Contribution of tachykinin and kinin receptors in central autonomic control of blood pressure and behavioural activity in hypertensive rats

This work aims at studing the role of tachykinin NK-3 receptor (R) and kinin B1R in central autonomic regulation of blood pressure (BP) and to determine whether the B1R is overexpressed and functional in rat models of hypertension by measuring the effect of a B1R agonist on behavioural activity. Assumptions: (1) NK-3R located in the ventral tegmental area (VTA) modulates the mesolimbic dopaminergic system and has a tonic activity in hypertension; (2) B1R is overexpressed in the brain of hypertensive rats and has a tonic activity, which contributes to hypertension via a dopamine mechanism; (3) the inhibition of NK-3R and B1R with selective antagonists, reduces central dopaminergic hyperactivity and reverses hypertension. A model of genetic hypertension and a model of experimental hypertension were used: spontaneously hypertensive rats (SHR, 16 weeks) and Wistar-Kyoto (WKY) rats infused for 14 days with angiotensin II (Ang II) (200 ng / kg / min, subcutaneous (s.c.) with Alzet mini pump). The age-matched untreated WKY rats served as common controls. In the first study (article # 1), the cardiovascular response in SHR was evaluated following intracebroventricular (i.c.v.) and/or intra-VTA injection of an agonist (senktide) and antagonists (SB222200 and R-820) of NK-3R. These responses have also been characterized using selective dopamine antagonists DA-D1R (SCH23390), DA-D2R (raclopride) or non-selective dopamine DA-D2R (haloperidol). Also the VTA has been destroyed by ibotenic acid. The pressor response induced by senktide and the anti-hypertensive response induced by SB222200 or R-820 were more pronounced by intra-VTA. These responses were prevented by pre-treatment with raclopride and haloperidol. The lesion of the VTA has prevented the pressor response relayed by senktide (i.c.v.) and the anti-hypertensive effect of R-820 (i.c.v.). In addition, SB222200 (intra-VTA) prevented the pressor response of senktide (i.c.v.) and conversely, senktide (i.c.v.) prevented the antihypertensive effect of SB222200 (intra-VTA). The second study (article # 2) showed that the B1R antagonist (SSR240612) administered by gavage or i.c.v. reverses hypertension in both models. This anti-hypertensive effect was prevented by raclopride and haloperidol. In contrast, the two B1R antagonists (R-715 and R-954) injected s.c., which do not cross the blood-brain barrier reduced weakly blood pressure in hypertensive rats. In the third study (article # 3), the i.c.v. injection of a selective kinin B1R agonist Sar[DPhe8][des-Arg9]BK caused behavioural responses in SHR and Ang II-treated rats and had no effect in control WKY rats . The responses elicited by B1R agonist were blocked by an antagonist of NK-1 (RP67580), an antagonist of NMDA glutamate receptor (DL-AP5), an inhibitor of nitric oxide synthase (NOS) (L -NNA) as well as raclopride and SCH23390.The responses were modestly affected by the inhibitor of inducible NOS (iNOS). The B1R mRNA (measured by RT-PCR) was significantly increased in the hypothalamus, the VTA and the nucleus accumbens of hypertensive animals (SHR and treated with Ang II) compared with control rats. These neuropharmacological studies suggest that: (1) the NK-3R from the VTA is involved in the maintenance of hypertension in SHR by increasing DA transmission in the midbrain; (2) the B1R in SHR and Ang II-treated rats contributes to hypertension via a central mechanism involving DA-D2R; (3) the central B1R increases locomotor activity and nocifensive behaviours via the release of substance P (NK-1), DA and nitric oxide in both rat models of hypertension. Thus, the brain tachykinin NK-3R and kinin B1R represent potential therapeutic targets for the treatment of hypertension. The modulation of the mesolimbic/mesocortical dopaminergic pathway by these receptors suggests their involvement in other physiological functions (pleasure, motor activity, coordination of the response to stress) and pathophysiology (anxiety, depression).

