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Concept: Buspirone

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Recently, the biased and highly selective 5-HT1A agonists, NLX-112, F13714 and F15599, have been shown to alleviate dyskinesia in rodent and primate models of Parkinson’s disease, while marginally interfering with antiparkinsonian effects of levodopa. To provide more detailed information on the processes underlying the alleviation of dyskinesia, we have here investigated changes in the spectral contents of local field potentials in cortico-basal ganglia-thalamic circuits following treatment with this novel group of 5-HT1A agonists or the prototypical agonist, 8-OH-DPAT. Dyskinetic symptoms were consistently associated with 80 Hz oscillations, which were efficaciously suppressed by all 5-HT1A agonists and reappeared upon co-administration of the antagonist, WAY100635. At the same time, the peak-frequency of fast 130 Hz gamma oscillations and their cross-frequency coupling to low-frequency delta oscillations were modified to a different extent by each of the 5-HT1A agonists. These findings suggest that the common antidyskinetic effects of these drugs may be chiefly attributable to a reversal of the brain state characterized by 80 Hz gamma oscillations, whereas the differential effects on fast gamma oscillations may reflect differences in pharmacological properties that might be of potential relevance for non-motor symptoms.

Concepts: Pharmacology, Parkinson's disease, Receptor antagonist, Agonist, Inverse agonist, Buprenorphine, 5-HT receptor, Buspirone

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A series of novel aralkyl piperazine derivatives were synthesized, and evaluated for their serotonin reuptake inhibitory and 5-HT1A/5-HT7 receptors affinities activity. Antidepressant activities in vivo of the compounds were screened using the forced swimming test (FST) and tail suspension test (TST). The results indicated that compounds 21k (RUI, IC50 = 31 nM; 5-HT1A, 5-HT7, ki = 62, 12 nM) and 21n (RUI, IC50 = 25 nM; 5-HT1A, 5-HT7, ki = 28, 3.3 nM) exhibited high affinities for the 5-HT1A/5-HT7 receptors coupled with potent serotonin reuptake inhibition. Specifically, the most promising compound 21n possessed a good oral pharmacokinetic properties and an acceptable hERG profile, and showed potent antidepressant-like effect in the FST and TST models.

Concepts: Serotonin, Synthesis, Selective serotonin reuptake inhibitor, Pharmacokinetics, Tricyclic antidepressant, 5-HT receptor, Nefazodone, Buspirone

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Although serotonin 5-HT1A receptors constitute attractive therapeutic targets, there is a lack of potential clinical candidates that have a high degree of selectivity and full agonist efficacy. Recently, novel 5-HT1A receptor ‘biased agonists,’ F15599 (a.k.a. NLX-101) and F13714 have been reported that exhibit distinctive properties for in vitro signaling, neurochemical, electrophysiological effects and in brain imaging. The present study characterized their effects in rat models of anxiety (elevated plus-maze and Vogel test), in depressive-like behavior (forced swim test) and on the induction of the three serotonergic behaviors (forepaw treading, flat body posture, and lower lip retraction). The prototypical 5-HT1A receptor ligands, (±)8-OH-DPAT and buspirone were tested as comparators. In the elevated plus-maze, F15599, F13714 and (±)8-OH-DPAT dose-dependently increased the amount and percentage of time spent in the open arms with minimal effective doses (MED) of 5 mg/kg p.o., 2.5 mg/kg p.o. and 1.25 mg/kg s.c., respectively. The effects of the three agonists were abolished by pretreatment with the selective 5-HT1A receptor antagonist, WAY100635 (0.63 mg/kg s.c.). Buspirone did not show significant activity in the EPM. In contrast, in the Vogel test only buspirone was active, significantly increasing the number of licks and shocks accepted (active dose: 1.25 mg/kg s.c.). However, WAY100635 failed to reverse the effects of buspirone in this test, suggesting that they were not 5-HT1A receptor-mediated. In the forced swim test, F15599, F13714 and (±)8-OH-DPAT were potently active, abolishing immobility (MED: 0.63 mg/kg p.o., 0.63 mg/kg p.o. and 0.16 mg/kg s.c., respectively). Buspirone was not active. In measures of serotonergic behavior, F13714 and (±)8-OH-DPAT robustly elicited all three signs of serotonergic behaviors, whereas F15599 and buspirone elicited only lower-lip retraction. Taken together, these observations highlight the distinct profiles of activity of 5-HT1A agonists and suggest that the novel biased agonist F15599 combines pronounced activity in a test of anxiety (elevated plus-maze) with potent antidepressant-like effects and low propensity to induce serotonergic behaviors. These data suggest that selective biased agonists could constitute promising pharmacotherapeutics for mood disorders.

