<p>Sexual risk behavior among young adults is a serious public health concern; 50% will contract a sexually transmitted infection (STI) before the age of 25. The current study collected self-report personality and sexual history data, as well as neuroimaging, experimental behavioral (e.g., real-time hypothetical sexual decision making data), and self-report sexual arousal data from 120 heterosexual young adults ages 18-26. In addition, longitudinal changes in self-reported sexual behavior were collected from a subset (n = 70) of the participants. The primary aims of the study were (1) to predict differences in self-report sexual behavior and hypothetical sexual decision-making (in response to sexually explicit audio-visual cues) as a function of ventral striatum (VS) and amygdala activity, (2) test whether the association between sexual behavior/decision-making and brain function is moderated by gender, self-reported sexual arousal, and/or trait-level personality factors (i.e., self-control, impulsivity, and sensation seeking) and (3) to examine how the main effects of neural function and interaction effects predict sexual risk behavior over time. Our hypotheses were mostly supported across the sexual behavior and decision-making outcome variables, such that neural risk phenotypes (heightened reward-related ventral striatum activity coupled with decreased threat-related amygdala activity) were associated with greater lifetime sexual partners at baseline measured and over time (longitudinal analyses). Impulsivity moderated the relationship between neural function and self-reported number of sexual partners at baseline and follow up measures, as well as experimental condom use decision-making. Sexual arousal and sensation seeking moderated the relationship between neural function and baseline and follow up self-reports of number of sexual partners. Finally, unique gender differences were observed in the relationship between threat and reward-related neural reactivity and self-reported sexual risk behavior. The results of this study provide initial evidence for the potential role for neurobiological approaches to understanding sexual decision-making and risk behavior. With continued research, establishing biomarkers for sexual risk behavior could help inform the development of novel and more effective individually tailored sexual health prevention and intervention efforts.</p> / Dissertation

A administração sistêmica de canabidiol (CBD), o principal constituinte não psicomimético da Cannabis sativa, induz efeito antidepressivo em modelos préclínicos. O mecanismo de ação do canabidiol, no entanto, permanece pouco conhecido, podendo envolver a ativação de receptores serotoninérgicos do tipo 1A (5-HT1A). Ademais, as estruturas encefálicas envolvidas nesses efeitos permanecem desconhecidas. O córtex pré-frontal medial ventral (CPFmv), dividido em infra-límbico (IL) e pré-límbico (PL), recebe densa inervação serotoninérgica e desempenha importante papel na modulação da resposta emocional ao estresse e na neurobiologia da depressão. Dessa forma, o objetivo do presente trabalho foi avaliar a hipótese de que a administração de canabidiol no CPFmv, diferenciado em PL e IL, produz efeito tipo-antidepressivo por meio da ativação de receptores 5- HT1A. Para tanto, ratos Wistar canulados bilateralmente no CPFmv, receberam CBD (10, 30, 60 nmol/0,2?l) ou veículo intra-PL e CBD (30, 45 e 60nmol/0,2?l) ou veículo intra-IL e foram submetidos ao teste do nado forçado ou ao teste do campo aberto. Outro grupo de animais recebeu microinjeção (intra PL ou IL) do agonista de receptores 5-HT1A, 8-OH-DPAT (5, 10nmol/0,2?l) e foram submetidos aos mesmos testes. Um grupo adicional recebeu um antagonista 5-HT1A, WAY1006365 (10, 30nmol/0,2?l), seguido pela administração de 8-OH-DPAT (10nmol0,2?l) ou CBD (10 nmol0,2?l) intra-PL, ou 8-OH-DPAT (10nmol0,2?l) ou CBD (45 nmol0,2?l) intra-IL, e avaliados no teste do nado forçado. Os resultados demonstraram que a administração de CBD e de 8-OH-DPAT, intra-PL e intra-IL, reduziu significativamente o tempo de imobilidade no teste do nado forçado, um efeito tipoantidepressivo, sem alterar a atividade locomotora dos animais no teste do campo aberto. Além disso, a administração de WAY100635 intra-PL e intra-IL não alterou o tempo de imobilidade per se, mas foi capaz de bloquear os efeitos da administração do CBD e do 8-OH-DPAT. Esses resultados sugerem que a administração local do CBD no CPFmv induz efeito tipo-antidepressivo por meio da ativação de receptores 5-HT1A. Portanto, é possível que o CPFmv esteja envolvido no efeito tipoantidepressivo induzido pelo CBD. / Systemic administration of cannabidiol (CBD), the main non-psychotomimetic constituent of Cannabis sativa, induces antidepressant-like effects in pre-clinical models. The mechanism of action of Cannabidiol, which remains poorly understood, may involve serotonergic type 1A receptors activation (5-HT1A). Furthermore, the brain structures involved in these effects are still unknown. The ventral medial prefrontal cortex (vmPFC), divided in infra-limbic (IL) and pre-limbic (PL) subregions, receives dense serotonergic innervation and plays an important role in the modulation of emotional responses to stress and in the neurobiology of depression. Thus, the aim of this study was evaluate the hypothesis that the administration of cannabidiol into the vmPFC, differentiated into IL and PL, would induce antidepressant-like effect by activating 5-HT1A receptors. Therefore, male Wistar rats with cannulae bilaterally implanted into the Il and PL were given CBD (10, 30, 45, 60 nmol/0,2?l) or vehicle and were submitted to the forced swimming test or to the open field test. Another group of animals received microinjections (intra PL or IL) of the 5- HT1A agonist 8-OH-DPAT (5, 10nmol/0,2?l) and was submitted to the same tests. An additional group received an 5-HT1A antagonist, WAY100635 (10, 30 nmol/0,2?l.), followed by the administration of 8-OH-DPAT (10 nmol/0,2?l) or CBD (10 nmol0,2?l) intra-PL, or 8-OH-DPAT (10nmol0,2?l) or CBD (45 nmol0,2?l) intra- IL, and avaluated in the forced swimming test. The results showed that CBD and 8- OH-DPAT administration, intra-PL and intra-IL, significantly reduced the immobility time in the forced swimming test, an antidepressant-like effect, without changing the locomotor activity of the animals in the open field test. Moreover, the administration of WAY100635, intra-PL and intra-IL, did not change the immobility time per se, but blocked the CBD- and 8-OH-DPAT-induced effects. These results suggest that the local administration of CBD into the vmPFC induces antidepressant-like effects through the activation of 5-HT1A receptors. Therefore, it is possible that the vmPFC is involved in CBD-induced antidepressant-like effect.

Introdução: Devido ao aumento do volume abdominal, a posição prona é difícil e desconfortável para a gestante. Por isso, até hoje não foi testado se, nessa posição, a grávida teria seus padrões hemodinâmicos materno-fetais alterados. Objetivos: Analisar a influência da posição prona nos parâmetros hemodinâmicos materno-fetais e no conforto da mulher grávida, em um protótipo de maca especialmente construído para gestantes. Método: Estudo prospectivo, observacional e transversal, com 30 gestantes, em seguimento pré-natal, e 16 não gestantes, como grupo de controle. Os dois grupos foram subdivididos para participar de dois tipos de sequências randomizadas de posições, investigando-se se a mudança na ordem das sequências traria, nas gestantes e seus fetos, alguma variação significativa de valores hemodinâmicos. As posições utilizadas neste estudo foram: prona, supina, semissentada e decúbito lateral esquerdo. Foram avaliados os seguintes parâmetros hemodinâmicos: frequência cardíaca, pressão arterial sistólica, pressão arterial diastólica, saturação de oxigênio e frequência respiratória maternos e linha de base e variabilidade fetais. Para a análise estatística, foi utilizada a análise não paramétrica para medidas repetidas; e, para verificar se a posição anterior à prona teria alguma influência no desempenho dessa última, foram criadas variáveis de variação, que foram comparadas pelo teste de Wilcoxon. Resultados: Comparandose os índices da posição prona aos obtidos nos demais posicionamentos, observou-se que todos os parâmetros mantiveram-se dentro dos valores de normalidade e não houve, nesses valores, interferência das posições anteriores à prona. O grupo de gestantes revelou médias significativamente maiores do que as do grupo de não gestantes em relação às frequências cardíaca (p < 0,004), na sequência 1; e p < 0,001, na 2) e respiratória (na sequência 1, p=0,041; e, na 2, p=0,012). Na análise do grupo de gestantes, observou-se que, em ambas as sequências, as pressões arteriais sistólica e diastólica apresentaram, na posição prona, valores menores que os apresentados nas demais posições. Nesse grupo, observou-se diferença significativa na pressão arterial sistólica, quando se comparou, na sequência 1, a posição prona à semissentada (p < 0,001), à supina (p < 0,01) e ao decúbito lateral esquerdo (p < 0,01); e, na sequência 2, quando se comparou a posição prona às semissentada (p < 0,001) e à supina (p=0,013). Ainda no grupo de grávidas, a pressão arterial diastólica apresentou diferença significativa nas duas sequências: na sequência 1, a posição prona foi comparada às posições semissentada (p < 0,006), supina (p=0,023) e decúbito lateral esquerdo (p=0,017); na sequência 2, foi comparada ao posicionamento semissentado (p < 0,005) e supino (p=0,008). Quanto à saturação do oxigênio, na sequência 2 do grupo de grávidas houve diferença significativa quando se compararam os valores obtidos na posição prona aos obtidos na semissentada (p=0,021) e na supina (p=0,003). Em ambas as sequências, não houve diferença significativa na linha de base fetal, quando se comparou a posição prona com o decúbito lateral esquerdo. Não foram observadas variações significativas na variabilidade fetal nas sequências avaliadas. Todas as pacientes declararam terem se sentido confortáveis durante a permanência em cada uma das posições. Conclusão: