Synaptic plasticity through a naturalistic lens

From the myriad of studies on neuronal plasticity, investigating its underlying molecular mechanisms up to its behavioral relevance, a very complex landscape has emerged. Recent efforts have been achieved toward more naturalistic investigations as an attempt to better capture the synaptic plasticity underpinning of learning and memory, which has been fostered by the development of in vivo electrophysiological and imaging tools. In this review, we examine these naturalistic investigations, by devoting a first part to synaptic plasticity rules issued from naturalistic in vivo-like activity patterns. We next give an overview of the novel tools, which enable an increased spatio-temporal specificity for detecting and manipulating plasticity expressed at individual spines up to neuronal circuit level during behavior. Finally, we put particular emphasis on works considering brain-body communication loops and macroscale contributors to synaptic plasticity, such as body internal states and brain energy metabolism

Two-photon Imaging of Microglial Processes' Attraction Toward ATP or Serotonin in Acute Brain Slices

International audienceMicroglial cells are resident innate immune cells of the brain that constantly scan their environment with their long processes and, upon disruption of homeostasis, undergo rapid morphological changes. For example, a laser lesion induces in a few minutes an oriented growth of microglial processes, also called "directional motility", toward the site of injury. A similar effect can be obtained by delivering locally ATP or serotonin (5-hydroxytryptamine [5-HT]). In this article, we describe a protocol to induce a directional growth of microglial processes toward a local application of ATP or 5-HT in acute brain slices of young and adult mice and to image this attraction over time by multiphoton microscopy. A simple method of quantification with free and open-source image analysis software is proposed. A challenge that still characterizes acute brain slices is the limited time, decreasing with age, during which the cells remain in a physiological state. This protocol, thus, highlights some technical improvements (medium, air-liquid interface chamber, imaging chamber with a double perfusion) aimed at optimizing the viability of microglial cells over several hours, especially in slices from adult mice

Pathway-specific action of gamma-hydroxybutyric acid in sensory thalamus and its relevance to absence seizures

The systemic injection of -hydroxybutyric acid (GHB) elicits spike and wave discharges (SWDs), the EEG hallmark of absence seizures, and represents a well established, widely used pharmacological model of this nonconvulsive epilepsy. Despite this experimental use of GHB, as well as its therapeutic use in narcolepsy and its increasing abuse, however, the precise cellular mechanisms underlying the different pharmacological actions of this drug are still unclear. Because sensory thalamic nuclei play a key role in the generation of SWDs and sleep rhythms, and because direct injection of GHB in the ventrobasal (VB) thalamus elicits SWDs, we investigated GHB effects on corticothalamic EPSCs and GABAergic IPSCs in VB thalamocortical (TC) neurons. GHB (25

Engineering two-dimensional superconductivity and Rashba spin-orbit coupling in LaAlO/SrTiO quantum wells by selective orbital occupancy

The discovery of two-dimensional electron gases (2DEGs) at oxide interfaces-involving electrons in narrow d -bands-has broken new ground, enabling the access to correlated states that are unreachable in conventional semiconductors based on s - and p - electrons. There is a growing consensus that emerging properties at these novel quantum wells-such as 2D superconductivity and magnetism-are intimately connected to specific orbital symmetries in the 2DEG sub-band structure. Here we show that crystal orientation allows selective orbital occupancy, disclosing unprecedented ways to tailor the 2DEG properties. By carrying out electrostatic gating experiments in LaAlO₃/SrTiO₃ wells of different crystal orientations, we show that the spatial extension and anisotropy of the 2D superconductivity and the Rashba spin-orbit field can be largely modulated by controlling the 2DEG sub-band filling. Such an orientational tuning expands the possibilities for electronic engineering of 2DEGs at LaAlO₃/SrTiO₃ interfaces. Two-dimensional electron gases at oxide interfaces induce exotic behaviours. By studying samples with different crystal orientation, Herranz et al. show that the extension and anisotropy of the oxide quantum well properties can be controlled through selective sub-band filling via orientational tuning

Dynamique spatio-temporelle et régulation de l'activité de la<br />protéine kinase activée par l'adénosine monophosphate cyclique<br />dans des préparations de neurones en tranche<br />et<br />Les mécanismes cellulaires d'action du GHB dans le thalamus<br />ventrobasal.

