The short form of dopamine D2 receptor (D2S) functions as a presynaptic autoreceptor on dopamine neurons and has an inhibitory effect on dopaminergic tone. D2-MAPKs pathway is involved in many physiological events like production of prolactin and tyrosine hydroxylase (TH) expression. However, the effect of D2S receptor signalling on MAPKs is cell type specific, and is not fully understood.A recent study in our lab has identified a Gαi-interacting ras-MAPK inhibitor RASA3. Here, we showed that RASA3 is the key effector in D2-induced inhibition of MAPK by knockdown of endogenous RASA3 in the GH4 cell using RASA3 siRNA. We have also transfected a dominant negative RASA3 to compete with the endogenous RASA3 for the binding site on Ras. Both RASA3-siRNA and dominant negative RASA3 blocked D2S-induced inhibition of MAPK activation, clearly implicating that RASA3 is a key effector in Gαi3-dependent D2S mediated MAPKs inhibition To determine whether RASA3’s inhibitory effect could be reconstituted in fibroblast cells, the effect of RASA3 on D2-mediated ERK1/2 activation in COS7 cells was tested. Our results show that both active Gαi2 (or Gαi3) and active RASA3 are required for optimal inhibition of ERK1/2 activation in fibroblast COS7 cells.

The role of brain dopamine (DA) systems in the control of anticipatory and consummatory aspects of the sexual behavior of male rats was examined in the present experiments. Experiment I explored the statistical relationship among anticipatory and consummatory measures of male sexual behavior using multiple correlations and factor analysis. Level changing, a measure of anticipatory behavioral excitement, was not related statistically to any of the consummatory measures of copulation, whereas several consummatory measures were correlated. The factor analysis revealed the existence of five factors: copulatory rate, initiation, hit rate, mount count, and anticipation; given tentative names based on the measures that loaded most heavily onto each factor. These results established that anticipatory and consummatory measures of male sexual behavior are unrelated statistically. Experiment II examined the dose-response effects of several DA receptor antagonists on anticipatory and consummatory measures of male sexual behavior. Systemic administration of the typical neuroleptics haloperidol and pimozide, and the Dl-selective antagonist SCH 23390, significantly reduced the number of level changes, increased the intromission latencies, and decreased the number of intromissions and the total number of ejaculations. The atypical neuroleptic clozapine and the D2-selective antagonist sulpiride reduced the number of level changes and significantly increased the intromission latencies, but did not affect the number of intromissions or ejaculations. In almost every case, the doses required to reduce level changing were lower than those required to increase the intromission latencies, indicating that the measure of anticipatory sexual behavior was more sensitive to disruption by DA antagonists than were consummatory measures of sexual behavior. The antiemetic agent metoclopramide decreased the number of intromissions but did not affect other anticipatory or consummatory measures of sexual behavior significantly. High doses of haloperidol, pimozide, or clozapine delayed or abolished level changing and the initiation of copulation. These results indicated that anticipatory and consummatory measures of male sexual behavior are affected differentially by DA antagonists. Experiment III provided the first evidence that haloperidol affects anticipatory and consummatory measures of male sexual behavior selectively in different brain DA terminals. Bilateral infusions of haloperidol to the nucleus accumbens reduced level changing without affecting the initiation of copulation or other consummatory measures. Bilateral infusions of haloperidol to the striatum increased the total number of ejaculations but did not affect other consummatory or anticipatory measures. Unilateral infusions of haloperidol to the medial preoptic area (MPOA) produced nearly all of the effects of systemic administration, including reduced number of level changes, increased intromission latencies, and decreased number of intromissions and ejaculations. These results indicated that DA in the nucleus accumbens and striatum are involved in the display of anticipatory sexual behavior and copulatory rate, respectively, whereas DA in the MPOA is involved in anticipatory sexual behavior, the initiation of copulation, and copulatory rate. In Experiment IV, in vivo voltammetry revealed a differential pattern of DA efflux in the nucleus accumbens and striatum, and catecholamine efflux in the MPOA, during anticipatory and consummatory phases of sexual behavior in male rats. Increased DA efflux in the nucleus accumbens and increased catecholamine efflux in the MPOA were associated with the presentation of a receptive female behind a screen and with the initiation of copulation. Efflux in both regions decreased following ejaculation but increased prior to each reinitiation of copulation. DA efflux in the striatum increased nonspecifically during copulation. Use of in vivo microdialysis confirmed the general pattern of DA efflux in the nucleus accumbens and striatum observed with voltammetry. These results were interpreted as supporting a role of DA terminals in the nucleus accumbens and MPOA, but not the striatum, in the display of anticipatory sexual behavior and in the initiation of copulation. In particular, the increased release of DA in the MPOA was viewed as sensitizing hypothalamic mechanisms involved in the control of penile erection whereas the increased release of DA in the nucleus accumbens was viewed as sensitizing motor programs necessary for the execution of anticipatory sexual responses and the initiation of mounting. / Arts, Faculty of / Psychology, Department of / Graduate

