Doctor of Phylosophy (PhD) / Schizophrenia is a severe, chronic and disabling mental disorder with a worldwide prevalence of approximately 1 %. It is a lifelong illness characterized by psychotic symptoms which typically first appear in late adolescence/early adulthood. The symptoms of schizophrenia are usually categorized as positive (hallucinations and delusions), negative (blunted affect and poverty of speech) and cognitive (memory, attention and executive function impairments). Schizophrenia is thought to arise from an interaction between several susceptibility genes and environmental factors, one of them being the use of cannabis, the most widely used illicit drug in the world. Human population studies show that cannabis use is associated with schizophrenia, and it is now well recognised that cannabis use increases the risk of developing schizophrenia by approximately twofold. The reasons for the association between cannabis and schizophrenia remain controversial and different theories have been proposed to explain the nature of this relationship. According to the self-medication hypothesis of schizophrenia, patients with psychotic disorders use cannabis to alleviate aversive symptoms of the disorder or the side effects associated with antipsychotic medications. Other theories posit that cannabis is a component cause contributing to the development of schizophrenia. Supporting this, an increasing body of evidence shows that cannabis use increases the incidence and severity of psychotic symptoms and that cannabis use most frequently precedes the onset of schizophrenia. As a large majority of cannabis users do not develop schizophrenia, a gene-environment interaction appears necessary for the development of the disorder. That is, cannabis use may unmask latent schizophrenia in individuals that have a genetic predisposition to the disorder. Family studies provide strong evidence of a genetic contribution to the aetiology of schizophrenia. Several candidate genes are likely involved in the disorder, but this thesis will specifically focus on the neuregulin 1 (NRG1) gene. NRG1 was first proposed as a schizophrenia susceptibility gene in 2002 and linkage studies have since replicated this association in diverse populations around the world. In addition, changes in expression of Nrg1 isoforms and its receptor ErbB4 have been reported in the brain of schizophrenia patients. NRG1 polymorphism has also been associated with cognitive and behavioural differences in schizophrenia patients compared to healthy individuals. Collectively, NRG1 is now recognized as one of the most promising genes that confer an increased risk of developing schizophrenia. The creation of knockout mice lacking a specific gene offers an exciting new approach in the study of mental disorders. While several mutant mice for Nrg1 and ErbB4 receptor have been developed, this thesis focussed on mice that are heterozygous for the transmembrane domain of the Nrg1 gene (named Nrg1 HET mice). These mice exhibit a schizophrenia-like phenotype including hyperactivity that can be used as a reflection of positive symptoms of schizophrenia. Furthermore, they display impairments in social recognition memory and prepulse inhibition (PPI), a model of attentional deficits observed in schizophrenia patients. In addition, the brains of Nrg1 HET contain fewer functional NMDA receptors and more 5-HT2A receptors than wild type-like (WT) animals which is consistent with the neurotransmitters imbalance observed in schizophrenic patients. The phenotype of Nrg1 HET mice is age-dependent, another aspect that mirror the late adolescent/early adulthood onset of schizophrenia symptoms. The present thesis aimed at developing an animal model of genetic vulnerability to cannabinoid-precipitated schizophrenia by utilising Nrg1 HET mice to observe if these animals show an altered behavioural and neuronal response to cannabinoid exposure. We hypothesise that Nrg1 deficiency will alter the neurobehavioural