Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 126-150). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 84-100).

The dopamine transporter (DAT) is a plasma membrane-bound protein, localized on peri-synaptic terminals of dopaminergic (DA) neurons. DAT is responsible for terminating DA signaling by rapid removal of the transmitter from the synaptic cleft region. DA signaling relies on a critical balance between release and removal of the neurotransmitter within synaptic clefts. Recycling of DAT between intracellular endosomal compartments and the plasma membrane regulates DAT function. This dynamic trafficking occurs in both a constitutive and regulated manner to increase or decrease the number of transporters on the cell surface available for transmitter reuptake. Therapeutic drugs and/or drugs of abuse, including psychostimulants and ethanol, cause maladaptive changes in DA signaling in mesolimbic areas of the brain, leading to addictive behaviors. DAT is the primary site of action for psychostimulants such as, cocaine, methylphenidate, and amphetamine. These drugs can alter the function and/or regulation of the transporter. Ethanol, one of the most widely abused drugs in society, is known to activate DA pathways in reward and reinforcement areas of the brain. However, the effect of ethanol on DAT function and regulation is less clear. The studies presented here explore the action of ethanol on DAT function in mammalian cell systems, and the subcellular trafficking mechanisms that regulate the transporter. To delineate mechanisms of ethanol action on DAT, several lines of HEK-293 cells stably expressing DAT or ethanol-insensitive DAT mutants were generated. Short-term ethanol exposure was found to potentiate DAT function, and ethanol sensitivity is mediated by specific amino acids in the first intracellular loop. This increase in function was accompanied by an enhancement of DAT expressed on the cell surface. The changes in DAT localization and the absence of consensus phosphorylation sites in the ethanol sensitive regions of the transporter, led to the hypothesis that ethanol modulates DAT uptake by altering the dynamic trafficking of the transporter. In the present studies, we found ethanol directly regulates DAT function by altering specific step of the endosomal recycling pathway. Further analysis of the ethanol-sensitive first intracellular loop revealed this region might also play a role in conformational changes required for substrate binding. The findings presented in these studies describe a novel molecular mechanism of ethanol action on DAT, and provide a framework to further understand the action of ethanol on synaptic dopamine regulation. / text

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.

Thesis (doctoral)--University of Lund, 1995. / Added t.p. with thesis statement inserted.

Thesis (doctoral)--University of Lund, 1995. / Added t.p. with thesis statement inserted.

Thesis (M.S.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2005. / Includes bibliographical references (p. 24-27).

After unilateral lesions of the mesotelencephalic dopamine (DA) system, the administration of DA receptor agonists results in circling. This response is believed to reflect an asymmetry in mesotelencephalic DA activity. Moreover, drug-induced circling is thought to be directed away from the projection of higher dopaminergic activity. Recently, it has been reported that circling can be established and maintained using operant procedures in surgically intact and drug naive rats. The phenomenon of conditioned circling has been associated with an asymmetrical change in DA metabolism within the striatum and nucleus accumbens. The present series of experiments was designed to characterize further the involvement of mesotelencephalic DA in conditioned circling. Rats trained to circle for water according to a continuous schedule of reinforcement did not exhibit increased DA metabolism within either the striatum or the nucleus accumbens (Experiment I). However, a bilateral augmentation was observed when rates of responding were increased by implementing an intermittent schedule of reinforcement (Experiment II). Concurrent increases in the biosynthesis of DA, as estimated by accumulation of DOPA following the administration of a DOPA decarboxylase inhibitor, were not observed (Experiment III). Experiments IVa and IVb examined the extent to which inherent directional biases, which play a role in determining the magnitude and direction of drug-induced circling, influenced the acquisition and performance of the conditioned circling response. No effects were evident. Moreover, a symmetrical, bilateral enhancement in DA metabolism was observed in the striatum, irrespective of directional preferences. While conditioned circling can be established and maintained by reinforcing the response with food, food itself influenced DA metabolism and therefore precluded the detection of changes in DA metabolism specific to the circling response. Specifically, striatal and accumbens DA metabolism was augmented to a similar extent in animals given matched amounts of non-contingently presented food (Experiment V). Concentrations of DA, DOPAC and homovanillic acid (HVA) were found to be differentially distributed throughout the striatum (Experiment Via), suggesting a possible chemical basis for the heterogeneity of striatal DAergic functions. Changes in striatal DA metabolism associated with conditioned circling were observed only within localized regions of the anterior striatum (Experiment VIb). All changes noted were, however, bilateral in nature. Finally, unilateral lesions of the mesotelencephalic DA projection, following the establishment of the conditioned circling response, disrupted responding, irrespective of the relative locus of the lesion (i.e. ipsilateral or contralateral to the direction of turning) (Experiment VII). However, the extent of the behavioral deficit was more severe following contralaterally placed lesions. It is concluded that circling, established and maintained by positive reinforcement, is subserved by a bilateral augmentation in DA metabolism within the nucleus accumbens and discrete regions of the striatum. However, lesion studies indicate an asymmetrical involvement of the ipsilateral and contralateral projections in this response. / Medicine, Faculty of / Graduate

It is well established that chronic treatment with neuroleptic agents which selectively block dopamine (DA) receptors in the brain leads to the development of DA receptor supersensitivity. However comparing the degree and duration of the changes in receptor sensitivity obtained by different investigators has been extremely difficult, because of the numerous differences that exist in individual methods of producing and examining DA receptor supersensitivity. By examining the DA receptor supersensitivity that ensues following chronic treatment with different doses and durations of pimozide, at various intervals after withdrawal from treatment, the overall parametric changes can be more directly compared. To measure the changes in DA receptor sensitivity following chronic pimozide treatment, both behavioral (d.-amphetamine-induced locomotor activity; apomorphine-induced stereotypy) and biochemical (DA receptor binding assay) techniques were utilized. With increasing doses of chronic pimozide treatment, the degree and duration of the resulting DA receptor supersensitivity increased as measured both behaviorally and biochemically. Similarily, the longer durations of chronic pimozide treatment had a greater effect on the degree and duration of the increased DA receptor sensitivity than did the shorter durations of treatment. Correlations were found between the biochemical and behavioral results both between groups of animals treated chronically with different doses and durations of pimozide and within individual groups of animals. In addition, the changes in receptor sensitivity following chronic pimozide treatment was due to an increase in the number of DA receptors with no change in the affinity of these receptors to DA. These results following chronic treatment with neuroleptics demonstrate that the behavioral supersensitivity observed in animals in response to either the direct DA agonist apomorphine or the indirect DA agonist d-amphetamine, may be a result of an increased number of DA receptors. Finally, the supersensitive DA receptors that develop as a result of chronic treatment with neuroleptics are discussed with regard to their possible relevance as an animal model of the iatrogenic disease, tardive dyskinesia, observed clinically in schizophrenic patients withdrawn from neuroleptic therapy. / Medicine, Faculty of / Graduate

No description available.