No posicionamento prono, os padrões hemodinâmicos materno-fetais mantiveram-se dentro dos valores da normalidade. Na maca especialmente desenvolvida para gestantes, essa posição foi considerada segura e confortável / Introduction: Due to the increase of the abdominal volume, the prone position is a difficult and uncomfortable position for pregnant women. Hence, so far, it has not been tested if, in this position, a pregnant woman would have her maternal fetal hemodynamic parameters altered. Objectives: The objectives of this study were to analyze the influence of prone position in maternal-fetal hemodynamic parameters and the comfort of the pregnant woman on a prototype stretcher specially built for pregnant women. Method: A prospective, observational, crossover study with 30 pregnant women in antenatal segment, and 16 non pregnant women as a control group. The two groups were subdivided to take part in two types of randomized sequences of positions, investigating if the change in the order of the sequences would bring a significant alteration in the maternal fetal hemodynamic values. The positions used in this study were: prone, supine position, fowler position and left lateral. The following hemodynamic parameters were assessed: maternal heart rate, systolic blood pressure, diastolic blood pressure, oxygen saturation and respiratory rate and baseline and fetal variability. To the statistical analysis we used the non-parametric analysis for repeated measures and to verify if the position prior to the prone position would have any influence in it and variables of variation were created and compared to the Wilcoxon test. Results: Comparing the prone positions indexes to the other ones obtained, we observed that all the parameters were within the standards of normality and there was no interference in positions prior to the prone position in these values. The pregnant group showed means significantly higher than the ones of the non-pregnant women regarding the heart rate in sequence 1 (p < 0.004) and in sequence 2 (p < 0.001) and respiratory rate in sequence 1 (p= 0.041) and sequence 2 (p= 0.012). In the analysis of the pregnant group we observed that in prone position the systolic blood pressure and the diastolic blood pressure showed lower values than the other in both sequences. In the systolic blood pressure in the pregnant group sequence 1 the comparison of prone position with the fowler position (p < 0.001), with the supine position (p < 0.001) and with the left lateral (p < 0.001) in the pregnant group sequence 2 the comparison of the prone position with the fowler position (p < 0.001) and with the supine position (p= 0.013) it is observed a significant difference. In the diastolic blood pressure in comparison of the prone position in the pregnant group sequence 1 with the fowler position (p < 0.006), with supine position (p= 0.023) and with the left lateral (p= 0.017) and the pregnant group sequence 2 with the fowler position (p < 0.005) and with the supine position (p= 0.008) it is observed a significant difference. To the oxygen saturation in the pregnant group sequence 2 there was a significant difference when compared to the prone position with the fowler position (p= 0.021) and the prone position with the supine position (p= 0.003). In both sequences there were no significant differences in the fetal baseline between prone position with the left lateral. There were not observed any significant variations in the fetal variability in the sequences assessed. All the patients declared having felt comfortable during their stay in each one of the positions. Conclusion: In the prone positioning the maternal-fetal hemodynamic parameters were within the standards of normality and this position on the stretcher especially designed for pregnant women, considered as a safe and comfortable position

As both the major input and output of the hippocampal formation, the entorhinal cortex (EC) occupies a pivotal position in the medial temporal lobe. The discovery of grid cells in the medial entorhinal cortex (mEC) has led to this region being widely implicated in spatial information processing. Importantly, the EC is also the first area affected by dementia pathology, with neurons appearing particularly susceptible to degeneration. Despite this, little is known about how pathology affects the functional output of mEC neurons, either in their ability to coordinate firing to produce network oscillations, or to represent information regarding the external environment. This thesis will use electrophysiological techniques to examine how dementia pathology contributes to the breakdown of mEC neuronal networks using the rTg4510 mouse model of tauopathy. The first 2 results chapters will show how the anatomical organisation along the dorso-ventral axis of the mEC has profound influence on the network activity that can be observed both in brain slices and awake-behaving mice. It will further show how deficits in network activity in rTg4510 mice occur differentially across this axis, with dorsal mEC appearing more vulnerable to