Motor-skill learning in a novel running-wheel task is dependent on D1 dopamine receptors in the striatum

Voluntary Running Improves Behavioral and Structural Abnormalities in a Mouse Model of CDKL5 Deficiency Disorder

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a rare neurodevelopmental disease caused by mutations in the X-linked CDKL5 gene. CDD is characterized by a broad spectrum of clinical manifestations, including early-onset refractory epileptic seizures, intellectual disability, hypotonia, visual disturbances, and autism-like features. The Cdkl5 knockout (KO) mouse recapitulates several features of CDD, including autistic-like behavior, impaired learning and memory, and motor stereotypies. These behavioral alterations are accompanied by diminished neuronal maturation and survival, reduced dendritic branching and spine maturation, and marked microglia activation. There is currently no cure or effective treatment to ameliorate the symptoms of the disease. Aerobic exercise is known to exert multiple beneficial effects in the brain, not only by increasing neurogenesis, but also by improving motor and cognitive tasks. To date, no studies have analyzed the effect of physical exercise on the phenotype of a CDD mouse model. In view of the positive effects of voluntary running on the brain of mouse models of various human neurodevelopmental disorders, we sought to determine whether voluntary daily running, sustained over a month, could improve brain development and behavioral defects in Cdkl5 KO mice. Our study showed that long-term voluntary running improved the hyperlocomotion and impulsivity behaviors and memory performance of Cdkl5 KO mice. This is correlated with increased hippocampal neurogenesis, neuronal survival, spine maturation, and inhibition of microglia activation. These behavioral and structural improvements were associated with increased BDNF levels. Given the positive effects of BDNF on brain development and function, the present findings support the positive benefits of exercise as an adjuvant therapy for CDD.

Early Changes in Striatal Activity and Motor Kinematics in a Huntington's Disease Mouse Model

BACKGROUND

Huntington's disease is a progressive neurodegenerative disorder with no disease-modifying treatments. Patients experience motor, cognitive, and psychiatric disturbances, and the dorsal striatum is the main target of neurodegeneration. Mouse models of Huntington's disease show altered striatal synaptic signaling in vitro, but how these changes relate to behavioral deficits in vivo is unclear.

OBJECTIVES

We aimed to investigate how striatal activity correlates with behavior in vivo during motor learning and spontaneous behavior in a Huntington's disease mouse model at two disease stages.

METHODS

We used fiber photometry to record jGCaMP7f fluorescence, a read-out of neuronal activity, in the dorsal striatum of YAC128 (yeast artificial chromosome-128CAG) mice during accelerating rotarod and open-field behavior.

RESULTS

Mice showed increased striatal activity on the rotarod, which diminished by late stages of learning, leading to an inverse correlation between latency to fall and striatal activity. The 2- to 3-month-old YAC128 mice did not show a deficit in latency to fall, but displayed significant differences in paw kinematics, including increased paw slip frequency and variability in paw height. These mice exhibited a weaker correlation between latency to fall and striatal activity and aberrant striatal activity during paw slips. At 6 to 7 months, the YAC128 mice showed significantly reduced latency to fall, impaired paw kinematics, and increased striatal activity while on the rotarod. In the open field, the YAC128 mice showed elevated neuronal activity at rest.

CONCLUSIONS

We uncovered impaired motor coordination at a stage thought to be premotor manifest in YAC128 mice and aberrant striatal activity during the accelerating rotarod and open-field exploration. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Dopaminergic Modulation of Forced Running Performance in Adolescent Rats: Role of Striatal D1 and Extra-striatal D2 Dopamine Receptors