responses of animals to cannabinoids. The experiments detailed within the first research chapter (Chapter 2) aimed at examining the behavioural effects of an acute exposure to the main psychoactive constituent of cannabis, Δ9-tetrahydrocannabinol (THC), in Nrg1 HET mice using a range of behavioural tests of locomotion, exploration, anxiety and sensorimotor gating. Relative to WT control mice, Nrg1 HET mice were more sensitive to both the locomotor suppressant action of THC, as measured in the open field test, and to the anxiogenic effects of THC in the light-dark test, although the effects in this procedure may be confounded by the drug-free hyperactive phenotype of Nrg1 HET mice. Importantly, Nrg1 HET mice expressed a greater THC-induced enhancement in PPI than WT mice. Taken together, the data presented in Chapter 2 show that a deficiency in a schizophrenia susceptibility gene Nrg1 enhanced the behavioural impact of THC. After having established a link between Nrg1 deficiency and increased sensitivity to the behavioural effects of cannabinoids in Chapter 2, Chapter 3 assessed the neuronal activity underlying the effects of an acute THC exposure on Nrg1 HET mice by using c-Fos immunohistochemistry. In the ventral part of the lateral septum (LSV), THC selectively increased c-Fos expression in Nrg1 HET mice with no corresponding effect being observed in WT mice. In addition, a non-significant trend for THC to promote a greater increase in c-Fos expression in Nrg1 HET mice than WT mice was observed in the central nucleus of the amygdala, the bed nucleus of the stria terminalis and the paraventricular nucleus of the hypothalamus. Consistent with Nrg1 HET mice exhibiting a schizophrenia-related phenotype, these mice expressed greater drug-free levels of c-Fos in the shell of the nucleus accumbens and the LSV. Interestingly, the effects of genotype on c-Fos expression, drug-free or following THC exposure, were only observed when animals experienced behavioural testing prior to perfusion. This suggests that an interaction with stress was necessary for the promotion of these effects. As the risk of developing psychosis in vulnerable individuals increases with the frequency of cannabis use, Chapter 4 assessed the effects of repeated exposure to cannabinoids on Nrg1 HET mice. As THC was not available at the time, the synthetic analogue of THC, CP 55,940, was used in this experiment. Behavioural testing showed that tolerance to CP 55,940-induced hypothermia and locomotor suppression developed more rapidly in Nrg1 HET mice compared to WT mice. On the contrary, tolerance to the anxiogenic-like effect of CP 55,940 in the light-dark test was observed in WT mice, however no such tolerance occurred to this effect in Nrg1 HET mice. Similarly, no tolerance developed to CP 55,940-induced thigmotaxis in Nrg1 HET mice as measured in the open field. For PPI, on the first day of exposure opposite effects were observed, with CP 55,940 treatment facilitating PPI in Nrg1 HET mice and decreasing it in WT mice. However, the differential effect of CP 55,940 on PPI was not maintained with repeated testing as both genotypes became tolerant to the effects of the cannabinoid on sensorimotor gating. In addition, a selective increase in Fos B/ΔFos B expression, a marker of longer-term neuronal changes, was observed in the LSV of Nrg1 HET mice following chronic CP 55,940 exposure, with no corresponding effect seen in WT mice. These results collectively demonstrate that the neuregulin system is involved in the neuroadaptive response to repeated cannabinoid exposure. One of the main schizophrenia endophenotypes observed in human studies are cognitive impairments of higher executive functions. Thus Chapter 5 aimed to develop a procedure to allow evaluation of cannabis-induced working memory deficits in mice. Few studies have investigated the effects of chronic cannabinoid exposure on memory performance and whether tolerance occurs to cannabinoidinduced memory