the mouse cheek model of acute itch and of MC903-induced atopic dermatitis displaying serotonergic chronic itch. Acupuncture significantly reduced acute itch triggered by compound 48/80, chloroquine, or especially serotonin. It also markedly reduced scratching behaviors evoked by the serotonin 5-HT2 receptor agonist α-methylserotonin and selective 5-HT7 receptor agonist LP 44. In addition, acupuncture treatment at LI11 had the preventive and therapeutic effects on persistent itch as well as the robust skin inflammation with epidermal thickening in mice with MC903-induced atopic dermatitis. It also considerably reduced the increased expression of 5-HT2A, 5-HT2B and 5-HT7 receptors in atopic dermatitis-like skin lesions in mice treated with MC903. Taken together, these findings highlight that acupuncture significantly ameliorates not only skin inflammation, but also acute and chronic serotonergic itch, possibly through blockade of serotonin 5-HT2 and 5-HT7 receptors.

Serotonergic Modulation of Spontaneous and Evoked Transmitter Release in Layer II Pyramidal Cells of Rat Somatosensory Cortex.

As axons from the raphe nuclei densely innervate the somatosensory cortex, we investigated how serotonin (5-HT) modulates transmitter release in layer II pyramidal cells of rat barrel cortex. In the presence of tetrodotoxin and gabazine, 10 µM 5-HT caused a waxing and waning in the frequency of miniature excitatory postsynaptic currents (mEPSC) with no effect on amplitude. Specifically, within 15 min of recording the mEPSC frequency initially increased by 28 ± 7%, then dropped to below control (-15 ± 3%), before resurging back to 27 ± 7% larger than control. These changes were seen in 47% of pyramidal cells (responders) and were mediated by 5-HT2C receptors (5-HT2CR). Waxing resulted from phospholipase C activation, IP3 production, and Ca2+ release from presynaptic stores. Waning was prevented if PKC was blocked. In contrast, in paired recordings, the unitary EPSC amplitude was reduced by 50 ± 3% after 5-HT exposure in almost all cases with no significant effect on paired-pulse ratio and synaptic dynamics. This sustained EPSC reduction was also caused by 5-HT2R, but was mediated by presynaptic Gßγ subunits likely limiting influx through CaV2 channels. EPSC reduction, together with enhanced spontaneous noise in a restricted subset of inputs, could temporarily diminish the signal-to-noise ratio and affect the computation in the neocortical microcircuit.

Ritanserin blocks CaV1.2 channels in rat artery smooth muscles: electrophysiological, functional, and computational studies.

CaV1.2 channel blockers or 5-HT2 receptor antagonists constitute effective therapy for Raynaud's syndrome. A functional link between the inhibition of 5-HT2 receptors and CaV1.2 channel blockade in arterial smooth muscles has been hypothesized. Therefore, the effects of ritanserin, a nonselective 5-HT2 receptor antagonist, on vascular CaV1.2 channels were investigated through electrophysiological, functional, and computational studies. Ritanserin blocked CaV1.2 channel currents (ICa1.2) in a concentration-dependent manner (Kr = 3.61 µM); ICa1.2 inhibition was antagonized by Bay K 8644 and partially reverted upon washout. Conversely, the ritanserin analog ketanserin (100 µM) inhibited ICa1.2 by ~50%. Ritanserin concentration-dependently shifted the voltage dependence of the steady-state inactivation curve to more negative potentials (Ki = 1.58 µM) without affecting the slope of inactivation and the activation curve, and decreased ICa1.2 progressively during repetitive (1 Hz) step depolarizations (use-dependent block). The addition of ritanserin caused the contraction of single myocytes not yet dialyzed with the conventional method. Furthermore, in depolarized rings, ritanserin, and to a lesser extent, ketanserin, caused a concentration-dependent relaxation, which was antagonized by Bay K 8644. Ritanserin and ketanserin were docked at a region of the CaV1.2 α1C subunit nearby that of Bay K 8644; however, only ritanserin and Bay K 8644 formed a hydrogen bond with key residue Tyr-1489. In conclusion, ritanserin caused in vitro vasodilation, accomplished through the blockade of CaV1.2 channels, which was achieved preferentially in the inactivated and/or resting state of the channel. This novel activity encourages the development of ritanserin derivatives for their potential use in the treatment of Raynaud's syndrome.

