Mutations in Eml1 lead to ectopic progenitors and neuronal heterotopia in mouse and human.

Neuronal migration disorders such as lissencephaly and subcortical band heterotopia are associated with epilepsy and intellectual disability. DCX, PAFAH1B1 and TUBA1A are mutated in these disorders; however, corresponding mouse mutants do not show heterotopic neurons in the neocortex. In contrast, spontaneously arisen HeCo mice display this phenotype, and our study revealed that misplaced apical progenitors contribute to heterotopia formation. While HeCo neurons migrated at the same speed as wild type, abnormally distributed dividing progenitors were found throughout the cortical wall from embryonic day 13. We identified Eml1, encoding a microtubule-associated protein, as the gene mutated in HeCo mice. Full-length transcripts were lacking as a result of a retrotransposon insertion in an intron. Eml1 knockdown mimicked the HeCo progenitor phenotype and reexpression rescued it. We further found EML1 to be mutated in ribbon-like heterotopia in humans. Our data link abnormal spindle orientations, ectopic progenitors and severe heterotopia in mouse and human

Mice lacking the serotonin 5-HT2B receptor as an animal model of resistance to selective serotonin reuptake inhibitors antidepressants

Depressive disorders are among the most prevalent neuropsychiatric dysfunctions worldwide, with high rates of resistance to antidepressant treatment. Genetic factors clearly contribute to the manifestation of depression as well as to the response to antidepressants. Transgenic mouse models appear as seminal tools to disentangle this complex disorder. Here, we analyzed new key aspects of the phenotype of knock-out mice for the gene encoding the serotonin 2B receptor (Htr2B−/−), including basal phenotype, ability to develop a depressive-like phenotype upon chronic isolation, and effect of chronic exposure to fluoxetine on chronically stressed Htr2B−/− mice. We find, here, that Htr2B−/− mice display an antidepressant-like phenotype, which includes reduced latency to feed in the novelty suppressed feeding test, basal increase in hippocampal BDNF levels, no change in TrkB and p75 protein levels, and an increased preference for sucrose consumption compared to wild type (Htr2B+/+) mice. Nevertheless, we show that these mice can develop depressive-like behaviors when socially isolated during four weeks. Selective serotonin reuptake inhibitors (SSRI) have been previously shown to be ineffective in non-stressed Htr2B−/− mice. We evaluated, here, the effects of the SSRI fluoxetine in chronically stressed Htr2B−/− mice and similarly no behavioral or plastic effect was induced by this antidepressant. All together, these results highlight the suitability to study resistance to SSRI antidepressants of this mouse model displaying panoply of conditions among which behavioral, neurotrophic and plastic causative factors can be analyzed.Fil: Diaz, Silvina Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Biología Celular y Neurociencia "Prof. Eduardo de Robertis". Universidad de Buenos Aires. Facultad de Medicina. Instituto de Biología Celular y Neurociencia; Argentina. Inserm; Francia. Universite Pierre et Marie Curie; FranciaFil: Narboux Nême, Nicolas. Inserm; Francia. Universite Pierre et Marie Curie; FranciaFil: Boutourlinsky, Katia. Inserm; Francia. Universite Pierre et Marie Curie; FranciaFil: Doly, Stéphane. Inserm; Francia. Universite Pierre et Marie Curie; FranciaFil: Maroteaux, Luc. Inserm; Francia. Universite Pierre et Marie Curie; Franci

Layer 2/3 Pyramidal Neurons Control the Gain of Cortical Output

International audienceGraphical Abstract Highlights d Cortical layer 2/3 (L2/3) input evokes both excitatory and inhibitory currents in L5 d L2/3 input has a net excitatory effect in L5 d L2/3 input amplifies sensory-evoked responses in L5 d L2/3 input modulates the gain of sensory-evoked responses in L

Role of the N-terminal region in G protein-coupled receptor functions: negative modulation revealed by 5-HT2B receptor polymorphisms.

