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1.
Nat Neurosci ; 26(10): 1762-1774, 2023 10.
Article in English | MEDLINE | ID: mdl-37537242

ABSTRACT

Dopamine neurons are characterized by their response to unexpected rewards, but they also fire during movement and aversive stimuli. Dopamine neuron diversity has been observed based on molecular expression profiles; however, whether different functions map onto such genetic subtypes remains unclear. In this study, we established that three genetic dopamine neuron subtypes within the substantia nigra pars compacta, characterized by the expression of Slc17a6 (Vglut2), Calb1 and Anxa1, each have a unique set of responses to rewards, aversive stimuli and accelerations and decelerations, and these signaling patterns are highly correlated between somas and axons within subtypes. Remarkably, reward responses were almost entirely absent in the Anxa1+ subtype, which instead displayed acceleration-correlated signaling. Our findings establish a connection between functional and genetic dopamine neuron subtypes and demonstrate that molecular expression patterns can serve as a common framework to dissect dopaminergic functions.


Subject(s)
Dopaminergic Neurons , Substantia Nigra , Dopaminergic Neurons/physiology , Substantia Nigra/physiology , Signal Transduction , Axons
2.
Neurobiol Dis ; 175: 105925, 2022 12.
Article in English | MEDLINE | ID: mdl-36372290

ABSTRACT

As the ability to capture single-cell expression profiles has grown in recent years, neuroscientists studying a wide gamut of brain regions have discovered remarkable heterogeneity within seemingly related populations (Saunders et al., 2018a; Zeisel et al., 2015). These "molecular subtypes" have been demonstrated even within brain nuclei expressing the same neurotransmitter (Saunders et al., 2018a; Poulin et al., 2020; Ren et al., 2019; Okaty et al., 2020). Recently, dopamine (DA) neurons of the substantia nigra pars compacta (SNc) and adjacent ventral tegmental area (VTA) have been revealed to be diverse not only when comparing between these two dopaminergic nuclei, but within them, and with the distribution of identified subtypes often agnostic to traditional neuroanatomical boundaries (Saunders et al., 2018a; Hook et al., 2018; Kramer et al., 2018; La Manno et al., 2016; Poulin et al., 2014; Tiklova et al., 2019; Poulin et al., 2018). Such molecularly defined subpopulations have been the subject of several recent studies. Investigations of these subtypes have ultimately unveiled many distinctive properties across several domains, such as their axonal projections and functional properties (Poulin et al., 2018; Wu et al., 2019; Pereira Luppi et al., 2021; Evans et al., 2017; Evans et al., 2020). These key differences between subtypes have begun to corroborate the biological relevance of DA neuron taxonomic schemes. We hypothesize that these putative molecular subtypes, with their distinctive circuits, could shed light on the wide variety of dopamine-related symptoms observed across several diseases including depression, chronic pain, addiction, and Parkinson's Disease. While it is difficult to reconcile how a single neurotransmitter can be involved in so many seemingly unrelated phenotypes, one solution could be the existence of several individual dopaminergic pathways serving different functions, with molecular subtypes serving as distinct nodes for these pathways. Indeed, this conceptual framework is already the dogma for anatomically distinct DA pathways, including the mesocortical, mesolimbic and mesostriatal pathways (Bjorklund & Dunnett, 2007). Here, we discuss our existing knowledge of DA neuron subtypes and attempt to provide a roadmap for how their distinctive properties can provide novel insights into the motor symptoms of Parkinson's disease (PD) (Fig. 1A). By exploring the differences between molecular subtypes and correlating this to their relative degeneration within the SNc, we may gain a deeper understanding of the cell-intrinsic mechanisms underlying why some DA neurons degenerate more than others in PD. Similarly, by mapping the inputs, projections, and functions of individual subtypes, we may better understand their individual roles in the circuit-level dysfunction of dopaminergic diseases.