Resilience and Individualized Community Integration Interventions for Persons with Traumatic Brain Injuries

Investigators, caregivers, administrators and service users in the field of rehabilitation are increasingly interested in the concept of resilience, but the literature has very little to offer on interventions aimed at supporting the resilience of persons and their loved ones. This article describes the Personnalized Accompagnement Community Integration (ICII), which is intended to support the resilience of persons with moderate to severe traumatic brain injuries (TBIs). An ICII implementation is currently underway and is expected to support social participation and stimulate the resilience of persons with TBIs. It is based on four frames of reference: community integration founded on the person’s perception of their community integration, the ecosystemic model, the handicap production process (HPP) model, and the goal-setting process. ICII adopts an intervention perspective centered on the life plan of the person with a TBI.

Implication du glutamate et de l'oxyde nitrique dans la modulation de la dépression synaptique à court terme à la jonction neuromusculaire de Rana pipiens

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

Plasticité synaptique dans l’aire tegmentaire ventrale : implication des endocannabinoïdes

Le système dopaminergique (DA) méso-corticolimbique du cerveau, qui prend son origine dans l'aire tegmentaire ventrale (ATV), est fortement impliqué dans les comportements motivés et la toxicomanie. Les drogues d'abus activent ce système et y induisent une plasticité synaptique de longue durée. Les neurones DA de l'ATV reçoivent sur leur arborisation dendritique une grande densité de terminaisons glutamatergiques. Les drogues d'abus induisent une potentialisation à long terme (PLT) de ces contacts glutamatergiques. La PLT est une augmentation prolongée de la transmission synaptique, qui semble sous-tendre la mémoire et l'apprentissage. Les endocannabinoïdes (ECs) sont des neurotransmetteurs qui agissent de façon rétrograde sur des récepteurs présynaptiques (CB1) pour diminuer la libération des neurotransmetteurs comme le glutamate. Les neurones libèrent les ECs à partir de leur compartiment somatodendritique suite à une stimulation des afférences et la dépolarisation membranaire qui s’ensuit. La neurotensine (NT) est un neuropeptide retrouvé de façon abondante dans le système DA du cerveau. Il a été découvert que la NT peut induire la libération des ECs dans le striatum. En faisant appel à une combinaison d’approches immunohistochimique, électrophysiologique et pharmacologique chez la souris, nous avons confirmé dans la première étude de cette thèse la présence des récepteurs CB1 sur les terminaisons glutamatergiques des neurones DA de l'ATV, et avons montré que leur activation induit une diminution de la libération de glutamate. Par ailleurs, nous avons montré que des trains de stimulation peuvent induire la libération des ECs. Nous avons découvert qu'en présence d'un antagoniste des récepteurs CB1, il y a facilitation de l’induction de la PLT. Cette observation suggère que les ECs ont un effet inhibiteur sur l’induction de la PLT, plutôt que sur son expression. Nous avons déterminé que le 2-arachidonoylglycerol (2-AG) est l’EC qui est principalement responsable de cette action inhibitrice. Finalement, la PLT induite en présence d’un antagoniste CB1 est aussi dépendante d'une activation des récepteurs NMDA du glutamate. Les travaux réalisés dans la deuxième étude de cette thèse ont montré que la NT est présente dans une sous-population de terminaisons axonales glutamatergiques dans l’ATV. Une application exogène de NT induit une diminution prolongée de l'amplitude des courants postsynaptiques excitateurs (CPSEs). Cette diminution est bloquée en présence d'un antagoniste non-sélectif des récepteurs à la NT, ainsi qu'en présence d'un antagoniste sélectif pour le récepteur de NT de type 1 (NTS1). Confirmant l’implication d’une production d’ECs, la baisse des CPSEs par la NT a été bloquée en présence d’un antagoniste des récepteurs CB1 ou d’un bloqueur de la synthèse de 2-AG. La chélation du calcium intracellulaire n'empêchait pas l’effet inhibiteur de la NT sur les CPSEs, cependant, l'inhibition des protéines G ou de la phospholipase C a complètement bloqué la dépression synaptique induite par la NT. Par ailleurs, nos travaux ont montré que la nature prolongée de la dépression synaptique induite par la NT exogène s’explique par une libération soutenue des ECs, et non pas à une activation prolongée des NTR. Finalement, notre observation qu’un antagoniste des récepteurs de la NT ne facilite pas l’induction de la PLT, comme le fait un antagoniste du récepteur CB1, suggère que la stimulation répétitive des afférences glutamatergiques nécessaire à l’induction de la PLT n’induit pas de libération des ECs via la libération de NT, nous permettant ainsi de conclure que la sécrétion de NT n'agit pas dans ces conditions comme un facteur de régulation négative de la PLT.

