Implication des chimiokines dans la neurotransmission dopaminergique nigrostriée

Les chimiokines sont des cytokines chimiotactiques. Nous avons établi que les chimiokines SDF-1 et MCP-1 et leurs récepteurs sont exprimés constitutivement par les neurones dopaminergiques (DA) de la substance noire (SN) de rat, suggérant un rôle modulateur de ces chimiokines sur l activité du système DA nigrostrié. Nous avons alors montré par électrophysiologie qu elles exercent des effets multiples et présynaptiques sur l excitabilité des neurones DA et que, sous l action de SDF-1, des neurones faiblement dépolarisés passent à un mode de décharge en bouffée connu pour faire libérer plus de DA. Nous avons démontré in vitro que SDF-1 est capable de potentialiser de manière dose dépendante la libération de DA induite par KCl. Par microdialyse intracérébrale nous avons montré que SDF-1 ou MCP-1, injecté unilatéralement dans la SN, induit une augmentation de la concentration extracellulaire de DA dans le striatum ipsilatéral, se traduisant par un comportement de rotation contralatérale.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Differential involvement of intracellular domains of the rat NTS1 neurotensin receptor in coupling to G proteins: a molecular basis for agonist-directed trafficking of receptor stimulus.

In this work, we evidenced characteristic features of agonist-induced trafficking of receptor stimulus for the rat neurotensin receptor 1 (NTS1). Thus, reverse potency orders between two agonists, EISAI-1 and neuromedin N, were observed in inositol 1,4,5-trisphosphate and cAMP assays in Chinese hamster ovary cells transfected with this receptor. Indeed, compared with other agonists, EISAI-1 presented lower relative potency toward inositol 1,4,5-trisphosphate production than toward cAMP accumulation, guanosine 5'-O -(3-[35 S]thio)triphosphate binding, and [3H]arachidonic acid production. These results indicated pathway-dependent differences in EISAI-1 intrinsic efficacies, favoring activations of Gs- and Gi/o-related pathways over the Gq/11-related pathway. Moreover, although coupling to Gq/11 and Gi/o involved the third intracellular loop and the C-terminal domain of the NTS1 receptor, respectively, we demonstrated that deletion of the latter domain suppressed agonist-induced cAMP accumulation, suggesting that this domain also mediated coupling to Gs. Together, these results indicated that, unlike other agonists, EISAI-1 discriminated between the pathways involving the receptor C-terminal domain and that involving the third intracellular loop. These properties of EISAI-1 were also observed in cortical neurons endogenously expressing the NTS1 receptor. They were further attributed to the functionalization of its COOH end by an ethyl group, because the unesterified analog EISAI-2 presented normal behavior on inositol 1,4,5-trisphosphate production. These findings support the hypothesis of agonist-selective receptor states with distinct conformations or accessibilities of intracellular domains. They also suggest that the differential involvement of these domains in coupling to G proteins might represent a molecular basis for agonist-selective responses through G protein-coupled receptors

The chemokine stromal cell-derived factor-1/CXCL12 activates the nigrostriatal dopamine system.

We recently demonstrated that dopaminergic (DA) neurons of the rat substantia nigra constitutively expressed CXCR4, receptor for the chemokine stromal cell-derived factor-1 (SDF-1)/CXCL12 (SDF-1). To check the physiological relevance of such anatomical observation, in vitro and in vivo approaches were used. Patch clamp recording of DA neurons in rat substantia nigra slices revealed that SDF-1 (10 nmol/L) induced: (i) a depolarization and increased action potential frequency; and (ii) switched the firing pattern of depolarized DA neurons from a tonic to a burst firing mode. This suggests that SDF-1 could increase DA release from neurons. Consistent with this hypothesis, unilateral intranigral injection of SDF-1 (50 ng) in freely moving rat decreased DA content and increased extracellular concentrations of DA and metabolites in the ipsilateral dorsal striatum, as shown using microdialysis. Furthermore, intranigral SDF-1 injection induced a contralateral circling behavior. These effects of SDF-1 were mediated via CXCR4 as they were abrogated by administration of a selective CXCR4 antagonist. Altogether, these data demonstrate that SDF-1, via CXCR4, activates nigrostriatal DA transmission. They show that the central functions of chemokines are not restricted, as originally thought, to neuroinflammation, but extend to neuromodulatory actions on well-defined neuronal circuits in non-pathological conditions

Toll like receptor 4 mediates cell death in a mouse MPTP model of Parkinson disease

International audienceIn mammalians, toll-like receptors (TLR) signal-transduction pathways induce the expression of a variety of immune-response genes, including inflammatory cytokines. It is therefore plausible to assume that TLRs are mediators in glial cells triggering the release of cytokines that ultimately kill DA neurons in the substantia nigra in Parkinson disease (PD). Accordingly, recent data indicate that TLR4 is up-regulated by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment in a mouse model of PD. Here, we wished to evaluate the role of TLR4 in the acute mouse MPTP model of PD: TLR4-deficient mice and wild-type littermates control mice were used for the acute administration way of MPTP or a corresponding volume of saline. We demonstrate that TLR4-deficient mice are less vulnerable to MPTP intoxication than wild-type mice and display a decreased number of Iba1+ and MHC II+ activated microglial cells after MPTP application, suggesting that the TLR4 pathway is involved in experimental PD