Bernard Frances

Copper chelator induced efficient episodic memory recovery in a non-transgenic Alzheimer's mouse model.

Alzheimer’s disease (AD) is a neurodegenerative syndrom involving many different biological parameters, including the accumulation of copper metal ions in Aβ amyloid peptides due to a perturbation of copper circulation and homeostasis within the brain. Copper-containing amyloids activated by endogenous reductants are able to generate an oxidative stress that is involved in the toxicity of abnormal amyloids and contribute to the progressive loss of neurons in AD. Since only few drugs are currently available for the treatment of AD, we decided to design small molecules able to interact with copper and we evaluated these drug-candidates with non-transgenic mice, since AD is mainly an aging disease, not related to genetic disorders. We created a memory deficit mouse model by a single icv injection of Aβ1–42 peptide, in order to mimic the early stage of the disease and the key role of amyloid oligomers in AD. No memory deficit was observed in the control mice with the antisense Aβ42-1 peptide. Here we report the capacity of a new copper-specific chelating agent, a bis-8-aminoquinoline PA1637, to fully reverse the deficit of episodic memory after three weeks of treatment by oral route on non-transgenic amyloid-impaired mice. Clioquinol and memantine have been used as comparators to validate this fast and efficient mouse model.

Central apelin controls glucose homeostasis via a nitric oxide-dependent pathway in mice

AIMS Apelin and its receptor have emerged as promising targets for the treatment of insulin resistance. Indeed, peripheral administration of apelin stimulates glucose utilization and insulin sensitivity via a nitric oxide (NO) pathway. In addition to being expressed on peripheral metabolically active adipose tissues, apelin is also found in the brain. However, no data are available on the role of central effects of apelin on metabolic control. We studied glucose metabolism in response to acute and chronic intracerebroventricular (i.c.v.) injection of apelin performed in normal and obese/diabetic mice. RESULTS We demonstrate that i.c.v. injection of apelin into fed mice improves glucose control via NO-dependent mechanisms. These results have been strengthened by transgenic (eNOS-KO mice), pharmacological (L-NMMA i.c.v. treated mice), and real-time measurement of NO release with amperometric probes detection. High-fat diet-fed mice displayed a severely blunted response to i.c.v. apelin associated with a lack of NO response by the hypothalamus. Moreover, central administration of high dose apelin in fasted normal mice provoked hyperinsulinemia, hyperglycemia, glucose intolerance, and insulin resistance. CONCLUSION These data provide compelling evidence that central apelin participates in the regulation of glucose homeostasis and suggest a novel pathophysiological mechanism involved in the transition from normal to diabetic state.

Identification of neuropeptide FF-related peptides in rodent spinal cord

Peptides which should be generated from the neuropeptide FF (NPFF) precursor were identified in mouse and rat spinal cord, by using reverse phase high pressure liquid chromatography with radioimmunoassay and electrospray mass spectrometry detection. In both species, two octapeptides, NPFF (Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-amide) and NPSF (Ser-Leu-Ala-Ala-Pro-Gln-Arg-Phe-amide) were identified but a longer peptide NPA-NPFF (Asn-Pro-Ala-Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-amide) was present at the highest concentration in rat spinal cord. In mouse, the homologous peptide, SPA-NPFF (Ser-Pro-Ala-Phe-Leu-Phe-Gln-Pro-Gln-Arg-Phe-amide) was not detected. Both peptides NPFF and NPSF reverse morphine-induced analgesia in the tail flick test. Our data reveal species differences in the maturation of NPFF precursor.