impairment. Here we studied the effects of repeated exposure to THC on spatial memory and the expression of the immediate early gene zif268 in mice. One group of animals were not pre-treated with THC while another group was given 13 daily injections of THC prior to memory training and testing in the Morris water maze. Both groups were administered THC throughout the memory training and testing phases of the experiment. THC decreased spatial memory and reversal learning, even in animals that received the THC pre-treatment and were tolerant to the locomotor suppressant effects of the drug. Zif268 immunoreactivity was reduced in the CA3 of the hippocampus and in the prefrontal cortex only in non pre-treated animals, indicating that while tolerance to the effects of cannabinoids on neuronal activity arose, cannabinoid-promoted memory impairment in these animals persisted even after 24 days of exposure. Taken together these data demonstrate that the spatial memory impairing effects of THC are resistant to tolerance following extended administration of the drug. Such a model could be applied to Nrg1 HET mice in future studies to observe if cannabinoid-induced working memory impairments and the development of tolerance to this effect are altered relative to WT mice. In conclusion, this thesis provides the first evidence that partial deletion of the schizophrenia susceptibility gene Nrg1 modulates the neurobehavioural actions of acutely and chronically administered cannabinoids. Nrg1 HET mice appear more sensitive to the acute neurobehavioural effects of cannabinoids. Notably, acutely administered THC facilitated attentional function by increasing PPI in Nrg1 HET mice. However, with repeated cannabinoid administration this acute benefit was lost. The Nrg1 HET mice displayed a long-lasting anxiogenic profile that was resistant to tolerance. Conversely, Nrg1 HET mice developed tolerance to the locomotor suppressant and hypothermic effects of cannabinoids more rapidly than WT mice, indicating a distorted neuroadaptive response in these animals. Another major finding of this thesis is that the lateral septum appears to be an important brain region dysregulated by cannabinoids in Nrg1 HET mice. Cumulatively, this research highlights the fact that neuregulin 1 and cannabinoid systems appear to interact in the central nervous system. This may ultimately enhance our understanding of how gene-environment interactions are responsible for cannabis-induced development of schizophrenia.

Au cours de ce travail, nous avons cherché de préciser le rôle de cette famille de facteur de croissance dans le choix dun destin cellulaire au cours du développement, tout en gardant à lesprit leur éventuel potentiel dans le cadre dune thérapie cellulaire chez ladulte. Nous avons donc tenté de répondre aux questions suivantes : 1) est-il possible dinfluencer le choix dun destin cellulaire particulier dans les cellules souches nerveuses sous leffet des Neurégulines ; 2) si oui, quel(s) serait (seraient) le(s) mécanisme(s) moléculaire(s) éventuellement recrutable ou applicable en terme de régénération. Le chapitre II est consacré à létude des Neurégulines-1 et leurs effets sur la prolifération et la différenciation des cellules souches nerveuses in vitro. Dans ce chapitre, nous décrivons un mécanisme moléculaire original responsable de la modulation de la différenciation par les Neurégulines-1 et qui établit un line direct entre les influences intrinsèques et extrinsèques telles que nous les avons rappelées en préambule du point 2 de cette introduction (Edlund and Jessell, 1999). La plupart des résultats de ce chapitre font lobjet dun article actuellement sous presse (appendice 2). Dans le chapitre III, nous décrivons les résultats préliminaires obtenus dans létude du rôle du rôle de Nrg-2 dans ces mécanismes. Cest sur la base de la similitude structurelle et topologique des isoformes codées par les deux gènes que nous avons entrepris cette dernière partie de notre travail.

