Biology subjects

Lebowitz, J. J.

Publications and source records attributed to Lebowitz, J. J..

7 recordsLinked to original sources

bioRxiv2025

The synaptic vesicle priming protein Munc13 mediates evoked somatodendritic dopamine release

Midbrain dopamine neurons secrete dopamine from their somata and dendrites in addition to their axonal release. Shared and distinct properties have been proposed for somatodendritic and axonal release, but the mechanisms of somatodendritic release remain unclear. We here used mouse genetics, electrophysiology, and imaging to define roles of the synaptic vesicle priming protein Munc13 in somatodendritic release in comparison to axonal secretion. Munc13 ablation in dopamine neurons decreased evoked but not spontaneous somatodendritic dopamine transmission measured as D2 receptor-mediated currents. Imaging with a fluorescent dopamine sensor confirmed this finding and established comparable importance for Munc13 in somatodendritic and axonal secretion. Pharmacological experiments revealed that release from adrenergic terminals contributes to D2 receptor-mediated currents, and their relative contribution was enhanced after Munc13 knockout. Altogether, these data establish important roles for Munc13 in evoked somatodendritic release. These roles are similar to Munc13 functions in axonal dopamine release and at fast synapses. Spontaneous midbrain dopamine release does not necessitate Munc13 in dopamine neurons and may rely on a release pathway that is independent of the prototypical release machinery employed at synapses.

neuroscience↗

bioRxiv2024

Reductions of Grin2a in adolescent dopamine neurons confers aberrant salience and related psychosis phenotype

Psychosis is a hallmark of schizophrenia. It involves a collection of symptoms that are typically associated with disrupted dopamine signaling and emerges during adolescence or early adulthood. Most schizophrenia-associated genes, however, involve glutamatergic or other ubiquitous targets that do not explain the latent expression of psychosis or dopaminergic abnormalities. Here, we describe an etiologically relevant model for the adolescent onset of dopamine-related dysfunction in schizophrenia. We focused on GRIN2A, the gene encoding the GluN2A subunit of the NMDA receptor, as both the common loss-of-function variants and the rare missense variants in this gene are risk factors for schizophrenia. We find that GluN2A levels distinctly decline in dopamine neuron-containing regions throughout adolescence while remaining stable in other regions. This suggested that adolescent dopamine neurons may be particularly vulnerable to further reductions in GluN2A caused by a damaging variant of GRIN2A. Consistent with this idea, we find that selective knockout of Grin2a in adolescent rat dopamine neurons results in a psychosis-relevant behavioral phenotype. This manipulation also reduced dopamine release in response to unexpected outcomes in young adults, reflective of prediction error signaling abnormalities observed in the clinical population. These data provide mechanistic insight into how GRIN2A mutations may contribute to the delayed onset of dopamine-related symptoms and provide a model for identifying course altering treatments for schizophrenia.

neuroscience↗

bioRxiv2023

Dopamine D2 receptors in mossy cells reduce excitatory transmission and are essential for hippocampal function

Hilar mossy cells (MCs) are principal excitatory neurons of the dentate gyrus (DG) that play critical roles in hippocampal function and have been implicated in brain disorders such as anxiety and epilepsy. However, the mechanisms by which MCs contribute to DG function and disease are poorly understood. Expression from the dopamine D2 receptor (D2R) gene (Drd2) promoter is a defining feature of MCs, and previous work indicates a key role for dopaminergic signaling in the DG. Additionally, the involvement of D2R signaling in cognition and neuropsychiatric conditions is well-known. Surprisingly, though, the function of MC D2Rs remain largely unexplored. In this study, we show that selective and conditional removal of Drd2 from MCs of adult mice impaired spatial memory, promoted anxiety-like behavior and was proconvulsant. To determine the subcellular expression of D2Rs in MCs, we used a D2R knockin mouse which revealed that D2Rs are enriched in the inner molecular layer of the DG, where MCs establish synaptic contacts with granule cells. D2R activation by exogenous and endogenous dopamine reduced MC to dentate granule cells (GC) synaptic transmission, most likely by a presynaptic mechanism. In contrast, removing Drd2 from MCs had no significant impact on MC excitatory inputs and passive and active properties. Our findings support that MC D2Rs are essential for proper DG function by reducing MC excitatory drive onto GCs. Lastly, impairment of MC D2R signaling could promote anxiety and epilepsy, therefore highlighting a potential therapeutic target. SIGNIFICANCEGrowing evidence indicates that hilar mossy cells (MCs) of the dentate gyrus play critical but incompletely understood roles in memory and brain disorders, including anxiety and epilepsy. Dopamine D2 receptors (D2Rs), implicated in cognition and several psychiatric and neurological disorders, are considered to be characteristically expressed by MCs. Still, the subcellular localization and function of MC D2Rs are largely unknown. We report that removing the Drd2 gene specifically from MCs of adult mice impaired spatial memory and was anxiogenic and proconvulsant. We also found that D2Rs are enriched where MCs synaptically contact dentate granule cells (GC) and reduce MC-GC transmission. This work uncovered the functional significance of MC D2Rs, thus highlighting their therapeutic potential in D2R- and MC-associated pathologies.