International audienceThe putative role of the N-terminal region of rhodopsin-like 7 transmembrane biogenic amine receptors in agonist-induced signaling has not yet been clarified despite recent advances in 7 transmembrane receptor structural biology. Given the existence of N-terminal nonsynonymous polymorphisms (R6G;E42G) within the HTR2B gene in a drug-abusing population, we assessed whether these polymorphisms affect 5-hydroxytryptamine 2B (5-HT2B) receptor in vitro pharmacologic and coupling properties in transfected COS-7 cells. Modification of the 5-HT2B receptor N terminus by the R6G;E42G polymorphisms increases such agonist signaling pathways as inositol phosphate accumulation as assessed by either classic or operational models. The N-terminal R6G;E42G mutations of the 5-HT2B receptor also increase cell proliferation and slow its desensitization kinetics compared with the wild-type receptor, further supporting a role for the N terminus in transduction efficacy. Furthermore, by coexpressing a tethered wild-type 5-HT2B receptor N terminus with a 5-HT2B receptor bearing a N-terminal deletion, we were able to restore original coupling. This reversion to normal activity of a truncated 5-HT2B receptor by coexpression of the membrane-tethered wild-type 5-HT2B receptor N terminus was not observed using a membrane-tethered 5-HT2B receptor R6G;E42G N terminus. These data suggest that the N terminus exerts a negative control over basal as well as agonist-stimulated receptor activity that is lost in the R6G;E42G mutant. Our findings reveal a new and unanticipated role of the 5-HT2B receptor N terminus as a negative modulator, affecting both constitutive and agonist-stimulated activity. Moreover, our data caution against excluding the N terminus and extracellular loops in structural studies of this 7 transmembrane receptor family

Inhibition of Cav3.2 T-type Calcium Channels by Its Intracellular I-II Loop

International audienceVoltage-dependent calcium channels (Cav) of the T-type family (Cav3.1, Cav3.2, and Cav3.3) are activated by low threshold membrane depolarization and contribute greatly to neuronal network excitability. Enhanced T-type channel activity, especially Cav3.2, contributes to disease states, including absence epilepsy. Interestingly, the intracellular loop connecting domains I and II (I-II loop) of Cav3.2 channels is implicated in the control of both surface expression and channel gating, indicating that this I-II loop plays an important regulatory role in T-type current. Here we describe that co-expression of this I-II loop or its proximal region (⌬1-Cav3.2; Ser 423 –Pro 542) together with recombinant full-length Cav3.2 channel inhibited T-type current without affecting channel expression and membrane incorporation. Similar T-type current inhibition was obtained in NG 108-15 neuroblastoma cells that constitutively express Cav3.2 channels. Of interest, ⌬1-Cav3.2 inhibited both Cav3.2 and Cav3.1 but not Cav3.3 currents. Efficacy of ⌬1-Cav3.2 to inhibit native T-type channels was assessed in thalamic neurons using viral transduction. We describe that T-type current was significantly inhibited in the ventrobasal neurons that express Cav3.1, whereas in nucleus reticularis thalami neurons that express Cav3.2 and Cav3.3 channels, only the fast inactivating T-type current (Cav3.2 component) was significantly inhibited. Altogether, these data describe a new strategy to differentially inhibit Cav3 isoforms of the T-type calcium channels

Role of serotonin via 5-HT2B receptors in the reinforcing effects of MDMA in mice

The amphetamine derivative 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) reverses dopamine and serotonin transporters to produce efflux of dopamine and serotonin, respectively, in regions of the brain that have been implicated in reward. However, the role of serotonin/dopamine interactions in the behavioral effects of MDMA remains unclear. We previously showed that MDMA-induced locomotion, serotonin and dopamine release are 5-HT2B receptor-dependent. The aim of the present study was to determine the contribution of serotonin and 5-HT 2B receptors to the reinforcing properties of MDMA. We show here that 5-HT2B 2/2 mice do not exhibit behavioral sensitization or conditioned place preference following MDMA (10 mg/kg) injections. In addition, MDMA-induced reinstatement of conditioned place preference after extinction and locomotor sensitization development are each abolished by a 5-HT2B receptor antagonist (RS127445) in wild type mice. Accordingly, MDMA-induced dopamine D1 receptor-dependent phosphorylation of extracellular regulated kinase in nucleus accumbens is abolished in mice lacking functional 5-HT2B receptors. Nevertheless, high doses (30 mg/kg) of MDMA induce dopamine-dependent but serotonin and 5-HT2B receptor-independent behavioral effects. These results underpin the importance of 5-HT 2B receptors in the reinforcing properties of MDMA and illustrate the importance of dosedependen

5-HT(2B) receptors are required for serotonin-selective antidepressant actions

The therapeutic effects induced by serotonin-selective reuptake inhibitor (SSRI) antidepressants are initially triggered by blocking the serotonin transporter and rely on long-term adaptations of pre- and post-synaptic receptors. We show here that long-term behavioral and neurogenic SSRI effects are abolished after either genetic or pharmacological inactivation of 5-HT(2B) receptors. Conversely, direct agonist stimulation of 5-HT(2B) receptors induces an SSRI-like response in behavioral and neurogenic assays. Moreover, the observation that (i) this receptor is expressed by raphe serotonergic neurons, (ii) the SSRI-induced increase in hippocampal extracellular serotonin concentration is strongly reduced in the absence of functional 5-HT(2B) receptors and (iii) a selective 5-HT(2B) agonist mimics SSRI responses, supports a positive regulation of serotonergic neurons by 5-HT(2B) receptors. The 5-HT(2B) receptor appears, therefore, to positively modulate serotonergic activity and to be required for the therapeutic actions of SSRIs. Consequently, the 5-HT(2B) receptor should be considered as a new tractable target in the combat against depression

Effect of 5-HT2B receptor inhibition on locomotor activity and behavioral sensitization after MDMA injection.

