David M. Lovinger

The brain flexibly reorganizes action sequences to optimize behavioral outcomes through reinforcement learning and adaptive motor control. Although the primary motor cortex (M1) is essential for skill learning and dexterous movement, how cortical microcircuits refine the timing and structure of action sequences remains unclear. We show that M1 somatostatin interneurons (SST-Ins) display synchronized, action-locked calcium activity during acquisition of a lever-press task in freely moving mice, in contrast to the sequential activation of pyramidal neurons. Following extended training under a stable task schedule, SST-IN activity was no longer coupled to action execution. However, when task demands were modified to require faster and more temporally constrained action sequences, SST-IN activity redistributed and correlated with trial-by-trial changes in sequences, rather than diminishing. Inhibition of SST-INs disrupted temporal organization and impaired efficient motor execution. These findings highlight the unexpected role of M1 SST-INs in refining motor programs into more efficient and task-specific structures.

Accurate pose estimation underpins quantitative analysis of behavior, yet many deep learning-based tracking tools remain optimized for offline workflows that rely on fragmented software pipelines, workstation-grade GPUs, or external middleware to enable real-time deployment. Here we present an integrated software-hardware ecosystem for pose estimation that spans dataset creation, model training, offline analysis, and real-time deployment on embedded edge-computing devices. SqueakPose Studio provides a software suite for whole-frame, deep learning-based pose estimation that unifies dataset creation, manual and model-assisted labeling, model training, validation, and large-scale offline inference. The system leverages modern object-detection architectures to enable efficient end-to-end training and inference without patch-based sampling or multi-stage postprocessing, and supports execution on CPUs, GPUs, and Apple Silicon. For experimental settings requiring continuous recording and synchronized data acquisition, SqueakView enables real-time model deployment, video capture, and sensor logging on embedded edge-computing hardware, while MouseHouse provides a compact, modular enclosure designed for home cage-based experiments that integrates embedded GPU compute, microcontroller-based timing, and peripheral I/O. A shared data format and deterministic timing architecture ensure consistency across offline analysis and real-time deployment. Together, SqueakPose Studio, SqueakView, and MouseHouse provide a unified platform for pose estimation that supports both conventional offline analysis and embedded, real-time experimentation, without reliance on workstation-grade hardware or external middleware.

Parkinson's disease (PD) is a progressive, neurodegenerative disease characterized by motor dysfunction and dopamine deficits. The MitoPark (MP) mouse model of PD recapitulates several facets of Parkinson's disease, including gradual development of motor deficits, which enables the study of potential therapeutic interventions. One therapeutic strategy involves decreasing the mitochondrial metabolic load by inducing ketosis and providing an alternative energy source for neurons, leading to decreased neuronal oxidative stress. Thus, we hypothesized that administration of a ketone ester–enriched diet (KEED) would improve motor and dopamine release deficits in MP mice. Motor function (rotarod and open field tests), dopamine release (fast‐scan cyclic voltammetry), tissue dopamine levels (gas chromatography–mass spectrometry) and dopamine neurons and axons (immunofluorescence) were assessed in MP, and control mice fed either the standard or a KEED. When started on the ketone diet before motor dysfunction onset, MP mice had improved motor function relative to standard diet (SD) MP mice. While the KEED did not preserve dopamine neurons or striatal dopamine axons, dopamine release in ketone diet MP mice was greater than SD MP mice but less than control mice. In a follow‐up experiment, we began the ketone diet after motor dysfunction onset and observed a modest preservation of motor function in ketone diet MP mice relative to SD MP mice. The improvement in motor dysfunction indicates that a KEED or ketone supplement may have a beneficial effect on delaying motor deficit progression in Parkinson's disease.

Functional deficits in basal ganglia (BG) circuits contribute to cognitive and motor dysfunctions in alcohol use disorder. Chronic alcohol exposure alters synaptic function and neuronal excitability in the dorsal striatum, but it remains unclear how it affects BG output that is mediated by the substantia nigra pars reticulata (SNr). Here, we describe a neuronal subpopulation-specific synaptic organization of striatal and subthalamic (STN) inputs to the medial and lateral SNr. Chronic alcohol exposure (CIE) potentiated dorsolateral striatum (DLS) inputs but did not change dorsomedial striatum and STN inputs to the SNr. Chemogenetic inhibition of DLS direct pathway neurons revealed an enhanced role for DLS direct pathway neurons in execution of an instrumental lever-pressing task. Overall, we reveal a subregion-specific organization of striatal and subthalamic inputs onto the medial and lateral SNr and find that potentiated DLS-SNr inputs are accompanied by altered BG control of action execution following CIE.

