Psychological stressors such as social stress and bullying are prevalent in today’s society. Disorders such as PTSD, depression and social anxiety disorder can be either caused or exacerbated by social stress and treatment options are not always effective in providing relief for these disorders. Our laboratory studies a form of social stress termed conditioned defeat, whereby a defeated Syrian hamster no longer displays species-typical territorial aggression but instead is submissive and defensive toward an intruder in its own cage. We hypothesized that the nucleus accumbens is a necessary component of the circuit mediating the acquisition and expression of conditioned defeat and that dopamine is necessary within the nucleus accumbens for inducing memory processes as well as expression of behavioral responses to stressful situations. We also hypothesized that defeat activates dopaminergic and/or nondopaminergic neurons in the ventral tegmental area (VTA) and that dopamine released by neurons projecting from the VTA to the nucleus accumbens and basolateral amygdala (BLA) increases neuronal activation of these structures during defeat. We found that dopamine, but not GABA, modulates memory of social defeat within the nucleus accumbens. However, GABA does affect the expression of behavioral responses to social defeat. Defeat also increased Fos activation of non-dopaminergic neurons, but it did not increase activation of dopaminergic neurons. Baclofen infusion into the VTA prior to defeat, which was hypothesized to specifically inhibit dopaminergic neurons, did not affect Fos activation within the nucleus accumbens and the basolateral amygdala. These experiments determined that dopamine does modulate memory of social defeat within the nucleus accumbens, but it is currently unclear what the source of this dopamine is. Future experiments are planned to determine this source of dopamine that could be a target of treatment for disorders that are caused or exacerbated by social stress.

Thesis advisor: Michael Numan / Maternal behavior is a primary social characteristic of mammals. By studying maternal behavior in rats, broader inferences can be made about the neural circuits that influence maternal behavior in other mammals, including humans. Maternal behavior of rats includes nest building, pup grooming, nursing, and pup retrieval. The projections from the medial preoptic area of the hypothalamus (MPOA) to the ventral tegmental area (VTA) of the mesolimbic dopamine system are known to regulate maternal behavior in post-partum rats. The aim of the present study was to examine how inhibition of the basolateral amygdala (BLA), an area that projects to the nucleus accumbens-ventral palldium (NA-VP) circuit of the mesolimbic dopamine system, bilaterally with muscimol (a GABA-A agonist) might interrupt the retrieval of pups by post-partum rats. Females injected with muscimol, but not those injected with saline, displayed significant deficits in retrieval behavior, suggesting that the BLA is a region important for the promotion of maternal behavior. The effects were also reversible, as all females displayed normal maternal behavior 24-hours post-injection. Follow-up studies should use asymmetric neuron-specific lesions of the BLA and the VP to show that the projections from the BLA to the VP are essential for maternal behavior. / Thesis (BA) — Boston College, 2010. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: College Honors Program. / Discipline: Psychology Honors Program. / Discipline: Psychology.

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No description available.

Stress promotes the use of methamphetamine and other recreational substances and is often implicated in relapse to stimulant use. Thus, it is of critical importance to examine the consequences of the co-occurance of stress and methamphetamine use. Activity of the glutamatergic N-methyl D-aspartate (NMDA) receptor system appears to be involved in the neurotoxic effects of both chronic stress and methamphetamine exposure. The current studies investigated the hypothesis that chronic pre-exposure to the stress hormone corticosterone (CORT) results in an increase of NMDA receptor activity and that this will potentiate the neurotoxic effects of methamphetamine (METH). Co-cultures of the ventral tegmental area, nucleus accumbens, and medial prefrontal cortex were pre-exposed to CORT (1 μM) for 5 days prior to co-exposure to METH (100 μM) for 24 hours to investigate the combined effects on neurotoxicity and protein density of NMDA receptor subunits. The combination of CORT and METH resulted in significant neurotoxicity within the medial prefrontal cortex compared to either CORT or METH alone. The CORT+METH-induced toxicity was attenuated by co-exposure to the NMDA receptor antagonist (2R)-amino-5-phosphonovaleric acid (APV; 50 μM) during the 24 hour CORT and METH co-exposure. Although CORT alone did not significantly alter the density of the NR1 and NR2B subunits of the NMDA receptor, METH exposure for 24 hours resulted in a significant loss of the polyamine sensitive NR2B subunit. Co-exposure to CORT and METH also resulted in decreased extracellular glutamate while not significantly altering extracellular dopamine. These results suggest an enhancement of NMDA receptor systems or downstream effectors in areas of the mesolimbic reward pathway following chronic pre-exposure to CORT, which leads to enhanced neuronal vulnerability to future excitotoxic insults. This may be of critical importance as use of psychostimulants such as METH and other drugs of abuse may produce excitotoxic events in these areas, thus further compromising neuronal viability.