Structural and functional brain abnormalities in children with subclinical depression

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Étude du système dopaminergique pré- et postsynaptique : régulation de l'autorécepteur D2 par la neurotensine et formation des synapses excitatrices dans le striatum

La dopamine (DA) est un neurotransmetteur impliqué dans la modulation de fonctions essentielles du cerveau telles que le contrôle des mouvements volontaires, le système de récompense et certains aspects de la cognition. Depuis sa découverte, la DA a attiré énormément d'attention scientifique en partie à cause des pathologies majeures associées aux dysfonctions du système DAergique, comme la maladie de Parkinson, la schizophrénie et la toxicomanie. On retrouve la majorité des neurones qui synthétisent la DA au niveau du mésencéphale ventral, dans les noyaux de la substance noire compacte (SNc) et de l'aire tegmentaire ventrale (ATV). Ces neurones projettent leurs axones dans un très dense réseau de fibres qui s'organisent en trois voies DAergiques classiques: la voie nigrostriée, la voie mésolimbique et la voie mésocorticale. La transmission DAergique s'effectue par l'activation de récepteurs de la DA qui font partie de la grande famille des récepteurs couplés aux protéines G (RCPGs). Les récepteurs de la DA sont abondamment exprimés aussi bien par les neurones DAergiques que par les neurones des régions cibles, ce qui implique que la compréhension de la signalisation et des fonctions particulières des récepteurs de la DA pré- et postsynaptiques représente un enjeu crucial dans l'étude du système DAergique. Cette thèse de doctorat se sépare donc en deux volets distincts: le premier s'intéresse à la régulation du récepteur D2 présynaptique par la neurotensine (NT), un neuropeptide intimement lié à la modulation du système DAergique; le deuxième s'intéresse au côté postsynaptique du système DAergique, plus particulièrement à la ségrégation de l'expression des récepteurs de la DA dans le striatum et aux fonctions de ces récepteurs dans l'établissement des circuits neuronaux excitateurs prenant place dans cette région. Dans la première partie de cette thèse, nous démontrons que l'activation du récepteur à haute affinité de la NT, le NTR1, provoque une internalisation hétérologue du récepteur D2, avec une amplitude et une cinétique différente selon l'isoforme D2 observé. Cette internalisation hétérologue dépend de la protéine kinase C (PKC), et nous montrons que la surexpression d'un récepteur D2 muté sur des sites de phosphorylation par la PKC ii ainsi que l'inhibition de l'expression de β-arrestine1 par ARNs interférents dans des neurones DAergiques bloquent complètement l'interaction fonctionnelle entre le NTR1 et le D2. Dans la deuxième partie de cette thèse, nous démontrons d'abord que la ségrégation de l'expression des récepteurs D1 et D2 dans le striatum est déjà bien établie dès le 18e jour embryonnaire, bien qu'elle progresse encore significativement aux jours 0 et 14 postnataux. Nos résultats témoignent aussi d'un maintien complet de cette ségrégation lorsque les neurones striataux sont mis en culture aussi bien en présence ou en absence de neurones corticaux et/ou mésencéphaliques. Ensuite, nous montrons que la présence de neurones mésencéphaliques stimule la formation d’épines et de synapses excitatrices sur les neurones striataux épineux exprimant le récepteur D2 (MSN-D2). Le co-phénotype glutamatergique des neurones dopaminergiques semble nécessaire à une grande partie de cet effet. Par ailleurs, le nombre total de terminaisons excitatrices formées sur les MSN-D2 par les neurones corticaux et mésencéphaliques apparaît être régit par un équilibre dynamique. Finalement, nous démontrons que le blocage de la signalisation des récepteurs D1 et D2 de la DA n'est pas nécessaire pour la formation des synapses excitatrices des MSN-D2, alors que l'antagonisme des récepteurs glutamatergiques ionotropes diminue la densité d'épines dendritiques et contrôle de façon opposée le nombre de terminaisons excitatrices corticales et mésencéphaliques. Globalement, ce travail représente une contribution significative pour une meilleure compréhension du fonctionnement normal du système DAergique. Ces découvertes sont susceptibles d’être utiles pour mieux comprendre les dysfonctions de ce système dans le cadre de pathologies du cerveau comme la maladie de Parkinson.

