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Parkinson's disease (PD) patients express motor symptoms only after 60–80% striatal dopamine (DA) depletion. The presymptomatic phase of the disease may be sustained by biochemical modifications within the striatum. We used an appropriate specific1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkey model (Mounayar et al., 2007) to study the compensatory mechanisms operating in recovery from PD motor symptoms. We assessed the levels of DA and its metabolites (DOPAC, homovanillic acid), GABA, glutamate (Glu), serotonin (5-HT) and its metabolite (5HIAA) by repeated intracerebral microdialysis in awake animals before exposure to MPTP during full expression of the motor symptoms induced by MPTP and after recovery from these symptoms. Measurements were obtained from two functionally and anatomically different striatal areas: the associative-limbic territory and sensorimotor territory. Animals with motor symptoms displayed an extremely large decrease in levels of DA and its metabolites and an increase in Glu and GABA levels, as reported by other studies. However, we show here for the first time that serotonin levels increased in these animals. We found that increases in DA levels in the sensorimotor and/or associative-limbic territory and high levels of 5-HT and of its metabolite, 5HIAA, were associated with recovery from motor symptoms in this model. Determining whether similar changes in DA and 5-HT levels are involved in the compensatory mechanisms delaying the appearance of motor symptoms in the early stages of PD might make it possible to develop new treatment strategies for the disease.

International audience; RATIONALE: Several studies have suggested that nicotine treatment can modulate the behavioral and neurochemical responses to other psychostimulants, such as cocaine. OBJECTIVES: The current study examined the hypothesis that nicotinic acetylcholine receptor (nAChR) blockade influences the ability of cocaine to elicit increases in extracellular dopamine levels. MATERIALS AND METHODS: Pharmacological studies using nicotinic antagonists as well as genetic inactivation of beta2* nAChRs were used to determine the effect of nAChR blockade on dopamine levels in ventral striatum elicited by acute or repeated administrations of cocaine in mice. RESULTS: Administration of mecamylamine (a general nicotinic antagonist that is not highly selective for individual nAChR subtypes) or co-administration of methyllycaconitine (a more selective antagonist of alpha7* nAChRs) with dihydro-beta-erythroidine (a more selective antagonist of beta2* nAChRs and other heteromeric nAChR subtypes) prevented sensitization of cocaine-elicited increases in extracellular DA levels in the ventral striatum in wild-type mice. In contrast, neither of the more specific antagonists alone was effective in preventing sensitization. Finally, methyllycaconitine administration prevents sensitization in beta2-/- mice but not in beta2+/+ or wild-type mice. CONCLUSIONS: These data indicate that inhibition of both alpha7* and beta2* nAChRs is necessary to prevent development of sensitization of cocaine-elicited increases in extracellular dopamine levels in the ventral striatum of mice.

International audience; Nicotinic acetylcholine receptors (nAChRs) of α4β2 and α7 subtypes expressed in the brain neurons are involved in regulating memory and cognition. Their level is decreased upon several neurodegenerative disorders including Alzheimer's disease (AD), although the reasons for such a decrease are not completely understood. To test whether the nAChR-specific antibodies can affect the brain nAChRs and influence the behavior, we either immunized mice with recombinant extracellular domains of α4 and α7, subunits α4(1-209) and α7(1-208), or injected them with α7(1-208)-specific antibodies. A decrease of α4β2- and α7-nAChRs accompanied with an increase of α4β4-nAChRs in brain membranes of immunized mice was observed. Both α4(1-209)- and α7(1-208)-specific antibodies were detected in the brain membrane lysates of immunized mice. Antibody injection resulted in brain nAChR decrease only if mice were co-injected intraperitoneally with bacterial lipopolysaccharide. Brain sections of immunized mice were analyzed for the binding of [125I]-α-bungarotoxin and [125I]-epibatidine. A decrease in α-bungarotoxin binding in striatum (nucleus accumbens and caudate putamen) accompanied with an increase of epibatidine binding in the forebrain and caudate putamen was observed in mice immunized with either α4 or α7 nAChR domains compared to those immunized with BSA. Mice immunized with α7(1-208) demonstrated significantly worse episodic memory measured in a novel object recognition task compared to non-immunized animals but did not differ from the controls in locomotor or anxiety-related tests. These results suggest that nAChR-specific antibodies are able to penetrate the brain upon inflammation with resulting decreases of brain nAChRs and worsening episodic memory.

