Altération du métabolisme énergétique des astrocytes induite par des lymphocytes T activés par le rétrovirus HTLV-1 et répercussions sur le devenir oligodendrocytaire dans un modèle de coculture

Dans le cas des 2 maladies neuroinflammatoires démyélinisantes (TSP /HAM, une paraparésie induite par le virus HTLV-1 ou de la sclérose en plaques, SEP), on observe une destruction de la myéline et une perte axonale associées à l'infiltration du système nerveux central par des lymphocytes T activés et une astrogliose réactionnelle dans les régions cérébrales lésées. Notre hypothèse de travail est la suivante : les lymphocytes T infiltrés activent les astrocytes dont les perturbations fonctionnelles conduisent à la démyélinisation, en vertu de la dépendance fonctionnelle des oligodendrocytes sur les astrocytes. L'objectif du travail développé dans cette thèse a été d'étudier la fonction énergétique des astrocytes et les répercussions des perturbations astrocytaires sur la survie et le fonctionnement oligodendrocytaires. Dans un premier temps, nous avons étudié les effets de coculture transitoire (20 heures) des astrocytes avec les lymphocytes T activés par infection par HTLV-1. Les astrocytes activés par contact avec les lymphocytes T infectés par HTLV-1 voient leur métabolisme énergétique significativement altéré (augmentation de la sécrétion de lactate, de la consommation de glucose et diminution de la concentration d'ATP intracellulaire) La protéine virale Tax est au moins en partie responsable des effets observés. Les jonctions gap interastrocytaires ne semblent pas être significativement impliquées dans les effets de lymphocytes. Dans un deuxième temps, pour étudier les conséquences fonctionnelles des perturbations énergétiques astrocytaires, nous avons mis en place un paradigme de coculture transitoire oligodendrocytes/lymphocytes T activés. Nos résultats montrent que le lactate sécrété, en abondance par les astrocytes activés, permet de protéger spécifiquement les oligodendrocytes immatures exprimant GalCer versus les précurseurs oligodendrocytaire exprimant NG2. Cet effet passe par la capture specifique du lactate par les oligodendrocytes via les transporteurs membranaires des acides monocarboxyliques, probablement en améliorant l'équilibre énergétique dans ces cellulesLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Acute morphine induces oscillatory discharge of noradrenergic locus coeruleus neurons in the waking monkey

International audienceNeurons were recorded extracellularly from the locus coeruleus (LC) of a waking, chair-restrained cynomolgus monkey before and for 0.5-4 h after intramuscular injections of morphine sulfate (0.3-10 mg/kg). Tonic discharge of each LC neuron tested (n = 11) decreased after morphine injection; this effect appeared to be dose-dependent for the range of 0.3-3.0 mg/kg. Unexpectedly, these same doses of morphine also induced a pronounced burst-pause discharge pattern in all LC neurons recorded. Thus, whereas in the naive animal pauses in discharge longer than 3 s were rare during waking, after morphine injection LC neurons frequently exhibited pauses in impulse activity of 10 s or longer during non-drowsy waking. The bursts in activity following morphine corresponded to orienting behaviors or apparent alertness, whereas pauses were associated with eye closure or slowly drifting gaze. Closer analysis revealed that this burst-pause activity pattern was somewhat regular, with a period of about 15-35 s. This observation was confirmed by autocorrelogram analysis. In view of previous findings in rodent LC, we suggest that acute morphine elicits a dual effect on primate LC neurons: inhibition of discharge by direct effects on opiate receptors located on LC cells, and periodic phasic activation mediated by excitatory afferents to the LC

A method to maintain normal respiratory and metabolic state in artificially respired rats

International audienceAnalysis of arterial blood gases (ABG) in awake, paralyzed, locally anesthetized, and artificially respired rats revealed the development with time of severe hypoxemia associated with metabolic acidosis despite adequate ventilation as assessed by normal PaCO2. These respiratory and metabolic disturbances may underlie the progressive deterioration experienced with this preparation frequently used in neuropharmacological experiments. We report here that the intravascular infusion of bicarbonated artificial plasma, associated with continuous positive pressure ventilation, prevents the deterioration of the respiratory and metabolic state in this preparation, which can be maintained within the range of that of the freely moving animal. This stabilized preparation may thus be highly suitable for neuropharmacological experiments extending for several hours