Improving exercise capacity during adolescence impacts positively on cognitive and motor functions. However, the neural mechanisms contributing to enhance physical performance during this sensitive period remain poorly understood. Such knowledge could help to optimize exercise programs and promote a healthy physical and cognitive development in youth athletes. The central dopamine system is of great interest because of its role in regulating motor behavior through the activation of D1 and D2 receptors. Thus, the aim of the present study is to determine whether D1 or D2 receptor signaling contributes to modulate the exercise capacity during adolescence and if this modulation takes place through the striatum. To test this, we used a rodent model of forced running wheel that we implemented recently to assess the exercise capacity. Briefly, rats were exposed to an 8-day period of habituation in the running wheel before assessing their locomotor performance in response to an incremental exercise test, in which the speed was gradually increased until exhaustion. We found that systemic administration of D1-like (SCH23390) and/or D2-like (raclopride) receptor antagonists prior to the incremental test reduced the duration of forced running in a dose-dependent manner. Similarly, locomotor activity in the open field was decreased by the dopamine antagonists. Interestingly, this was not the case following intrastriatal infusion of an effective dose of SCH23390, which decreased motor performance during the incremental test without disrupting the behavioral response in the open field. Surprisingly, intrastriatal delivery of raclopride failed to impact the duration of forced running. Altogether, these results indicate that the level of locomotor response to incremental loads of forced running in adolescent rats is dopamine dependent and mechanistically linked to the activation of striatal D1 and extra-striatal D2 receptors.

Neurotransmitters, Cell Types, and Circuit Mechanisms of Motor Skill Learning and Clinical Applications

Animals acquire motor skills to better survive and adapt to a changing environment. The ability to learn novel motor actions without disturbing learned ones is essential to maintaining a broad motor repertoire. During motor learning, the brain makes a series of adjustments to build novel sensory–motor relationships that are stored within specific circuits for long-term retention. The neural mechanism of learning novel motor actions and transforming them into long-term memory still remains unclear. Here we review the latest findings with regard to the contributions of various brain subregions, cell types, and neurotransmitters to motor learning. Aiming to seek therapeutic strategies to restore the motor memory in relative neurodegenerative disorders, we also briefly describe the common experimental tests and manipulations for motor memory in rodents.

Functional Dissection of Basal Ganglia Inhibitory Inputs onto Substantia Nigra Dopaminergic Neurons

Substantia nigra (SNc) dopaminergic neurons respond to aversive stimuli with inhibitory pauses in firing followed by transient rebound activation. We tested integration of inhibitory synaptic inputs onto SNc neurons from genetically defined populations in dorsal striatum (striosome and matrix) and external globus pallidus (GPe; parvalbumin- and Lhx6-positive), and examined their contribution to pause-rebound firing. Activation of striosome projections, which target "dendron bouquets" in the pars reticulata (SNr), consistently quiets firing and relief from striosome inhibition triggers rebound activity. Striosomal inhibitory postsynaptic currents (IPSCs) display a prominent GABA-B receptor-mediated component that strengthens the impact of SNr dendrite synapses on somatic excitability and enables rebounding. By contrast, GPe projections activate GABA-A receptors on the soma and proximal dendrites but do not result in rebounding. Lastly, optical mapping shows that dorsal striatum selectively inhibits the ventral population of SNc neurons, which are intrinsically capable of rebounding. Therefore, we define a distinct striatonigral circuit for generating dopamine rebound.

Dopamine D1 receptor signalling in dyskinetic Parkinsonian rats revealed by fiber photometry using FRET-based biosensors

As with many G protein-coupled receptors (GPCRs), the signalling pathways regulated by the dopamine D1 receptor (D1R) are dynamic, cell type-specific, and can change in the face of disease or drug exposures. In striatal neurons, the D1R activates cAMP/protein kinase A (PKA) signalling. However, in Parkinson's disease (PD), alterations in this pathway lead to functional upregulation of extracellular regulated kinases 1/2 (ERK1/2), contributing to L-DOPA-induced dyskinesia (LID). In order to detect D1R activation in vivo and to study the progressive dysregulation of D1R signalling in PD and LID, we developed ratiometric fiber-photometry with Förster resonance energy transfer (FRET) biosensors and optically detected PKA and ERK1/2 signalling in freely moving rats. We show that in Parkinsonian animals, D1R signalling through PKA and ERK1/2 is sensitized, but that following chronic treatment with L-DOPA, these pathways become partially desensitized while concurrently D1R activation leads to greater induction of dyskinesia.

