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.

The lateral septum is heavily implicated in anxiety regulation, with lesions or pharmacological inhibition of this region suppressing rats' defensive responses in various rat models of anxiety. My first objective was to explore the functional relationship between the lateral septum and its major afferent structure, the ventral hippocampus. Although these structures are extensively connected, it was not clear if they work in concert to regulate anxiety-like behaviours. This idea was tested using a pharmacological disconnection technique, whereby communication between these two structures was disabled by infusing the GABAA agonist muscimol into one side of the lateral septum and the contralateral side of the ventral hippocampus. Increases in open-arm exploration were evident when muscimol was co-infused into one side of the lateral septum and the contralateral ventral hippocampus. By contrast, open arm exploration was not altered when muscimol was co-infused into one side of the lateral septum and the ipsilateral ventral hippocampus. These results support the contention that the ventral hippocampus and the lateral septum regulate rats' open arm exploration in a serial fashion, and that this involves ipsilateral projections from the former to the latter site. My second objective was to further characterize the neuropharmacological aspects of lateral septal regulation of behavioural defence. The lateral septum contains high levels of NPY Y1 and Y2 receptor binding sites in the brain, yet little is known about their contribution in anxiety regulation at this site. Therefore, the second aim of my thesis was to characterize the contribution of NPY and its Y1 and Y2 receptor subtypes in the lateral septal regulation of anxiety in the elevated plus maze, novelty-induced suppression of feeding, and shock-probe burying tests. I determined that distinct NPY receptors differentially contribute to NPY-mediated anxiolysis in a test specific manner, with the Y1 receptor mediating NPY-induced anxiolysis in the novelty-induced suppression of feeding test, and the Y2 receptor mediating NPY13-36-induced anxiolysis in the plus-maze test. Taken together, the results from these studies reinforce the view that the regulation of anxiety involves a variety of different, yet overlapping neural processes. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2012-09-25 18:02:11.172

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.

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.

Compared to other structures, such as the amygdala, the lateral septum’s (LS) role in the regulation of anxiety and/or behavioural defense is relatively understudied. Thus, the overarching goal of this thesis was to further investigate its contribution to rats’ anxiety-related behaviours. In Chapter 2, we demonstrate, for the first time, that while the dorsal LS does not mediate rats’ appetitive motivation or anxiety in the novelty induced suppression of feeding (NISF) paradigm, it does modulate their defensive behaviours in the elevated plus maze (EPM) and shock probe burying tests (SPBT). In Chapter 3, we are the first to show that bilateral infusions of histamine, a neurochemical previously linked to anxiety, into the LS reduce rats’ anxiety-related behaviours in the EPM and NISF. In addition, we report a novel double dissociation between lateral septal H1 and H2, and H3 receptors in their regulation of rats’ defensive behaviours in those two paradigms. More specifically, the H1 and H2 receptors contribute to rats’ hyponeophagia in the NISF but not their open arm exploration in the EPM, while the H3 receptors modulate rats’ defensive behaviors in the EPM but not in the NISF. Finally, in Chapter 4, we report for the first time that infusions of histamine into the LS, which produce behavioural anxiolysis, increase rather than decrease the frequency of reticular-elicited hippocampal theta activity, a putative neurophysiological correlate of anxiolytic-drug action. Altogether, the data in this thesis increase our understanding of how the LS contributes to rats’ defensive behaviours and adds to the existing literature regarding the neurobiology of fear/anxiety. More importantly though, the data presented here could ultimately aid in the development of novel drugs to treat anxiety disorders in humans. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2013-12-17 17:27:34.014

Compared to other structures, such as the amygdala, the lateral septum’s (LS) role in the regulation of anxiety and/or behavioural defense is relatively understudied. Thus, the overarching goal of this thesis was to further investigate its contribution to rats’ anxiety-related behaviours. In Chapter 2, we demonstrate, for the first time, that while the dorsal LS does not mediate rats’ appetitive motivation or anxiety in the novelty induced suppression of feeding (NISF) paradigm, it does modulate their defensive behaviours in the elevated plus maze (EPM) and shock probe burying tests (SPBT). In Chapter 3, we are the first to show that bilateral infusions of histamine, a neurochemical previously linked to anxiety, into the LS reduce rats’ anxiety-related behaviours in the EPM and NISF. In addition, we report a novel double dissociation between lateral septal H1 and H2, and H3 receptors in their regulation of rats’ defensive behaviours in those two paradigms. More specifically, the H1 and H2 receptors contribute to rats’ hyponeophagia in the NISF but not their open arm exploration in the EPM, while the H3 receptors modulate rats’ defensive behaviors in the EPM but not in the NISF. Finally, in Chapter 4, we report for the first time that infusions of histamine into the LS, which produce behavioural anxiolysis, increase rather than decrease the frequency of reticular-elicited hippocampal theta activity, a putative neurophysiological correlate of anxiolytic-drug action. Altogether, the data in this thesis increase our understanding of how the LS contributes to rats’ defensive behaviours and adds to the existing literature regarding the neurobiology of fear/anxiety. More importantly though, the data presented here could ultimately aid in the development of novel drugs to treat anxiety disorders in humans. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2013-12-17 17:27:34.014