neuroscience↗

bioRxiv2022

Gait Abnormalities and Aberrant D2 Receptor Expression and Signaling in a Mouse Model of the Human Pathogenic Mutation DRD2I212F

A dopamine D2 receptor mutation was recently identified in a family with a novel hyperkinetic movement disorder (Mov Disord 36: 729-739, 2021). That allelic variant D2-I212F is a constitutively active and G protein-biased receptor. We now describe mice engineered to carry the D2-I212F variant, Drd2I212F. The mice exhibited gait abnormalities resembling those in other mouse models of chorea and/or dystonia, and had decreased striatal D2 receptor expression. Electrically evoked IPSCs in midbrain dopamine neurons and striatum from Drd2I212F mice exhibited slow onset and decay compared to wild type mice. In the presence of dopamine, current decay initiated by photolytic release of sulpiride from CyHQ-sulpiride was slower in midbrain slices from Drd2I212F mice than Drd2+/+ mice. Furthermore, in contrast to wild type mice in which dopamine is more potent at neurons in the nucleus accumbens than in the dorsal striatum, reflecting activation of Go vs. Gi1, dopamine had similar potencies in those two brain regions of Drd2I212F mice. Repeated cocaine treatment, which decreases dopamine potency in the nucleus accumbens of wild type mice, had no effect on dopamine potency in Drd2I212F mice. The results demonstrate the utility of this mouse model for investigating the role of pathogenic DRD2 variants in early-onset hyperkinetic movement disorders.

neuroscience↗

bioRxiv2021

Synaptotagmin-7 enhances phasic dopamine release

Dopamine released from substantia nigra pars compacta (SNc) neurons modulates movement, motivation, and reward. In addition to their tonic firing pattern, dopamine neurons also fire high-frequency bursts that cause superlinear increases in dopamine release. To study this poorly understood form of short-term plasticity, we used the fluorescent dopamine sensor dLight1.3b to examine the role of the calcium-binding protein synaptotagmin-7 (SYT7). We report that SYT7 mediates a hidden component of facilitation, which was unmasked by lowering initial release probability, or by low-frequency stimulation of nerve terminals. In Syt7 KO neurons, there was profound synaptic depression that significantly reduced release during stimulations that mimic in vivo firing patterns of SNc neurons. D2-mediated inhibitory postsynaptic currents in the SNc revealed a similar role for SYT7 in somatodendritic release. Our results indicate that SYT7 drives short-term facilitation of release from dopamine neurons, which likely underlies frequency-dependence of dopamine signaling in vivo.

neuroscience↗

bioRxiv2021

Novel insights in the pathophysiology of α-synuclein dysregulation on D2 receptor activity contributing to the vulnerability of dopamine neurons

Pathophysiological damages and loss of function of dopamine neurons precedes their demise and contributes to the early phases of Parkinsons disease. The presence of aberrant intercellular pathological inclusions of the protein -synuclein within ventral midbrain dopaminergic neurons is one of the cardinal features of Parkinsons disease. We employed multiple complementary approaches in molecular biology, electrophysiology, and live-cell imaging to investigate how excessive -synuclein levels alters multiple characteristics of dopaminergic neuronal dynamics and dopamine transmission prior to neuronal demise. These studies demonstrate that -synuclein dysregulation of D2 receptor autoinhibition contributes to the vulnerability of dopaminergic neurons, and that modulation thereof can ameliorate the resulting pathophysiology. These novel findings provide mechanistic insights in the insidious loss of dopaminergic function and neurons that characterize Parkinsons disease progression with significant therapeutic implications.

neuroscience↗

bioRxiv2019

Mechanism of manganese dysregulation of dopamine neuronal activity

Manganese exposure produces Parkinsons-like neurological symptoms, suggesting a selective dysregulation of dopamine transmission. It is unknown, however, how manganese accumulates in dopaminergic brain regions or how it regulates the activity of dopamine neurons. Our in vivo studies suggest manganese accumulates in dopamine neurons of the ventral tegmental area and substantia nigra via nifedipine-sensitive Ca2+ channels. Manganese produces a Ca2+ channel-mediated current which increases neurotransmitter release and rhythmic firing activity of dopamine neurons. These increases are prevented by blockade of Ca2+ channels and depend on downstream recruitment of Ca2+-activated potassium channels to the plasma membrane. These findings demonstrate the mechanism of manganese-induced dysfunction of dopamine neurons, and reveal a potential therapeutic target to attenuate manganese-induced impairment of dopamine transmission.\n\nSignificance StatementManganese is a trace element critical to many physiological processes. Overexposure to manganese is an environmental risk factor for neurological disorders such as a Parkinsons disease-like syndrome known as manganism. We found manganese dose-dependently increased the excitability of dopamine neurons, decreased the amplitude of action potentials, and narrowed action potential width. Blockade of Ca2+ channels prevented these effects as well as manganese accumulation in the mouse midbrain in vivo. Our data provide a potential mechanism for manganese-regulation of dopaminergic neurons.

cell biology↗