changes in oscillatory function than ventral. The third results chapter will begin to explore the relationship between global network activity and the external environment, showing that rTg4510 mice display clear deficits in the relationship between oscillation properties and locomotor activity. Finally, the underlying basis for these changes will be examined, through the recording of single-unit activity in these mice. It will show a decreased tendency for mEC neurons to display firing rates modulated by running speed, as well as an almost complete breakdown of grid cell periodicity after periods of tau overexpression. Understanding how dementia pathology produces changes to neuronal function and ultimately cognition is key for understanding and treating the disease. This thesis will therefore provide novel insights into the dysfunction of the EC during dementia pathology.

Maternal behaviours are those that increase offspring survival. Estrogens affect maternal behaviour by activating Estrogen Receptors (ER) in the brain. Maternal brain plasticity was explored by characterizing the effects of exposure to a mixture of environmental pollutants on number of ERs. Following exposure to the toxicants during pregnancy and lactation, brains of female rats were collected, sectioned at 30 μm and immunohistochemistry for ERα performed. Immuno-positive cells in the mPOA, VTA and NAc were counted. A two way ANOVA revealed no main effect of Treatment on the number of immunopositive cells for all three brain regions. However, a significant difference between the High and Low Doses with the high dose reducing the number of ERα+ cells in the mPOA and VTA. Our work showcases the importance of studying the effects of multiple chemical co-exposures on the mother's brain, as maternal brain changes impact maternal behaviour consequently affecting offspring neurodevelopment.

Introdução: Devido ao aumento do volume abdominal, a posição prona é difícil e desconfortável para a gestante. Por isso, até hoje não foi testado se, nessa posição, a grávida teria seus padrões hemodinâmicos materno-fetais alterados. Objetivos: Analisar a influência da posição prona nos parâmetros hemodinâmicos materno-fetais e no conforto da mulher grávida, em um protótipo de maca especialmente construído para gestantes. Método: Estudo prospectivo, observacional e transversal, com 30 gestantes, em seguimento pré-natal, e 16 não gestantes, como grupo de controle. Os dois grupos foram subdivididos para participar de dois tipos de sequências randomizadas de posições, investigando-se se a mudança na ordem das sequências traria, nas gestantes e seus fetos, alguma variação significativa de valores hemodinâmicos. As posições utilizadas neste estudo foram: prona, supina, semissentada e decúbito lateral esquerdo. Foram avaliados os seguintes parâmetros hemodinâmicos: frequência cardíaca, pressão arterial sistólica, pressão arterial diastólica, saturação de oxigênio e frequência respiratória maternos e linha de base e variabilidade fetais. Para a análise estatística, foi utilizada a análise não paramétrica para medidas repetidas; e, para verificar se a posição anterior à prona teria alguma influência no desempenho dessa última, foram criadas variáveis de variação, que foram comparadas pelo teste de Wilcoxon. Resultados: Comparandose os índices da posição prona aos obtidos nos demais posicionamentos, observou-se que todos os parâmetros mantiveram-se dentro dos valores de normalidade e não houve, nesses valores, interferência das posições anteriores à prona. O grupo de gestantes revelou médias significativamente maiores do que as do grupo de não gestantes em relação às frequências cardíaca (p < 0,004), na sequência 1; e p < 0,001, na 2) e respiratória (na sequência 1, p=0,041; e, na 2, p=0,012). Na análise do grupo de gestantes, observou-se que, em ambas as sequências, as pressões arteriais sistólica e diastólica apresentaram, na posição prona, valores menores que os apresentados nas demais posições. Nesse grupo, observou-se diferença significativa na pressão arterial sistólica, quando se comparou, na sequência 1, a posição prona à semissentada (p < 0,001), à supina (p < 0,01) e ao decúbito lateral esquerdo (p < 0,01); e, na sequência 2, quando se comparou a posição prona às semissentada (p < 0,001) e à supina (p=0,013). Ainda no grupo de grávidas, a pressão arterial diastólica apresentou diferença significativa nas duas sequências: na sequência 1, a posição prona foi comparada às posições semissentada (p < 0,006), supina (p=0,023) e decúbito lateral esquerdo (p=0,017); na sequência 2, foi comparada ao posicionamento semissentado (p < 0,005) e supino (p=0,008). Quanto à saturação do oxigênio, na sequência 2 do grupo de grávidas houve diferença significativa quando se compararam os valores obtidos na posição prona aos obtidos na semissentada (p=0,021) e na supina (p=0,003). Em ambas as sequências, não houve diferença significativa na linha de base fetal, quando se comparou a posição prona com o decúbito lateral esquerdo. Não foram observadas variações significativas na