Approximately 1 in 6 infants are born prematurely each year. Typically, these infants spend 25 days in the Neonatal Intensive Care Unit (NICU) where they experience 10-18 painful and inflammatory procedures each day. Remarkably, pre-emptive analgesics and/or anesthesia are administered less than 30% of the time. Unalleviated pain during the perinatal period is associated with permanent decreases in pain sensitivity, blunted cortisol responses and high rates of neuropsychiatric disorders. To date, the mechanism(s) by which these long-term changes in stress and pain behavior occur, and whether such alterations can be prevented by appropriate analgesia at the time of injury, remains unclear. We have previously reported in rats that inflammation experienced on the day of birth permanently upregulates central opioid tone, resulting in a significant reduction in adult pain sensitivity. However, the impact on early life pain on anxiety- and stress-related behavior and HPA axis regulation is not known. Therefore the goal of this dissertation was to determine the long-term impact of a single neonatal inflammatory pain experience on adult anxiety- and stress-related responses. Neuroanatomical changes in stress-associated neurocircuits were also examined. As the endogenous pain control system and HPA axis are in a state of exaggerated developmental plasticity early in postnatal life, and these systems work in concert to respond to noxious or aversive stimuli, this dissertation research aimed to answer the following questions: (1) Does neonatal injury produce deficits in adult stress-related behavior and alter stress-related neuroanatomy through an opioid-dependent mechanism? (2) Does neonatal injury alter receptor systems regulating the activation and termination of the stress response in adulthood? (3) Are stress- and pain-related neurotransmitters altered within the first week following early life pain? (4) Is early activation of the pain system necessary for the long-term changes in anxiety- and stress-related behavior? Together these studies demonstrate the degree, severity and preventability of the long-term deficits in stress responding associated with a single painful experience early in life. The goal of this research is to promote change in the treatment of infant pain in the NICU to reduce long-term sensory and mental health complications associated with prematurity.

Approximately 1 in 6 infants are born prematurely each year. Typically, these infants spend 25 days in the Neonatal Intensive Care Unit (NICU) where they experience 10-18 painful and inflammatory procedures each day. Remarkably, pre-emptive analgesics and/or anesthesia are administered less than 30% of the time. Unalleviated pain during the perinatal period is associated with permanent decreases in pain sensitivity, blunted cortisol responses and high rates of neuropsychiatric disorders. To date, the mechanism(s) by which these long-term changes in stress and pain behavior occur, and whether such alterations can be prevented by appropriate analgesia at the time of injury, remains unclear. We have previously reported in rats that inflammation experienced on the day of birth permanently upregulates central opioid tone, resulting in a significant reduction in adult pain sensitivity. However, the impact on early life pain on anxiety- and stress-related behavior and HPA axis regulation is not known. Therefore the goal of this dissertation was to determine the long-term impact of a single neonatal inflammatory pain experience on adult anxiety- and stress-related responses. Neuroanatomical changes in stress-associated neurocircuits were also examined. As the endogenous pain control system and HPA axis are in a state of exaggerated developmental plasticity early in postnatal life, and these systems work in concert to respond to noxious or aversive stimuli, this dissertation research aimed to answer the following questions: (1) Does neonatal injury produce deficits in adult stress-related behavior and alter stress-related neuroanatomy through an opioid-dependent mechanism? (2) Does neonatal injury alter receptor systems regulating the activation and termination of the stress response in adulthood? (3) Are stress- and pain-related neurotransmitters altered within the first week following early life pain? (4) Is early activation of the pain system necessary for the long-term changes in anxiety- and stress-related behavior? Together these studies demonstrate the degree, severity and preventability of the long-term deficits in stress responding associated with a single painful experience early in life. The goal of this research is to promote change in the treatment of infant pain in the NICU to reduce long-term sensory and mental health complications associated with prematurity.