<p><b>Locomotor sensitization after MDMA two-injection protocol in WT and 5-HT_2B^−/− mice (A–D):</b> MDMA (10 mg/kg i.p.) increases locomotor activity after the first injection (1^st) in WT mice but not in 5-HT_2B^−/− mice <b>A</b>) or RS127445-treated WT mice <b>B</b>). The stimulant effect of a challenge dose of MDMA (10 mg/kg) 7 days later (2^nd) was significantly enhanced compared to the first injection in WT mice, while it had no effect in 5-HT_2B^−/− mice <b>A</b>) or RS127445 pre-treated WT mice <b>B</b>). To evaluate the role of 5-HT_2B receptors in the development of locomotor sensitization, WT mice were treated with RS127445 30 min before the first injection of MDMA. The increased responsiveness to the challenge injection of MDMA in absence of RS127445 was totally abolished <b>C</b>). MDMA (30 mg/kg i.p.) induces locomotor activity after the first injection in WT and 5-HT_2B^−/− mice compared to saline injection <b>D</b>). The stimulant effect of a challenge dose of MDMA (30 mg/kg) was significantly enhanced compared to the first injection in both WT and 5-HT_2B^−/− mice <b>D</b>). Data (means±SEM, <i>n</i> = 8−14 per group) were analyzed by two-way ANOVA with genotype (<b>A–D</b>) or RS127445 pre-treatment (<b>B–C</b>) and MDMA treatment as main factors. A significant interaction was observed for the locomotor activity in figure <b>A</b>) <i>F</i> (2,66) = 12.86 <i>p</i><0.01, and <b>B</b>) <i>F</i> (2,54) = 11.49 <i>p</i><0.01, as well as a main effect of genotype <i>F</i> (2, 66) = 15.68, p<0.001 (<b>A</b>) or RS127445 pre-treatment <i>F</i> (2, 54) = 10.24, p<0.05 (<b>B</b>) and of MDMA treatment <i>F</i> (1,66) = 9.26, p<0.001 (<b>A</b>), and <i>F</i> (1,54) = 17.04, p<0.001 (<b>B</b>). No significant interaction was observed for the locomotor activity in figure <b>C</b>) <i>F</i> (2,66) = 3.57, ns, whereas a main effect of RS127445 pre-treatment at the 1^st MDMA injection, <i>F</i> (2,66) = 28.56, p<0.001, and of MDMA treatment <i>F</i> (1,66) = 6.64, p<0.01 were detected. Neither a significant interaction, <i>F</i> (2,50) = 0.25, ns, nor a main effect of genotype <i>F</i> (1,50) = 0.9, ns, was observed for the locomotor activity in figure <b>D</b>), whereas a main effect of MDMA treatment, <i>F</i> (2,50) = 82.72, <i>p</i><0.001, was detected. Bonferroni tests were used for post-hoc comparisons. The null hypothesis was rejected at the p<0.05 level; *p<0.05; **p<0.01; ***p<0.001 compared to saline-treated mice. °p<0.05; °°°p<0.001 compared to MDMA 1^st injection. <b>Locomotor sensitization after repeated MDMA injection in WT and 5-HT_2B^−/− mice (E):</b> MDMA (10 mg/kg i.p.) increases locomotor activity after the first injection (day 1; d1) in WT mice but not in 5-HT_2B^−/− mice compare to saline injection. Repeated MDMA injection during the following days (Day 2 to 5, d2–d5) increases locomotor activity only in WT mice. The stimulant effect of a challenge dose of MDMA (10 mg/kg) 5 days later (day 10; d10) was significantly enhanced compared to the first injection in WT mice, while it had no effect in 5-HT_2B^−/− mice. Data (means±SEM, <i>n</i> = 8 per group) were analyzed by two-way ANOVA with genotype and MDMA treatment as main factors. Bonferroni tests were used for post-hoc comparisons. The null hypothesis was rejected at the p<0.05 level; **p<0.01; ***p<0.001 compared to saline-treated mice. °°°p<0.001 compared to MDMA day 1 injection.</p