Modifications of Hippocampal Circuits and Early Disruption of Adult Neurogenesis in the Tg2576 Mouse Model of Alzheimer's Disease

At advanced stages of Alzheimer’s disease, cognitive dysfunction is accompanied by severe alterations of hippocampal circuits that may largely underlie memory impairments. However, it is likely that anatomical remodeling in the hippocampus may start long before any cognitive alteration is detected. Using the well-described Tg2576 mouse model of Alzheimer’s disease that develops progressive age-dependent amyloidosis and cognitive deficits, we examined whether specific stages of the disease were associated with the expression of anatomical markers of hippocampal dysfunction. We found that these mice develop a complex pattern of changes in their dentate gyrus with aging. Those include aberrant expression of neuropeptide Y and reduced levels of calbindin, reflecting a profound remodeling of inhibitory and excitatory circuits in the dentate gyrus. Preceding these changes, we identified severe alterations of adult hippocampal neurogenesis in Tg2576 mice. We gathered converging data in Tg2576 mice at young age, indicating impaired maturation of new neurons that may compromise their functional integration into hippocampal circuits. Thus, disruption of adult hippocampal neurogenesis occurred before network remodeling in this mouse model and therefore may account as an early event in the etiology of Alzheimer’s pathology. Ultimately, both events may constitute key components of hippocampal dysfunction and associated cognitive deficits occurring in Alzheimer’s disease.

Involvement of hippocampal CA3 KATP channels in contextual memory

This paper evaluates the involvement of hippocampal ATP-sensitive potassium channels (K(ATP)) in learning and memory. After confirming expression of the Kir6.2 subunit in the CA3 region of C57BL/6J mice, we performed intra-hippocampal pharmacological injections of specific openers and blockers of K(ATP) channels. The opener diazoxide, the blocker tolbutamide, or a mixture of both, were bilaterally injected in the CA3 region before we subjected the animals to a fear conditioning paradigm. Diazoxide strongly impaired contextual memory of mice at both doses tested. This impairment was specifically reversed by co-injecting the blocker tolbutamide. Moreover, we studied the mnemonic abilities of mice deleted for the Kir6.2 subunit. These mice were backcrossed to C57BL/6J mice and tested in two learning paradigms. We found a significant impairment of contextual and tone memories in the Kir6.2 knock-out mice when compared with heterozygous or wild-type animals. Furthermore, these animals were also slightly impaired in a spatial version of the Morris water maze task. Our data suggest a specific involvement of hippocampal K(ATP) Kir6.2/SUR1 channels in memory processes.

1H NMR Metabolomic Signatures in Five Brain Regions of the AβPPswe Tg2576 Mouse Model of Alzheimer's Disease at Four Ages

In the quest for biomarkers of onset and progression of Alzheimers disease, a 1H NMR-based metabolomic study was performed on the simple single-transgenic Tg2576 mouse model. These mice develop a slow cognitive decline starting by 6 months and express amyloid plaques from 10 months of age. The metabolic profiles of extracts from five brain regions (frontal cortex, rhinal cortex, hippocampus, midbrain, and cerebellum) of Tg2576 male mice were compared to those of controls, at 1, 3, 6 and 11 months of age. The most obvious differences were due to brain regions. Age was also a discriminating parameter. Metabolic perturbations were already detected in the hippocampus and the rhinal cortex of transgenic mice as early as 1 month of age with decreased concentrations of glutamate (Glu) and N-acetylaspartate (NAA) compared to those in wild-type animals. Metabolic changes were more numerous in the hippocampus and the rhinal cortex of 3 month-old transgenic mice and involved Glu, NAA, myo-inositol, creatine, phosphocholine, and γ-aminobutyric acid (only in the hippocampus) whose concentrations decreased. A metabolic disruption characterized by an increase in the hippocampal concentrations of Glu, creatine, and taurine was detected in 6 month-old transgenic mice. At this time point, the chemical profile of the cerebellum was slightly affected. At 11 months, all the brain regions analyzed (except the frontal cortex) were metabolically altered, with mainly a marked increase in the formation of the neuroprotective metabolites creatine and taurine. Our findings demonstrate that metabolic modifications occur long before the onset of behavioral impairment.