variabilidade fetal nas sequências avaliadas. Todas as pacientes declararam terem se sentido confortáveis durante a permanência em cada uma das posições. Conclusão: No posicionamento prono, os padrões hemodinâmicos materno-fetais mantiveram-se dentro dos valores da normalidade. Na maca especialmente desenvolvida para gestantes, essa posição foi considerada segura e confortável / Introduction: Due to the increase of the abdominal volume, the prone position is a difficult and uncomfortable position for pregnant women. Hence, so far, it has not been tested if, in this position, a pregnant woman would have her maternal fetal hemodynamic parameters altered. Objectives: The objectives of this study were to analyze the influence of prone position in maternal-fetal hemodynamic parameters and the comfort of the pregnant woman on a prototype stretcher specially built for pregnant women. Method: A prospective, observational, crossover study with 30 pregnant women in antenatal segment, and 16 non pregnant women as a control group. The two groups were subdivided to take part in two types of randomized sequences of positions, investigating if the change in the order of the sequences would bring a significant alteration in the maternal fetal hemodynamic values. The positions used in this study were: prone, supine position, fowler position and left lateral. The following hemodynamic parameters were assessed: maternal heart rate, systolic blood pressure, diastolic blood pressure, oxygen saturation and respiratory rate and baseline and fetal variability. To the statistical analysis we used the non-parametric analysis for repeated measures and to verify if the position prior to the prone position would have any influence in it and variables of variation were created and compared to the Wilcoxon test. Results: Comparing the prone positions indexes to the other ones obtained, we observed that all the parameters were within the standards of normality and there was no interference in positions prior to the prone position in these values. The pregnant group showed means significantly higher than the ones of the non-pregnant women regarding the heart rate in sequence 1 (p < 0.004) and in sequence 2 (p < 0.001) and respiratory rate in sequence 1 (p= 0.041) and sequence 2 (p= 0.012). In the analysis of the pregnant group we observed that in prone position the systolic blood pressure and the diastolic blood pressure showed lower values than the other in both sequences. In the systolic blood pressure in the pregnant group sequence 1 the comparison of prone position with the fowler position (p < 0.001), with the supine position (p < 0.001) and with the left lateral (p < 0.001) in the pregnant group sequence 2 the comparison of the prone position with the fowler position (p < 0.001) and with the supine position (p= 0.013) it is observed a significant difference. In the diastolic blood pressure in comparison of the prone position in the pregnant group sequence 1 with the fowler position (p < 0.006), with supine position (p= 0.023) and with the left lateral (p= 0.017) and the pregnant group sequence 2 with the fowler position (p < 0.005) and with the supine position (p= 0.008) it is observed a significant difference. To the oxygen saturation in the pregnant group sequence 2 there was a significant difference when compared to the prone position with the fowler position (p= 0.021) and the prone position with the supine position (p= 0.003). In both sequences there were no significant differences in the fetal baseline between prone position with the left lateral. There were not observed any significant variations in the fetal variability in the sequences assessed. All the patients declared having felt comfortable during their stay in each one of the positions. Conclusion: In the prone positioning the maternal-fetal hemodynamic parameters were within the standards of normality and this position on the stretcher especially designed for pregnant women, considered as a safe and comfortable position

Previous research investigating the neural circuitry underlying memory consolidation has primarily focused on single “nodes” in the circuit rather than the neural connections between brain regions, despite the likely importance of these connections in mediating different aspects or forms of memory. This focus has, in part, been due to technical limitations; however the advent of optogenetics has altered our capabilities in this regard, enabling optical control over neural pathways with temporal and spatial precision. The current set of experiments took advantage of optogenetics to control activity in specific pathways connecting brain regions in rats immediately after different kinds of learning. Chapter 2 first established the use of optogenetics to manipulate activity in the basolateral amygdala (BLA), which has been shown to modulate memory consolidation for a variety of types of learning likely through its connections to various downstream regions. Using a one-trial inhibitory avoidance task, a simple and robust fear learning paradigm, we found that both post-training