Neurocentre Magendie



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3 publication(s) depuis Novembre 2008:

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10/01/2012 | Proc Natl Acad Sci U S A   IF 9.6
Specific neural substrate linking respiration to locomotion.
Gariepy JF, Missaghi K, Chevallier S, Chartre S, Robert M, Auclair F, Lund JP, Dubuc R

When animals move, respiration increases to adapt for increased energy demands; the underlying mechanisms are still not understood. We investigated the neural substrates underlying the respiratory changes in relation to movement in lampreys. We showed that respiration increases following stimulation of the mesencephalic locomotor region (MLR) in an in vitro isolated preparation, an effect that persists in the absence of the spinal cord and caudal brainstem. By using electrophysiological and anatomical techniques, including whole-cell patch recordings, we identified a subset of neurons located in the dorsal MLR that send direct inputs to neurons in the respiratory generator. In semi-intact preparations, blockade of this region with 6-cyano-7-nitroquinoxaline-2,3-dione and (2R)-amino-5-phosphonovaleric acid greatly reduced the respiratory increases without affecting the locomotor movements. These results show that neurons in the respiratory generator receive direct glutamatergic connections from the MLR and that a subpopulation of MLR neurons plays a key role in the respiratory changes linked to movement.

04/2011 | cell signal   IF 4.2
Role of ssarrestins in bradykinin B2 receptor-mediated signalling.
Zimmerman B, Simaan M, Akoume MY, Houri N, Chevallier S, Seguela P, Laporte SA

G protein-coupled receptors (GPCRs) can engage multiple pathways to activate ERK1/2 via both G proteins and/or ssarrestin. Receptor recruitment of ssarrestin is also important for GPCR desensitization, internalization and resensitization. Modulation of the receptor/ssarrestin interaction through modification of either component would presumably alter the output generated by receptor activation. Here we examined how ssarrestins regulate bradykinin (BK) B2 receptor (B2R) signalling and desensitization by either truncating ssarrestin1 or ssarrestin2 or by alanine substitution of a serine/threonine cluster in the C-terminal tail of B2R (B2R-4A), conditions which all affect the avidity of the B2R/ssarrestin complex. We first demonstrate that BK-mediated ERK1/2 activation is biphasic containing an early peak (between 2-5min) followed by sustained activation for at least 60min. The early but not the sustained phase was predictably affected by inhibition of either Galphaq/11 or Galphai/o, whereas loss of ssarrestin2 but not ssarrestin1 resulted in diminished prolonged ERK1/2 activation. ssarrestin2's role was further examined using a truncation mutant with augmented avidity for the agonist-occupied receptor, revealing an increase in both immediate and extended ERK1/2 signalling. We also show that ERK1/2 is recruited to the B2R/ssarrestin complex on endosomes as well as the plasma membrane. Moreover, we investigated ssarrestin's role using the B2R-4A, which is deficient in ssarrestin binding and does not internalize. We show that ERK1/2 signalling downstream of the receptor is entirely G protein-dependent and receptor-mediated intracellular calcium mobilization studies revealed a lack of desensitization. Functionally, the lack of desensitization resulted in increased cell growth and migration compared to the wild-type receptor, which was sensitive to MEK inhibition. These results highlight ssarrestin's crucial role in the maintenance of proper B2R signalling.

26/11/2008 | J Neurosci   IF 5.9
Phosphoinositides regulate P2X4 ATP-gated channels through direct interactions.
Bernier LP, Ase AR, Chevallier S, Blais D, Zhao Q, Boue-Grabot E, Logothetis D, Seguela P

P2X receptors are ATP-gated nonselective cation channels highly permeable to calcium that contribute to nociception and inflammatory responses. The P2X(4) subtype, upregulated in activated microglia, is thought to play a critical role in the development of tactile allodynia following peripheral nerve injury. Posttranslational regulation of P2X(4) function is crucial to the cellular mechanisms of neuropathic pain, however it remains poorly understood. Here, we show that the phosphoinositides PI(4,5)P(2) (PIP(2)) and PI(3,4,5)P(3) (PIP(3)), products of phosphorylation by wortmannin-sensitive phosphatidylinositol 4-kinases and phosphatidylinositol 3-kinases, can modulate the function of native and recombinant P2X(4) receptor channels. In BV-2 microglial cells, depleting the intracellular levels of PIP(2) and PIP(3) with wortmannin significantly decreased P2X(4) current amplitude and P2X(4)-mediated calcium entry measured in patch clamp recordings and ratiometric ion imaging, respectively. Wortmannin-induced depletion of phosphoinositides in Xenopus oocytes decreased the current amplitude of P2X(4) responses by converting ATP into a partial agonist. It also decreased their recovery from desensitization and affected their kinetics. Injection of phosphoinositides in wortmannin-treated oocytes reversed these effects and application of PIP(2) on excised inside-out macropatches rescued P2X(4) currents from rundown. Moreover, we report the direct interaction of phospholipids with the proximal C-terminal domain of P2X(4) subunit (Cys(360)-Val(375)) using an in vitro binding assay. These results demonstrate novel regulatory roles of the major signaling phosphoinositides PIP(2) and PIP(3) on P2X(4) function through direct channel-lipid interactions.