Change in serotonergic modulation contributes to the synaptic imbalance of neuronal circuit at the prefrontal cortex in the 15q11-13 duplication mouse model of autism.

The prefrontal cortex (PFC) has been extensively studied in autism spectrum disorder (ASD) in an attempt to understand the deficits in executive and other higher brain functions related to sociability and emotion. Disruption of the excitatory/inhibitory (E/I) balance of cortical circuits is thought to underlie the pathophysiology of ASD. Recently, we showed that 15q dup mice (a model for ASD with human chromosome 15q11-13 paternal duplication) exhibit disruption of the E/I balance in layer 2/3 pyramidal neurons of the somatosensory cortex due to a decrease in the number of inhibitory synapses. However, whether there is a pathological abnormality in E/I balance in the PFC of 15q dup mice remains unknown. In this study, we found that 15q dup facilitates the activity-induced LTP of glutamate synapses onto layer 5 pyramidal neurons by shifting the E/I balance to an excitatory state, which this was associated with differences in synaptic glutamatergic and GABAergic inputs onto GABAergic fast-spiking interneurons (FSINs). Furthermore, we found that FSIN excitability was well-modulated and regulated by the constitutive activation of 5-HT2 receptors in PFC microcircuits. These results provide new insights into the cellular mechanisms underlying maintenance of optimal E/I balance in the PFC.

Blockade of 5-HT2 receptors with sarpogrelate uncovers 5-HT7 receptors inhibiting the tachycardic sympathetic drive in pithed rats.

Our group has previously shown in pithed rats that the cardiac sympathetic drive, which produces tachycardic responses, is inhibited by 5-HT via the activation of prejunctional 5-HT1B/1D/5 receptors. Interestingly, when 5-HT2 receptors are chronically blocked with sarpogrelate, the additional role of cardiac sympatho-inhibitory 5-HT1F receptors is unmasked. Although 5-HT2 receptors mediate tachycardia in rats, and the chronic blockade of 5-HT2 receptors unmasked 5-HT7 receptors mediating cardiac vagal inhibition, the role of 5-HT7 receptors in the modulation of the cardiac sympathetic tone remains virtually unexplored. On this basis, male Wistar rats were pretreated during 14 days with sarpogrelate (a 5-HT2 receptor antagonist) in drinking water (30 mg/kg/day; sarpogrelate-pretreated group) or equivalent volumes of drinking water (control group). Subsequently, the rats were pithed to produce increases in heart rate by either electrical preganglionic spinal (C7 -T1 ) stimulation of the cardiac sympathetic drive or iv administration of exogenous noradrenaline. The iv continuous infusion of AS-19 (a 5-HT7 receptor agonist; 10 µg/kg/min) (i) inhibited the tachycardic responses to sympathetic stimulation, but not those to exogenous noradrenaline only in sarpogrelate-pretreated rats. This inhibition was completely reversed by SB258719 (a selective 5-HT7 receptor antagonist; 1 mg/kg, iv) or glibenclamide (an ATP-sensitive K+ channel blocker; 20 mg/kg, iv). These results suggest that chronic 5-HT2 receptor blockade uncovers a cardiac sympatho-inhibitory mechanism mediated by 5-HT7 receptors, involving a hyperpolarization due to the opening of ATP-sensitive K+ channels. Thus, these findings support the role of 5-HT7 receptors in the modulation of the cardiac sympathetic neurotransmission.

Crucial Roles of 5-HT and 5-HT2 Receptor in Diabetes-Related Lipid Accumulation and Pro-Inflammatory Cytokine Generation in Hepatocytes.