While cortico-striatal circuit deficits contribute to Alcohol Use Disorder, the impact of alcohol on synaptic function in the basal ganglia output, the substantia nigra pars reticulata (SNr), remains unclear. Here, we found that the inputs from the dorsomedial (DMS) and dorsolateral striatum (DLS) differ in their presynaptic properties and target molecularly distinct subpopulations of SNr neurons. We also discovered that indirect pathway subthalamic (STN) inputs to the medial and lateral SNr have different presynaptic properties and that STN inputs are stronger in the lateral SNr. Chronic alcohol exposure (CIE) potentiated DLS inputs but did not affect the strength and presynaptic release properties of DMS and subthalamic inputs to SNr neurons. Chemogenetic inhibition of DLS direct pathway projection neurons impaired action performance in an operant conditioning task in CIE mice but not control mice. Overall, our work identifies a synaptic mechanism whereby chronic alcohol induces a gain of function for action control in direct pathway neurons in the dorsolateral striatum. Teaser Chronic alcohol selectively potentiates DLS synaptic inputs to the SNr, enhancing their role in action control.

The development of genetically encoded dopamine sensors such as dLight has provided a new approach to measuring slow and fast dopamine dynamics both in brain slices and in vivo, possibly enabling dopamine measurements in areas like the dorsolateral striatum (DLS) where previously such recordings with fast-scan cyclic voltammetry (FSCV) were difficult. To test this, we first evaluated dLight photometry in mouse brain slices with simultaneous FSCV and found that both techniques yielded comparable results, but notable differences in responses to dopamine transporter inhibitors, including cocaine. We then used in vivo fiber photometry with dLight in mice to examine responses to cocaine in DLS. We also compared dopamine responses during Pavlovian conditioning across the striatum. We show that dopamine increases were readily detectable in DLS and describe transient dopamine kinetics, as well as slowly developing signals during conditioning. Overall, our findings indicate that dLight photometry is well suited to measuring dopamine dynamics in DLS.

Learning action sequences is necessary for normal daily activities. Medium spiny neurons (MSNs) in the dorsal striatum (dStr) encode action sequences through changes in firing at the start and/or stop of action sequences or sustained changes in firing throughout the sequence. Acetylcholine (ACh), released from cholinergic interneurons (ChIs), regulates striatal function by modulating MSN and interneuron excitability, dopamine and glutamate release, and synaptic plasticity. Cholinergic neurons in dStr pause their tonic firing during the performance of learned action sequences. Activation of dopamine type-2 receptors (D2Rs) on ChIs is one mechanism of ChI pausing. In this study we show that deleting D2Rs from ChIs by crossing D2-floxed with ChAT-Cre mice (D2Flox-ChATCre), which inhibits dopamine-mediated ChI pausing and leads to deficits in an operant action sequence task and lower breakpoints in a progressive ratio task. These data suggest that D2Flox-ChATCre mice have reduced motivation to work for sucrose reward, but show no generalized motor skill deficits. D2Flox-ChATCre mice perform similarly to controls in a simple reversal learning task, indicating normal behavioral flexibility, a cognitive function associated with ChIs. In vivo electrophysiological recordings show that D2Flox-ChatCre mice have deficits in sequence encoding, with fewer dStr MSNs encoding entire action sequences compared to controls. Thus, ChI D2R deletion appears to impair a neural substrate of action chunking. Virally replacing D2Rs in dStr ChIs in adult mice improves action sequence learning, but not the lower breakpoints, further suggesting that D2Rs on ChIs in the dStr are critical for sequence learning, but not for driving the motivational aspects of the task. Significance statement: The role of striatal projection neurons in encoding action sequences has been extensively studied, and cholinergic interneurons play a central role in striatal physiology, but we do not yet understand how cholinergic interneurons contribute to action sequencing. Using a combination of mouse genetics, behavior, and in vivo electrophysiology this work shows that genetic deletion of D2 receptors from striatal cholinergic interneurons disrupts the learning, performance, and encoding of action sequences, without changing general locomotion or motor skill learning. Virally replacing D2 receptors specifically in dorsal striatal cholinergic interneurons is sufficient to rescue the sequence behavior. Our observations may be useful in understanding and treating movement disorders in which dopamine and acetylcholine are imbalanced.

Ethanol (EtOH) has effects on numerous cellular molecular targets, and alterations in synaptic function are prominent among these effects. Acute exposure to EtOH activates or inhibits the function of proteins involved in synaptic transmission, while chronic exposure often produces opposing and/or compensatory/homeostatic effects on the expression, localization, and function of these proteins. Interactions between different neurotransmitters (e.g., neuropeptide effects on release of small molecule transmitters) can also influence both acute and chronic EtOH actions. Studies in intact animals indicate that the proteins affected by EtOH also play roles in the neural actions of the drug, including acute intoxication, tolerance, dependence, and the seeking and drinking of EtOH. The present chapter is an update of our previous Lovinger and Roberto (Curr Top Behav Neurosci 13:31–86, 2013) chapter and reviews the literature describing these acute and chronic synaptic effects of EtOH with a focus on adult animals and their relevance for synaptic transmission, plasticity, and behavior.