stimulation and inhibition of BLA activity could enhance or impair later retention of the task, respectively. Enhancement was specific to stimulation using trains of 40, but not 20, Hz light pulses. Chapters 3 and 4 examined the projections from the BLA to the ventral hippocampus (VH) and medial entorhinal cortex (mEC) as the BLA’s ability to influence the consolidation for many types of memory is believed to be mediated through discrete projections to distinct brain regions. Indeed, the BLA innervates both structures, and prior studies suggest that the mEC and VH have distinct roles in memory processing related to contextual and nociceptive (footshock) learning, such as those involved in contextual fear conditioning (CFC). Optogenetic stimulation or inhibition of the BLA-VH or BLA-mEC pathway after training on a modified CFC task, in which the nociceptive or emotional stimulus (the footshock) and the context are separated, enabled experimental manipulations to selectively affect the consolidation for learning about one component and not the other. Optogenetic stimulation/inhibition was given to each candidate pathway immediately after the relevant training to determine its role in influencing consolidation for that component of the CFC learning. Chapter 3 results showed that stimulation of the BLA-VH pathway following footshock, but not context, training enhanced retention, an effect that was specific to trains of 40 Hz stimulation. Post-footshock photoinhibition of the same pathway impaired retention for the task. Similar investigations of the BLA-mEC pathway in Chapter 4 produced complementary findings. Post-context, but not footshock, stimulation of the pathway enhanced retention. In this particular case, only trains of 8 Hz stimulation were effective at enhancing retention. These results are the first, to our knowledge, to find that BLA inputs to different structures selectively modulate consolidation for different aspects of learning, thus enhancing our understanding of the neural connections underlying the consolidation of contextual fear conditioning and providing a critical foundation for future research.

<p>The symptoms of Parkinson's disease occur due to degeneration of dopamine neurons in substantia nigra. It has been demonstrated that glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor when it comes to protect and enhance survival of dopamine neurons in animal models of Parkinson's disease. The aim of this study was to evaluate short- and long-term effects of GDNF on survival and nerve fiber outgrowth of dopamine cells and astrocytic migration in mouse fetal ventral mesencephalic (VM) tissue. Primary tissue cultures were made of mouse fetal VM tissue and evaluated at 7 and 21 days in vitro (DIV) in terms of dopaminergic nerve fiber outgrowth and astrocytic migration when developed with GDNF present, partially, or completely absent. The results revealed that VM tissue cultured in the absence of GDNF did not exhibit any significant differences in migration of astrocytes or dopaminergic nerve fiber outgrowth neither after 7 DIV nor after 21 DIV, when compared with tissue cultured with GDNF present. Migration of astrocytes and dopaminergic nerve fiber outgrowth reached longer distances when tissue was left to develop for 21 DIV in comparison with 7 DIV. In order to study the long-term effects of GDNF, mouse fetal dopaminergic tissue was transplanted into the ventricles of adult mice and evaluated after 6 months. No surviving dopamine neurons were present in the absence of GDNF. In contrast dopamine neurons developed with GDNF did survive, indicating that GDNF is an essential neurotrophic factor when it comes to long-term dopamine cell survival. More cases have to be assessed in the future in order to strengthen the findings. Thus, transplanted dopamine neurons will be assessed after 3 and 12 months in order to map out when dopamine neurons deprived of GDNF undergo degeneration.</p>

Normal aging is associated with a decline in different cognitive domains and local structural atrophy as well as decreases in dopamine concentration and receptor density. To date, it is largely unknown how these reductions in dopaminergic neurotransmission affect human brain regions responsible for reward-based decision making in older adults. Using a learning criterion in a probabilistic object reversal task, we found a learning stage by age interaction in the dorsolateral prefrontal cortex (dIPFC) during decision making. While young adults recruited the dlPFC in an early stage of learning reward associations, older adults recruited the dlPFC when reward associations had already been learned. Furthermore, we found a reduced change in ventral striatal BOLD signal in older as compared to younger adults in response to high probability rewards. Our data are in line with behavioral evidence that older adults show altered stimulus-reward learning and support the view of an altered fronto-striatal interaction during reward-based decision making in old age, which contributes to prolonged learning of reward associations.