Dopamine D1 and muscarinic acetylcholine receptors in dorsal striatum are required for high speed running

Dopamine (DA) signaling in the basal ganglia plays important roles in motor control. Motor deficiencies were previously reported in dopamine receptor D1 (D1R) and D2 (D2R) knockout mice. While these results indicate the involvement of DA receptors in motor execution, the null knockout (KO) mouse lacks the specificity necessary to determine when and where in the brain D1R and D2R function in motor execution. To address these questions, we restricted the loss of function temporally and spatially by using D1R conditional knockdown (cKD) mice and mice injected with antagonists against DA receptors directly into the dorsal striatum. In addition, we address the DA and acetylcholine (ACh) balance hypothesis by using antagonists against ACh receptors. We tested the motor ability of the mice with a newly devised task named the accelerating step-wheel. In this task, the maximum running speed was measured in a situation where the wheel rotation speed was gradually accelerated in one trial. We found significant decreases in the maximum running speed of D1R cKD mice and the mice injected with the antagonist against D1R or muscarinic ACh receptor. These results indicated that D1R and muscarinic ACh receptor in the dorsal striatum play pivotal roles in the execution of walking/running.

Wheel Running Improves Motor Function and Spinal Cord Plasticity in Mice With Genetic Absence of the Corticospinal Tract

Our previous studies showed that mutant mice with congenital absence of the corticospinal tract (CST) undergo spontaneous remodeling of motor networks to partially compensate for absent CST function. Here, we asked whether voluntary wheel running could further improve locomotor plasticity in CST-deficient mice. Adult mutant mice were randomly allocated to a “runners” group with free access to a wheel, or a “non-runners” group with no access to a wheel. In comparison with non-runners, there was a significant motor improvement including fine movement, grip strength, decreased footslip errors in runners after 8-week training, which was supported by the elevated amplitude of electromyography recording and increased neuromuscular junctions in the biceps. In runners, terminal ramifications of monoaminergic and rubrospinal descending axons were significantly increased in spinal segments after 12 weeks of exercise compared to non-runners. 5-ethynyl-2′-deoxyuridine (EDU) labeling showed that proliferating cells, 90% of which were Olig2-positive oligodendrocyte progenitors, were 4.8-fold more abundant in runners than in non-runners. In 8-week runners, RNAseq analysis of spinal samples identified 404 genes up-regulated and 398 genes down-regulated, and 69 differently expressed genes involved in signal transduction, among which the NF-κB, PI3K-Akt and cyclic AMP (cAMP) signaling were three top pathways. Twelve-week training induced a significant elevation of postsynaptic density protein 95 (PSD95), synaptophysin 38 and myelin basic protein (MBP), but not of brain derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) and insulin like growth factor-1 (IGF-1). Thus, locomotor training activates multiple signaling pathways, contributes to neural plasticity and functional improvement, and might palliate locomotor deficits in patients.

Proteomic Profile of Carbonylated Proteins Screen Regulation of Apoptosis via CaMK Signaling in Response to Regular Aerobic Exercise

To research carbonylated proteins and screen molecular targets in the rat striatum on regular aerobic exercise, male Sprague-Dawley rats (13 months old, n = 24) were randomly divided into middle-aged sedentary control (M-SED) and aerobic exercise (M-EX) groups (n = 12 each). Maximum oxygen consumption (VO_2max) gradually increased from 50%-55% to 65%-70% for a total of 10 weeks. A total of 36 carbonylated proteins with modified oxidative sites were identified by Electrospray Ionization-Quadrupole-Time of Flight-Mass Spectrometer (ESI-Q-TOF-MS), including 17 carbonylated proteins unique to the M-SED group, calcium/calmodulin-dependent protein kinase type II subunit beta (CaMKIIβ), and heterogeneous nuclear ribonucleoprotein A2/B1 (Hnrnpa2b1), among others, and 19 specific to the M-EX group, ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCH-L1), and malic enzyme, among others. Regular aerobic exercise improved behavioral and stereological indicators, promoted normal apoptosis (P < 0.01), alleviated carbonylation of the CaMKIIβ and Hnrnpa2b1, but induced carbonylation of the UCH-L1, and significantly upregulated the expression levels of CaMKIIβ, CaMKIIα, and Vdac1 (p < 0.01) and Hnrnpa2b1 and UCH-L1 (p < 0.01), as well as the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin pathways (PI3K/Akt/mTOR) pathway-related genes Akt and mTOR. Regular aerobic exercise for 10 weeks (incremental for the first 6 weeks followed by constant loading for 4 weeks) enhanced carbonylation of CaMKIIβ, Hnrnpa2b1, and modulated apoptosis via activation of CaMK and phosphoinositide 3-kinase/protein kinase B/mTOR signaling. It also promoted normal apoptosis in the rat striatum, which may have protective effects in neurons.

