Facteurs d'apprentissage chez les Modèles Murins de Mémoire et Evaluation des Effets du Dimebon

1. Factors of learning in mouse models of memory The impact of several most relevant biological factors in contextual learning in mice was investigated in the first part of our study. It is of general importance to estimate an impact of each of them in animals’ acquisition of various learning tasks during practical experimental work. First, factors of strain differences, aging and stress, investigated in our work can confound behavioural testing in memory paradigms. Second, they can be used as a basis of behavioural models of memory deficits and, thus, model pathological conditions in humans. Step-down avoidance task performed on three strains (namely C57BL/6N, CD1 and BALB/c) has clearly highlighted differences of abilities in learn contextual memory in these strains. The step-down avoidance task was also applied on C57BL/6N old of 3-months or 7-months; older mice displayed lower scores of memory then the young onces, thus, even mild aging impaired contextual learning in this strain. Third, we investigated learning of C57BL/6 mice subjected to chronic stress in a fear conditioning paradigm. Our study showed that the acquisition of this task was disrupted in stressed group, as reflected by decreased scores of freezing behavior. The assessment of investigated here factors of learning provides a possibility to validate animal models of memory and evaluate their sensitivity. 2. Evaluation of effects of dimebon Dimebon, a heterocyclic compounds previously adopted in clinic as antihistaminic, has recently revealed enhancing cognitive properties in pre-clinical and clinical studies The aim of the present study was to identify the most optimal dosing and adequate memory test(s), which would be sensitive to the memory enhancing effects of dimebon. Amongst the different studies realized, Dimebon revealed enhancement in memory in the step-down avoidance test, a one trial hippocampus-dependant task, at dose 0.5 mg/kg administered acutely and in the Y-Maze test, a multiple training paradigm at dose 0.1 mg/kg delivered chronically. In conclusion, our study supports therefore that the step-down avoidance and Y-maze paradigms are the most convenient assays allowing a rapid and reliable assessment of effects of of drugs with memory enhancing properties such as dimebon and dimebon-like

Mechanism of neuroprotective effets of thiamine and precursors with higher bioavaibility

Thiamine is very important for brain functioning and its deficiency causes specific lesions. This is mainly due to decreased levels of its diphosphorylated derivative thiamine diphosphate (ThDP), an essential cofactor for key enzymes in brain energy metabolism. Brain thiamine deficiency is not only the result of reduced thiamine intake, but also a consequence of chronic alcoholism, gastrointestinal diseases, diabetes, absorption of anti-thiamine factors, aging or reduced transport activity. As thiamine transport across the blood-brain barrier is relatively slow, thiamine precursors with higher bioavailability have been developed. One such compound is benfotiamine (BFT). After oral intake, BFT is dephosphorylated by intestinal alkaline phosphatase to the lipophilic S-benzoylthiamine, which freely diffuses across the intestinal mucosa and is transformed to thiamine. After administration of BFT, much higher blood thiamine levels are reached than after administration of an equivalent amount of thiamine. BFT was first shown to be efficient against diabetes-related complications. More recently, it was shown to have highly beneficial effects in mouse models of neurodegenerative diseases. In particular, it decreases brain amyloid deposits and tau hyperphosphorylation. The aim of our thesis was to investigate the mechanisms involved in central nervous system effects of BFT. In a first part, using the mouse neuroblastoma cell line N2a, we demonstrated that BFT indeed requires prior dephosphorylation to S-benzoylthiamine in order to enter the cells and raise intracellular thiamine concentrations. Surprisingly, when orally administered to mice, BFT strongly increased blood thiamine concentration but did not increase brain ThDP levels, suggesting that potential central nervous system effects are cofactor-independent. It has been suggested that treatment with benfotiamine induces an increase in brain GSK-3ß phosphorylation, thereby decreasing its activity. As GSK-3ß is in part responsible for tau hyperphosphorylation, such a mechanism might explain a reduced formation of neurofibrillary tangles in the above-mentioned models of neurodegeneration. Using N2a cells, we indeed confirm a stimulation of the RTK – PI3K – Akt pro-survival pathway. As it is known that benfotiamine treatment has potent beneficial effects in 2 different mouse models of neurodegeneration and that exposure of WT mice to intense stress is also harmful for the hippocampus, we investigated the effects of predator stress on adult hippocampal neurogenesis. The latter has been shown to be impaired by stress in rodents. We therefore tested the effects of thiamine and BFT treatment on hippocampal neurogenesis in predator-stressed mice. Our results show that both thiamine and BFT prevented the reduction of neurogenesis induced by stress, benfotiamine being most effective. Moreover, we show that thiamine and benfotiamine counteract stress-induced bodyweight loss and increase of anxiety-like behavior. Both treatments elevated brain levels of thiamine, but not of the coenzyme thiamine diphosphate (ThDP), again suggesting that the beneficial effects observed are not linked to the cofactor role of ThDP. Our study demonstrates for the first time that thiamine and benfotiamine prevent stress-induced inhibition of hippocampal neurogenesis and accompanying physiological changes, probably by non-cofactor-dependent mechanisms. The use of thiamine precursors might thus be considered as a complementary therapy in several neuropsychiatric disorders, especially depression caused by chronic stress