Contexte : L’ocytocine (OT) et la vasopressine (VP) modulent les comportements sociaux. Leurs rôles ont été étudiés indépendamment l’un de l’autre mais des effets combinatoires de ces deux peptides sont à envisager puisqu’ils sont tous les deux libérés au cours des comportements sociaux. Dans le septum latéral (SL), une structure cérébrale intégrant des informations sociales, l’ocytocine et la vasopressine sont libérées au cours des interactions sociales et modulent la reconnaissance ainsi que la discrimination sociale.Objectif : Comprendre la fonction duale de l’ocytocine et de la vasopressine mise en jeu lors des interactions sociales dans un cadre physiologique et pathologique. Méthode : Chez la souris mâle, nous avons utilisé l’activité électroencéphalographique (EEG) comme marqueur et avons caractérisé des traces EEG dépendantes de l’OT et de la VP. Nous avons manipulé le système OT et le système VP au sein du septum au cours d’un protocole de reconnaissance/discrimination sociale en utilisant des outils pharmacologiques ou optogénétiques. Des expériences d’électrophysiologie sur tranche ont permis de caractériser la réponse électrophysiologique des neurones du septum latéral à l’application de chacun de ces peptides.Résultats : L’étude de l’activité EEG nous a permis de discriminer des effets induits par l’action septale de l’OT et la VP dans la bande de fréquence theta. Ces résultats suggèrent que la VP serait libérée dans le septum au cours de la première rencontre avec un juvénile alors que l’OT serait libérée au cours du processus d’habituation. La modulation de l’action de l’OT et de la VP sur le SL démontre que l’activation des récepteurs V1a au cours de la première rencontre est essentielle à la discrimination sociale tandis que l’activation des récepteurs à l’OT au cours du processus d’habituation permet de regain d’intérêt lorsqu’un nouveau juvénile sera présenté. Nous montrons aussi que l’OT et la VP modulent l’activité électrique de la quasi-totalité des neurones septaux. La nature de ces modulations définit 3 catégories de neurones qui communiquent entre eux via des signaux GABAergiques. Chez la souris Magel2KO, un modèle murin de troubles des comportements sociaux, la balance des effets septaux de l’OT et de la VP est altérée. Ceci suggère que cette régulation pourrait être impliquée dans certaines conditions pathologiques.Conclusion : Ces résultats mettent en évidence qu’il est essentiel, lorsque l’on étudie l’ocytocine, d’étudier le système vasopressinergique. Avec cette approche, nous avons montré que l’activation séquentielle du SL par l’OT et la VP est importante pour la régulation des interactions sociales. De plus, cette séquence d’évènements est altérée dans un modèle animal présentant des troubles sociaux. / Context : Oxytocin (OT) and vasopressin (VP) modulate social behaviors. The roles of OT and VP have been interrogated so far in isolation whereas combinatorial effects are anticipated as both hormones are secreted during social behavior. In the lateral septum (LS), a brain area processing behavioral social cues, OT and VP are released during social interaction and modulate social recognition or discrimination. Aim : To understand the dual function of OT and VP during social behavior in physiological and pathological conditions. Methods : In male mice, we used electroencephalographic (EEG) activity as a readout to characterize OT and VP dependent electrophysiological signatures and their sequence. We manipulated OT and VP systems to LS during social recognition/discrimination paradigm using pharmacology and optogenetic tools. Using slice electrophysiology, we characterized electrophysiological responses of LS neurons to both of these hormons.Results : Measurement of EEG theta activity allowed us to discriminate between OT and VP dependent LS modulation and indicated that VP would be released in the LS during 1st encounter with a juvenile while OT would be released during the habituation process. Modulation of OT and VP actions on the LS demonstrate that V1a activation during 1st encounter is essential for social discrimination and OT receptor activation during the habituation process allows the regain of interest for a new juvenile. We also demonstrated that OT and VP modulate electrical activity of almost all LS neurons. The nature of this modulation define 3 neuronal categories that communicate with each other through GABAergic signalling. Magel2KO mouse, which features social deficits, presents an altered balance of LS regulation by OT and VP. It suggests that this regulation could be involved in some pathological symptomatology.Conclusions : These results shed a light on the necessity to study vasopressin along with oxytocin. Doing this, we showed that vasopressinergic and oxytocinergic activation of the LS are sequentially important during the social recognition paradigm. Futhermore, this sequence of events is impaired in a mouse model featuring deficits of OT and social disabilities.