Doctor of Phylosophy (PhD) / Schizophrenia is a severe, chronic and disabling mental disorder with a worldwide prevalence of approximately 1 %. It is a lifelong illness characterized by psychotic symptoms which typically first appear in late adolescence/early adulthood. The symptoms of schizophrenia are usually categorized as positive (hallucinations and delusions), negative (blunted affect and poverty of speech) and cognitive (memory, attention and executive function impairments). Schizophrenia is thought to arise from an interaction between several susceptibility genes and environmental factors, one of them being the use of cannabis, the most widely used illicit drug in the world. Human population studies show that cannabis use is associated with schizophrenia, and it is now well recognised that cannabis use increases the risk of developing schizophrenia by approximately twofold. The reasons for the association between cannabis and schizophrenia remain controversial and different theories have been proposed to explain the nature of this relationship. According to the self-medication hypothesis of schizophrenia, patients with psychotic disorders use cannabis to alleviate aversive symptoms of the disorder or the side effects associated with antipsychotic medications. Other theories posit that cannabis is a component cause contributing to the development of schizophrenia. Supporting this, an increasing body of evidence shows that cannabis use increases the incidence and severity of psychotic symptoms and that cannabis use most frequently precedes the onset of schizophrenia. As a large majority of cannabis users do not develop schizophrenia, a gene-environment interaction appears necessary for the development of the disorder. That is, cannabis use may unmask latent schizophrenia in individuals that have a genetic predisposition to the disorder. Family studies provide strong evidence of a genetic contribution to the aetiology of schizophrenia. Several candidate genes are likely involved in the disorder, but this thesis will specifically focus on the neuregulin 1 (NRG1) gene. NRG1 was first proposed as a schizophrenia susceptibility gene in 2002 and linkage studies have since replicated this association in diverse populations around the world. In addition, changes in expression of Nrg1 isoforms and its receptor ErbB4 have been reported in the brain of schizophrenia patients. NRG1 polymorphism has also been associated with cognitive and behavioural differences in schizophrenia patients compared to healthy individuals. Collectively, NRG1 is now recognized as one of the most promising genes that confer an increased risk of developing schizophrenia. The creation of knockout mice lacking a specific gene offers an exciting new approach in the study of mental disorders. While several mutant mice for Nrg1 and ErbB4 receptor have been developed, this thesis focussed on mice that are heterozygous for the transmembrane domain of the Nrg1 gene (named Nrg1 HET mice). These mice exhibit a schizophrenia-like phenotype including hyperactivity that can be used as a reflection of positive symptoms of schizophrenia. Furthermore, they display impairments in social recognition memory and prepulse inhibition (PPI), a model of attentional deficits observed in schizophrenia patients. In addition, the brains of Nrg1 HET contain fewer functional NMDA receptors and more 5-HT2A receptors than wild type-like (WT) animals which is consistent with the neurotransmitters imbalance observed in schizophrenic patients. The phenotype of Nrg1 HET mice is age-dependent, another aspect that mirror the late adolescent/early adulthood onset of schizophrenia symptoms. The present thesis aimed at developing an animal model of genetic vulnerability to cannabinoid-precipitated schizophrenia by utilising Nrg1 HET mice to observe if these animals show an altered behavioural and neuronal response to cannabinoid exposure. We hypothesise that Nrg1 deficiency will alter the neurobehavioural responses of animals to cannabinoids. The experiments detailed within the first research chapter (Chapter 2) aimed at examining the behavioural effects of an acute exposure to the main psychoactive constituent of cannabis, Δ9-tetrahydrocannabinol (THC), in Nrg1 HET mice using a range of behavioural tests of locomotion, exploration, anxiety and sensorimotor gating. Relative to WT control mice, Nrg1 HET mice were more sensitive to both the locomotor suppressant action of THC, as measured in the open field test, and to the anxiogenic effects of THC in the light-dark test, although the effects in this procedure may be confounded by the drug-free hyperactive phenotype of Nrg1 HET mice. Importantly, Nrg1 HET mice expressed a greater THC-induced enhancement in PPI than WT mice. Taken together, the data presented in Chapter 2 show that a deficiency in a schizophrenia susceptibility gene Nrg1 enhanced the behavioural impact of THC. After having established a link between Nrg1 deficiency and increased sensitivity to the behavioural effects of cannabinoids in Chapter 2, Chapter 3 assessed the neuronal activity underlying the effects of an acute THC exposure on Nrg1 HET mice by using c-Fos immunohistochemistry. In the ventral part of the