International audience; Developing cortical networks generate a variety of coherent activity patterns that participate in circuit refinement. Early network oscillations (ENOs) are the dominant network pattern in the rodent neocortex for a short period after birth. These large-scale calcium waves were shown to be largely driven by glutamatergic synapses albeit GABA is a major excitatory neurotransmitter in the cortex at such early stages, mediating synapse-driven giant depolarizing potentials (GDPs) in the hippocampus. Using functional multineuron calcium imaging together with single-cell and field potential recordings to clarify distinct network dynamics in rat cortical slices, we now report that the developing somatosensory cortex generates first ENOs then GDPs, both patterns coexisting for a restricted time period. These patterns markedly differ by their developmental profile, dynamics, and mechanisms: ENOs are generated before cortical GDPs (cGDPs) by the activation of glutamatergic synapses mostly through NMDARs; cENOs are low-frequency oscillations (approximately 0.01 Hz) displaying slow kinetics and gradually involving the entire network. At the end of the first postnatal week, GABA-driven cortical GDPs can be reliably monitored; cGDPs are recurrent oscillations (approximately 0.1 Hz) that repetitively synchronize localized neuronal assemblies. Contrary to cGDPs, cENOs were unexpectedly facilitated by short anoxic conditions suggesting a contribution of glutamate accumulation to their generation. In keeping with this, alterations of extracellular glutamate levels significantly affected cENOs, which are blocked by an enzymatic glutamate scavenger. Moreover, we show that a tonic glutamate current contributes to the neuronal membrane excitability when cENOs dominate network patterns. Therefore, cENOs and cGDPs are two separate aspects of neocortical network maturation that may be differentially engaged in physiological and pathological processes.

International audience; CONTEXT: Adipocyte formation in human adult adipose tissue (hAT) originates from resident progenitor cell differentiation in the stroma vascular fraction of the AT. The processes involved in the self-renewal of this cell population remain to be defined. OBJECTIVE: The objective was to study in situ and in vitro hAT progenitor cell (defined as CD34(+)/CD31(-) cells) proliferation. DESIGN AND PARTICIPANTS: In situ progenitor cell proliferation was assessed by immunohistochemistry and flow cytometry analyses on hAT from lean to obese subjects using the proliferation marker Ki-67. The effects of adipokines, hypoxia, and conditioned media (CM) from adipocytes, capillary endothelial cells, and macrophages isolated by an immunoselection approach were studied on hAT progenitor cell growth. Cell death in hAT was assessed by the terminal deoxynucleotidyl transferase-mediated dUTP-fluorescein end labeling method. RESULTS: Ki-67-positive staining was observed in AT progenitor cells. Fat mass enlargement in obese patients was associated with an increased Ki-67(+) progenitor cell population together with a new fraction of small adipocytes and increased cell death. HIF-1alpha mRNA expression in freshly harvested progenitor cells was positively correlated with body mass index. Adipocyte- and capillary endothelial cell-CM, hypoxia, leptin, IL-6, lysophosphatidic acid, and vascular endothelial growth factor, all increased hAT progenitor cell proliferation in vitro. Macrophage-CM had an antiproliferative effect that was suppressed by an antioxidant. CONCLUSIONS: The fraction of proliferative progenitor cells in adult hAT is modulated by the degree of adiposity. Changes in the progenitor cell microenvironment involving adipokines, hypoxia, and oxidative stress might play a key role in the control of the self-renewal of the local pool of AT progenitor cells.