<p> Cell therapy for Parkinson's disease will greatly benefit from progress in methods aimed at visualizing the dopamine system and cell replacement techniques. Currently, cell therapy has been met with varied success, in part due to differences in cell sources, transplantation procedures, and our lack of understanding of cell fate post-transplantation. The standardization of transplantation procedures will enhance our ability to draw comparisons between studies and improve cell therapy outcomes. We developed a method to label neural stem/progenitor cells (NSPCs) with technetium-99m and then visualize the cells with single photon emission computed tomography (SPECT) subsequent to grafting in the brain. This labeling method permitted a high uptake of the tracer into the cells without causing damage to the DNA or altering cell viability. The labeling caused a significant decrease (75%) in the proliferative capacity of the SPCs and caused a trend towards an increase in neuronal differentiation. Using this technique paves the way to standardize the location of the transplant and quantify the number transplanted cells while increasing the production of neurons.</p> <p> Experiments were performed to visualize the dopamine system with [(123)I]altropane at pre-and post-transplant time points in the 6-0HDA rat model of Parkinson's disease. [(123)I]altropane binding correlated with the content of dopamine in the stria tum. However, [(123)I]altropane binding was not correlated with dopamine content in the substantia nigra and did not show a correlation with the amphetamine rotations. However, there was a significant correlation with the cylinder test and the postural instability test. When the data was assessed using linear regression, the r^2 value of the linear relationship was low indicating that [(123)I]altropane SPECT is not a good predictor of behavioural outcome due to a weak linear relationship. Our data indicates that [(123)I]altropane predicts the integrity of the striatal dopamine nerve terminals, but does not predict the integrity of the nigrostriatal system. The results are discussed in relation to the use of [(123)I]altropane in comparison to other dopamine SPECT and PET agents. </p> / Thesis / Doctor of Philosophy (PhD)

雖然焦慮是一種普遍存在之情感性心智活動，迄今仍無充份解釋之實證資料。本研究主要是利用一種焦慮症相關的動物模式，即抬高式T形迷津，探討與焦慮症有關的神經行為機制。整部研究分兩大實驗，分別探討抬高式T形迷津的行為建構動力與破壞依核次級區域在抬高式T形迷津或其他焦慮作業上之行為表現。在實驗一檢驗抬高式T形迷津的行為內涵方面，共有四個實驗：實驗一A探討抬高式T形迷津抑制性躲避行為是否呈現消除現象；實驗一B探討破壞制約害怕神經網路對抬高式T形迷津之抑制性躲避行為的影響，並檢測自發性運動量的改變是否造成干擾效果；實驗一C探討事前暴露經驗對脫逃行為的意義；實驗一D檢測脫逃及抑制性躲避實驗程序互相干擾之可能性。實驗二探討可能涉及抬高式T形迷津或其他焦慮作業的神經機制，針對破壞依核次級區域對焦慮行為的影響進行檢測。