lateral septum (LSV), THC selectively increased c-Fos expression in Nrg1 HET mice with no corresponding effect being observed in WT mice. In addition, a non-significant trend for THC to promote a greater increase in c-Fos expression in Nrg1 HET mice than WT mice was observed in the central nucleus of the amygdala, the bed nucleus of the stria terminalis and the paraventricular nucleus of the hypothalamus. Consistent with Nrg1 HET mice exhibiting a schizophrenia-related phenotype, these mice expressed greater drug-free levels of c-Fos in the shell of the nucleus accumbens and the LSV. Interestingly, the effects of genotype on c-Fos expression, drug-free or following THC exposure, were only observed when animals experienced behavioural testing prior to perfusion. This suggests that an interaction with stress was necessary for the promotion of these effects. As the risk of developing psychosis in vulnerable individuals increases with the frequency of cannabis use, Chapter 4 assessed the effects of repeated exposure to cannabinoids on Nrg1 HET mice. As THC was not available at the time, the synthetic analogue of THC, CP 55,940, was used in this experiment. Behavioural testing showed that tolerance to CP 55,940-induced hypothermia and locomotor suppression developed more rapidly in Nrg1 HET mice compared to WT mice. On the contrary, tolerance to the anxiogenic-like effect of CP 55,940 in the light-dark test was observed in WT mice, however no such tolerance occurred to this effect in Nrg1 HET mice. Similarly, no tolerance developed to CP 55,940-induced thigmotaxis in Nrg1 HET mice as measured in the open field. For PPI, on the first day of exposure opposite effects were observed, with CP 55,940 treatment facilitating PPI in Nrg1 HET mice and decreasing it in WT mice. However, the differential effect of CP 55,940 on PPI was not maintained with repeated testing as both genotypes became tolerant to the effects of the cannabinoid on sensorimotor gating. In addition, a selective increase in Fos B/ΔFos B expression, a marker of longer-term neuronal changes, was observed in the LSV of Nrg1 HET mice following chronic CP 55,940 exposure, with no corresponding effect seen in WT mice. These results collectively demonstrate that the neuregulin system is involved in the neuroadaptive response to repeated cannabinoid exposure. One of the main schizophrenia endophenotypes observed in human studies are cognitive impairments of higher executive functions. Thus Chapter 5 aimed to develop a procedure to allow evaluation of cannabis-induced working memory deficits in mice. Few studies have investigated the effects of chronic cannabinoid exposure on memory performance and whether tolerance occurs to cannabinoidinduced memory impairment. Here we studied the effects of repeated exposure to THC on spatial memory and the expression of the immediate early gene zif268 in mice. One group of animals were not pre-treated with THC while another group was given 13 daily injections of THC prior to memory training and testing in the Morris water maze. Both groups were administered THC throughout the memory training and testing phases of the experiment. THC decreased spatial memory and reversal learning, even in animals that received the THC pre-treatment and were tolerant to the locomotor suppressant effects of the drug. Zif268 immunoreactivity was reduced in the CA3 of the hippocampus and in the prefrontal cortex only in non pre-treated animals, indicating that while tolerance to the effects of cannabinoids on neuronal activity arose, cannabinoid-promoted memory impairment in these animals persisted even after 24 days of exposure. Taken together these data demonstrate that the spatial memory impairing effects of THC are resistant to tolerance following extended administration of the drug. Such a model could be applied to Nrg1 HET mice in future studies to observe if cannabinoid-induced working memory impairments and the development of tolerance to this effect are altered relative to WT mice. In conclusion, this thesis provides the first evidence that partial deletion of the schizophrenia susceptibility gene Nrg1 modulates the neurobehavioural actions of acutely and chronically administered cannabinoids. Nrg1 HET mice appear more sensitive to the acute neurobehavioural effects of cannabinoids. Notably, acutely administered THC facilitated attentional function by increasing PPI in Nrg1 HET mice. However, with repeated cannabinoid administration this acute benefit was lost. The Nrg1 HET mice displayed a long-lasting anxiogenic profile that was resistant to tolerance. Conversely, Nrg1 HET mice developed tolerance to the locomotor suppressant and hypothermic effects of cannabinoids more rapidly than WT mice, indicating a distorted neuroadaptive response in these animals. Another major finding of this thesis is that the lateral septum appears to be an important brain region dysregulated by cannabinoids in Nrg1 HET mice. Cumulatively, this research highlights the fact that neuregulin 1 and cannabinoid systems appear to interact in the central nervous system. This may ultimately enhance our understanding of how gene-environment interactions are responsible for cannabis-induced development of schizophrenia.

