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Dopamine is widely observed to signal anticipation of future rewards and thus thought to be a key contributor to affectively charged decision making. However, the experiments supporting this view have not dissociated rewards from the actions that lead to, or are occasioned by, them. Here, we manipulated dopamine pharmacologically and examined the effect on a task that explicitly dissociates action and reward value. We show that dopamine enhanced the neural representation of rewarding actions, without significantly affecting the representation of reward value as such. Thus, increasing dopamine levels with levodopa selectively boosted striatal and substantia nigra/ventral tegmental representations associated with actions leading to reward, but not with actions leading to the avoidance of punishment. These findings highlight a key role for dopamine in the generation of appetitively motivated actions.

Innovative technology allows for personalization of stimulation frequency in dual-site deep brain stimulation (DBS), offering promise for challenging symptoms in advanced Parkinson’s disease (PD), particularly freezing of gait (FoG). Early results suggest that combining standard subthalamic nucleus (STN) stimulation with substantia nigra pars reticulata (SNr) stimulation may improve FoG outcomes. However, patient response and the optimal SNr stimulation frequency vary. Our randomized controlled trial studied patients with advanced PD and persistent FoG, while recording gait kinematics through wearable inertial sensors, along with clinical assessments and patient-reported outcomes. In a with-subjects design, we compared a no-stimulation control with four stimulation conditions: Mono-site STN stimulation at 119 Hz and three dual-site protocols (STN + SNr) with SNr stimulation at 119 Hz, 71 Hz, or 30 Hz, keeping total electrical energy delivered (TEED) constant between SNr conditions. Significant interindividual variability was observed for the optimal stimulation protocol, with comparable proportions favoring STN, STN + SNr119, and STN + SNr71. Changes in spatial and temporal gait parameters, such as stride length and swing time, correlated significantly with FoG clinical improvements, with high correlation coefficients (> 0.8). Optimized stimulation parameters also led to improvements in patient-reported outcomes, highlighting the potential of digital biomarkers in tailoring DBS protocols for individualized outcomes.

Here, we present an approach for identifying brainstem dopaminergic pathways using resting state functional MRI. In a group of healthy individuals, we searched for significant functional connectivity between dopamine-rich midbrain areas (substantia nigra; ventral tegmental area) and a striatal region (caudate) that was modulated by both a pharmacological challenge (the administration of the dopaminergic agonist bromocriptine) and a dopamine-sensitive cognitive trait (an individual's working memory capacity). A significant inverted-U shaped connectivity pattern was found in a subset of midbrain-striatal connections, demonstrating that resting state fMRI data is sufficiently powerful to identify brainstem neuromodulatory brain networks.

Parkinson’s disease is characterized by loss of dopamine neurons in the substantia nigra 1 . Similar to other major neurodegenerative disorders, there are no disease-modifying treatments for Parkinson’s disease. While most treatment strategies aim to prevent neuronal loss or protect vulnerable neuronal circuits, a potential alternative is to replace lost neurons to reconstruct disrupted circuits 2 . Here we report an efficient one-step conversion of isolated mouse and human astrocytes to functional neurons by depleting the RNA-binding protein PTB (also known as PTBP1). Applying this approach to the mouse brain, we demonstrate progressive conversion of astrocytes to new neurons that innervate into and repopulate endogenous neural circuits. Astrocytes from different brain regions are converted to different neuronal subtypes. Using a chemically induced model of Parkinson’s disease in mouse, we show conversion of midbrain astrocytes to dopaminergic neurons, which provide axons to reconstruct the nigrostriatal circuit. Notably, re-innervation of striatum is accompanied by restoration of dopamine levels and rescue of motor deficits. A similar reversal of disease phenotype is also accomplished by converting astrocytes to neurons using antisense oligonucleotides to transiently suppress PTB. These findings identify a potentially powerful and clinically feasible approach to treating neurodegeneration by replacing lost neurons. Depletion of the RNA-binding protein PTB (also known as PTBP1) in astrocytes reprograms these cells to become functional neurons and, in a mouse model of Parkinson’s disease, reverses the disease phenotype.

Midbrain dopamine (DA) neurons have diverse functions that can in part be explained by their heterogeneity. Although molecularly distinct subtypes of DA neurons have been identified by single-cell gene expression profiling, fundamental features such as their projection patterns have not been elucidated. Progress in this regard has been hindered by the lack of genetic tools for studying DA neuron subtypes. Here we develop intersectional genetic labeling strategies, based on combinatorial gene expression, to map the projections of molecularly defined DA neuron subtypes. We reveal distinct genetically defined dopaminergic pathways arising from the substantia nigra pars compacta and from the ventral tegmental area that innervate specific regions of the caudate putamen, nucleus accumbens and amygdala. Together, the genetic toolbox and DA neuron subtype projections presented here constitute a resource that will accelerate the investigation of this clinically significant neurotransmitter system.