BACKGROUND/AIMS: Previously, we confirmed that liver-synthesized 5-HT rather than non-liver 5-HT, acting on the 5-HT2 receptor (5-HT2R), modulates lipid-induced excessive lipid synthesis (ELS). Here, we further revealed the effects of the hepatocellular 5-HT system in diabetes-related disorders. METHODS: Studies were conducted in male ICR mice, human HepG2 cells, and primary mouse hepatocytes (PMHs) under gene or chemical inhibition of the 5-HT system, key lipid metabolism, and inflammation-related factors. Protein and messenger RNA expression and levels of the factors were determined via western blotting, reverse transcription PCR, and quantitative assay kits, respectively. Hepatic steatosis with inflammation and fibrosis, intracellular lipid droplet accumulation (LDA), and reactive oxygen species (ROS) location were determined via hematoxylin and eosin, Masson's trichrome, Oil red O, and fluorescent-specific staining, respectively. RESULTS: Palmitic acid induced the activation of the 5-HT system: the activation of 5-HT2R, primarily 5-HT2AR, in addition to upregulating monoamine oxidase A (MAO-A) expression and 5-HT synthesis, by activating the G protein/ phospholipase C pathway modulated PKCε activation, resulting in ELS with LDA; the activation of NF-κB, which mediates the generation of pro-inflammatory cytokines, was primarily due to ROS generation in the mitochondria induced by MAO-A-catalyzed 5-HT degradation, and secondarily due to the activation of PKCε. These effects of the 5-HT system were also detected in palmitic acid- or high glucose-treated PMHs and regulated multiple inflammatory signaling pathways. In diabetic mice, co-treatment with antagonists of both 5-HT synthesis and 5-HT2R significantly abolished hepatic steatosis, inflammation, and fibrosis as well as hyperglycemia and dyslipidemia. CONCLUSION: Activation of the hepatocellular 5-HT system plays a crucial role in inducing diabetes-related hepatic dysfunction and is a potential therapeutic target.

5-HT 2 receptor mediates high-fat diet-induced hepatic steatosis and very low density lipoprotein overproduction in rats.

BACKGROUND: 5-HT has been shown to mediate abnormality of hepatic lipid metabolism through activation of mammalian target of rapamycin (mTOR). However, it is unclear whether 5-HT is directly involved in high-fat diet (HFD)-induced hepatic steatosis. MATERIALS AND METHODS: Male rats were allocated into seven groups with control, either HFD feeding, 5-HT treatment, or HFD feeding and 5-HT treatment with or without sarpogrelate treatment, all of which were executed for 4 weeks. HepG2 cells were exposed to 5-HT or palmitic acid (PA) with or without rapamycin or Sar treatment. RESULTS: Rats fed with HFD or exposed to 5-HT led to abnormalities with activated hepatic mTOR-S6K pathway, overproduction of hepatic triglycerides and VLDL with steatosis, and hyperlipidemia, which were exacerbated by a combination of HFD and 5-HT. Sarpogrelate significantly inhibited above abnormalities induced by HFD and 5-HT, alone or in a combination. Additionally, HFD caused up-regulation of 5-HT2 receptors (5-HT2R), including 5-HT2AR and 5-HT2BR, and 5-HT synthesis in the liver, without obvious influence on other 5-HT receptors gene expression. In HepG2 cells, both PA and 5-HT induced overproduction of triglycerides and VLDL with lipid droplets, and PA up-regulated 5-HT2AR and 5-HT2BR expression and 5-HT synthesis as well. Rapamycin fully abolished PA or 5-HT-induced mTOR activation, which was more effective than sarpogrelate. However, the inhibitory effects of rapamycin on PA or 5-HT-induced overproduction of triglycerides and VLDL were less than sarpogrelate. CONCLUSIONS: Up-regulation of hepatic 5-HT2R and 5-HT synthesis by HFD is crucial for HFD-induced overproduction of hepatic triglycerides and VLDL with hyperlipidemia.

Chronic 5-HT2 receptor blockade unmasks the role of 5-HT1F receptors in the inhibition of rat cardioaccelerator sympathetic outflow.