Selective alterations of brain osmolytes in acute liver failure: protective effect of mild hypothermia.

The principal cause of mortality in patients with acute liver failure (ALF) is brain herniation resulting from intracranial hypertension caused by a progressive increase of brain water. In the present study, ex vivo high-resolution 1H-NMR spectroscopy was used to investigate the effects of ALF, with or without superimposed hypothermia, on brain organic osmolyte concentrations in relation to the severity of encephalopathy and brain edema in rats with ALF due to hepatic devascularization. In normothermic ALF rats, glutamine concentrations in frontal cortex increased more than fourfold at precoma stages, i.e. prior to the onset of severe encephalopathy, but showed no further increase at coma stages. In parallel with glutamine accumulation, the brain organic osmolytes myo-inositol and taurine were significantly decreased in frontal cortex to 63\% and 67\% of control values, respectively, at precoma stages (p<0.01), and to 58\% and 67\%, respectively, at coma stages of encephalopathy (p<0.01). Hypothermia, which prevented brain edema and encephalopathy in ALF rats, significantly attenuated the depletion of myo-inositol and taurine. Brain glutamine concentrations, on the other hand, did not respond to hypothermia. These findings demonstrate that experimental ALF results in selective changes in brain organic osmolytes as a function of the degree of encephalopathy which are associated with brain edema, and provides a further rationale for the continued use of hypothermia in the management of this condition.

Increase brain lactate in hepatic encephalopathy: Cause or consequence?

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome which develops as a result of liver failure or disease. Increased concentrations of brain lactate (microdialysate, cerebrospinal fluid, tissue) are commonly measured in patients with HE induced by either acute or chronic liver failure. Whether an increase in brain lactate is a cause or a consequence of HE remains undetermined. A rise in cerebral lactate may occur due to (1) blood-borne lactate (hyperlactataemia) crossing the blood-brain barrier, (2) increased glycolysis due to energy failure or impairment and (3) increased lactate production/release or decreased lactate utilization/uptake. This review explores the different reasons for lactate accumulation in the brain during liver failure and describes the possible roles of lactate in the pathogenesis of HE.

L-ornithine-L-aspartate in experimental portal-systemic encephalopathy: therapeutic efficacy and mechanism of action.

Strategies aimed at the lowering of blood ammonia remain the treatment of choice in portal-systemic encephalopathy (PSE). L-ornithine-L-aspartate (OA) has recently been shown to be effective in the prevention of ammonia-precipitated coma in humans with PSE. These findings prompted the study of mechanisms of the protective effect of OA in portacaval-shunted rats in which reversible coma was precipitated by ammonium acetate administration (3.85 mmol/kg i.p.). OA infusions (300 mg/kg/h, i.v) offered complete protection in 12/12 animals compared to 0/12 saline-infused controls. This protective effect was accompanied by significant reductions of blood ammonia, concomitant increases of urea production and significant increases in blood and cerebrospinal fluid (CSF) glutamate and glutamine. Increased CSF concentrations of leucine and alanine also accompanied the protective effect of OA. These findings demonstrate the therapeutic efficacy of OA in the prevention of ammonia-precipitated coma in portacaval-shunted rats and suggest that this protective effect is both peripherally-mediated (increased urea and glutamine synthesis) and centrally-mediated (increased glutamine synthesis).

Neuropathological changes in the brain of pigs with acute liver failure.