Keloid disease (KD) is a cutaneous fibroproliferative tumour characterised by heterogeneity, locally aggressive invasion and therapeutic resistance. Clinical, histological and molecular differences between the keloid scar centre and margin as well as recent evidence of the importance of epithelial-mesenchymal interactions (EMI) in KD pathobiology contribute to the complexity and diversity of KD, which coupled with the lack of a validated animal model have hindered research and effective management. Despite significant progress in the field of KD research, reliance on conventional monolayer cell culture and whole tissue analysis methods have failed to fully reflect the natural architecture, pathology and complexity of KD in vivo. In order to address these challenges, a site-specific in situ approach was therefore employed here for the first time in KD research. The first aim of this work was to compare the value of this contemporary approach with traditional methods of tissue dissection. The second aim was to compare the genomic expression between well-defined, distinct keloid sites and normal skin (NS). The third aim was to develop and explore hypotheses arising from this site-specific gene expression profiling approach, so as to enhance understanding of KD pathobiology as a basis for improved diagnostic and therapeutic strategies in future KD management. The fourth aim was to probe these hypotheses with relevant functional in vitro studies. The current site-specific in situ approach was achieved through a combination of laser capture microdissection and whole genome microarray, allowing separation of epidermis from dermis for keloid centre, margin and extralesional sites compared with NS. This in situ approach yielded selective, accurate and sensitive data, exposing genes that were overlooked with alternative methods of dissection. Identification of significant upregulation of the aldo-keto reductase enzyme AKR1B10 in all three sites of the keloid epidermis (KE) in situ, implicated dysregulation of the retinoic acid (RA) pathway in KD pathogenesis. This hypothesis was supported by showing that induced AKR1B10 overexpression in NS keratinocytes reproduced the keloid RA pathway expression pattern. Moreover, co-transfection with a luciferase reporter plasmid revealed reduced RA response element activity. Paracrine signals released by AKR1B10-overexpressing keratinocytes into conditioned medium resulted in TGFβ1 and collagen upregulation in keloid fibroblasts, suggesting the disturbed RA metabolism exerts a pro-fibrotic effect through pathological EMI, thus further supporting the hypothesis of RA deficiency in KE. Gene expression profiling further revealed an upregulation of NRG1 and ErbB2 in keloid margin dermis. Exogenous NRG1 led to enhanced keloid fibroblast migration with increased Src and PTK2 expression, which were attenuated with ErbB2 siRNA studies. Together with the observed failure to recover this expression with NRG1 treatment, suggested the novel KD pathobiology hypothesis that NRG1/ErbB2/Src/PTK2 signaling plays a role in migration at the keloid margin. In addition to these hypotheses, LCM methodology with comprehensive analysis of the data permitted the development of additional novel working hypotheses that will inform future KD research, including inflammatory gene dysregulation and cancer-like stem cells that may contribute to the therapeutic resistance characteristic of KD.