Status of electrical power supply of OUFTI-1 nanosatellite as of mid-2012: design, implementation, and tests

We describe the principles and performances the OUFTI-1 nanosatellite electrical power supply (EPS), which is designed to provide subsystems with the required voltages and currents, with as high a reliability as possible.OUFTI-1 nanosatellit

Simultaneous versus solitary pharmacological manipulation of NMDA- and AMPA- receptors: effects of new drugs on contextual learning and its extinction

Both the attenuation of the NMDA-receptor mediated transmission via low affinity blockade mechanism, and the stimulation of AMPA receptor-mediated signaling were shown to result in beneficial neurobiological effects, such as an enhancement of memory and neurogenesis. We aimed to compare the effects of acute pharmacological manipulations of these mechanisms, exerted simultaneously or solely in mice, on learning of two mouse tasks with distinct predominant dependency on either glutamate receptor subtype. In a step-down avoidance task, memantine, low affinity NMDA receptor blocker (5 mg/kg), but not ampakine QQX (5 mg/kg) increased memory scores. In contrast, extinction of contextual fear conditioning was significantly enhanced by the latter, but not by the first drug. Among four new isothiourea derivates used at the doses 0.5-1 mg/kg, one compound that showed a maximal potency with respect to both glutamatergic mechanisms, as well as dimebon (1 mg/kg), had the most prominent memory enhancing effects. Thus, simultaneous low affinity blocade of the NMDA receptor and stimulation of AMPA-mediated transmission can result in eminent pro-cognitive activities. These data point to the importance of multi-target drug mechanism in the regulation of cognitive functions and suggest its potential for clinical implications

Dimebon enhances hippocampus-dependent learning in both appetitive and inhibitory memory tasks in mice

Dimebon, a compound recently proposed for a treatment of Alzheimer’s disorder was suggested to have memory enhancing properties in pre-clinical and clinical studies. We investigated whether dimebon at doses acutely (0.1 mg/kg and 0.5 mg/kg) or repeatedly (0.1 mg/kg) administered to mice via i.p. injections, increases memory scores respectively in an appetitive and an inhibitory learning task. Acute treatment with dimebon at the dose 0.1 mg/kg did not affect learning scores in either 3-month-old C57BL/6N or CD1 mice. Acute treatment with higher dose of dimebon (0.5mg/kg) was found to enhance inhibitory learning in 3- and 7-month-old mice as shown in the step-down avoidance paradigm in C57BL/6N mice. No effects on learning were seen in CD1 mice. In a model of appetitive learning, a spatial version of the Y-maze, repeated treatment with dimebon increased the rate of correct choices and decreased the latency of accessing a water reward after water deprivation. Repeated administration of dimebon also increased the duration of drinking behaviour during training/testing procedures although behaviours in others tests or water consumption were not altered. Acute treatment of water-deprived and non-water-deprived mice with dimebon also did not affect their water intake. Our data suggest that dimebon enhances hippocampus-dependent learning in both appetitive and inhibitory tasks in mice

Altered emotionality, hippocampus-dependent performance and expression of NMDA receptor subunit mRNAs in chronically stressed mice.