Serotonin (5-hydroxytryptamine; 5-HT) inhibits the rat cardioaccelerator sympathetic outflow by 5-HT1B/1D/5 receptors. Because chronic blockade of sympatho-excitatory 5-HT2 receptors is beneficial in several cardiovascular pathologies, this study investigated whether sarpogrelate (a 5-HT2 receptor antagonist) alters the pharmacological profile of the above sympatho-inhibition. Rats were pretreated for 2 weeks with sarpogrelate in drinking water (30 mg/kg per day; sarpogrelate-treated group) or equivalent volumes of drinking water (control group). Animals were pithed and prepared for spinal stimulation (C7-T1) of the cardioaccelerator sympathetic outflow or for intravenous (i.v.) bolus injections of noradrenaline. Both procedures produced tachycardic responses remaining unaltered after saline. Continuous i.v. infusions of 5-HT induced a cardiac sympatho-inhibition that was mimicked by the 5-HT receptor agonists 5-carboxamidotryptamine (5-CT; 5-HT1/5A), CP 93,129 (5-HT1B), or PNU 142633 (5-HT1D), but not by indorenate (5-HT1A) in both groups; whereas LY344864 (5-HT1F) mimicked 5-HT only in sarpogrelate-treated rats. In sarpogrelate-treated animals, i.v. GR 127935 (310 µg/kg; 5-HT1B/1D/1F receptor antagonist) attenuated 5-CT-induced sympatho-inhibition and abolished LY344864-induced sympatho-inhibition; while GR 127935 plus SB 699551 (1 mg/kg; 5-HT5A receptor antagonist) abolished 5-CT-induced inhibition. These results confirm the cardiac sympatho-inhibitory role of 5-HT1B, 5-HT1D, and 5-HT5A receptors in both groups; nevertheless, sarpogrelate treatment specifically unmasked a cardiac sympatho-inhibition mediated by 5-HT1F receptors.

Further investigation of the effects of 5-hydroxytryptamine, 8-OH-DPAT and DOI to mediate contraction and relaxation responses in the intestine and emesis in Suncus murinus.

5-HT receptors are implicated in many gastrointestinal disorders. However, the precise role of 5-HT in mediating GI responses in Suncus murnius is still unclear. Therefore in this study, the effects of 5-HT and its agonists were investigated in Suncus. The involvement of 5-HT2C receptors in mediating emesis was also investigated. The ability of 5-HT and its agonists/antagonists at 5-HT1A and 5-HT2 to modify GI motility was investigated in vitro and in vivo. WAY100635 (a 5-HT1A antagonist) inhibited the contraction response to 5-HT in the proximal segments without affecting the maximum response; whilst enhancing the contraction to 5-HT (>30.0nM) in the distal intestine. The selective 5-HT2A and 5-HT2B receptor antagonists MDL-100907 and RS-127445 attenuated 5-HT-induced contractions (<10.0µM) in the distal segments. RS-127445 also attenuated 5-HT-induced contractions in the central segments. The selective 5-HT2C receptor antagonist SB-242084, attenuated the responses to 5-HT (> 3.0nM) in the proximal and central but not the distal regions. 8-OH-DPAT-induced relaxation was resistant to the antagonism by 5-HT1A/7 antagonists. DOI in the presence of 5-HT1A/2A/2B/2C antagonists induced greater contraction responses (>1.0µM) in most tissues, whilst RS-127445, or SB-242084, reduced the responses to DOI (< 1.0µM) in some tissues. SB-242084 also suppressed emesis-induced by motion and intragastric CuSO4. In conclusion, within different regions of intestine, 5-HT2 receptors are differently involved in contraction and emetic responses and that 8-OH-DPAT induces relaxation via non-5-HT1A/7 receptors. Suncus could provide a model to investigate these diverse actions of 5-HT.

Peripheral endocannabinoid concentrations are not associated with verbal memory impairment during MDMA intoxication.