International audience; The architecture of parallel fiber axons contacting cerebellar Purkinje neurons retains spatial information over long distances. Parallel fiber synapses can trigger local dendritic calcium spikes, but whether and how this calcium signal leads to plastic changes that decode the parallel fiber input organization is unknown. By combining voltage and calcium imaging, we show that calcium signals, elicited by parallel fiber stimulation and mediated by voltage-gated calcium channels, increase non-linearly during high-frequency bursts of electrically constant calcium spikes, because they locally and transiently saturate the endogenous buffer. We demonstrate that these non-linear calcium signals, independently of NMDA or metabotropic glutamate receptor activation, can induce parallel fiber long-term potentiation. Two-photon imaging in coronal slices revealed that calcium signals inducing long-term potentiation can be observed by stimulating either the parallel fiber or the ascending fiber pathway. We propose that local dendritic calcium spikes, evoked by synaptic potentials, provide a unique mechanism to spatially decode parallel fiber signals into cerebellar circuitry changes.

International audience; The neurobiological mechanisms by which high-frequency stimulation of the subthalamic nucleus (STN-HFS) alleviates the motor symptoms of Parkinson's disease (PD) remain unclear. In this study, we analyzed the effects of STN-HFS on motor behavior in intact or hemiparkinsonian rats (6-hydroxydopamine lesion of the substantia nigra pars compacta) and investigated the correlation between these effects and extracellular glutamate (Glu) and GABA levels, assessed by intracerebral microdialysis in the substantia nigra pars reticulata (SNr). STN-HFS at an intensity corresponding to the threshold inducing contralateral forelimb dyskinesia, increased Glu levels in the SNr of both intact and hemiparkinsonian rats. In contrast, STN-HFS at half this intensity did not affect Glu levels in the SNr in intact or hemiparkinsonian rats but increased GABA levels in hemiparkinsonian rats only. STN-HFS-induced forelimb dyskinesia was blocked by microinjection of the Glu receptor antagonist kynurenate into the SNr and facilitated by microinjection of a mixture of the Glu receptor agonists AMPA and NMDA into the SNr. These new neurochemical data suggest that STN-HFS-induced forelimb dyskinesia is mediated by glutamate, probably via the direct activation of STN axons, shedding light on the mechanisms of STN-HFS in PD.

International audience; Dopamine, a neurotransmitter released by the lateral olivocochlear efferents, has been shown tonically to inhibit the spontaneous and sound-evoked activity of auditory nerve fibres. This permanent inhibition probably requires the presence of an efficient transporter to remove dopamine from the synaptic cleft. Here, we report that the dopamine transporter is located in the lateral efferent fibres both below the inner hair cells and in the inner spiral bundle. Perilymphatic perfusion of the dopamine transporter inhibitors nomifensine and N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine into the cochlea reduced the spontaneous neural noise and the sound-evoked compound action potential of the auditory nerve in a dose-dependent manner, leading to both neural responses being completely abolished. We observed no significant change in cochlear responses generated by sensory hair cells (cochlear microphonic, summating potential, distortion products otoacoustic emissions) or in the endocochlear potential reflecting the functional state of the stria vascularis. This is consistent with a selective action of dopamine transporter inhibitors on auditory nerve activity. Capillary electrophoresis with laser-induced fluorescence (EC-LIF) measurements showed that nomifensine-induced inhibition of auditory nerve responses was due to increased extracellular dopamine levels in the cochlea. Altogether, these results show that the dopamine transporter is essential for maintaining the spontaneous activity of auditory nerve neurones and their responsiveness to sound stimulation.

International audience; PURPOSE: The aim of this study was to investigate whether the nucleus parafascicularis (Pf) of the thalamus could be a relay of the control of epileptic seizures by the superior colliculus (SC). The Pf is one of the main ascending projections of the SC, the disinhibition of which has been shown to suppress seizures in different animal models and has been proposed as the main relay of the nigral control of epilepsy. METHODS: Rats with genetic absence seizures (generalized absence epilepsy rat from Strasbourg or GAERS) were used in this study. The effect of bilateral microinjection of picrotoxin, a gamma-aminobutyric acid (GABA) antagonist, in the SC on the glutamate and GABA extracellular concentration within the Pf was first investigated by using microdialysis. In a second experiment, the effect of direct activation of Pf neurons on the occurrence of absence seizures was examined with microinjection of low doses of kainate, a glutamate agonist. RESULTS: Bilateral injection of picrotoxin (33 pmol/side) in the SC suppressed spike-and-wave discharges for 20 min. This treatment resulted in an increase of glutamate but not GABA levels in the Pf during the same time course. Bilateral injection of kainate (35 pmol/side) into the Pf significantly suppressed spike-and-wave discharges for 20 min, whereas such injections were without effects when at least one site was located outside the Pf. CONCLUSIONS: These data suggest that glutamatergic projections to the Pf could be involved in the control of seizures by the SC. Disinhibition of these neurons could lead to seizure suppression and may be involved in the nigral control of epilepsy.

