Conséquences à long terme d'une exposition chronique aux cannabinoïdes durant l'adolescence chez le rat (Approches comportementale, fonctionnelle et structurale)

La consommation de cannabis chez les adolescents et les jeunes adultes constitue un facteur de risque de développement de symptômes psychotiques. L objectif de cette thèse était d étudier les conséquences à l âge adulte d une exposition chronique aux cannabinoïdes pendant l adolescence. Nous avons réalisé ces études chez le Rat et démontré que l administration chronique d un agoniste des récepteurs cannabinoïdes, le CP55, 940, durant l adolescence (JPN 29 à 50) entraîne à l âge adulte des déficits significatifs et durables de la mémoire à court terme et de la mémoire de travail spatiale. Le même traitement administré à l âge adulte (JPN 70 à 91) n entraîne pas de déficits cognitifs à long terme. L apport de ces travaux et leur originalité a été de contribuer à la compréhension des mécanismes sous-jacents au développement de ces déficits cognitifs. Nous avons mis en évidence, chez ces rats à l âge adulte, une diminution significative de l amplitude de la PLT induite sur le circuit reliant l hippocampe au cortex préfrontal, fortement impliqué dans les processus de mémoire et dans la physiopathologie de la schizophrénie. Ce déficit de PLT a été mis en relation avec des modifications de la morphologie des neurones pyramidaux de la couche II/III du cortex préfrontal et de certains marqueurs de la plasticité synaptique. Ces résultats confirment que l'adolescence est une période critique et vulnérable aux effets délétères des cannabinoïdes sur les processus cognitifs. L étude des bases neurobiologiques de ces effets, en particulier en ce qui concerne les altérations des circuits préfrontaux, devrait améliorer notre compréhension des mécanismes de l'émergence de la psychose et conduire à de nouvelles stratégies thérapeutiques et de prévention.Cannabis use among adolescents and young adults is a risk factor for developing psychotic symptoms. The aim of this thesis was to study the consequences at different levels (behavioral, functional and structural in adulthood) of chronic exposure to synthetic cannabinoids during adolescence in the rat. We showed that chronic administration of a cannabinoid receptor agonist, CP 55940, during adolescence (PND 29-50) in rats leads to significant long-term deleterious effects in short-term memory and in spatial working memory in adulthood. The same treatment administered in adulthood (PND 70-91) does not cause long-term cognitive deficits. We further demonstrated that cannabinoid during adolescence leads in adults to a significant decrease in the expression of LTP induced in hippocampal to prefrontal cortex synapses, a circuit directly involved in memory processes and in the pathophysiology of schizophrenia. This alteration could be associated with changes in the morphology of pyramidal neurons in layer II / III of PFC and/or in the density of synaptic markers that we also identified in these cannabinoid-treated rats. These findings demonstrate that adolescence is a critical and vulnerable period to the deleterious effects of cannabinoids on cognitive processes. The neurobiological basis for this effect, especially with regard to alterations to prefrontal circuitry, which we partially provide should improve our understanding of the emergence of psychosis and lead to new therapeutic strategies and prevention.PARIS5-Bibliotheque electronique (751069902) / SudocPARIS-BIUM-Bib. électronique (751069903) / SudocSudocFranceF

Neuropathological and Reelin Deficiencies in the Hippocampal Formation of Rats Exposed to MAM; Differences and Similarities with Schizophrenia

Adult rats exposed to methylazoxymethanol (MAM) at embryonic day 17 (E17) consistently display behavioral characteristics similar to that observed in patients with schizophrenia and replicate neuropathological findings from the prefrontal cortex of psychotic individuals. However, a systematic neuropathological analysis of the hippocampal formation and the thalamus in these rats is lacking. It is also unclear if reelin, a protein consistently associated with schizophrenia and potentially involved in the mechanism of action of MAM, participates in the neuropathological effects of this compound. Therefore, a thorough assessment including cytoarchitectural and neuromorphometric measurements of eleven brain regions was conducted. Numbers of reelin positive cells and reelin expression and methylation levels were also studied.Compared to untreated rats, MAM-exposed animals showed a reduction in the volume of entorhinal cortex, hippocampus and mediodorsal thalamus associated with decreased neuronal soma. The entorhinal cortex also showed laminar disorganization and neuronal clusters. Reelin methylation in the hippocampus was decreased whereas reelin positive neurons and reelin expression were unchanged.Our results indicate that E17-MAM exposure reproduces findings from the hippocampal formation and the mediodorsal thalamus of patients with schizophrenia while providing little support for reelin's involvement. Moreover, these results strongly suggest MAM-treated animals have a diminished neuropil, which likely arises from abnormal neurite formation; this supports a recently proposed pathophysiological hypothesis for schizophrenia

