Raphe AMPA receptors and nicotinic acetylcholine receptors mediate ketamine-induced serotonin release in the rat prefrontal cortex.

Several lines of evidence indicate that ketamine has a rapid antidepressant-like effect in rodents and humans, but underlying mechanisms are unclear. In the present study, we investigated the effect of ketamine on serotonin (5-HT) release in the rat prefrontal cortex by in vivo microdialysis. A subcutaneous administration of ketamine (5 and 25 mg/kg) significantly increased the prefrontal 5-HT level in a dose-dependent manner, which was attenuated by local injection of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) antagonists into the dorsal raphe nucleus (DRN). Direct stimulation of AMPARs in the DRN significantly increased prefrontal 5-HT level, while intra-DRN injection of ketamine (36.5 nmol) had no effect. Furthermore, intra-DRN injection of an α 4 ß 2-nicotinic acetylcholine receptor (nAChR) antagonist, dihydro-ß-erythroidine (10 nmol), significantly attenuated the subcutaneous ketamine-induced increase in prefrontal 5-HT levels. These results suggest that AMPARs and α 4 ß 2-nAChRs in the DRN play a key role in the ketamine-induced 5-HT release in the prefrontal cortex.

Japanese subgroup analysis of EV-301: An open-label, randomized phase 3 study to evaluate enfortumab vedotin versus chemotherapy in subjects with previously treated locally advanced or metastatic urothelial carcinoma.

BACKGROUND: Enfortumab vedotin (EV) is an antibody-drug conjugate showing significant overall survival (OS) benefit versus chemotherapy for patients with previously treated locally advanced or metastatic urothelial carcinoma (la/mUC) in EV-301. This subgroup analysis was conducted to further analyze the efficacy and safety in a Japanese population. METHODS: In the open-label, phase 3 EV-301 trial, patients with la/mUC were randomized 1:1 to EV 1.25 mg/kg on Days 1, 8, and 15 for 28-day cycles or investigator-preselected standard chemotherapy (SC; docetaxel or paclitaxel for patients in Japan) on Day 1 of each 21-day cycle. Primary endpoint was OS and secondary efficacy endpoints included progression-free survival (PFS) and overall response rate (ORR). Safety/tolerability was also evaluated. RESULTS: As of the July 15, 2020 cut-off date for the interim analysis, the Japanese subgroup included 86 patients (EV: n = 36; SC: n = 50). Median OS was 15.18 months for EV and 10.55 months for SC (HR: 0.437 [95% CI: 0.209, 0.914]). Median PFS was 6.47 months for EV and 5.39 months for SC (HR: 0.464 [95% CI: 0.258, 0.835]). Confirmed ORR was 34.4% for EV and 21.3% for SC. A higher proportion of patients receiving SC versus EV had treatment-related adverse events (TRAEs; 97.9% vs. 91.7%, respectively), including grade ≥ 3 TRAEs (75.0% vs. 63.9%). CONCLUSIONS: This subgroup analysis confirmed that EV, with consistent efficacy and safety/tolerability in the EV-301 Japanese subgroup and overall study population, represents an important treatment option for previously treated patients with la/mUC.

Manipulation of dorsal raphe serotonergic neurons modulates active coping to inescapable stress and anxiety-related behaviors in mice and rats.

Major depression and anxiety disorders are a social and economic burden worldwide. Serotonergic signaling has been implicated in the pathophysiology of these disorders and thus has been a crucial target for pharmacotherapy. However, the precise mechanisms underlying these disorders are still unclear. Here, we used species-optimized lentiviral vectors that were capable of efficient and specific transduction of serotonergic neurons in mice and rats for elucidation of serotonergic roles in anxiety-like behaviors and active coping behavior in both species. Immunohistochemical analyses revealed that lentiviral vectors with an upstream sequence of tryptophan hydroxylase 2 gene efficiently transduced serotonergic neurons with a specificity of approximately 95% in both mice and rats. Electrophysiological recordings showed that these lentiviral vectors induced sufficient expression of optogenetic tools for precise control of serotonergic neurons. Using these vectors, we demonstrate that acute activation of serotonergic neurons in the dorsal raphe nucleus increases active coping with inescapable stress in rats and mice in a time-locked manner, and that acute inhibition of these neurons increases anxiety-like behaviors specifically in rats. These findings further our understanding of the pathophysiological role of dorsal raphe serotonergic neurons in different species and the role of these neurons as therapeutic targets in major depression and anxiety disorders.