此部分包含三個實驗，實驗二A探討依核次級區域受損對傳統焦慮動物模式抬高式十字迷津行為的影響；實驗二B採用已在實驗一建立行為效度的抬高式T形迷津，檢驗破壞依核次級區域後的迷津行為表現，並檢驗依核次級區域受損是否影響受試自發性運動量變化，以致干擾抬高式T形迷津的行為表現。另為深入探討依核的功能角色，實驗二C利用其他嫌惡作業測試破壞依核次級區域對制約躲避電擊行為的影響。實驗一結果顯示抑制性躲避行為是一包含制約害怕及探索行為等多重歷程的行為模式，而脫逃行為對情緒狀態的改變不敏感，且易受抑制性躲避作業的影響。實驗二發現破壞依核殼區同時減抑受試在抬高式十字迷津的危機評估行為、抬高式T形迷津之抑制性躲避行為及制約躲避電擊行為；而破壞依核核區的減抑效果僅見於抬高式T形迷津與制約躲避電擊作業。三個嫌惡作業的結果顯示依核核區與殼區皆涉及制約害怕歷程，但兩區的受損會表現不同焦慮行為，並在抬高式十字迷津之危機評估行為中表現出來。綜合上述二大部分實驗結果，本研究對抬高式T形迷津的行為內涵有更進一步的瞭解，並特別藉依核次級區域破壞的行為測試資料，推估中腦多巴胺系統與傳統理論所指邊緣系統在實證性解釋焦慮具同樣關鍵角色。 / Although anxiety is a well-recognized affective mental reaction, its phenomenon is not fully characterized by the empirical data. By employing a recently developed animal model named the elevated T maze (ETM), the present study investigated the neurobehavioral mechanisms of anxiety. There were two major parts of experiments designed to respectively examine the validity of this task and the involvement of limbic related areas on anxious behavior. Regarding the first part of experiments, Experiment 1A examined the effects of extinction on the inhibitory avoidance of ETM; Experiment 1B evaluated the lesions of six limbic related areas on the measures of inhibitory avoidance and escape; Experiment 1C investigated how pre-exposure experience of stress would affect the ETM behavior; Experiment 1D tested the potential affectiveness derived from different sequences of the test procedure on EMT. The second part of experiments mainly focused on comparing the lesion effects of nucleus accumbens subareas (core and shell) on behavioral measures from three anxiety-related tasks. Elevated plus maze, ETM, and active avoidance were adopted respectively in the experiments of 2A, 2B, and 2C. Results of the first part of experiments indicated 1) inhibitory avoidance of ETM containing fear conditioning and exploration components, and 2) less sensitivity to experimental manipulation for the escape of ETM. In the second part of experiments, the shell lesion significant attenuated the risk assessment behavior of elevated plus maze and inhibitory avoidance of ETM and active avoidance tasks, whereas the core lesion only produced the latter part of impairment. Both core and shell subareas are thus inferred to be involved in the conditioned avoidance, and lesions of these two areas may exert different patterns of anxious behavior. Together, the present study further characterized behavioral components of ETM. With a more systemic work in comparing lesion data of nucleus accumbens over three anxiety-related tasks, it is then suggested that the midbrain dopamine system is as crucial as the traditionally-known limbic system the traditional in terms of providing empirical explanation for the anxiety.

