Browsing by Subject "dopamine"

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    Dopamine binds a D1-D2 heteromer coupled to Gq to activate a phospholipase C dependent mechanism to increase dendritic branching in the developing Medium Spiny Neuron
    (2018-05-04) Pelkey, Lauren, J
    The Medium Spiny Neuron (MSN) composes approximately 95% of the neurons in the striatum in the brain. MSNs are GABAergic neurons that modulate the movement and reward pathways. Cortical and substantia nigra pars compacta neurons release glutamate and dopamine on MSNs, respectively. These inputs are required for the MSN to grow into its typical highly branched, spiny morphology. The Lanier lab found that dopamine increases dendritic branching in the developing MSN. The goal of the current study is to find the mechanism by which dopamine enhances MSN dendritic arborization. The hypothesis is that dopamine increases dendritic branching by binding a D1-D2 heteromer coupled to Gq, which activates phospholipase C (PLC). A striatal-cortical co-culture prepared from day 16 mouse embryos was used to grow MSNs with their afferent cortical neurons. The experimental treatments were: 1) D1 receptor agonist SKF81297, D2 receptor agonist quinpirole, and both SKF81297 & quinpirole, 2) chemogenetic activation of Gq, and 3) PLC antagonist U73122. Treatments were administered in vitro at day 4, and regularly administered until fixation at day 19. It was found that SKF81297 and quinpirole, together and in isolation, were not able to replicate dopamine’s increased branching effect. In addition, it was found that Gq activation, using a chemogenetic approach, resulted in increased branching almost to the same extent as dopamine addition caused. Further, U73122 had no effect on branching on its own, but U73122 significantly attenuated dopamine’s branching effects. Taken together, this data support the hypothesis that dopamine enhances branching by binding a D1-D2 heteromer coupled to Gq, to activate phospholipase C.
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    Dopamine binds a D1-D2 heteromer coupled to Gq to activate phospholipase C to increase dendritic branching in the developing Medium Spiny Neuron
    (2018-04-22) Pelkey, Lauren, J
    The Medium Spiny Neuron (MSN) composes over 90% of the neurons in the striatum in the brain. MSNs are GABAergic neurons that modulate the movement and reward pathways. Cortical and substantia nigra pars compacta neurons release glutamate and dopamine on MSNs, respectively. These inputs are required for the MSN to grow into its typical highly branched, spiny morphology. The Lanier lab found that dopamine increases dendritic branching in the developing MSN. The goal of the current study is to find the mechanism by which dopamine enhances MSN dendritic arborization. The hypothesis is that dopamine increases dendritic branching by binding a D1-D2 heteromer coupled to Gq, which activates phospholipase C (PLC). A striatal-cortical co-culture prepared from day 16 mouse embryos was used to grow MSNs with their afferent cortical neurons. The experimental treatments were: 1) D1 receptor agonist SKF81297, D2 receptor agonist quinpirole, and both SKF81297 & quinpirole, 2) chemogenetic activation of Gq, and 3) PLC antagonist U73122. After 19 days, co-cultures were fixed and treated with antibody to DARPP-32 to identify MSNs. It was found that SKF81297 and quinpirole, together and in isolation, were not able to replicate dopamine’s increased branching. In addition, it was found that Gq activation by Clozapine N-oxide addition to DREADDs expressing MSNs resulted in increased branching almost to the same extent as dopamine addition caused. Further, U73122 had no effect on branching on its own, but U73122 significantly attenuated dopamine’s branching effects. Taken together, this data support the hypothesis that dopamine enhances branching by binding a D1-D2 heteromer coupled to Gq, to activate phospholipase C.
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    Dopaminergic control of neuroeconomic decision making
    (2023) Kocharian, Adrina
    Dopamine in the nucleus accumbens is an important neural substrate for valuation and decision-making. Dominant theories generally discretize and homogenize decision-making, when it is in fact a continuous process, with evaluation and re-evaluation components that extend beyond simple outcome prediction into consideration of past and future value. Furthermore, individual animals use distinct strategies to achieve their goals, requiring different computational processes. Extensive work has examined mesolimbic dopamine in the context of reward prediction error, but major gaps persist in our understanding of how dopamine tracks imagined past and future rewards to influence decision confidence. Moreover, there is little consideration of strategy-dependent differences in value processing that may shape dopaminergic encoding. In the studies presented in this dissertation we used an economic foraging task in mice, and found that strategy-specific dopamine dynamics reflected decision confidence during evaluation, as well as both past and future counterfactual value during re-evaluation. We found that inhibition of dopamine terminals altered counterfactual processing during re-evaluation. Individually-tailored optogenetic stimulation of mesolimbic dopamine terminals altered decision confidence during evaluation and carried over to counterfactual re-evaluation, in a strategy-specific manner. We provide evidence that mesolimbic dopamine is tightly linked to decision confidence and counterfactual information, through signals that go beyond reward prediction errors to more complex encoding of imagined past and future value.