N-Methyl-D-aspartate receptor (NMDAR)-mediated neurotransmission in the hippocampus is implicated in cognitive and emotional disturbances during stress-related disorders. Here, using quantitative RT-PCR, we investigated the hippocampal expression of NR2A, NR2B and NR1 subunit mRNAs in a mouse stress paradigm that mimics clinically relevant conditions of simultaneously affected emotionality and hippocampus-dependent functions. A 2-week stress procedure, which comprised ethologically valid stressors, exposure to a rat and social defeat, was applied to male C57BL/6J mice. For predation stress, mice were introduced into transparent containers that were placed in a rat home cage during the night; social defeat was applied during the daytime using aggressive CD1 mice. This treatment impaired hippocampus-dependent performance during contextual fear conditioning. A correlation between this behavior and food displacement performance was demonstrated, suggesting that burrowing behavior is affected by the stress procedure and is hippocampus-dependent. Stressed mice (n = 22) showed behavioral invigoration and anomalous anxiolytic-like profiles in the O-maze and brightly illuminated open field, unaltered short-term memory in the step-down avoidance task and enhanced aggressive traits, as compared to non-stressed mice (n = 10). Stressed mice showed increased basal serum corticosterone concentrations, hippocampal mRNA expression for the NR2A subunit of the NMDAR and in the NR2A/NR2B ratio; mRNA expression of NR2B and NR1 was unchanged. Thus, stress-induced aberrations in both hippocampal-dependent performance and emotional abnormalities are associated with alterations in hippocampal mRNA NR2A levels and the NR2A/NR2B ratio and not with mRNA expression of NR2B or NR1

Anomalous behaviour in the diffusion of polyethylene oxide through dialysis membrane

Dialysis is a common technique adopted in biochemistry to purify biopharmaceutical drugs. This methodology is also of interest in macromolecular chemistry and pharmaceutical nanotechnology in order to purify synthetic macromolecules and nanodrug carriers designed for drug delivery purposes. However, based on their original applications, the diffusion characteristic of the dialysis membrane is given in respect to the diffusion rate of globular proteins. So the diffusion capacity is function of molecular weight cut-off, i.e. corresponding to the maximum molecular weight of a globular macromolecule to be able to cross the membrane. The diffusion kinetics of synthetic macromolecules is expected to differ significantly from globular proteins due to at least the following differences : Specific relationship between hydrodynamic diameter and molecular weight, Flexibility Ionic density Solubility/miscibility/adsorption behaviour with the dialysis membrane Polymer chain entanglement above a critical concentration. In view to validate the application of this technique to purify synthetic macromolecules, we have compared the diffusion ability of neutral polyethyetylene oxide (PEO) standards or poly(dimethyl-aminoethyl-methacrylate) (PMADAM) to protein standards (human insulin and ovalbumin)

Dimebon Enhances Hippocampus-Dependent Learning in Mouse Models of Appetitive Y-Maze and Inhibitory Step-Down Memory Tasks in Mice

Dimebon, a compound recently proposed for a treatment of Alzheimer’s disorder, was suggested to have memory enhancing properties in pre-clinical and clinical studies. We investigated whether dimebon at doses acutely (0.1 mg/kg and 0.5 mg/kg) or repeatedly (0.1 mg/kg) administered to mice via i.p. injections, increases memory scores respectively in an appetitive and an inhibitory learning task. Acute treatment with dimebon at the dose 0.1 mg/kg did not affect learning scores in 3-month-old C57BL/6N. Acute treatment with higher dose of dimebon (0.5mg/kg) was found to enhance inhibitory learning in 3-month-old mice as shown in the step-down avoidance paradigm in C57BL/6N mice. In a model of appetitive learning, a spatial version of the Y-maze, repeated treatment with dimebon increased the rate of correct choices and decreased the latency of accessing a water reward after water deprivation. Repeated administration of dimebon also increased the duration of drinking behaviour during training/testing procedures although water consumption behaviour was not altered. Additional behavioural tests were carried out to investigate possible non-specific effects of dimebon on parameters of drinking, anxiety and exploration/locomotion. Our data suggest that dimebon enhances hippocampus-dependent learning in both appetitive and inhibitory tasks in mice