Activation of Metabotropic Glutamate Receptor Type 2/3 Supports the Involvement of the Hippocampal Mossy Fiber Pathway on Contextual Fear Memory Consolidation.

Elucidating the functional properties of the dentate gyrus (DG), CA3, and CA1 areas is critical for understanding the role of the dorsal hippocampus in contextual fear memory processing. In order to specifically disrupt various hippocampal inputs, we used region-specific infusions of DCG-IV, the metabotropic glutamate receptor agonist, which selectively disrupts entorhinal outputs as well as mossy fiber transmission in the hippocampus. The consequences of these injections were studied using a contextual fear conditioning (CFC) paradigm. Selective contextual memory impairment was observed in DG- and CA3-, but not in CA1-treated mice. Our results emphasize the major role played by the DG and CA3 areas in the early phases of contextual memory processing, particularly during the acquisition and early consolidation phases of CFC.

Effects of the genetic background on cognitive performances of TG2576 mice

Animal models of genetic diseases obtained by transferring human mutated genes in the mouse are widely used in biomedical based research. They constitute efficient tools to study mechanisms underlying abnormal phenotypes. Unfortunately, the phenotype of the transgene is often obscured by the genetic background of the embryonic stem cells and that of the recipient strain used to create the transgenic line. It is also known, from the literature, that repeatedly backcrossing a transgenic strain to an inbred background may have unfavorable effects that can result in the loss of the transgenic line. In order to analyze the influences of the genetic background on the transgene expression, we studied the effects of the hAPPswe transgene involved in Alzheimers Amyloid Pathology, in 3 genetic backgrounds differing by their genetic heterogeneity (homozygous vs heterozygous) and the strain of origin (C57BL6, CBA, B6SJL F1) after only one generation backcrossing. Three different behavioral paradigms were used to assess the psychological and cognitive phenotypic differences: elevated plus maze, morris navigation task and contextual fear conditioning. Our data indicate that the best solution to maintain the transgenic line is to backcross repeatedly the transgenic mice into the F1 hybrid cross that was used to create the transgenic strain, whereas phenotyping should be performed comparatively after only one generation backcrossing into various well chosen F1 or inbred backgrounds.

Anisomycin Injection in Area CA3 of the Hippocampus Impairs Both Short-Term and Long-Term Memories of Contextual Fear.

Protein synthesis is involved in the consolidation of short-term memory into long-term memory. Previous electrophysiological data concerning LTP in CA3 suggest that protein synthesis in that region might also be necessary for short-term memory. We tested this hypothesis by locally injecting the protein synthesis inhibitor anisomycin in hippocampal area CA1 or CA3 immediately after contextual fear conditioning. As previously shown, injections in CA1 impaired long-term memory but spared short-term memory. Conversely, injections in CA3 impaired both long-term and short-term memories. We conclude that early steps of experience-induced plasticity occurring in CA3 and underlying short-term memory require protein synthesis.

Involvement of Protein Degradation by the Ubiquitin Proteasome System in Opiate Addictive Behaviors

Plastic changes in the nucleus accumbens (NAcc), a structure occupying a key position in the neural circuitry related to motivation, are among the critical cellular processes responsible for drug addiction. During the last decade, it has been shown that memory formation and related neuronal plasticity may rely not only on protein synthesis but also on protein degradation by the ubiquitin proteasome system (UPS). In this study, we assess the role of protein degradation in the NAcc in opiate-related behaviors. For this purpose, we coupled behavioral experiments to intra-accumbens injections of lactacystin, an inhibitor of the UPS. We show that protein degradation in the NAcc is mandatory for a full range of animal models of opiate addiction including morphine locomotor sensitization, morphine conditioned place preference, intra-ventral tegmental area morphine self-administration and intra-venous heroin self-administration but not for discrimination learning rewarded by highly palatable food. This study provides the first evidence of a specific role of protein degradation by the UPS in addiction.