Effects of the experimental administration of oral estrogen on prefrontal functions in healthy young women

17-Beta-estradiol (E2) stimulates neural plasticity and dopaminergic transmission in the prefrontal cortex, which is critically involved in attentional control, working memory, and other executive functions. Studies investigating E2's actions on prefrontally mediated behavior in the course of the menstrual cycle or during hormone replacement therapy are inconclusive, with numerous null findings as well as beneficial and detrimental effects. The current study focused on the effect of E2 on attentional performance, as animal studies indicate that supraphysiological doses (i.e., above estrous cycle levels) of E2 have beneficial effects on measures of attention in female rodents. To translate these findings to humans, we administered 12 mg E2-valerate or placebo orally to 34 naturally cycling women in the low-hormone early follicular phase using a randomized, double-blinded, pre-post design. Behavioral performance was tested twice during baseline and E2 peak, where E2 levels reached mildly supraphysiological levels in the E2 group. Aside from mainly prefrontally mediated tasks of attention, working memory, and other executive functions, we employed tasks of affectively modulated attention, emotion recognition, and verbal memory. E2 administration had a significant, but subtle negative impact on general processing speed and working memory performance. These effects could be related to an overstimulation of dopaminergic transmission. The negative effect of supraphysiological E2 on working memory connects well to animal literature. There were no effects on attentional performance or any other measure. This could be explained by different E2 levels being optimal for changing behavioral performance in specific tasks, which likely depends on the brain regions involved.

The Intersection of Central Dopamine System and Stroke: Potential Avenues Aiming at Enhancement of Motor Recovery

Dopamine, a major neurotransmitter, plays a role in a wide range of brain sensorimotor functions. Parkinson's disease and schizophrenia are two major human neuropsychiatric disorders typically associated with dysfunctional dopamine activity levels, which can be alleviated through the druggability of the dopaminergic systems. Meanwhile, several studies suggest that optimal brain dopamine activity levels are also significantly impacted in other serious neurological conditions, notably stroke, but this has yet to be fully appreciated at both basic and clinical research levels. This is of utmost importance as there is a need for better treatments to improve recovery from stroke. Here, we discuss the state of knowledge regarding the modulation of dopaminergic systems following stroke, and the use of dopamine boosting therapies in animal stroke models to improve stroke recovery. Indeed, studies in animals and humans show stroke leads to changes in dopamine functioning. Moreover, evidence from animal stroke models suggests stimulation of dopamine receptors may be a promising therapeutic approach for enhancing motor recovery from stroke. With respect to the latter, we discuss the evidence for several possible receptor-linked mechanisms by which improved motor recovery may be mediated. One avenue of particular promise is the subtype-selective stimulation of dopamine receptors in conjunction with physical therapy. However, results from clinical trials so far have been more mixed due to a number of potential reasons including, targeting of the wrong patient populations and use of drugs which modulate a wide array of receptors. Notwithstanding these issues, it is hoped that future research endeavors will assist in the development of more refined dopaminergic therapeutic approaches to enhance stroke recovery.

Reduced striatal dopamine release during motor skill acquisition in Parkinson's disease

Background

Striatal dopamine is functionally important for the acquisition of motor skills. However, it remains controversial as to whether intrinsic processing of motor learning is impaired in patients with Parkinson’s disease (PD), and if yes, whether the impairment is associated with altered striatal dopamine release. Additionally, most neuro-imaging studies of patients with PD have focused on motor sequence learning. In contrast, skill acquisition, specifically, the reconstruction of muscle control of isolated movements, has barely been studied.