BACKGROUND: Preclinical data have suggested involvement of the endocannabinoid (eCB) system in MDMA-induced memory impairment. Clinical research has shown that blockade of the 5-HT2 receptor nulls memory impairment during MDMA intoxication. Interestingly, studies have demonstrated that the eCB and the 5-HT system interact. It was hypothesized that MDMA would cause an increase in eCB concentrations together with a decrease in memory performance, and that combining MDMA with a 5-HT2 receptor blocker ketanserin would lead to a counteraction of the MDMA effects on eCB concentrations and memory. METHODS: Twenty healthy recreational polydrug users entered a double-blind placebo-controlled within-subject study. Participants received a pre-treatment (ketanserin 40 mg, placebo) followed 30 min later by a treatment (MDMA 75 mg, placebo). Verbal memory was tested by means of a 30-word learning test. Endocannabinoid concentrations (anandamide (2-AG); N-arachidonylethanolamine (AEA)) were assessed in blood at baseline, before (90 min post-treatment) and after cognitive tests (150 min post-treatment). RESULTS: Findings showed that MDMA impaired memory 90 min post-treatment in the word learning task. This effect was a replication of previous studies using the same dose of MDMA (75 mg) and the same learning paradigm. Contrary to our hypothesis, MDMA did not affect eCB concentrations, nor did ketanserin block MDMA-induced memory impairment. Ketanserin caused an increase in AEA concentrations, 180 min after administration. CONCLUSION: Current findings suggest that peripherally measured endocannabinoids are not associated with the verbal memory deficit during MDMA intoxication. TRIAL REGISTRATION NUMBER: NTR3691.

MDMA-Induced Dissociative State not Mediated by the 5-HT2A Receptor.

Previous research has shown that a single dose of MDMA induce a dissociative state, by elevating feelings of depersonalization and derealization. Typically, it is assumed that action on the 5-HT2A receptor is the mechanism underlying these psychedelic experiences. In addition, other studies have shown associations between dissociative states and biological parameters (heart rate, cortisol), which are elevated by MDMA. In order to investigate the role of the 5-HT2 receptor in the MDMA-induced dissociative state and the association with biological parameters, a placebo-controlled within-subject study was conducted including a single oral dose of MDMA (75 mg), combined with placebo or a single oral dose of the 5-HT2 receptor blocker ketanserin (40 mg). Twenty healthy recreational MDMA users filled out a dissociative states scale (CADSS) 90 min after treatments, which was preceded and followed by assessment of a number of biological parameters (cortisol levels, heart rate, MDMA blood concentrations). Findings showed that MDMA induced a dissociative state but this effect was not counteracted by pre-treatment with ketanserin. Heart rate was the only biological parameter that correlated with the MDMA-induced dissociative state, but an absence of correlation between these measures when participants were pretreated with ketanserin suggests an absence of directional effects of heart rate on dissociative state. It is suggested that the 5-HT2 receptor does not mediate the dissociative effects caused by a single dose of MDMA. Further research is needed to determine the exact neurobiology underlying this effect and whether these effects contribute to the therapeutic potential of MDMA.

Divergent cAMP signaling differentially regulates serotonin-induced spinal motor plasticity.

Spinal metabotropic serotonin receptors encode transient experiences into long-lasting changes in motor behavior (i.e. motor plasticity). While interactions between serotonin receptor subtypes are known to regulate plasticity, the significance of molecular divergence in downstream G protein coupled receptor signaling is not well understood. Here we tested the hypothesis that distinct cAMP dependent signaling pathways differentially regulate serotonin-induced phrenic motor facilitation (pMF); a well-studied model of spinal motor plasticity. Specifically, we studied the capacity of cAMP-dependent protein kinase A (PKA) and exchange protein activated by cAMP (EPAC) to regulate 5-HT2A receptor-induced pMF within adult male rats. Although spinal PKA, EPAC and 5-HT2A each elicit pMF when activated alone, concurrent PKA and 5-HT2A activation interact via mutual inhibition thereby blocking pMF expression. Conversely, concurrent EPAC and 5-HT2A activation enhance pMF expression reflecting additive contributions from both mechanisms. Thus, we demonstrate that distinct downstream cAMP signaling pathways enable differential regulation of 5-HT2A-induced pMF. Conditional activation of independent signaling mechanisms may explain experience amendable changes in plasticity expression (i.e. metaplasticity), an emerging concept thought to enable flexible motor control within the adult central nervous system.