Abstract Objective. Cerebral edema is a serious complication of acute liver failure (ALF), which may lead to intracranial hypertension and death. An accepted tenet has been that the blood-brain barrier is intact and that brain edema is primarily caused by a cytotoxic etiology due to hyperammonemia. However, the neuropathological changes in ALF have been poorly studied. Using a well characterized porcine model we aimed to investigate ultrastructural changes in the brain from pigs suffering from ALF. Materials and methods. Sixteen female Norwegian Landrace pigs weighing 27-35 kg were randomised into two groups: ALF (n = 8) and sham operated controls (n = 8). ALF was induced with an end-to-side portacaval shunt followed by ligation of the hepatic arteries. Biopsies were harvested from three different areas of the brain (frontal lobe, cerebellum, and brain stem) following eight hours of ALF and analyzed using electron microscopy. Results. Profound perivascular and interstitial edema were found in all three areas. Disruption of pericytic and astrocytic processes were seen, reflecting breakdown/lesion of the blood-brain barrier in animals suffering from ALF. Furthermore, neurons and axons were edematous and surrounded by vesicles. Severe damage to Purkinje neuron (necrosis) and damaged myelin were seen in the cerebellum and brain stem, respectively. Biopsies from sham operated animals were normal. Conclusions. Our data support the concept that vasogenic brain edema plays an important role in the development of intracranial hypertension in pigs with ALF.

Effect of portacaval anastomosis on glutamine synthetase protein and gene expression in brain, liver and skeletal muscle.

The effects of chronic liver insufficiency resulting from end-to-side portacaval anastomosis (PCA) on glutamine synthetase (GS) activities, protein and gene expression were studied in brain, liver and skeletal muscle of male adult rats. Four weeks following PCA, activities of GS in cerebral cortex and cerebellum were reduced by 32\% and 37\% (p<0.05) respectively whereas GS activities in muscle were increased by 52\% (p<0.05). GS activities in liver were decreased by up to 90\% (p<0.01), a finding which undoubtedly reflects the loss of GS-rich perivenous hepatocytes following portal-systemic shunting. Immunoblotting techniques revealed no change in GS protein content of brain regions or muscle but a significant loss in liver of PCA rats. GS mRNA determined by semi-quantitative RT-PCR was also significantly decreased in the livers of PCA rats compared to sham-operated controls. These findings demonstrate that PCA results in a loss of GS gene expression in the liver and that brain does not show a compensatory induction of enzyme activity, rendering it particularly sensitive to increases in ammonia in chronic liver failure. The finding of a post-translational increase of GS in muscle following portacaval shunting suggests that, in chronic liver failure, muscle becomes the major organ responsible for the removal of excess blood-borne ammonia.

Direct molecular and spectroscopic evidence for increased ammonia removal capacity of skeletal muscle in acute liver failure.

BACKGROUND/AIMS: It has been proposed that, in acute liver failure, skeletal muscle adapts to become the principle organ responsible for removal of blood-borne ammonia by increasing glutamine synthesis, a reaction that is catalyzed by the cytosolic ATP-dependent enzyme glutamine synthetase. To address this issue, glutamine synthetase expression and activities were measured in skeletal muscle of rats with acute liver failure resulting from hepatic devascularization. METHODS: Glutamine synthetase protein and gene expression were investigated using immunoblotting and semi-quantitative RT-PCR analysis. Glutamine synthetase activity and glutamine de novo synthesis were measured using, respectively, a standard enzymatic assay and [13C]-nuclear magnetic resonance spectroscopy. RESULTS: Glutamine synthetase protein (but not gene) expression and enzyme activities were significantly up-regulated leading to increased de novo synthesis of glutamine and increased skeletal muscle capacity for ammonia removal in acute liver failure. In contrast to skeletal muscle, expression and activities of glutamine synthetase in the brain were significantly decreased. CONCLUSIONS: These findings demonstrate that skeletal muscle adapts, through a rapid induction of glutamine synthetase, to increase its capacity for removal of blood-borne ammonia in acute liver failure. Maintenance of muscle mass together with the development of agents with the capacity to stimulate muscle glutamine synthetase could provide effective ammonia-lowering strategies in this disorder.

Identifying the direct effects of ammonia on the brain.