Method

In this study, we used a repetitive skill training task to measure the peak acceleration of left thumb movement during a process to achieve fine tuning of motor skill. Using ¹¹C-raclopride (RAC) positron emission tomography, we investigated changes in striatal dopamine levels in two conditions of a skill acquisition task: initial skill training (Day 1) and acquired condition (Day 2) with eight patients with PD and age-matched healthy subjects (HS).

Result

In HS, the mean acceleration of each session improved through repeated training sessions on Day 1. However, in patients with PD, the training-associated increase was less than that for HS, and this suggests that repetitive skill training does not result in the effective improvement of motor performance. The regions of interest (ROI) analysis revealed that the RAC-binding potential (BP) was significantly reduced in the right putamen on Day 1 compared with Day 2 in HS. In patients with PD, BP within the right putamen was unchanged. Further, we found that patients with PD had increased dopamine levels within the right ventral striatum (VST) and right caudate (CAU) on Day 2, which was greater than that in HS. These results suggest the impaired activation of the putamen during skill acquisition in patients with PD and compensated hyperactivation of the VST and CAU for the reduced dopamine release within the dorsal putamen (DPU).

Conclusion

Our findings suggest that patients with PD had insufficiency in the process to improve motor skills. Different patterns of striatal dopamine release are relevant to the impairment of these motor functions in patients with PD, at the early stage of the disease.

Short-term manganese inhalation decreases brain dopamine transporter levels without disrupting motor skills in rats

Manganese (Mn) is used in industrial metal alloys and can be released into the atmosphere during methylcyclopentadienyl manganese tricarbonyl combustion. Increased Mn deposition in the brain after long-term exposure to the metal by inhalation is associated with altered dopamine metabolism and neurobehavioral problems, including impaired motor skills. However, neurotoxic effects of short-term exposure to inhaled Mn are not completely characterized. The purpose of this study is to define the neurobehavioral and neurochemical effects of short-term inhalation exposure to Mn at a high concentration using rats. Male Sprague-Dawley rats were exposed to MnCl2 aerosol in a nose-only inhalation chamber for 3 weeks (1.2 µm, 39 mg/m(3)). Motor coordination was tested on the day after the last exposure using a rotarod device at a fixed speed of 10 rpm for 2 min. Also, dopamine transporter and dopamine receptor protein expression levels in the striatum region of the brain were determined by Western blot analysis. At a rotarod speed of 10 rpm, there were no significant differences in the time on the bar before the first fall or the number of falls during the two-minute test observed in the exposed rats, as compared with controls. The Mn-exposed group had significantly higher Mn levels in the lung, blood, olfactory bulb, prefrontal cortex, striatum, and cerebellum compared with the control group. A Mn concentration gradient was observed from the olfactory bulb to the striatum, supporting the idea that Mn is transported via the olfactory pathway. Our results demonstrated that inhalation exposure to 39 mg/m(3) Mn for 3 weeks induced mild lung injury and modulation of dopamine transporter expression in the brain, without altering motor activity.

Development and testing of a new system for assessing wheel-running behaviour in rodents

Background

Wheel running is one of the most widely studied behaviours in laboratory rodents. As a result, improved approaches for the objective monitoring and gathering of more detailed information is increasingly becoming important for evaluating rodent wheel-running behaviour. Here our aim was to develop a new quantitative wheel-running system that can be used for most typical wheel-running experimental protocols.

Findings

Here we devise a system that can provide a continuous waveform amenable to real-time integration with a high-speed video ideal for wheel-running experimental protocols. While quantification of wheel running behaviour has typically focused on the number of revolutions per unit time as an end point measure, the approach described here allows for more detailed information like wheel rotation fluidity, directionality, instantaneous velocity, and acceleration, in addition to total number of rotations, and the temporal pattern of wheel-running behaviour to be derived from a single trace. We further tested this system with a running-wheel behavioural paradigm that can be used for investigating the neuronal mechanisms of procedural learning and postural stability, and discuss other potentially useful applications.

Conclusions

This system and its ability to evaluate multiple wheel-running parameters may become a useful tool for screening new potentially important therapeutic compounds related to many neurological conditions.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-2059-6) contains supplementary material, which is available to authorized users.