Discriminative stimulus properties of 1.25mg/kg clozapine in rats: Mediation by serotonin 5-HT2 and dopamine D4 receptors.

The atypical antipsychotic drug clozapine remains one of most effective treatments for schizophrenia, given a lack of extrapyramidal side effects, improvements in negative symptoms, cognitive impairment, and in symptoms in treatment-resistant schizophrenia. The adverse effects of clozapine, including agranulocytosis, make finding a safe clozapine-like a drug a goal for drug developers. The drug discrimination paradigm is a model of interoceptive stimulus that has been used in an effort to screen experimental drugs for clozapine-like atypical antipsychotic effects. The present study was conducted to elucidate the receptor-mediated stimulus properties that form this clozapine discriminative cue by testing selective receptor ligands in rats trained to discriminate a 1.25mg/kg dose of clozapine from vehicle in a two choice drug discrimination task. Full substitution occurred with the 5-HT2A inverse agonist M100907 and the two preferential D4/5-HT2/α1 receptor antagonists Lu 37-114 ((S)-1-(3-(2-(4-(1H-indol-5-yl)piperazin-1-yl)ethyl)indolin-1-yl)ethan-1-one) and Lu 37-254 (1-(3-(4-(1H-indol-5-yl)piperazin-1-yl)propyl)-3,4-dihydroquinolin-2(1H)-one). Partial substitution occurred with the D4 receptor antagonist Lu 38-012 and the α1 adrenoceptor antagonist prazosin. Drugs selective for 5-HT2C, 5-HT6 muscarinic, histamine H1, and benzodiazepine receptors did not substitute for clozapine. The present findings suggest that 5-HT2A inverse agonism and D4 receptor antagonism mediate the discriminative stimulus properties of 1.25mg/kg clozapine in rats, and further confirm that clozapine produces a complex compound discriminative stimulus.

Morphine-induced Straub tail reaction in mice treated with serotonergic compounds.

Constitutively active 5-HT2 receptors have been suggested to contribute to motoneuronal excitability, muscle spasms and spasticity. Accordingly, 5-HT2C receptor inverse agonists have been demonstrated in pilot experiments to reduce spasticity in animal model of spasticity and patients with spinal cord injuries. Thus, 5-HT2C receptor inverse agonists may represent a novel class of anti-spasticity agents justifying a search for compounds with robust 5-HT2C receptor inverse agonist activity either among the existing medications or via a dedicated drug discovery program. Morphine-induced Straub tail response in mice is regarded as a model of transient spasticity that may be suitable for supporting such drug discovery efforts. Subcutaneous injection of morphine (10-60mg/kg) induced a dose-dependent Straub tail reaction in male Swiss mice with maximum response obtained 15-30min after the morphine administration. When given prior to morphine, 5-HT2B/2C receptor inverse agonists cyproheptadine (1-10mg/kg, i.p.) and SB206553 (0.3-3mg/kg, i.p.) diminished Straub tail reaction dose-dependently without affecting spontaneous locomotor activity. In contrast, 5-HT2B/2C receptor antagonist methysergide (1-5.6mg/kg, i.p.) and 5-HT2C receptor antagonist SB242084 (1-5.6mg/kg, i.p.) as well as 5-HT2A receptor inverse agonist pimavanserin (1-10mg/kg, i.p.) had no appreciable effects on Straub tail response. Taken together, the findings indicate that constitutive activity of 5-HT2B/2C receptor may be involved in the mechanisms of morphine-induced spasticity. Thus, morphine-induced Straub tail response may be evaluated further as a candidate higher throughput test to identify 5-HT2C receptor inverse agonists with anti-spasticity effects in vivo.