Fluoroethylnormemantine, A Novel Derivative of Memantine, Facilitates Extinction Learning Without Sensorimotor Deficits

International audienceBackground: Memantine, a noncompetitive N-methyl-D-aspartate receptor antagonist, has been approved for use in Alzheimer's disease, but an increasing number of studies have investigated its utility for neuropsychiatric disorders. Here, we characterized a novel compound, fluoroethylnormemtantine (FENM), which was derived from memantine with an extra Fluor in an optimized position for in vivo biomarker labeling. We sought to determine if FENM produced similar behavioral effects as memantine and/or if FENM has beneficial effects against fear, avoidance, and behavioral despair. Methods: We administered saline, FENM, or memantine prior to a number of behavioral assays, including paired-pulse inhibition, open field, light dark test, forced swim test, and cued fear conditioning in male Wistar rats. Results: Unlike memantine, FENM did not produce nonspecific side effects and did not alter sensorimotor gating or locomotion. FENM decreased immobility in the forced swim test. Moreover, FENM robustly facilitated fear extinction learning when administered prior to either cued fear conditioning training or tone reexposure. Conclusions: These results suggest that FENM is a promising, novel compound that robustly reduces fear behavior and may be useful for further preclinical testing

Non-cell autonomous OTX2 transcription factor regulates anxiety-related behavior in the mouse

International audienceThe OTX2 homeoprotein transcription factor is expressed in the dopaminergic neurons of the ventral tegmental area, which projects to limbic structures controlling complex behaviors. OTX2 is also produced in choroid plexus epithelium, from which it is secreted into cerebrospinal fluid and transferred to limbic structure parvalbumin interneurons. Previously, adult male mice subjected to early-life stress were found susceptible to anxiety-like behaviors, with accompanying OTX2 expression changes in ventral tegmental area or choroid plexus. Here, we investigated the consequences of reduced OTX2 levels in Otx2 heterozygote mice, as well as in Otx2 +/AA and scFvOtx2 tg/0 mouse models for decreasing OTX2 transfer from choroid plexus to parvalbumin interneurons. Both male and female adult mice show anxiolysis-like phenotypes in all three models. In Otx2 heterozygote mice, we observed no changes in dopaminergic neuron numbers and morphology in ventral tegmental area, nor in their metabolic output and projections to target structures. However, we found reduced expression of parvalbumin in medial prefrontal cortex, which could be rescued in part by adult overexpression of Otx2 specifically in choroid plexus, resulting in increased anxiety-like behavior. Taken together, OTX2 synthesis by the choroid plexus followed by its secretion into the cerebrospinal fluid is an important regulator of anxiety phenotypes in the mouse

The GhsrQ343X allele favors the storage of fat by acting on nutrient partitioning

International audienceThe Growth Hormone Secretagogue Receptor (GHSR) mediates key properties of the gut hormone ghrelin on metabolism and behavior. Nevertheless, most recent observations also support that the GHSR is a constitutively active G protein-coupled receptor endowed of a sophisticated tuning involving a balance of endogenous ligands. Demonstrating the feasibility of shifting GHSR canonical signaling in vivo, we previously reported that a model with enhanced sensitivity to ghrelin ( Ghsr Q343X mutant rats) developed fat accumulation and glucose intolerance. Herein, we investigated the contribution of energy homeostasis to the onset of this phenotype, as well as behavioral responses to feeding or pharmacological challenges, by comparing Ghsr M/M rats to wild-type littermate rats 1) as freely behaving animals and 2) in feeding and locomotor paradigms. Herein, Ghsr M/M rats showed enhanced locomotor response to a GHSR agonist while locomotor or anorexigenic responses to amphetamine or cabergoline (dopamine receptor 2 agonist), respectively, were preserved. Ad libitum fed Ghsr M/M rats consumed and conditioned for sucrose similarly to littermate control rats. In calorie-restricted conditions, Ghsr M/M rats retained food anticipatory activity and maintained better their body weight and glycemia. Importantly, prior to fat accumulation, male Ghsr M/M rats preferentially used carbohydrates as fuel substrate without alterations of energy intake, energy expenditure or physical activity and showed alterations of the GHSR system (i.e. enhanced ratio of GHSR hormones LEAP2:acyl-ghrelin and increased Ghsr expression in the hypothalamus). Overall, the present study provides proof of concept that shifted GHSR signaling can specifically alter nutrient partitioning resulting in modified balance of carbohydrate/lipid utilization