Manganese-Disrupted Interaction of Dopamine D1 and NMDAR in the Striatum to Injury Learning and Memory Ability of Mice

Manganese (Mn) is widely regarded as a neurotoxic heavy metal that causes learning and memory deficits. Recently, it has been proved that the striatum is related to memory and learning ability. However, no previous study focused on the effect of Mn-induced learning and memory deficits on the striatum. This study aims to investigate the probable interaction of dopamine D1 receptor (DR1) and N-methyl-D-aspartate receptor (NMDAR), two cognition-related receptors in the striatum during Mn exposure. Mice are randomly divided into four groups, including control group, 12.5 mg/kg MnCl₂ group, 25 mg/kg MnCl₂ group, and 50 mg/kg MnCl₂ group. The mice receive intraperitoneal injections of 0, 12.5, 25, and 50 mg/kg MnCl₂ once daily for 2 weeks. Then, learning and memory ability, pathological changes, expression, and interaction of DR1 and NMDAR are determined. It has been found that Mn disrupted spatial learning and memory ability of mice by Morris water maze test and the passive avoidance test. Pathological and ultrastructure were injured. Mn decreased the immunohistochemical activities, protein levels, and messenger RNA (mRNA) expression of DR1, NR1, and NR2A. Mn exposure inhibited interaction between DR1 and NMDAR in striatum by double immunofluorescent staining and co-immunoprecipitation. In conclusion, our study illustrated that Mn caused learning and memory dysfunction via injury of striatum and inhibition of interaction between DR1 and NMDAR in striatum.

Decreased dopamine receptor 1 activity and impaired motor-skill transfer in Dyt1 ΔGAG heterozygous knock-in mice

DYT1 dystonia is a movement disorder caused by a trinucleotide deletion (ΔGAG) in DYT1 (TOR1A), corresponding to a glutamic acid loss in the C-terminal region of torsinA. Functional alterations in the basal ganglia circuits have been reported in both DYT1 dystonia patients and rodent models. Dyt1 ΔGAG heterozygous knock-in (KI) mice exhibit motor deficits and decreased striatal dopamine receptor 2 (D2R) binding activity, suggesting a malfunction of the indirect pathway. However, the role of the direct pathway in pathogenesis of dystonia is not yet clear. Here, we report that Dyt1 KI mice exhibit significantly decreased striatal dopamine receptor 1 (D1R) binding activity and D1R protein levels, suggesting the alteration of the direct pathway. The decreased D1R may be caused by translational or post-translational processes since Dyt1 KI mice had normal levels of striatal D1R mRNA and a normal number of striatal neurons expressing D1R. Levels of striatal ionotropic glutamate receptor subunits, dopamine transporter, acetylcholine muscarinic M4 receptor and adenosine A2A receptor were not altered suggesting a specificity of affected polytopic membrane-associated proteins. Contribution of the direct pathway to motor-skill learning has been suggested in another pharmacological rat model injected with a D1R antagonist. In the present study, we developed a novel motor skill transfer test for mice and found deficits in Dyt1 KI mice. Further characterization of both the direct and the indirect pathways in Dyt1 KI mice will aid the development of novel therapeutic drugs.

Modafinil effects on behavior and oxidative damage parameters in brain of wistar rats

The effects of modafinil (MD) on behavioral and oxidative damage to protein and lipid in the brain of rats were evaluated. Wistar rats were given a single administration by gavage of water or MD (75, 150, or 300 mg/kg). Behavioral parameters were evaluated in open-field apparatus 1, 2, and 3 h after drug administration. Thiobarbituric acid reactive substances (TBARS) and protein carbonyl formation were measured in the brain. MD increased locomotor activity at the highest dose 1 and 3 h after administration. MD administration at the dose of 300 mg/kg increased visits to the center of open-field 1 h after administration; however, 3 h after administration, all administered doses of MD increased visits to the open-field center. MD 300 mg/kg increased lipid damage in the amygdala, hippocampus, and striatum. Besides, MD increased protein damage in the prefrontal cortex, amygdala, and hippocampus; however, this effect varies depending on the dose administered. In contrast, the administration of MD 75 and 300 mg/kg decreased the protein damage in the striatum. This study demonstrated that the MD administration induces behavioral changes, which was depending on the dose used. In addition, the effects of MD on oxidative damage parameters seemed to be in specific brain region and doses.