Effect of modafinil and amphetamine on the rat catecholaminergic neuron activity

International audienceWe have studied the effect of modafinil and amphetamine, two waking drugs, on the electrical activity of central dopaminergic and noradrenergic neurons in the rat. Modafinil (128 mg/kg, i.p.) was unable to modify the firing pattern of these neurons, while amphetamine (2 or 5 mg/kg, i.p.) consistently inhibited their activity. A pretreatment with modafinil did not change thereafter the effect of amphetamine. Contrary to amphetamine, the waking effect of modafinil does not seem to be mediated by the catecholaminergic neuron activity per se

Long-term effects of HTLV-1 on brain astrocytes: Sustained expression of Tax-1 associated with synthesis of inflammatory mediators

International audienceHTLV-1 is the causative agent of a chronic neurological disease, TSP/HAM. The persistently activated CTL response to the viral protein Tax-1 suggests the existence of persistent viral replication with continuous expression of Tax-1. Although CD4+ T-cell is the main target for HTLV-1, previous observations have indicated that the astrocyte, the major neural cell in close contact with blood vessel and thus with HTLV-1-infected T-cells infiltrating the CNS, may also be infected. We tested in vitro the hypothesis of persistent/restricted infection in human and rat astrocytes after transient contact with an infectious T-cell line (C91PL). Long-term analysis showed prolonged expression of Tax-1 in astrocytes, associated with secretion of inflammatory mediators (TNFalpha, IL1alpha, MMP-2, and MMP-9). These data suggest a possible contribution of Tax-1-expressing astrocytes to TSP/HAM pathogenesis

Selective induction of cytokines in mouse brain infected with canine distemper virus: structural, cellular and temporal expression

International audienceWe have previously shown that, in experimentally inoculated mice, canine distemper virus (CDV), a neurotropic virus, selectively infects certain brain structures (hypothalamus, hippocampus, monoaminergic nuclei, etc). Here we demonstrate that tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 beta and IL-6 transcripts are selectively expressed in these CDV-targeted structures, except in the dentate gyrus, where cytokines are induced without prior CDV replication. The time-course of TNF-alpha expression vs. viral replication in the hypothalamus was different from that in hippocampus. In addition, we show that a substantial number of neurons express TNF-alpha and IL-6. These findings provide new insights into the possible participation of cytokines in the neurological disorders triggered by CDV infection

Combining in vivo volume-controlled pressure microejection with extracellular unit recording

International audienceWe report a method for combining extracellular single-unit recording with pressure ejection, permitting microvolume quantification through the measurement of meniscus movement. Good optimization of both high quality recording and precise determination (in the nanoliter range) of the pressure-ejected volume can be obtained by using a recording electrode affixed to a calibrated, narrow inner diameter ejection pipette

Functional changes in astrocytes by human T-lymphotropic virus type-1 T-lymphocytes

International audienceThe human T-lymphotropic virus type-1 (HTLV-1) is the causative agent of a chronic progressive myelopathy (TSP/HAM) in which lesions of the central nervous system (CNS) are associated with infiltration of HTLV-1-infected T-cells. In a model that mimics the interaction between glial and T-cells, we show that transient contact with T-lymphocytes chronically infected with HTLV-1 induce profound metabolic alterations in astrocytes. Within the first week post-contact, an overall activation of astrocyte metabolism was observed as assessed by enhanced uptake of glutamate and glucose, and lactate release. In contrast, longer examination showed a reduced astrocytic accumulation of glutamate. The time course of the change in glutamate uptake was in fact biphasic. Previous observations indicated that HTLV-1 protein Tax-1 was involved in this delayed decrease, via the induction of TNF-alpha. The expression of the glial glutamate transporters, GLAST and GLT-1 decreased in parallel. These decreases in glutamate uptake and transporters' expression were associated with an imbalance in the expression of the catabolic enzymes of glutamate, GS and GDH, presumably due to Tax-1. Given the fact that impairment of glutamate management in astrocytes is able to compromise the functional integrity of neurons and oligodendrocytes, our results altogether give new insights into the physiopathology of TSP/HAM

Changes in astrocytic glutamate catabolism enzymes following neuronal degeneration or viral infection

International audienceFunctional changes in astrocytes are among the earliest cellular responses to a wide variety of insults to the central nervous system (CNS). Such responses significantly contribute to maintaining CNS homeostasis. In this context, by controlling energetic metabolism and overall excitability of the CNS, the modulation of glutamate uptake and catabolism in astrocytes is crucial. Here, we review specific modulations of the expression of glutamate catabolizing enzymes (glutamate dehydrogenase and glutamine synthetase) in response to CNS insults (degeneration of serotonergic neurons or viral infection by a human retrovirus, HTLV-I). The cellular and molecular mechanisms involved in the control of the glutamate catabolism are discussed in relation to neurological disorders