L’axe hypothalamo-hypophyso-surrénalien joue un rôle essentiel dans l’adaptation et la réponse au stress. Toutefois, l’hyperactivation de cet axe ou des niveaux chroniquement élevés de glucocorticoïdes (GC) entraînent des conséquences pathologiques. Le système dopaminergique mésocortical, qui se projette dans le cortex préfrontal médian (CPFm), joue un rôle adaptatif en protégeant contre le stress. Jusqu’à présent, les interactions fonctionnelles entre les GC (ex : corticostérone) et le système dopaminergique mésocortical ne sont pas élucidées. Dans ce mémoire, nous avons évalué les effets des GC sur les fonctions dopaminergiques préfrontales en élevant chroniquement, à l’aide de minipompes osmotiques, les niveaux de corticostérone aux concentrations physiologiques maximales (1 mg/kg/h pendant 7 jours). Ce traitement n’a pas modifié significativement, chez les rats stressés ou non, les niveaux post mortem de dopamine et de son métabolite dans le tissu du CPFm. Toutefois, l’évaluation par voltamétrie in vivo des changements de dopamine extracellulaire dans le CPFmv a permis d’observer que la corticostérone augmente significativement la libération de dopamine en réponse à l’exposition à l’odeur de renard et au pincement de la queue. Nos études nous permettent de conclure que la corticostérone potentialise la fonction dopaminergique mésocorticale qui, à son tour, facilite la régulation négative en période de stress. / The hypothalamic-pituitary-adrenal axis plays an essential role in responding and adapting to stress, however overactivation of this axis or chronically high levels of glucocorticoids lead to pathological outcomes. The mesocortical dopamine (DA) system, terminating in the medial prefrontal cortex (mPFC), plays an adaptive role in protecting against stress, yet the functional interactions between glucocorticoids (eg. corticosterone) and the mesocortical DA system are not clear. In the present studies, we investigated the effects of glucocorticoids on prefrontal DA function using osmotic minipumps to chronically elevate corticosterone levels in the high physiological range (1 mg/kg/hr for 7 days). Chronic corticosterone treatment did not significantly affect post mortem levels of DA and its metabolites in PFC tissue in either unstressed or stressed rats. However, using in vivo voltammetry to monitor changes in extracellular DA release in PFC, corticosterone significantly increased DA release in response to both types of stress examined, exposure to predator odor and tail pinch stress. We conclude that corticosterone indeed potentiates mesocortical DA function, which in turn facilitates negative feedback regulation in times of stress.

L’axe hypothalamo-hypophyso-surrénalien joue un rôle essentiel dans l’adaptation et la réponse au stress. Toutefois, l’hyperactivation de cet axe ou des niveaux chroniquement élevés de glucocorticoïdes (GC) entraînent des conséquences pathologiques. Le système dopaminergique mésocortical, qui se projette dans le cortex préfrontal médian (CPFm), joue un rôle adaptatif en protégeant contre le stress. Jusqu’à présent, les interactions fonctionnelles entre les GC (ex : corticostérone) et le système dopaminergique mésocortical ne sont pas élucidées. Dans ce mémoire, nous avons évalué les effets des GC sur les fonctions dopaminergiques préfrontales en élevant chroniquement, à l’aide de minipompes osmotiques, les niveaux de corticostérone aux concentrations physiologiques maximales (1 mg/kg/h pendant 7 jours). Ce traitement n’a pas modifié significativement, chez les rats stressés ou non, les niveaux post mortem de dopamine et de son métabolite dans le tissu du CPFm. Toutefois, l’évaluation par voltamétrie in vivo des changements de dopamine extracellulaire dans le CPFmv a permis d’observer que la corticostérone augmente significativement la libération de dopamine en réponse à l’exposition à l’odeur de renard et au pincement de la queue. Nos études nous permettent de conclure que la corticostérone potentialise la fonction dopaminergique mésocorticale qui, à son tour, facilite la régulation négative en période de stress. / The hypothalamic-pituitary-adrenal axis plays an essential role in responding and adapting to stress, however overactivation of this axis or chronically high levels of glucocorticoids lead to pathological outcomes. The mesocortical dopamine (DA) system, terminating in the medial prefrontal cortex (mPFC), plays an adaptive role in protecting against stress, yet the functional interactions between glucocorticoids (eg. corticosterone) and the mesocortical DA system are not clear. In the present studies, we investigated the effects of glucocorticoids on prefrontal DA function using osmotic minipumps to chronically elevate corticosterone levels in the high physiological range (1 mg/kg/hr for 7 days). Chronic corticosterone treatment did not significantly affect post mortem levels of DA and its metabolites in PFC tissue in either unstressed or stressed rats. However, using in vivo voltammetry to monitor changes in extracellular DA release in PFC, corticosterone significantly increased DA release in response to both types of stress examined, exposure to predator odor and tail pinch stress. We conclude that corticosterone indeed potentiates mesocortical DA function, which in turn facilitates negative feedback regulation in times of stress.