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    Dopaminergic signaling in the spinal cord suppresses locomotion in larval zebrafish development
    (2024-03) Walters, Deborah, L
    The significance of dopamine (DA) and its multifaceted role as a neurotransmitter in the central nervous system has undergone extensive investigation. The research focus of my project centers on dopamine’s role in modulating spinal locomotor circuits in larvae zebrafish. Previous research from our lab showed that larval zebrafish swimming patterns change during development from long episodes durations at 3 days post fertilization (dpf) to short episode durations at 4 dpf and coincides with gross to fine motor control. Dopamine receptor D4 signaling in the spinal cord is necessary in facilitating this switch, likely by modulating dopamine signaling and regulating the activity of motor neurons involved in generating locomotor patterns. We demonstrated that antagonism of D4R signaling starting at 3 dpf prevents the switch from long to short episode durations, while D4R antagonism at 4 dpf reverses the switch from short to long episode durations. We hypothesized that 3 dpf larvae possess sufficient dopaminergic receptors in the spinal cord to bind to DA, enabling the advancement of the developmental switch from immature, long swim patterns to a mature state resembling 4 dpf larvae by exposing larvae at 3 dpf to exogenous DA. To test this, we used transgenic zebrafish that expressed Channelrhodopsin (ChR) in glutamatergic neurons within the spinal cord, allowing for the activation of these neurons using blue-light stimulation. Fictive swimming was measured using peripheral nerve recordings in different conditions, of a baseline (t0), treatment of dopamine (t1), and washout (saline) (t2). Control (untreated) preparations exhibited no significant changes between conditions, indicating that repeated optogenetic stimulation by itself did not induce notable changes in locomotor activity. Dopamine application significantly decreased the number of bursts and episode duration during optogenetic stimulation locomotor activity without affecting number of episodes, burst duration, or inter-burst intervals. These results suggest that exogenous DA affected swim patterns in 3 dpf larvae to resemble their 5 dpf counterparts, indicating a sufficient expression level of dopamine receptors in spinal locomotor networks of 3 dpf larvae to prematurely advance the developmental switch. These results could elucidate how neurodegenerative and motor disorders develop and progress, and shed light on the mechanisms underlying spinal cord injury. These findings could potentially inform translational medical approaches creating novel therapeutic interventions for treating neurodegenerative diseases.
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    G protein-gated potassium channels in ventral tegmental area dopamine neurons temper behavioral sensitivity to cocaine
    (2019-02) McCall, Nora
    Drugs of abuse share the ability to enhance dopamine (DA) release in the mesocorticolimbic system. This increase in DA is thought to drive persistent adaptations in the brain and behavior that contribute to the progression of addiction. One such adaptation is a cocaine exposure-induced suppression of G protein-dependent inhibitory signaling in DA neurons of the ventral tegmental area (VTA), a cell population important for reward-related behavior. This cocaine-induced adaptation involves the internalization of G protein-gated inwardly rectifying K+ (GIRK/Kir3) channels, a key contributor to inhibitory G protein pathways that normally temper DA neurotransmission in the mesocorticolimbic system. Dopamine 2 receptor (D2R) activation mediates this adaptation. While methamphetamine, another psychostimulant, can induce a similar adaptation in inhibitory G protein signaling, other drugs of abuse, i.e. morphine, are unable to induce a GIRK channel adaptation. Thus, inhibitory G protein signaling in VTA DA neurons could be important for tempering the behavioral response to cocaine, and could represent an inhibitory “barrier” to addiction. The goal of this thesis research is to understand the impact of GIRK channel activity signaling on behavioral sensitivity to cocaine. The work in this thesis tests the hypothesis that the strength of inhibitory G protein signaling in VTA DA neurons is inversely related to behavioral sensitivity to cocaine. This hypothesis predicts decreasing GIRK channel activity in DA neurons will increase behavioral sensitivity to cocaine. To test this, a genetic strategy was employed, to ablate GIRK channels in DA neurons using DATCre(+):Girk2fl/fl mice. The strength of two significant G protein receptor-dependent signaling dependent on GIRK channels were significantly reduced in a dopamine neuron-specific manner. DATCre(+):Girk2fl/fl mice displayed increased locomotor responding to both acute and repeated cocaine, as well as increased responding for, and intake of, cocaine in intravenous self-administration. The DATCre(+):Girk2fl/fl manipulation parallels the cocaine-induced suppression of GIRK-dependent signaling in VTA DA neurons, and suggests the GIRK channel in DA neurons temper behavioral sensitivity to cocaine. This hypothesis was further tested in a VTA-specific manner using a Cre-dependent viral approach, overexpressing GIRK channels with opposing functional roles. The overexpression of GIRK2 increased inhibitory G protein signaling and decreased cocaine-induced locomotion, while conversely, overexpression of GIRK3 decreased inhibitory G protein signaling and increased cocaine-induced locomotion. Overall, this supports the hypothesis GIRK channel activity in VTA DA neurons tempers behavioral sensitivity to drugs of abuse. In addition to addiction, VTA DA neurons have been implicated in negative affective behaviors, notably following stress. Interestingly, manipulating GIRK channel activity did not alter depression- and anxiety-related behavior, suggests that inhibitory signaling in VTA DA neurons mediated by GIRK channels plays a minimal role in negative affective behaviors, at least in non-stress conditions. However, footshock, a more severe form of stress, elicited adaptations in GIRK channel activity in VTA DA neurons, suggesting that GIRK channel activity could influence behavior following stress. Taken together, the work in this thesis suggests the GIRK channel present in VTA DA neurons contributes to the behavioral effects of cocaine, and could represent a promising therapeutic target for psychostimulant addiction.