Concepts: Receptor, Receptor antagonist, Serotonin, Agonist, Inverse agonist, Buprenorphine, 5-HT receptor, Buspirone

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NLX-112 (a.k.a. F13640 or befiradol), exhibits nanomolar affinity, exceptional selectivity and high agonist efficacy at 5-hydroxytryptamine 5-HT1A receptors. It possesses marked activity in a variety of animal models of depression, pain and L-DOPA-induced dyskinesia. However, its influence on translational biomarkers of central 5-HT1A receptor activation has not been previously described. Here, we report on the activity, in rats, of NLX-112 to increase plasma corticosterone levels and produce hypothermia, two responses which are also elicited by 5-HT1A receptor agonists in humans. NLX-112 elicited dose-dependent hypothermia (minimal effective dose, MED: 0.31mg/kg p.o.) and also increased plasma corticosterone both by oral and intraperitoneal routes (MED: 0.63mg/kg in both cases). The increase in corticosterone induced by NLX-112 (0.63mg/kg p.o.) was abolished by co-administration of the selective 5-HT1A receptor antagonist, WAY100635. Additionally, NLX-112 also dose-dependently induced flat body posture, forepaw treading and lower lip retraction (MEDs 0.31-0.63mg/kg p.o.). The doses of NLX-112 which induce hypothermia or corticosterone release were similar to those inducing serotonergic behaviors but greater than those reported previously in models of therapeutic-like activity (range 0.04 to 0.16mg/kg). Overall, the present study provides information for clinical dose estimations of NLX-112 and suggests that therapeutic effects may occur at doses below those at which biomarker responses are observed.

Concepts: Pharmacology, Receptor antagonist, Serotonin, Agonist, Inverse agonist, Receptor theory, Buprenorphine, Buspirone

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Firing activity of serotonergic neurons is under regulatory control by somatodendritic 5-HT1A autoreceptors (5-HT1AARs). Enhanced 5-HT1AAR functioning may cause decreased serotonergic signaling in brain and has thereby been implicated in the etiology of mood and anxiety disorders. Tryptophan hydroxylase-2 knockout (Tph2(-/-)) mice exhibit sensitization of 5-HT1A agonist-induced inhibition of serotonergic neuron firing and thus represents a unique animal model of enhanced 5-HT1AAR functioning. To elucidate the mechanisms underlying 5-HT1AAR supersensitivity in Tph2(-/-) mice, we characterized the activation of G protein-coupled inwardly-rectifying potassium (GIRK) conductance by the 5-HT1A receptor agonist 5-carboxamidotryptamine using whole-cell recordings from serotonergic neurons in dorsal raphe nucleus. Tph2(-/-) mice exhibited a mean twofold leftward shift of the agonist concentration-response curve (p < 0.001) whereas the maximal response, proportional to the 5-HT1AAR number, was not different (p = 0.42) compared to Tph2(+/-) and Tph2(+/+) littermates. No differences were found in the basal inwardly-rectifying potassium conductance, determined in the absence of agonist, (p = 0.80) nor in total GIRK conductance activated by intracellular application of GTP-γ-S (p = 0.69). These findings indicate increased functional coupling of 5-HT1AARs to GIRK channels in Tph2(-/-) mice without a concomitant increase in 5-HT1AARs and/or GIRK channel density. In addition, no changes were found in α1-adrenergic facilitation of firing (p = 0.72) indicating lack of adaptive changes Tph2(-/-) mice. 5-HT1AAR supersensitivity may represents a previously unrecognized cause of serotonergic system hypofunction and associated disorders and provides a possible explanation for conflicting results on the correlation between 5-HT1AAR density and depression in clinical imaging studies.

Concepts: Neuron, Brain, Action potential, Serotonin, Agonist, 5-HT receptor, Raphe nuclei, Buspirone

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Worsening of suicidal ideation during the first weeks of antidepressant treatment is a poorly understood phenomenon that prompted regulatory bodies to issue specific warnings. To better understand the causes of this phenomenon, this study compared the risk of suicidal ideation worsening in patients taking different types of antidepressant medications. To this aim, 4017 depressed adult outpatients were followed by general practitioners and psychiatrists throughout France for 6 weeks after prescription of an antidepressant treatment. The main study outcomes were to monitor changes (worsening or improvement) in suicidal ideation between baseline (treatment onset) and the study end (week 6) and to determine the remission rates according to the treatment type. Depression severity was assessed with the patient-administered Hospital Anxiety and Depression Scale and suicidal ideation with the 9-item Montgomery-Asberg Depression Rating Scale and the Hopelessness Scale. Use of tianeptine, a mu-opioid receptor agonist was significantly associated with a lower risk of suicidal ideation worsening compared with other antidepressants in the first 6 weeks of treatment. Conversely, remission rates were not significantly affected by the treatment type. Our results highlight a potential interest of opioid agonists to reduce the risk of worsening of suicidal ideation at antidepressant initiation.