The activity of dopamine neurons in the substantia nigra pars compacta before movement initiation affects the probability and vigour of future movements. How dopamine neurons forge future movements Loss of dopamine neurons in a specific area of the brain, the substantia nigra pars compacta (SNc), causes failure to initiate and slowness of movement in patients with Parkinson's disease. Rui Costa and colleagues explore the role of these neurons in movement and reward. In mice, SNc dopamine neurons are transiently active before a self-initiated movement. The neurons affect movement initiation, but they are not selective for specific actions. Manipulation of dopamine neuron activity alters the probability of future movement initiation and the speed of movement, but does not affect ongoing movements. These findings suggest that dopamine signals serve as a general signal for gating and invigorating self-paced movements. Deciding when and whether to move is critical for survival. Loss of dopamine neurons (DANs) of the substantia nigra pars compacta (SNc) in patients with Parkinson’s disease causes deficits in movement initiation and slowness of movement 1 . The role of DANs in self-paced movement has mostly been attributed to their tonic activity, whereas phasic changes in DAN activity have been linked to reward prediction 2 , 3 . This model has recently been challenged by studies showing transient changes in DAN activity before or during self-paced movement initiation 4 , 5 , 6 , 7 . Nevertheless, the necessity of this activity for spontaneous movement initiation has not been demonstrated, nor has its relation to initiation versus ongoing movement been described. Here we show that a large proportion of SNc DANs, which did not overlap with reward-responsive DANs, transiently increased their activity before self-paced movement initiation in mice. This activity was not action-specific, and was related to the vigour of future movements. Inhibition of DANs when mice were immobile reduced the probability and vigour of future movements. Conversely, brief activation of DANs when mice were immobile increased the probability and vigour of future movements. Manipulations of dopamine activity after movement initiation did not affect ongoing movements. Similar findings were observed for the initiation and execution of learned action sequences. These findings causally implicate DAN activity before movement initiation in the probability and vigour of future movements.

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. The authors establish a connection between functional subtypes and genetic subtypes of dopamine neurons in mice and demonstrate that molecular expression patterns can serve as a common framework to dissect dopaminergic functions.

The authors trained mice to perform rapid action sequences while recording from neurons in the direct and indirect basal ganglia pathways. In addition to neurons whose activity reflected the start or stop of a sequence, they identified neurons that displayed sustained activity or inhibition throughout an entire action sequence. Chunking allows the brain to efficiently organize memories and actions. Although basal ganglia circuits have been implicated in action chunking, little is known about how individual elements are concatenated into a behavioral sequence at the neural level. Using a task in which mice learned rapid action sequences, we uncovered neuronal activity encoding entire sequences as single actions in basal ganglia circuits. In addition to neurons with activity related to the start/stop activity signaling sequence parsing, we found neurons displaying inhibited or sustained activity throughout the execution of an entire sequence. This sustained activity covaried with the rate of execution of individual sequence elements, consistent with motor concatenation. Direct and indirect pathways of basal ganglia were concomitantly active during sequence initiation, but behaved differently during sequence performance, revealing a more complex functional organization of these circuits than previously postulated. These results have important implications for understanding the functional organization of basal ganglia during the learning and execution of action sequences.

Environmental cues, through Pavlovian learning, become conditioned stimuli that guide animals toward the acquisition of rewards (for example, food) that are necessary for survival. We tested the fundamental role of midbrain dopamine neurons in conferring predictive and motivational properties to cues, independent of external rewards. We found that brief phasic optogenetic excitation of dopamine neurons, when presented in temporal association with discrete sensory cues, was sufficient to instantiate those cues as conditioned stimuli that subsequently both evoked dopamine neuron activity on their own and elicited cue-locked conditioned behavior. Notably, we identified highly parcellated functions for dopamine neuron subpopulations projecting to different regions of striatum, revealing dissociable dopamine systems for the generation of incentive value and conditioned movement invigoration. Our results indicate that dopamine neurons orchestrate Pavlovian conditioning via functionally heterogeneous, circuit-specific motivational signals to create, gate, and shape cue-controlled behaviors.

Midbrain dopaminergic neurons are essential for appropriate voluntary movement, as epitomized by the cardinal motor impairments arising in Parkinson’s disease. Understanding the basis of such motor control requires understanding how the firing of different types of dopaminergic neuron relates to movement and how this activity is deciphered in target structures such as the striatum. By recording and labeling individual neurons in behaving mice, we show that the representation of brief spontaneous movements in the firing of identified midbrain dopaminergic neurons is cell-type selective. Most dopaminergic neurons in the substantia nigra pars compacta (SNc), but not in ventral tegmental area or substantia nigra pars lateralis, consistently represented the onset of spontaneous movements with a pause in their firing. Computational modeling revealed that the movement-related firing of these dopaminergic neurons can manifest as rapid and robust fluctuations in striatal dopamine concentration and receptor activity. The exact nature of the movement-related signaling in the striatum depended on the type of dopaminergic neuron providing inputs, the striatal region innervated, and the type of dopamine receptor expressed by striatal neurons. Importantly, in aged mice harboring a genetic burden relevant for human Parkinson’s disease, the precise movement-related firing of SNc dopaminergic neurons and the resultant striatal dopamine signaling were lost. These data show that distinct dopaminergic cell types differentially encode spontaneous movement and elucidate howdysregulation of their firing in early Parkinsonism can impair their effector circuits.