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No description available.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M. Sc.)--University of Canterbury, 2006. / Typescript (photocopy). Includes bibliographical references (leaves 56-67). Also available via the World Wide Web.

Ethanol (EtOH) is a commonly used drug which exerts many of its effects by altering neurotransmission in the mesolimbic dopamine (DA) system. Although there is little debate that EtOH acts to increase the activity of DA neurons in the ventral tegmental area (VTA), and that this action is necessary for some of the reinforcing effects of EtOH, research in vitro has only been able to demonstrate an excitatory effect on VTA DA neurons in response to very high concentrations of EtOH. These concentrations, typically in the range of 50-100 mM, correspond to sedative or lethal levels for typical humans. Therefore, the significance of findings from in vitro experiments can be difficult to interpret. We sought to determine why high concentrations of EtOH are needed in vitro and whether this could be explained by simple experimental factors, including cytosolic washout from whole cell electrophysiological recordings; heterogeneity among VTA DA neurons, where previous studies may have inadvertently focused on an EtOH-insensitive population; or selection of animal population, where perhaps low EtOH response is characteristic in naïve, rather than EtOH-experienced, animals. To achieve this, we performed cell-attached recordings on a large number of midbrain DA neurons of EtOH-naïve and experienced mice. We report evidence for a highly EtOH-responsive, medially located population of VTA DA neurons. These neurons, found within the rostral linear and interfascicular nuclei and considered “atypical” in terms of physiological criteria ascribed to DA neurons, exhibited a concentration-dependent increase of firing activity in response to EtOH, with some neurons responsive to as little as 20 mM EtOH. In contrast, DA neurons in the lateral VTA and substantia nigra were either unresponsive or responded only to 100 mM EtOH. We then examined neuronal activity following adolescent binge-like alcohol drinking in mice, to determine whether EtOH experience drives increased EtOH sensitivity of DA neurons. We find that in medial VTA DA neurons, drinking experience greatly increased firing activity driven by subsequent exposure to EtOH itself, without altering other measures of intrinsic excitability. This enhanced sensitivity was no longer significant in the presence of glutamate receptor blockade. We attempted to further characterize the EtOH-sensitive, medially located VTA DA neurons by utilizing retrograde tracing to identify a population of nucleus accumbens medial shell-projecting neurons. We find that this population exhibits an increased sensitivity to 50 mM EtOH after adolescent drinking. As a result of these experiments, we have identified a previously uncharacterized, highly EtOH-responsive population of DA neurons in the medial VTA. This population demonstrates an excitatory response to 10 and 20 mM EtOH, concentrations which are more pharmacologically relevant than those typically tested in vitro. We further demonstrate evidence for experience-induced neural adaptations which result in enhanced sensitivity to EtOH in vitro. These adaptations are only apparent in medial VTA DA neurons, and this phenomenon only occurs in response to adolescent drinking. These data provide evidence for a novel form of plasticity in which neurons respond to a primary reinforcer, in this case EtOH, after drinking experience. These findings provide an anatomical and pharmacological distinction between DA neuron subpopulations that will facilitate future mechanistic studies on the actions of EtOH in the VTA.

The mushroom body (MB) is the site of odor association learning in Drosophila.  In the canonical model, there are two types of reinforcing dopamine neurons (DANs): one set for rewarding unconditioned stimuli (US), and one responding to aversive US.  When DANs are activated together with an odor (the conditioned stimulus, or CS), plasticity is induced in the downstream output neurons (MBONs).  We have identified a DAN (V1) that surprisingly responds preferentially to odors, and responds weakly or not at all to various classical US.  In order to explore the relationship between V1 odor responses and the established roles of the MB, I characterized the responses of DAN V1, and probed its relationship to odor-driven behavior, associative conditioning, and activity in other MB compartments. These data show that V1 receives recurrent input from identified MBONs, contributes to the activity of an MBON that enhances alerting behavior, and that its odor responses are modulated by conditioning. We therefore present the study of the alpha2 compartment, which V1 innervates, as the dissection of an atypical compartment of the MB, one that acts as a hub by which various information from other compartments and brain areas is integrated in order to alter a behavioral response to odor. This work furthers our understanding of the MB not simply as an engine of classical learning, but as a system of diverse interconnected modules that allow coordinated fine control of behavior.

Abstract not available

Medications that treat diseases such as Parkinson???s disease work by regulating dopamine transmission at synapses. Surprisingly, little is known about the mechanisms regulating dopamine release at synapses. In this thesis, we study mechanisms that regulate vesicle recycling in axons and dendrites of dopamine neurons. Key questions we addressed were: (1) Are vesicles in axons and dendrites associated with the same regulatory proteins, and thus by implication the same regulatory mechanisms, as in excitatory neurons; (2) Do vesicles undergo recycling, and (3) if so, are they characterised by a distinct pool size and rate of recycling. To study this, we cultured dopamine neurons and used immunocytochemistry to detect vesicular monoamine transporter 2 (VMAT2) and identify axons, dendrites and synaptic proteins, combined with labelling of recycling vesicles using FM 1-43. Vesicles in axons, but not in dendrites, were associated with presynaptic proteins such as Synaptophysin and Bassoon. We identified two kinds of presynaptic sites in axons: ???synaptic??? (located close to soma and dendrites??? and ???orphan???. The recycling vesicle pool size was smaller at orphan sites than at synaptic sites, and the initial rate of vesicle pool release was also lower at orphan sites. Both synaptic and orphan sites exhibited lower rates of vesicle pool release compared to hippocampal synapses, suggesting functional differences in presynaptic physiology between dopamine neurons and hippocampal neurons. In somatodendritic regions, VMAT2 was localised to the endoplasmic reticulum, Golgi, endosome, and large dense-core vesicles, suggesting that these vesicles might function as a part of the regulated secretory pathway in mediating dopamine release. None of the synaptic vesicle proteins we studied were detected in these regions, although some preliminary evidence of vesicle turnover was detected using FM 1-43 labelling. This thesis provides a detailed analysis of neurotransmitter release mechanisms in dopamine neurons. Our data suggests that presynaptic release of dopamine is mediated by mechanisms similar to those observed in excitatory neurons. In somatodendritic regions, our data suggests that VMAT2 is localised to organelles in secretory pathways, and that distinct mechanisms of release might be present at somatodendritic sites to those present in presynaptic sites. This thesis provides novel methods for analysing vesicle recycling in dopamine neurons, which provides the basis for further studies examining presynaptic function of dopamine neurons in normal brain function, disease, and therapeutic approaches.

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains vi, 86 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 75-85).