Genetically altered AMPA-type glutamate receptor kinetics in interneurons disrupt long-range synchrony of gamma oscillation

Gamma oscillations synchronized between distant neuronal populations may be critical for binding together brain regions devoted to common processing tasks. Network modeling predicts that such synchrony depends in part on the fast time course of excitatory postsynaptic potentials (EPSPs) in interneurons, and that even moderate slowing of this time course will disrupt synchrony. We generated mice with slowed interneuron EPSPs by gene targeting, in which the gene encoding the 67-kDa form of glutamic acid decarboxylase (GAD67) was altered to drive expression of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor subunit GluR-B. GluR-B is a determinant of the relatively slow EPSPs in excitatory neurons and is normally expressed at low levels in γ-aminobutyric acid (GABA)ergic interneurons, but at high levels in the GAD-GluR-B mice. In both wild-type and GAD-GluR-B mice, tetanic stimuli evoked gamma oscillations that were indistinguishable in local field potential recordings. Remarkably, however, oscillation synchrony between spatially separated sites was severely disrupted in the mutant, in association with changes in interneuron firing patterns. The congruence between mouse and model suggests that the rapid time course of AMPA receptor-mediated EPSPs in interneurons might serve to allow gamma oscillations to synchronize over distance

Non-Canonicaly Recruited TCRαβCD8αα IELs Recognize Microbial Antigens

In the gut, various subsets of intraepithelial T cells (IELs) respond to self or non-self-antigens derived from the body, diet, commensal and pathogenic microbiota. Dominant subset of IELs in the small intestine are TCRαβCD8αα+ cells, which are derived from immature thymocytes that express self-reactive TCRs. Although most of TCRαβCD8αα+ IELs are thymus-derived, their repertoire adapts to microbial flora. Here, using high throughput TCR sequencing we examined how clonal diversity of TCRαβCD8αα+ IELs changes upon exposure to commensal-derived antigens. We found that fraction of CD8αα+ IELs and CD4+ T cells express identical αβTCRs and this overlap raised parallel to a surge in the diversity of microbial flora. We also found that an opportunistic pathogen (Staphylococcus aureus) isolated from mouse small intestine specifically activated CD8αα+ IELs and CD4+ derived T cell hybridomas suggesting that some of TCRαβCD8αα+ clones with microbial specificities have extrathymic origin. We also report that CD8ααCD4+ IELs and Foxp3CD4+ T cells from the small intestine shared many αβTCRs, regardless whether the later subset was isolated from Foxp3CNS1 sufficient or Foxp3CNS1 deficient mice that lacks peripherally-derived Tregs. Overall, our results imply that repertoire of TCRαβCD8αα+ in small intestine expends in situ in response to changes in microbial flora

Nucleus-specific abnormalities of GABAergic synaptic transmission in a genetic model of absence seizures

Human and experimental studies indicate that molecular genetic changes in GABAA receptors may underlie the expression of spike-and-waves discharges (SWDs) occurring during absence seizures. However, the full spectrum of the genetic defects underlying these seizures has only been partially elucidated, the expression and functional profiles of putative abnormal protein(s) within the thalamocortical network are undefined, and the pathophysiological mechanism(s) by which these proteins would lead to absence paroxysms are poorly understood. Here we investigated GABAA inhibitory postsynaptic currents (IPSCs) in key thalamocortical areas, i.e., the somatosensory cortex, ventrobasal thalamus (VB) and nucleus reticularis thalami (NRT), in preseizure genetic absence epilepsy rats from Strasbourg (GAERS), a well-established genetic model of typical absence seizures that shows no additional neurological abnormalities, and compared their properties to age-matched non-epileptic controls (NECs). Miniature GABAA IPSCs of VB and cortical layers II/III neurons were similar in GAERS and NEC, whereas in GAERS NRT neurons they had 25% larger amplitude, 40% faster decay. In addition, baclofen was significantly less effective in decreasing the frequency of NRT mIPSCs in GAERS than in NEC, whereas no difference was observed for cortical and VB mIPSCS between the two strains. Paired-pulse depression was 45% smaller in GAERS NRT, but not in VB, and was insensitive to GABAB antagonists. These results point to subtle, nucleus-specific, GABAA receptor abnormalities underlying SWDs of typical absence seizures rather than a full block of these receptors across the whole thalamocortical network, and their occurrence prior to seizure onset suggests that they might be of epileptogenic significance

Single-cell analysis of thymocyte differentiation: identification of transcription factor interactions and a major stochastic component in αβ\alpha\beta-lineage commitment.

International audienceT cell commitment and $\alpha\beta$/$\gamma\delta$ lineage specification in the thymus involves interactions between many different genes. Characterization of these interactions thus requires a multiparameter analysis of individual thymocytes. We developed two efficient single-cell methods: (i) the quantitative evaluation of the co-expression levels of nine different genes, with a plating efficiency of 99-100% and a detection limit of 2 mRNA molecules/cell; and (ii) single-cell differentiation cultures, in the presence of OP9 cells transfected with the thymus Notch1 ligand DeltaL4. We show that during T cell commitment, Gata3 has a fundamental, dose-dependent role in maintaining Notch1 expression, with thymocytes becoming T-cell-committed when they co-express Notch1, Gata3 and Bc11b. Of the transcription factor expression patterns studied here, only that of Bcl11b was suggestive of a role in Pu1 down-regulation. Individual thymocytes became $\alpha\beta$$\gamma\delta$-lineage-committed at very different stages (from the TN2a stage onwards). However, 20% of TN3 cells are not $\alpha\beta$/$\gamma\delta$ lineage committed and TN4 cells comprise two main subpopulations with different degrees of maturity. The existence of a correlation between differentiation potential and expression of the pre-TCR showed that 83% of $\alpha\beta$-committed cells do not express the pre-TCR and revealed a major stochastic component in $\alpha\beta$-lineage specification

Identification of sleep-promoting neurons in vitro

The neurons responsible for the onset of sleep are thought to be located in the preoptic area and more specifically, in the ventrolateral preoptic nucleus (VLPO). Here we identify sleep-promoting neurons in vitro and show that they represent an homogeneous population of cells that must be inhibited by systems of arousal during the waking state. We find that two-thirds of the VLPO neurons are multipolar triangular cells that show a low-threshold spike. This proportion matches that of cells active during sleep in the same region. We then show, using single-cell reverse transcriptase followed by polymerase chain reaction, that these neurons probably contain gamma-aminobutyric acid (GABA). We also show that these neurons are inhibited by noradrenaline and acetylcholine, both of which are transmitters of wakefulness. As most of these cells are also inhibited by serotonin but unaffected by histamine, their overall inhibition by transmitters of wakefulness is in agreement with their relative inactivity during waking with respect to sleep. We propose that the reciprocal inhibitory interaction of such VLPO neurons with the noradrenergic, serotoninergic and cholinergic waking systems to which they project is a key factor for promoting sleep