Dans le système nerveux central, le principal effecteur de la voie de transduction de l'AMPcest la protéine kinase activée par l'AMPc (PKA). L'activation de la PKA est impliquée dans denombreux processus comme la modulation de l'excitabilité neuronale par phosphorylation decanaux ioniques, de l'homéostasie cellulaire par phosphorylation de cibles cytosoliques et de larégulation génique par phosphorylation de facteurs de transcription. La régulation de l'activité de laPKA ainsi que son activation spatiale et temporelle sont des paramètres indispensables à lacompréhension des mécanismes cellulaires à l'origine des effets de cette voie de seconds messagers.Faute d'approches méthodologiques adaptées, très peu d'études se sont intéressées à la dynamiquespatiale et temporelle, à la spécificité et à la régulation de l'activité de la PKA dans les neurones.Grâce aux sondes fluorescentes codées génétiquement, il est possible maintenant d'avoiraccès à ces paramètres. A l'aide d'un vecteur viral, nous avons fait exprimer une sonde sensible àl'activité PKA (sonde AKAR pour A-kinase activity reporter) dans des préparations de neurones entranches. Cette sonde utilise le principe du transfert d'énergie par résonance (FRET) et permet demesurer par imagerie ratiométrique l'activité kinase de la PKA. Nous avons montré que la sondeAKAR2, exprimée dans les neurones, modifie son spectre d'émission en réponse à une stimulationde la voie AMPc. L'utilisation d'une sonde mutante, dont le site de phosphorylation a été modifié,démontre que les changements observés dans le spectre d'émission de la sonde AKAR2 sont bienattribuables à une phosphorylation.Dans une première partie, nous avons étudié la phosphorylation de protéines cibles de laPKA dans différents compartiments subcellulaires en réponse à différentes stimulationsextracellulaires. La phosphorylation de la sonde AKAR2, nous a permis de suivre en temps réell'activité de la PKA dans le cytosol. Afin de mesurer l'activité de la PKA dans le noyau, nous avonsadressé la sonde AKAR2 en utilisant un signal de localisation nucléaire (NLS). Enfin, la mesure del'activité de la PKA à la membrane a été réalisée grâce à l'étude de la phosphorylation des canauxresponsables du courant de l'AHP lente (IsAHP). Nous avons montré que la phosphorylation descanaux ioniques est plus rapide que la phosphorylation des cibles cytosoliques, elles-mêmes plusrapide que la phosphorylation des protéines nucléaires. De plus, nous avons montré que l'activité dela PKA stimulée par l'activation de récepteurs couplés aux protéines G (RCPG) est différente del'activation directe des adénylyl cyclases (AC). En effet, l'activation de la PKA résultant de lastimulation des RCPG produit des amplitudes de phosphorylation plus faible de la sonde AKAR2dans le cytosol et le noyau.Dans une deuxième partie, nous avons étudié le rôle des phosphodiestérases de type 4(PDE4) dans la régulation des réponses β-adrénergiques. L'inhibition des PDE4 produit uneactivation de la PKA dans les neurones traduisant ainsi une activité tonique des AC. Nous montronségalement que l'inhibition des PDE4 permet de potentialiser l'activité de la PKA en réponse à defaibles concentrations d'agonistes β adrénergiques. Cette famille de PDEs, en dégradant l'AMPc,participe donc à la régulation et la propagation des signaux PKA dans les neurones.Enfin, au cours de ma thèse, je me suis également intéressé au γ-hydroxybutyrate (GHB)composé qui est utilisé pour soigner certains troubles du sommeil et provoque chez le ratl'apparition de signes comportementaux et de tracés encéphalographiques similaires à ceux observéschez l'humain lors de crises d'épilepsie de type absence. L'ensemble de ces effets du GHB passeprobablement par une action sur la boucle thalamocorticale mais les mécanismes cellulaires à leursorigines sont inconnus. Nous avons montré grâce à l'utilisation d'enregistrementsélectrophysiologiques, que les courants post-synaptiques inhibiteurs sont beaucoup moins sensiblesau GHB que les courants post-synaptiques excitateurs et les courants potassiques à rectificationentrante (GIRK). Cette différence de sensibilité serait à l'origine d'un déséquilibre de la balanceexcitation/inhibition reçue par les neurones thalamocorticaux ce qui participerait à la genèse d'uneactivité oscillante du potentiel membranaire de ces neurones

Dynamique spatio-temporelle et régulation de l'activité de la protéine kinase activée par l'adénosine monophosphate cyclique dans des préparations de neurones en tranche, et les mécanismes cellulaires d'action du GHB dans le thalamus ventrobasal

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Differential enhancement of ERK, PKA and Ca 2+ signaling in direct and indirect striatal neurons of Parkinsonian mice