Rhythmic oscillations in neuronal activity display variations in amplitude (power) over a range of frequencies. Attention and cognitive performance correlate with increases in cortical gamma oscillations (40-70Hz) that are generated by the coordinated firing of glutamatergic pyramidal neurons and GABAergic interneurons, and are modulated by dopamine. In the medial prefrontal cortex (mPFC) of rats, gamma power increases during treadmill walking, or after administration of an acute subanesthetic dose of the NMDA receptor antagonist ketamine. Ketamine is also used to mimic symptoms of schizophrenia, including cognitive deficits, in healthy humans and rodents. Additionally, the ability of a drug to modify ketamine-induced gamma power has been proposed to predict its pro-cognitive therapeutic efficacy. However, the mechanism underlying ketamine-induced gamma oscillations is poorly understood. We hypothesized that gamma oscillations induced by walking and ketamine would be generated by a shared mechanism in the mPFC and one of its major sources of innervation, the mediodorsal thalamus (MD). Recordings from chronically implanted electrodes in rats showed that both treadmill walking and ketamine increased gamma power, firing rates, and spike-gamma LFP correlations in the mPFC. By contrast, in the MD, treadmill walking increased all three measures, but ketamine decreased firing rates and spike-gamma LFP correlations while increasing gamma power. Therefore, walking- and ketamine-induced gamma oscillations may arise from a shared circuit in the mPFC, but different circuits in the MD. Recent work in normal animals suggests that dopamine D4 receptors (D4Rs) synergize with the neuregulin/ErbB4 signaling pathway to modulate gamma oscillations and cognitive performance. Consequently, we hypothesized that drugs targeting the D4Rs and ErbB receptors would show pro-cognitive potential by reducing ketamine-induced gamma oscillations in mPFC. However, when injected before ketamine, neither the D4R agonist nor antagonist altered ketamine’s effects on gamma power or firing rates in the mPFC, but the pan-ErbB antagonist potentiated ketamine’s increase in gamma power, and prevented ketamine from increasing firing rates. This indicates that D4Rs and ErbB receptors influence gamma power via distinct mechanisms that interact with NMDA receptor antagonism differently. Our results highlight the value of using ketamine-induced changes in gamma power as a means of testing novel pharmaceutical agents.

No description available.

L’utilisation du cannabis peut précipiter la schizophrénie, en particulier chez les individus qui présentent une vulnérabilité génétique aux désordres mentaux. Des recherches humaines et animales indiquent que la neuréguline 1 (Nrg1) est un gène de susceptibilité à la schizophrénie. L’objectif de cette thèse est d’examiner si une modification du gène Nrg1 chez des souris mutante module les effets neuronaux et comportementaux des cannabinoïdes après traitement aiguë et chronique. De plus cette thèse examine les effets d'un pré-traitement au delta9-tétrahydrocannabinol, le principal composant psychotropique du cannabis, sur un modèle de flexibilité cognitive chez la souris. / Cannabis use may precipitate schizophrenia, especially in individuals who have a genetic vulnerability to the disorder. Human and animal researches indicate that neuregulin 1 (Nrg1) is a susceptibility gene for schizophrenia. This thesis aim at investigating if partial deletion of Nrg1 in mutant mice modulate the neuronal and behavioural effects cannabinoids after acute or chronic treatment. In addition, this thesis examine the effects of a pre-treatment with delta9-tetrahydrocannabinol, the main psychoactive constituent of cannabis, in a model of cognitive flexibility in the mice.

No description available.