Indiana University-Purdue University Indianapolis (IUPUI) / Alcoholism carries significant personal and societal burdens, and yet we still lack effective treatments for alcohol use disorders. Several lines of research have demonstrated disruption of major white matter (WM) tracts in the brains of detoxified alcoholics. Additionally, there are several reports of alterations in the dopaminergic system of alcoholics. A better understanding of the relationships of brain structure and function in the alcoholic brain is necessary to move toward more efficacious pharmacological interventions. In this dissertation, there are three main chapters. First, reduced WM integrity was reported in a sample of individuals with active alcohol use disorder (AUD). This is a relatively understudied population, which is believed to represent a less severe phenotype compared to the in-treatment samples that are typically studied. Second, higher WM integrity was reported in a sample of college-age, active AUD. In a subsample of these individuals, graph theory measures of structural brain network connectivity were shown to be altered in cigarette-smoking social-drinking controls and smoking AUD subjects, compared to nonsmoking healthy individuals. Finally, a novel multimodal approach that combines diffusion weighted imaging and [11C]raclopride positron emission tomography identified differential relationships between frontostriatal connectivity and striatal dopamine tone in active AUD versus social-drinking controls. This suggests that aberrations in frontostriatal connectivity may contribute to reported differences in dopaminergic function in AUD. In summary, these results show that similar to detoxified/in-treatment alcoholics, active AUD samples present with WM integrity alterations, and changes in both structural connectivity and frontostriatal structure/function relationships. / 2021-10-02

Nurr1 is a transcription factor essential for the establishment, development, terminal differentiation and maintenance of mesencephalic dopamine neurons. Nurr1 is thought to coordinate the expression of dopamine neurotransmission genes. Nurr1-null heterozygous (+/-) mice have reduced Nurr1 function, which impacts dopamine neuron function in a region specific manner. Since aging can affect Nurr1 expression, we hypothesize that aging and +/- genotype will have significant effects on dopamine regulation and dopamine related behaviors. To test this hypothesis, regional neurochemistry and behavioral tests of wild type (+/+) and +/- mice at 3 months of age (young) and 12-16 months of age (aged)was performed. We also hypothesize that aging will reduce Nurr1 expression in substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA) and also reduce expression of the genes associated with dopamine (DA) neurotransmission that are regulated by Nurr1. To test this we isolated dopamine neurons in SNpc and VTA using laser capture microdissection, and measured the expression of Nurr1 and other associated DA neurotransmission genes using quantitative PCR. Nurr1 protein levels in DA neurons in SNpc and VTA and tyrosine hydroxylase (TH) protein levels in dopamine target regions were measured using quantitative immunohistochemistry. A significant increase in openield activity after stress in young +/- mice was observed. Significant reductions in tissue dopamine levels in the ventral striatum, including the core and shell of the nucleus accumbens were seen. In the SNpc, there was a significant increase in D2 receptor expression and a trend toward reduced TH expression, while in the VTA there was a significant decrease in D2 receptor expression and TH expression due to +/- genotype. The +/- genotype caused a significantly lower Nurr1 protein expression in the VTA which was not observed in the SNpc. Thus, it can be concluded that Nurr1 +/- genotype has a greater impact on the mesoaccumbens system as compared to the nigrostriatal system. The amount of Nurr1 protein expressed due to +/- genotype was not a 50% reduction as expected due to knockout of one gene of Nurr1 suggesting compensatory mechanisms that can maintain Nurr1 protein expression closer to the +/+ level.

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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

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