Activation of ventral tegmental area (VTA) dopaminergic (DA) neurons by ethanol has been implicated in the rewarding and reinforcing actions of ethanol. GABAergic transmission is thought to play an important role in regulating the activity of DA neurons. While at most central synapses ethanol generally increases inhibitory synaptic transmission, no studies have explored the effect of acute ethanol on GABAergic transmission in the VTA. Here we investigated how ethanol modulates GABAergic transmission in the VTA in relation to the overall action of ethanol on VTA-DA neuron activity. We demonstrated that ethanol dose-dependently enhances action potential-dependent and -independent GABA release onto VTA-DA neurons. Utilizing whole-cell voltage clamp recording techniques, ethanol increased both spontaneous and miniature inhibitory postsynaptic current (s/mIPSC) frequency while having minimal effect on s/mIPSC amplitude. The ethanol enhancement in GABA release was independent of GABAB auto-receptor inhibition of release. Intra-terminal calcium levels regulate neurotransmitter release, thus we investigated how modulation of calcium levels would affect the ethanol-enhancement in GABA release. Ethanol enhanced mIPSC frequency in the presence of the voltage-gated calcium channel blockers, cadmium chloride and nicardipine. However, blockade of intracellular calcium stores with 2-APB and cyclopiazonic acid eliminated the ethanol-enhancement of mIPSC frequency. Intracellular calcium stores are regulated via Gq protein-coupled receptors such as the 5-HT2C receptor. 5-HT2C receptor activation robustly enhanced mIPSC frequency whereas blockade inhibited the ethanol-enhancement in mIPSC frequency. These observations suggest that increased calcium release from intracellular stores via 5-HT2C receptor activation is involved in the ethanol-enhancement of GABA release onto VTA-DA neurons. Utilizing cell-attached current-clamp recordings, we demonstrated that the ethanol-enhancement of VTA-DA neuron activity is modulated by the concurrent enhancement in GABA release. Blockade and activation of GABAA receptors enhanced and reversed, respectively, the stimulatory effect of ethanol on VTA-DA neurons. Mu-opioid receptors (MORs) on GABAergic interneurons have been demonstrated to modulate both basal and ethanol-enhanced VTA-DA activity in vivo, though we failed to demonstrate such an effect in vitro. Overall, the results of this study suggest that the 5-HT2C receptor and intra-terminal calcium-dependent ethanol enhancement in GABA release acts to regulate the overall stimulatory effect of ethanol on VTA-DA activity. / text

No description available.

Neuropeptide B (NPB) and neuropeptide W(NPW) are endogenous neuropeptide ligands for the G protein-coupled receptors NPBWR1 and NPBWR2. Here we report that the majority of NPW neurons in the mesolimbic region possess tyrosine hydroxylase immunoreactivity, indicating that a small subset of dopaminergic neurons coexpress NPW. These NPW-containing neurons densely and exclusively innervate two limbic system nuclei in adult mouse brain: the lateral bed nucleus of the stria terminalis and the lateral part of the central amygdala nucleus (CeAL). In the CeAL of wild-type mice, restraint stress resulted in an inhibition of cellular activity, but this stress-induced inhibition was attenuated in the CeAL neurons of NPW-/- mice. Moreover, the response of NPW-/- mice to either formalin-induced pain stimuli or a live rat (i. e., a potential predator) was abnormal only when they were placed in a novel environment: The mice failed to show the normal species-specific self-protective and aversive reactions. In contrast, the behavior of NPW-/- mice in a habituated environment was indistinguishable from that of wildtype mice. These results indicate that the NPW/NPBWR1 system could play a critical role in the gating of stressful stimuli during exposure to novel environments.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (PhD) - Swinburne University of Technology, Brain Sciences Institute, 2005. / Submitted for the degreee of Doctor of Philosophy, Brain Sciences Institute, Swinburne University of Technology - 2005. Typescript. Bibliography: p. 159-197.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 179-229). Available also in a digital version from Dissertation Abstracts.

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

Numerous genetic variants displaying stereotypic circling behaviour have been described in rodents. The majority are recessive mutants expressing dopaminergic alterations in the striatum- often with associated vestibular defects. We describe a novel circling mouse (Cr) with intact vestibular function frequently obtained from crosses of non-transgenic wild type mice (WT) and transgenic growth hormone mice (TGM). We have characterized Cr with stereotypic circling, head bobbing, hyperkinesia, aggressiveness, and elevated dopamine when compared to the transgenic growth hormone mouse. The Cr also demonstrates self-mutilating behaviour found in mice with dysregulated striatal dopamine levels. Cr oppositely mirrors most traits of the TGM including alterations in sleep, activity, eating, and drinking. TGM displayed superior performance than WT in novel object recognition, but this decreased with aging. Comparatively, Cr performed poorly in this test. The memory of young TGM exceeded controls, whereas young Cr displayed poorer memory with an age related improvement. In a stepdown test of emotionality, TGM step down more readily, while Cr are more hesitant than WT. TGM and Cr also demonstrate opposite alterations in striatal dopamine. Further analysis demonstrated differential responsiveness of TGM and Cr under dopaminergic drugs, and potentially sexually dimorphic differences in behaviour associated with elevated GH in TGM. TGM are characterized by increased levels of circulating growth hormone and alterations in sleep and activity. We hypothesize that frequent generation of Cr may reflect unintended selection of modifier genes that counterbalance negative consequences of elevated GH in TGM. / Thesis / Master of Science (MSc)

<p>Mutations of the FOXP2 gene impair speech and language development in humans and shRNA-mediated suppression of the avian orthologue FoxP2 disrupts song learning in juvenile zebra finches. How diminished FoxP2 levels affect vocal control and alter the function of neural circuits important to learned vocalizations remains unclear. Using a combination of behavioral analysis, in vivo intracellular recordings in anaesthetized birds, pharmacology and extracellular recordings in singing birds, I addressed how FoxP2 knockdown in songbird striatum affects vocal control and signal propagation through circuits important for the control of learned vocalizations. In summary, I found that FoxP2 knockdown in the songbird striatum disrupts developmental and social modulation of song variability. Recordings in anaesthetized birds show that FoxP2 knockdown interferes with D1R-dependent modulation of activity propagation in a corticostriatal pathway important to song variability, an effect that may be partly attributable to reduced D1R and DARPP-32 protein levels. Furthermore, recordings in singing birds reveal that FoxP2 knockdown prevents social modulation of singing-related activity in this pathway. These findings show that reduced FoxP2 levels interfere with the dopaminergic modulation of vocal variability, which may impede song and speech development by disrupting reinforcement learning mechanisms.</p> / Dissertation

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.