L'obésité, caractérisée par une prise de poids excessive et un état inflammatoire, est une maladie métabolique qui devrait être prévenue car elle constitue un facteur de risque pour les maladies cardio-métaboliques. Les régimes riches en énergie et en graisses (high fat diet - HFD) sont une des causes de l'obésité. Plusieurs études suggèrent que les lipides alimentaires peuvent modifier la signalisation neuronale, l’excitabilité et la connectivité dans les aires cérébrales impliquées dans l’homéostasie énergétique. Dans le cerveau, les acides gras (AG) modulent la prise alimentaire, la prise de poids, et, plus récemment décrit, la motivation à obtenir de la nourriture. Ces effets semblent être médiés par l'incorporation des AG et/ou par leur métabolisme intra-neuronal, des mécanismes qui sont facilités par les protéines de transport, en particulier FATP1 (fatty acid transport protein-1). Il a aussi été montré que l’obésité altère l’intensité de l’effet de la dopamine (DA) et la neurotransmission dopaminergique dans le système mésolimbique, bien reconnu pour son implication dans les systèmes de récompense. Certaines études suggèrent que les neurones DA sont capables d’intégrer les AG, et que l'oléate, un acide gras à longue chaîne (AGLC), agit sur les neurones dans l’aire tegmentale ventrale (ventral tegmental area - VTA) d'où sont issus les neurones DA. L’oléate inhiberait l’activité neuronale dopaminergique, et donc les comportements de récompense. Cependant, notre compréhension du métabolisme des AG et de leur incorporation dans le VTA est encore trop partielle. Nous avons voulu : 1) mesurer la captation d’un analogue radiomarqué d’AGLC, le *FTHA, dans diverses régions du cerveau impliquées dans la régulation de la prise alimentaire; 2) vérifier si le blocage pharmacologique de l’entrée des AG dans les cellules, via un inhibiteur de FATP1, module les effets suppresseurs de l'oléate sur la récompense alimentaire lorsqu’injecté dans le VTA; et 3) évaluer les effets d’une longue HFD sur l’accumulation de graisse dans le cerveau, la neuroinflammation, et sur la barrière hémato- encéphalique (brain blood barrier - BBB) dans les régions impliquées dans la récompense. Pour l’objectif 1, nous avons élaboré un protocole permettant de quantifier l’incorporation et l’accumulation d’AG dans le cerveau. Après une injection de *FTHA dans la veine de la queue des souris, leurs cerveaux ont été disséqués, et la radioactivité était mesurée avec un compteur gamma. Nous avons montré que le cortex préfrontal et certaines zones associées au système de récompense (striatum dorsal-DS, VTA et noyau accumbens-NAC), mais pas l'hypothalamus médiobasal (mediobasal hypothalamus – MBH), incorporent le *FTHA. De plus, le VTA et le DS affichaient des taux de radioactivité plus importants et, plus rapidement, que les autres zones d’intérêt. Nous avons aussi déterminé que 15 minutes est le temps d'incubation optimal pour mesurer le *FTHA. Pour l’objectif 2, nous avons confirmé in vitro l’action de l’inhibiteur de la FATP1. Cependant, contrairement à des travaux antérieurs de notre équipe, nous n'avons pas trouvé de différence dans les comportements de récompense suite à des injections intra-VTA d'oléate et/ou de l’inhibiteur de la FATP1. Pour l’objectif 3, des souris ont été nourries soit avec une HFD riche en AG saturées, soit avec une diète contrôle durant 20 semaines. Elles sont devenues obèses et, via des techniques immunohistochimiques, nous avons montré que la HFD avait induit une plus grande activation microgliale dans le VTA et le NAC, ainsi qu’une plus grande perméabilité de la BBB au niveau du VTA. En revanche, nous n’avons pas trouvé de différences pour la teneur en lipides, le nombre de microglies, ou les protéines de jonction de la BBB. L'interprétation de nos résultats tient compte de certaines limites dues à nos approches méthodologiques et à la petite taille de nos échantillons. Néanmoins, s’ils sont confirmés, nos travaux pourraient contribuer à mieux comprendre comment les AG circulants sont incorporés dans le cerveau. Nous avons démontré que les AGLC traversent la BBB et s’accumulent dans plusieurs zones de récompense (DS, VTA) de façon plus importante que dans le MBH, une région réputée pour être associée à l’homéostasie énergétique et à la détection des nutriments. Nous avons aussi montré que l’obésité induite par l’HFD est associée à une augmentation de la