Concepts: Receptor antagonist, Serotonin, Escitalopram, Selective serotonin reuptake inhibitor, Bipolar disorder, Buprenorphine, Tricyclic antidepressant, Buspirone

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Separation anxiety disorder was recently recognized by fifth edition of the Diagnostic and Statistical Manual of Mental Disorders as a diagnosis in adults, but no publications to date have characterized a sample of patients seeking treatment for adult separation anxiety disorder (ASAD) or assessed treatment efficacy. We hypothesized that vilazodone, a selective serotonin reuptake inhibitor (SSRI) and serotonin 1a (5HT1a ) receptor partial agonist, would have efficacy in ASAD, because SSRIs have appeared efficacious in children with mixed diagnoses including separation anxiety disorder and in animal models of separation anxiety.

Concepts: Serotonin, Agonist, Antidepressant, Selective serotonin reuptake inhibitor, Panic disorder, Tricyclic antidepressant, Reuptake inhibitor, Buspirone

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This study was designed to examine an anxiety-like behavior in the adult gonadectomized (GDX) male rats subjected to testosterone propionate (TP) treatment alone or in combination with 8-OH-DPAT, a 5-HT1A receptor agonist, or with NAN-190, 5-HT1A receptor antagonist. Two weeks after gonadectomy, GDX rats were subjected by treatments with the solvent, TP (0.5 mg/kg, s.c.), 8-OH-DPAT (0.05 mg/kg, s.c.), NAN-190 (0.1 mg/kg, i.p.), TP in combination with 8-OH-DPAT or NAN-190 during 14 days. Anxiety behavior was assessed in the elevated plus maze (EPM) and the open field test (OFT). 8-OH-DPAT treatment failed to modify the anxiety-like behavior of GDX rats in the EPM as compared to the GDX rats given with oil solvent. NAN-190 injected alone or in combination with TP to GDX rats resulted in a significant anxiolytic-like effect as compared to the GDX given with oil solvent or TP application. Our data indicate that the combination of NAN-190 and TP is more effective than TP alone in GDX rats inducing a more profound anxiolytic-like effect in the EPM. Thus, the results of this study suggest that effects of 5-HT1A receptor agonist/antagonist can modify anxiety level in opposite direction in male rats after gonadectomy.

Concepts: Receptor, Ligand, Receptor antagonist, Agonist, Inverse agonist, Receptor theory, Buprenorphine, Buspirone

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It is known that diabetic (DBT) animals present dysregulation on the serotonergic system in several brain areas associated with anxiety-like responses. The aim of this study was to investigate the involvement of 5-HT1A receptors on dorsal periaqueductal gray (dPAG) in the behavioral response related to panic disorder in type-1 DBT animals. For this, the escape response by electric stimulation (ES) of dPAG in DBT and normoglycemic (NGL) animals was assessed. Both NGL and DBT animals were exposed to an open-field test (OFT) 28 days after DBT confirmation. The current threshold to induce escape behavior in DBT animals was reduced compared with NGL animals. No impairment in locomotor activity was observed when DBT animals were compared with NGL animals. An intra-dPAG injection of the 5-HT1A receptor agonist (±)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) increased the [INCREMENT] threshold in both DBT and NGL, suggesting a panicolytic-like effect. DBT animals presented a more pronounced panicolytic-like response compared with NGL as a higher [INCREMENT] threshold was observed after 8-OH-DPAT treatment, which could be a consequence of the increased expression of the 5-HT1A receptor in the dPAG from DBT animals. Our results are in line with the proposal that a deficiency in serotonergic modulation of the dPAG is involved in triggering the panic attack and the 5-HT1A receptors might be essential for the panicolytic-like response.

Concepts: Receptor antagonist, Serotonin, Opioid receptor, Inverse agonist, Panic attack, 5-HT receptor, Periaqueductal gray, Buspirone

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Selective serotonin reuptake inhibitor (SSRI) exposures among children younger than 6 years of age are generally well tolerated. Vilazodone is an SSRI with partial agonism at the 5-HT1A receptor with demonstrated clinical efficacy for depression whose off-label usage is likely to increase. Recent evidence suggests that unintentional ingestion of vilazodone in children under 6 years old is associated with more severe clinical effects than other SSRIs. We chose to evaluate dose and outcomes for pediatric vilazodone ingestions.

Concepts: Serotonin, Agonist, Antidepressant, Selective serotonin reuptake inhibitor, Sertraline, Tricyclic antidepressant, Reuptake inhibitor, Buspirone