International audienceParkinson's disease (PD) is characterized by severe locomotor deficits due to the disappearance of dopamine (DA) from the dorsal striatum. The development of PD symptoms and treatment-related complications such as dyskinesia have been proposed to result from complex alterations in intracellular signaling in both direct and indirect pathway striatal projection neurons (dSPNs and iSPNs, respectively) following loss of DA afferents. To identify cell-specific and dynamical modifications of signaling pathways associated with PD, we used a hemiparkinsonian mouse model with 6-hydroxydopamine (6-OHDA lesion) combined with two-photon fluorescence biosensors imaging in adult corticostriatal slices. After DA lesion, extracellular signal-regulated kinase (ERK) activation was found increased in response to DA D1 receptor (D1R) or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)

Whole-Cell Photobleaching Reveals Time-Dependent Compartmentalization of Soluble Proteins by the Axon Initial Segment

International audienceBy limiting protein exchange between the soma and the axon, the axon initial segment (AIS) enables the segregation of specific proteins and hence the differentiation of the somatodendritic compartment and the axonal compartment. Electron microscopy and super-resolution fluorescence imaging have provided important insights in the ultrastructure of the AIS. Yet, the full extent of its filtering properties is not fully delineated. In particular, it is unclear whether and how the AIS opposes the free exchange of soluble proteins. Here we describe a robust framework to combine whole-cell photobleaching and retrospective high-resolution imaging in developing neurons. With this assay, we found that cytoplasmic soluble proteins that are not excluded from the axon upon expression over tens of hours exhibit a strong mobility reduction at the AIS-i.e., are indeed compartmentalized-when monitored over tens of minutes. This form of compartmentalization is developmentally regulated, requires intact F-actin and may be correlated with the composition and ultrastructure of the submembranous spectrin cytoskeleton. Using computational modeling, we provide evidence that both neuronal morphology and the AIS regulate this compartmentalization but act on distinct time scales, with the AIS having a more pronounced effect on fast exchanges. Our results thus suggest that the rate of protein accumulation in the soma may impact to what extent and over which timescales freely moving molecules can be segregated from the axon. This in turn has important implications for our understanding of compartment-specific signaling in neurons

Pathway-Specific Action of γ-Hydroxybutyric Acid in Sensory Thalamus and Its Relevance to Absence Seizures

The systemic injection of -hydroxybutyric acid (GHB) elicits spike and wave discharges (SWDs), the EEG hallmark of absence seizures, and represents a well established, widely used pharmacological model of this nonconvulsive epilepsy. Despite this experimental use of GHB, as well as its therapeutic use in narcolepsy and its increasing abuse, however, the precise cellular mechanisms underlying the different pharmacological actions of this drug are still unclear. Because sensory thalamic nuclei play a key role in the generation of SWDs and sleep rhythms, and because direct injection of GHB in the ventrobasal (VB) thalamus elicits SWDs, we investigated GHB effects on corticothalamic EPSCs and GABAergic IPSCs in VB thalamocortical (TC) neurons. GHB (25

Floral scent and species divergence in a pair of sexually deceptive orchids

Speciation is typically accompanied by the formation of isolation barriers between lineages. Commonly, reproductive barriers are separated into pre- and post-zygotic mechanisms that can evolve with different speed. In this study, we measured the strength of different reproductive barriers in two closely related, sympatric orchids of the Ophrys insectifera group, namely Ophrys insectifera and Ophrys aymoninii to infer possible mechanisms of speciation. We quantified pre- and post-pollination barriers through observation of pollen flow, by performing artificial inter- and intraspecific crosses and analyzing scent bouquets. Additionally, we investigated differences in mycorrhizal fungi as a potential extrinsic factor of post-zygotic isolation. Our results show that floral isolation mediated by the attraction of different pollinators acts apparently as the sole reproductive barrier between the two orchid species, with later-acting intrinsic barriers seemingly absent. Also, the two orchids share most of their fungal mycorrhizal partners in sympatry, suggesting little or no importance of mycorrhizal symbiosis in reproductive isolation. Key traits underlying floral isolation were two alkenes and wax ester, present predominantly in the floral scent of O. aymoninii. These compounds, when applied to flowers of O. insectifera, triggered attraction and a copulation attempt of the bee pollinator of O. aymoninii and thus led to the (partial) breakdown of floral isolation. Based on our results, we suggest that adaptation to different pollinators, mediated by floral scent, underlies species isolation in this plant group. Pollinator switches may be promoted by low pollination success of individuals in dense patches of plants, an assumption that we also confirmed in our study.SCOPUS: ar.jinfo:eu-repo/semantics/publishe