Olanzapine augments the effect of selective serotonin reuptake inhibitors by suppressing GABAergic inhibition via antagonism of 5-HT6 receptors in the dorsal raphe nucleus.

The combination of the selective serotonin reuptake inhibitors (SSRIs) and atypical antipsychotic drugs shows better therapeutic efficacy than SSRI monotherapy in the treatment of depression. However, the underlying mechanisms responsible for the augmenting effects of olanzapine are not fully understood. Here, we report that olanzapine enhances the SSRI-induced increase in extracellular serotonin (5-HT) levels and antidepressant-like effects by inhibiting GABAergic neurons through 5-HT6 receptor antagonism in the dorsal raphe nucleus (DRN). In organotypic raphe slice cultures, treatment with olanzapine (1-100 µM) enhanced the increase in extracellular 5-HT levels in the presence of fluoxetine (10 µM) or citalopram (1 µM). The enhancing effect of olanzapine was not further augmented by the GABAA receptor antagonist bicuculline. Electrophysiological analysis revealed that olanzapine (50 µM) decreased the firing frequency of GABAergic neurons in acute DRN slices. Among many serotonergic agents, the 5-HT6 receptor antagonist SB399885 (1-100 µM) mimicked the effects of olanzapine by enhancing the SSRI-induced increase in extracellular 5-HT levels, which was not further augmented by bicuculline or olanzapine. SB399885 (50 µM) also decreased the firing frequency of GABAergic neurons in the DRN. In addition, an intraperitoneal administration of SB399885 (10 mg/kg) to mice significantly enhanced the antidepressant-like effect of a subeffective dose of citalopram (3 mg/kg) in the tail-suspension test. These results suggest that olanzapine decreases local inhibitory GABAergic tone in the DRN through antagonism of 5-HT6 receptors, thereby increasing the activity of at least part of serotonergic neurons, which may contribute to the augmentation of the efficacy of SSRIs.

Inhibition of histone deacetylases enhances the function of serotoninergic neurons in organotypic raphe slice cultures.

Inhibition of histone deacetylases (HDACs) is a promising approach for the treatment of mood disorders. However, the effects of HDAC inhibition on the serotonin (5-HT) system, a common target for psychiatric disorders, are poorly understood. Here, we show that a broad-spectrum HDAC inhibitor, trichostatin A (TSA), enhances the function of 5-HT neurons in organotypic raphe slice cultures. Sustained treatment with TSA (1µM) for 2 or 4 days significantly increased the 5-HT tissue content and tryptophan hydroxylase 2 (TPH2) expression, which were accompanied by hyper-acetylation of histone H3 in the promoter region of the TPH2 gene. TSA treatment for 4 days increased the extracellular 5-HT level, which was significantly suppressed in the presence of the selective AMPA receptor (AMPAR) antagonist NBQX. Moreover, the expression of both the AMPAR subunit GluA2 and Ca(2+)/calmodulin-dependent kinase II α (CaMKIIα) mRNAs were significantly increased by TSA treatment. Co-treatment with the CaMKII inhibitors KN-62 and KN-93 prevented the TSA-induced increase in 5-HT release, but had no effect on the increases in 5-HT tissue content. These results suggest that inhibition of HDACs increases 5-HT synthesis and release by epigenetic mechanisms, and that 5-HT release is mediated by the enhancement of AMPAR-mediated excitatory inputs and CaMKII signaling.