OBJETIVO: avaliar o efeito das neuregulinas 1-alfa e 1-beta na regeneração de nervos ciáticos de camundongos C57BL/6J, adultos, machos, através da técnica de tubulização. MÉTODOS: Utilizaram-se 18 animais, divididos em 3 grupos, implantando-se prótese de polietileno em falhas de 4,0 mm no nervo ciático esquerdo: grupo 1 contendo apenas colágeno purificado (Vitrogen®); grupo 2, colágeno associado a neuregulina 1-alfa; grupo 3 com colágeno e neuregulina 1-beta. O grupo controle foi formado por 6 segmentos de nervos ciáticos direitos. Após 4 semanas, os animais foram sacrificados; extraiu-se segmento do ponto médio do nervo regenerado no interior das próteses, padronizaram-se cortes histológicos e confecção das lâminas para análise histomorfométrica. Confrontaram-se os resultados estatisticamente. RESULTADOS: Os animais tratados com neuregulinas tiveram maior número de axônios mielinizados, com diferença estatisticamente significante quando comparados ao grupo colágeno. Não houve diferença estatística entre os grupos de neuregulinas 1-alfa e 1-beta. CONCLUSÃO: a adição de neuregulinas proporcionou aumento significativo do número de fibras mielinizadas. / PURPOSE: To evaluate the effect of neuregulins 1-alpha and 1-beta on the regeneration the sciatic nerves of male adult C57BL/6J mice, using the tubulization technique. METHODS: Eighteen animals were used, divided into three groups. A polyethylene prosthesis was implanted in a 4.0 mm defect of the left sciatic nerve, as follows: group 1 containing only purified collagen (Vitrogen®); group 2, collagen with neuregulin 1-alpha; group 3, collagen with neuregulin 1-beta. The control group was formed by six segments of right sciatic nerves. Four weeks later, the animals were sacrificed. A segment from the midpoint of the nerve regenerated inside the prostheses was extracted, histological sections were standardized and slides were made up for histomorphometric analysis. The results were statistically compared using the Tukey multiple comparisons test and Students t test. RESULTS: The animals treated with neuregulins had greater numbers of myelinized axons, with a statistically significant difference in relation to the collagen-only group. There was no statistical difference between the neuregulin 1-alpha and 1- beta groups. CONCLUSION: It was concluded that the addition of neuregulins provided a significant increase in the number of myelinized fibers.

The Neuregulin 1 (NRG1)-ErbB4 signalling pathway is implicated in critical processes for the development and function of neuronal circuits. Post mortem studies have reported that elevated expression of NRG1 type 1 isoform is associated with schizophrenia. Importantly previous behavioural studies in mice that overexpress the NRG1 type 1 isoform (NRG1^tg-type-I) have suggested a schizophrenia endophenotype including impairment in the hippocampus-dependent spatial working memory, prepulse inhibition (PPI) of the startle reflex and alterations in the gamma band rhythmogenesis This study aims to reveal the cellular targets of the NRG1-ErbB4 signalling pathway and putative alterations in the function of the hippocampal network in NRG1^tg-type-I mice. Immunocytochemical analysis showed that the NRG1 receptor ErbB4 is predominantly localized in interneurons comprising parvalbumin positive (PV) and cholecystokinin (CCK) expressing cells. Comparison of the density of ErbB4-positive cells between the hippocampus of wild type (WT) and NRG1^tg-type-I mice suggested that NRG1 over-expression resulted in decreased number of ErbB4 immunopositive hippocampal interneurons. This is consistent with the proposed role of the NRG1-ErbB4 signalling in the migration of GABAergic cells during neurodevelopment and with the NRG1-mediated internalisation of the ErbB4 receptors. CCK- positive cells are a major target of NRG1-ErbB4 signalling, and therefore the NMDA receptor and AMPA receptor components of glutamatergic transmission were analysed in this population of cells by performing whole cell recordings of evoked and miniature excitatory post synaptic currents. Glutamatergic neurotransmission in CCK-positive cells was found to be compromised in the hippocampus of NRG1^tg-type-I mice. This change was attributed to hypofunction of NMDA receptors but not AMPA receptors post-synaptically. Next, the inhibitory output of CCK-positive cells to pyramidal cells was examined. Analysis of the optogenetically elicited inhibitory post synaptic currents (IPSCs) did not reveal any changes in the properties of the GABAergic synapse formed by these cells due to NRG1 over-expression Finally, the effects of this NMDA receptor hypofunction in the recurrent inhibition were analysed by performing whole cell recordings during the gamma relevant optogenetic entrainment of the hippocampal network. It was found that the disynaptic inhibition, a key synaptic interaction for the generation of gamma oscillations, depends on the NMDA receptors and was altered in the hippocampus of NRG1^tg-type-I mice. Together these data point out a key modulatory role of the NRG1-ErbB4 signalling in the neurodevelopment of cortical microcircuits and a link between ErbB4 and NMDA receptor function with a possible association to schizophrenia pathogenesis.