Activation of the PI3K/AKT/mTOR Pathway in Cajal–Retzius Cells Leads to Their Survival and Increases Susceptibility to Kainate-Induced Seizures

International audienceCajal–Retzius cells (CRs) are a class of transient neurons in the mammalian cortex that play a critical role in cortical development. Neocortical CRs undergo almost complete elimination in the first two postnatal weeks in rodents and the persistence of CRs during postnatal life has been detected in pathological conditions related to epilepsy. However, it is unclear whether their persistence is a cause or consequence of these diseases. To decipher the molecular mechanisms involved in CR death, we investigated the contribution of the PI3K/AKT/mTOR pathway as it plays a critical role in cell survival. We first showed that this pathway is less active in CRs after birth before massive cell death. We also explored the spatio-temporal activation of both AKT and mTOR pathways and reveal area-specific differences along both the rostro–caudal and medio–lateral axes. Next, using genetic approaches to maintain an active pathway in CRs, we found that the removal of either PTEN or TSC1, two negative regulators of the pathway, lead to differential CR survivals, with a stronger effect in the Pten model. Persistent cells in this latter mutant are still active. They express more Reelin and their persistence is associated with an increase in the duration of kainate-induced seizures in females. Altogether, we show that the decrease in PI3K/AKT/mTOR activity in CRs primes these cells to death by possibly repressing a survival pathway, with the mTORC1 branch contributing less to the phenotype

Neuronal size and density in the hippocampal formation of MAM-treated rats and patients with schizophrenia.

1<p>Methylazoxymethanol during embryonic day 17.</p>2<p>Cornu ammonis.</p>3<p>Two dimensional.</p>4<p>Three dimensional.</p

Discontinuities and heterotopias in MAM and control animals.

<p>(A) Coronal slices at Bregma −3.8mm of the hippocampus, CA1, CA2 and CA3 from MAM exposed rats stained with anti-NeuN antibody and 3,3′-diaminobenzidine as chromogen. The rectangles in the first photo indicate where the magnification shown in the three following photos comes from. Arrows point to actual discontinuities. (B) Graph bars indicating discontinuity differences between MAM rats and control animals in hippocampal subfields CA1, CA2 and CA3. (C) Coronal slices at Bregma −3.8mm from MAM and control animals stained with anti-NeuN antibody and 3,3′-diaminobenzidine as chromogen. The rectangles within the two left photos indicate where the magnification shown in the two right photos comes from. The arrow points to an actual heterotopia. (D) Graph indicating number of heterotopias in MAM rats' hippocampus compared to control animals. Results represent the mean ± S.E.M. of 9 animals per group from which slides done by duplicate were analyzed. *p<0.05 and ***p<0.001.</p

Morphometric effects of MAM E17 treatment on brain structures.

<p>(A) Brain diagrams reproduced with permission from The Rat Brain Atlas by Paxinos and Watson 6 edition illustrating how anatomical areas were delineated. Bregma −3.8mm on left and Bregma −5.8mm on right. Areas and thicknesses were measured as delineated in the pictures. (B–C) Graphs indicating differences in brain area (B) and circumference (C) between control (white bars) and MAM-exposed animals (black bars). (D–E) Graphs indicating area differences between MAM and control animals at Bregma −3.6 (D) and −5.8mm (E). (F–G) Graphs indicating differences in thickness between MAM and control animals at Bregma −3.6 (F) and −5.8mm (G). Results represent the mean ± S.E.M. of 9 animals per group from which slides done by duplicate were analyzed. Amygdala (AMG), associative parietal cortex (PtA), cornu ammonis (CA), dentate gyrus (DG), entorhinal cortex (ERC), hippocampus (HIP), mediodorsal thalamic nucleus (MDT), perirhinal cortex (PER), piriform cortex (PIR), somato-sensory cortex barrel field 1 (S1BF), substantia nigra (SN), thalamus (THAL), ventral tegmental area (VTA). *p<0.05 **p<0.01 and ***p<0.001.</p