International audience; PURPOSE: The aim of this study was to investigate whether the nucleus parafascicularis (Pf) of the thalamus could be a relay of the control of epileptic seizures by the superior colliculus (SC). The Pf is one of the main ascending projections of the SC, the disinhibition of which has been shown to suppress seizures in different animal models and has been proposed as the main relay of the nigral control of epilepsy. METHODS: Rats with genetic absence seizures (generalized absence epilepsy rat from Strasbourg or GAERS) were used in this study. The effect of bilateral microinjection of picrotoxin, a gamma-aminobutyric acid (GABA) antagonist, in the SC on the glutamate and GABA extracellular concentration within the Pf was first investigated by using microdialysis. In a second experiment, the effect of direct activation of Pf neurons on the occurrence of absence seizures was examined with microinjection of low doses of kainate, a glutamate agonist. RESULTS: Bilateral injection of picrotoxin (33 pmol/side) in the SC suppressed spike-and-wave discharges for 20 min. This treatment resulted in an increase of glutamate but not GABA levels in the Pf during the same time course. Bilateral injection of kainate (35 pmol/side) into the Pf significantly suppressed spike-and-wave discharges for 20 min, whereas such injections were without effects when at least one site was located outside the Pf. CONCLUSIONS: These data suggest that glutamatergic projections to the Pf could be involved in the control of seizures by the SC. Disinhibition of these neurons could lead to seizure suppression and may be involved in the nigral control of epilepsy.

Background Extracellular ATP may modulate airway responsiveness. Studies on ATP-induced contraction and [Ca2+]i signalling in airway smooth muscle are rather controversial and discrepancies exist regarding both ATP effects and signalling pathways. We compared the effect of extracellular ATP on rat trachea and extrapulmonary bronchi (EPB) and both human and rat intrapulmonary bronchi (IPB), and investigated the implicated signalling pathways. Methods Isometric contraction was measured on rat trachea, EPB and IPB isolated rings and human IPB isolated rings. [Ca2+]i was monitored fluorimetrically using indo 1 in freshly isolated and cultured tracheal myocytes. Statistical comparisons were done with ANOVA or Student's t tests for quantitative variables and χ2 tests for qualitative variables. Results were considered significant at P < 0.05. Results In rat airways, extracellular ATP (10-6–10-3 M) induced an epithelium-independent and concentration-dependent contraction, which amplitude increased from trachea to IPB. The response was transient and returned to baseline within minutes. Similar responses were obtained with the non-hydrolysable ATP analogous ATP-γ-S. Successive stimulations at 15 min-intervals decreased the contractile response. In human IPB, the contraction was similar to that of rat IPB but the time needed for the return to baseline was longer. In isolated myocytes, ATP induced a concentration-dependent [Ca2+]i response. The contractile response was not reduced by thapsigargin and RB2, a P2Y receptor inhibitor, except in rat and human IPB. By contrast, removal of external Ca2+, external Na+ and treatment with D600 decreased the ATP-induced response. The contraction induced by α-β-methylene ATP, a P2X agonist, was similar to that induced by ATP, except in IPB where it was lower. Indomethacin and H-89, a PKA inhibitor, delayed the return to baseline in extrapulmonary airways. Conclusion Extracellular ATP induces a transient contractile response in human and rat airways, mainly due to P2X receptors and extracellular Ca2+ influx in addition with, in IPB, P2Y receptors stimulation and Ca2+ release from intracellular Ca2+ stores. Extracellular Ca2+ influx occurs through L-type voltage-dependent channels activated by external Na+ entrance through P2X receptors. The transience of the response cannot be attributed to ATP degradation but to purinoceptor desensitization and, in extrapulmonary airways, prostaglandin-dependent PKA activation.