Elevated concentrations of ammonia in the brain as a result of hyperammonemia leads to cerebral dysfunction involving a spectrum of neuropsychiatric and neurological symptoms (impaired memory, shortened attention span, sleep-wake inversions, brain edema, intracranial hypertension, seizures, ataxia and coma). Many studies have demonstrated ammonia as a major player involved in the neuropathophysiology associated with liver failure and inherited urea cycle enzyme disorders. Ammonia in solution is composed of a gas (NH(3)) and an ionic (NH(4) (+)) component which are both capable of crossing plasma membranes through diffusion, channels and transport mechanisms and as a result have a direct effect on pH. Furthermore, NH(4) (+) has similar properties as K(+) and, therefore, competes with K(+) on K(+) transporters and channels resulting in a direct effect on membrane potential. Ammonia is also a product as well as a substrate for many different biochemical reactions and consequently, an increase in brain ammonia accompanies disturbances in cerebral metabolism. These direct effects of elevated ammonia concentrations on the brain will lead to a cascade of secondary effects and encephalopathy.

Mild hypothermia prevents brain edema and attenuates up-regulation of the astrocytic benzodiazepine receptor in experimental acute liver failure.

BACKGROUND/AIMS: Mild hypothermia has proven useful in the clinical management of patients with acute liver failure. Acute liver failure in experimental animals results in alterations in the expression of genes coding for astrocytic proteins including the "peripheral-type" (astrocytic) benzodiazepine receptor (PTBR), a mitochondrial complex associated with neurosteroid synthesis. To gain further insight into the mechanisms whereby hypothermia attenuates the neurological complications of acute liver failure, we investigated PTBR expression in the brains of hepatic devascularized rats under normothermic (37 degrees C) and hypothermic (35 degrees C) conditions. METHODS: PTBR mRNA was measured using semi-quantitative RT-PCR in cerebral cortical extracts and densities of PTBR sites were measured by quantitative receptor autoradiagraphy. Brain pregnenolone content was measured by radioimmunoassay. RESULTS: At coma stages of encephalopathy, animals with acute liver failure manifested a significant increase of PTBR mRNA levels. Brain pregnenolone content and [(3)H]PK 11195 binding site densities were concomitantly increased. Mild hypothermia prevented brain edema and significantly attenuated the increased receptor expression and pregnenolone content. CONCLUSIONS: These findings suggest that an attenuation of PTBR up-regulation resulting in the prevention of increased brain neurosteroid content represents one of the mechanisms by which mild hypothermia exerts its protective effects in ALF.

Systemic oxidative stress is implicated in the pathogenesis of brain edema in rats with chronic liver failure.

Chronic liver failure leads to hyperammonemia, a central component in the pathogenesis of hepatic encephalopathy (HE); however, a correlation between blood ammonia levels and HE severity remains controversial. It is believed oxidative stress plays a role in modulating the effects of hyperammonemia. This study aimed to determine the relationship between chronic hyperammonemia, oxidative stress, and brain edema (BE) in two rat models of HE: portacaval anastomosis (PCA) and bile-duct ligation (BDL). Ammonia and reactive oxygen species (ROS) levels, BE, oxidant and antioxidant enzyme activities, as well as lipid peroxidation were assessed both systemically and centrally in these two different animal models. Then, the effects of allopurinol (xanthine oxidase inhibitor, 100mg/kg for 10days) on ROS and BE and the temporal resolution of ammonia, ROS, and BE were evaluated only in BDL rats. Similar arterial and cerebrospinal fluid ammonia levels were found in PCA and BDL rats, both significantly higher compared to their respective sham-operated controls (p<0.05). BE was detected in BDL rats (p<0.05) but not in PCA rats. Evidence of oxidative stress was found systemically but not centrally in BDL rats: increased levels of ROS, increased activity of xanthine oxidase (oxidant enzyme), enhanced oxidative modifications on lipids, as well as decreased antioxidant defense. In PCA rats, a preserved oxidant/antioxidant balance was demonstrated. Treatment with allopurinol in BDL rats attenuated both ROS and BE, suggesting systemic oxidative stress is implicated in the pathogenesis of BE. Analysis of ROS and ammonia temporal resolution in the plasma of BDL rats suggests systemic oxidative stress might be an important "first hit", which, followed by increases in ammonia, leads to BE in chronic liver failure. In conclusion, chronic hyperammonemia and oxidative stress in combination lead to the onset of BE in rats with chronic liver failure.