Subject(s)
Dopamine , Parkinson Disease , Humans , Dopamine/metabolism , Parkinson Disease/metabolism , Substantia Nigra/metabolism , Ventral Tegmental Area/metabolism , Dopaminergic Neurons/metabolism , Neurotransmitter Agents/metabolism
3.
Cell Rep ; 37(6): 109975, 2021 11 09.
Article in English | MEDLINE | ID: mdl-34758317

ABSTRACT

Dopamine (DA) neurons in the ventral tier of the substantia nigra pars compacta (SNc) degenerate prominently in Parkinson's disease, while those in the dorsal tier are relatively spared. Defining the molecular, functional, and developmental characteristics of each SNc tier is crucial to understand their distinct susceptibility. We demonstrate that Sox6 expression distinguishes ventrally and dorsally biased DA neuron populations in the SNc. The Sox6+ population in the ventral SNc includes an Aldh1a1+ subset and is enriched in gene pathways that underpin vulnerability. Sox6+ neurons project to the dorsal striatum and show activity correlated with acceleration. Sox6- neurons project to the medial, ventral, and caudal striatum and respond to rewards. Moreover, we show that this adult division is encoded early in development. Overall, our work demonstrates a dual origin of the SNc that results in DA neuron cohorts with distinct molecular profiles, projections, and functions.


Subject(s)
Corpus Striatum/pathology , Dopaminergic Neurons/pathology , Gene Expression Regulation, Developmental , Parkinson Disease/pathology , SOXD Transcription Factors/metabolism , SOXD Transcription Factors/physiology , Substantia Nigra/pathology , Aged , Aged, 80 and over , Animals , Case-Control Studies , Corpus Striatum/metabolism , Dopamine/metabolism , Dopaminergic Neurons/metabolism , Female , Humans , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Middle Aged , Parkinson Disease/genetics , Parkinson Disease/metabolism , SOXD Transcription Factors/genetics , Substantia Nigra/metabolism , Ventral Tegmental Area/metabolism , Ventral Tegmental Area/pathology
4.
J Vis Exp ; (162)2020 08 31.
Article in English | MEDLINE | ID: mdl-32925891

ABSTRACT

Neurofilament protein polymers move along axons in the slow component of axonal transport at average speeds of ~0.35-3.5 mm/day. Until recently the study of this movement in situ was only possible using radioisotopic pulse-labeling, which permits analysis of axonal transport in whole nerves with a temporal resolution of days and a spatial resolution of millimeters. To study neurofilament transport in situ with higher temporal and spatial resolution, we developed a hThy1-paGFP-NFM transgenic mouse that expresses neurofilament protein M tagged with photoactivatable GFP in neurons. Here we describe fluorescence photoactivation pulse-escape and pulse-spread methods to analyze neurofilament transport in single myelinated axons of tibial nerves from these mice ex vivo. Isolated nerve segments are maintained on the microscope stage by perfusion with oxygenated saline and imaged by spinning disk confocal fluorescence microscopy. Violet light is used to activate the fluorescence in a short axonal window. The fluorescence in the activated and flanking regions is analyzed over time, permitting the study of neurofilament transport with temporal and spatial resolution on the order of minutes and microns, respectively. Mathematical modeling can be used to extract kinetic parameters of neurofilament transport including the velocity, directional bias and pausing behavior from the resulting data. The pulse-escape and pulse-spread methods can also be adapted to visualize neurofilament transport in other nerves. With the development of additional transgenic mice, these methods could also be used to image and analyze the axonal transport of other cytoskeletal and cytosolic proteins in axons.


Subject(s)
Axonal Transport/physiology , Intermediate Filaments/metabolism , Models, Theoretical , Molecular Imaging/methods , Neurofilament Proteins/metabolism , Neurons/physiology , Tibial Nerve/metabolism , Animals , Cells, Cultured , Humans , Male , Mice , Mice, Transgenic , Microscopy, Confocal/methods , Microscopy, Fluorescence/methods
5.
Elife ; 82019 03 28.
Article in English | MEDLINE | ID: mdl-30920369

ABSTRACT

Interplay between dopaminergic and cholinergic neuromodulation in the striatum is crucial for movement control, with prominent models proposing pro-kinetic and anti-kinetic effects of dopamine and acetylcholine release, respectively. However, the natural, movement-related signals of striatum cholinergic neurons and their relationship to simultaneous variations in dopamine signaling are unknown. Here, functional optical recordings in mice were used to establish rapid cholinergic signals in dorsal striatum during spontaneous movements. Bursts across the cholinergic population occurred at transitions between movement states and were marked by widespread network synchronization which diminished during sustained locomotion. Simultaneous cholinergic and dopaminergic recordings revealed distinct but coordinated sub-second signals, suggesting a new model where cholinergic population synchrony signals rapid changes in movement states while dopamine signals the drive to enact or sustain those states.


Subject(s)
Cholinergic Neurons/physiology , Corpus Striatum/physiology , Dopaminergic Neurons/physiology , Movement , Nerve Net/physiology , Action Potentials , Animals , Mice , Models, Neurological
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