Parkinson’s disease is a disorder mainly characterized by progressive degeneration of dopamine producing neurons in the substantia nigra of the midbrain. The most commonly used treatment strategy is to pharmacologically restore the lost function by the administration of the dopaminergic precursor L-DOPA. Another treatment strategy is to replace the degenerated neurons with immature fetal ventral mesencephalic tissue, or ultimately stem cell-derived tissue. Grafting trials have, however, revealed poor reinnervation capacity of the grafts, leaving much of the striata dopamine-denervated. An additional drawback is the upcoming of dyskinesia (involuntary movements), a phenomenon also observed during L-DOPA treatment of Parkinson’s disease patients. Attempts to characterize nerve fiber formation from dopamine neurons have demonstrated that the nerve fibers are formed in two morphologically diverse outgrowth patterns, one early outgrowth seen in the absence of astrocytes and one later appearing outgrowth seen in co-existence with astrocytes. The overall objective of this thesis has been to study the dopaminergic outgrowth including guidance of nerve fiber formation, and to look into the mechanisms of L-DOPA-induced dyskinesia. The first paper in this thesis characterizes the different outgrowth patterns described above and their relation to different glial cells. The study demonstrated the two different outgrowth patterns to be a general phenomenon, applying not only to dopamine neurons. Attempts of characterization revealed no difference of origin in terms of dopaminergic subpopulations, i.e. A9 or A10, between the outgrowth patterns. Furthermore, the “roller-drum” technique was found optimal for studying the dual outgrowth sequences. The second and the third paper also utilized the “roller-drum” technique in order to promote both patterns of neuronal fiber formation. The effects of glial cell line-derived neurotrophic factor (GDNF) on the formation of dopamine nerve fibers, was investigated. Cultures prepared from gdnf knockout mice revealed that dopaminergic neurons survive and form nerve fiber outgrowth in the absence of GDNF. The dopaminergic nerve fibers exhibited an outgrowth pattern consistent with that previous observed in rat. GDNF was found to exert effect on the glial-associated outgrowth whereas the non-glial-associated was not affected. Astrocytic proliferation was inhibited using cytosine β-D-arabinofuranoside, resulting in reduced glial-associated outgrowth. The non-glial-associated dopaminergic outgrowth was on the other hand promoted, and was retained over longer time in culture. Furthermore, the non-glial-associated nerve fibers were found to target the fetal frontal cortex. Different developmental stages were shown to promote and affect the outgrowths differently. Taken together, these data indicate and state the importance of astrocytes and growth factors for neuronal nerve fiber formation and guidance. It also stresses the importance of fetal donor age at the time for transplantation. The fourth and fifth studies focus on L-DOPA dynamics and utilize in vivo chronoamperometry. In study four, 6-OHDA dopamine-depleted rats were exposed to chronic L-DOPA treatment and then rated as dyskinetic or non-dyskinetic. The electrochemical recordings demonstrated reduced KCl-evoked release in the intact striatum after chronic L-DOPA treatment. Time for maximal dopamine concentration after L-DOPA administration was found to be shorter in dyskinetic animals than in non-dyskinetic animals. The serotonergic nerve fiber content in the striatum was evaluated and brains from dyskinetic animals were found to exhibit significantly higher nerve fiber density compared to non-dyskinetic animals. Furthermore, the mechanisms behind the conversion of L-DOPA to dopamine in 6-OHDA dopamine-depleted rats were studied. Local administration of L-DOPA in the striatum increased the KCl-evoked dopamine release in the intact striatum. Acute application of L-DOPA resulted sometimes in a rapid conversion to dopamine, probably without vesicle packaging. This type of direct conversion is presumably occurring in non-neuronal tissue. Furthermore, KCl-evoked dopamine releases were present upon local application of L-DOPA in the dopamine-depleted striatum, suggesting that the conversion to dopamine took place elsewhere, than in dopaminergic nerve fibers. In conclusion, these studies state the importance of astrocytes for neuronal nerve fiber formation and elucidate the complexity of L-DOPA conversion in the brain.