perméabilité de la BBB dans le VTA, et que l’on peut étendre au VTA la relation entre l’obésité et la neuroinflammation. Notre travail apporte de nouvelles données dans le domaine du métabolisme et de l’incorporation des AG circulants dans le cerveau ainsi que sur les conséquences potentielles d’une exposition prolongée à une HFD. Comme les AG semblent s’accumuler dans le système de récompense et qu’ils pourraient modifier le comportement alimentaire des humains, nos résultats pourraient avoir des implications en obésité. / Obesity is a preventable metabolic disorder characterized by excessive weight gain and inflammation, which predisposes to numerous cardiometabolic diseases. One of the causes of obesity is the continued consumption of an energy dense, high-fat diet (HFD). Increasing evidence suggests that lipid nutrients can modify neural signaling, excitability and connectivity in brain areas involved in energy homeostasis. Moreover, fatty acids (FA) in the brain have been shown to modulate food intake, weight gain, and, more recently, food-motivated behavior. These effects seem to be mediated by FA uptake and intra-cellular metabolism, which is facilitated by FA transport proteins such as FATP1. Obesity has been shown to induce alterations in dopamine (DA) tone and signaling in the mesolimbic system, well known for its implication in reward. Evidence suggests that DA neurons detect FAs and that oleate, a long chain fatty acid (LCFA), acts on neurons in the ventral tegmental area (VTA), where DA neurons originate, to suppress DA neural activity and food-seeking. However, our understanding of FA metabolism and its uptake into VTA is still to be refined. We sought to evaluate whether: 1) the incorporation of a radiolabeled LCFA analog, *FTHA, in brain regions implicated in the regulation of food intake; 2) blocking FA entry into cells of the VTA, using a pharmacological inhibitor of FATP1, modulates the suppressive effects of oleate on food-motivated behavior; and 3) prolonged HFD has effects on fat accumulation, neuroinflammation, and blood brain barrier (BBB) integrity and leakage in reward-related areas. Under objective 1, we developed a protocol to allow the quantification of FA uptake in the brain using tail-vein injections of *FTHA, brain dissections, and gamma counter. We found that the prefrontal cortex and reward-related areas (dorsal striatum [DS], VTA and nucleus accumbens [NAC]), but not the mediobasal hypothalamus (MBH), incorporate *FTHA, that the VTA and DS emitted proportionally more radioactivity, and may do so more rapidly, than the other brain regions assessed. We also determined that a 15-minute incubation was optimal for *FTHA detection. Under objective 2, we showed in vitro a reduction in lipid accumulation in neurons after FATP1 inhibition. However, contrary to previous experiments conducted in our lab, we found no significant difference in food-motivated behavior following an intra-VTA oleate and/or FATP1 inhibitor injection. Under objective 3, mice were fed either a HFD (high saturated FAs) or a control diet for 20 weeks. They became obese, and via immunohistochemical techniques, we found that HFD induced greater microglial activation in the VTA and NAC, and greater BBB permeability in the VTA. However, we did not find differences in cerebral lipid content, number of microglial cells, or changes in BBB tight junction proteins. Interpretation of these experiments are discussed within certain methodological limitations and the small size of our samples. Nonetheless, if confirmed, our data may provide additional insight in the transport of peripheral FAs into the brain. We showed that LCFA pass through BBB and accumulate in reward-related areas. The VTA, and DS had significantly greater accumulation of *FTHA compared to the MBH, a region traditionally associated with energy homeostasis and nutrient sensing. We also showed that diet-induced obesity is associated with increased BBB permeability in the VTA, and we extended the established relationship between obesity and neuroinflammation to the VTA. This work brings forth new insights in the realm of FA uptake and metabolism in the brain, as well as their potential impacts after prolonged exposure. Our data may have potential implications for obesity, as this facilitates this macronutrient uptake in the reward system, and may alter postprandial food-seeking behaviors in humans.