Control of the nigrostriatal dopamine neuron activity and motor function by the tail of the ventral tegmental area

Midbrain dopamine neurons are implicated in various psychiatric and neurological disorders. The GABAergic tail of the ventral tegmental area (tVTA), also named the rostromedial tegmental nucleus (RMTg), displays dense projections to the midbrain and exerts electrophysiological control over dopamine cells of the VTA. However, the influence of the tVTA on the nigrostriatal pathway, from the substantia nigra pars compacta (SNc) to the dorsal striatum, and on related functions remains to be addressed. The present study highlights the role played by the tVTA as a GABA brake for the nigrostriatal system, demonstrating a critical influence over motor functions. Using neuroanatomical approaches with tract tracing and electron microscopy, we reveal the presence of a tVTA-SNc-dorsal striatum pathway. Using in vivo electrophysiology, we prove that the tVTA is a major inhibitory control center for SNc dopamine cells. Using behavioral approaches, we demonstrate that the tVTA controls rotation behavior, motor coordination, and motor skill learning. The motor enhancements observed after ablation of the tVTA are in this regard comparable with the performance-enhancing properties of amphetamine, a drug used in doping. These findings demonstrate that the tVTA is a major GABA brake for nigral dopamine systems and nigrostriatal functions, and they raise important questions about how the tVTA is integrated within the basal ganglia circuitry. They also warrant further research on the tVTA's role in motor and dopamine-related pathological contexts such as Parkinson's disease.

Brain mechanisms of acoustic communication in humans and nonhuman primates: An evolutionary perspective

Any account of “what is special about the human brain” (Passingham 2008) must specify the neural basis of our unique ability to produce speech and delineate how these remarkable motor capabilities could have emerged in our hominin ancestors. Clinical data suggest that the basal ganglia provide a platform for the integration of primate-general mechanisms of acoustic communication with the faculty of articulate speech in humans. Furthermore, neurobiological and paleoanthropological data point at a two-stage model of the phylogenetic evolution of this crucial prerequisite of spoken language: (i) monosynaptic refinement of the projections of motor cortex to the brainstem nuclei that steer laryngeal muscles, presumably, as part of a “phylogenetic trend” associated with increasing brain size during hominin evolution; (ii) subsequent vocal-laryngeal elaboration of cortico-basal ganglia circuitries, driven by human-specificFOXP2mutations.;>This concept implies vocal continuity of spoken language evolution at the motor level, elucidating the deep entrenchment of articulate speech into a “nonverbal matrix” (Ingold 1994), which is not accounted for by gestural-origin theories. Moreover, it provides a solution to the question for the adaptive value of the “first word” (Bickerton 2009) since even the earliest and most simple verbal utterances must have increased the versatility of vocal displays afforded by the preceding elaboration of monosynaptic corticobulbar tracts, giving rise to enhanced social cooperation and prestige. At the ontogenetic level, the proposed model assumes age-dependent interactions between the basal ganglia and their cortical targets, similar to vocal learning in some songbirds. In this view, the emergence of articulate speech builds on the “renaissance” of an ancient organizational principle and, hence, may represent an example of “evolutionary tinkering” (Jacob 1977).

Functional dynamics of primate cortico-striatal networks during volitional movements

The motor cortex and dorsal striatum (caudate nucleus and putamen) are key regions in motor processing but the interface between the cortex and striatum is not well understood. While dorsal striatum integrates information from multiple brain regions to shape motor learning and habit formation, the disruption of cortico-striatal circuits compromises the functionality of these circuits resulting in a multitude of neurologic disorders, including Parkinson's disease. To better understand the modulation of the cortico-striatal circuits we recorded simultaneously single neuron activity from four brain regions, primary motor, and sensory cortices, together with the rostral and caudal segments of the putamen in rhesus monkeys performing a visual motor task. Results show that spatial and temporal-task related firing relationships between these cortico-striatal circuit regions were modified by the independent administration of the two drugs (cocaine and baclofen). Spatial tuning and correlated firing of neurons from motor cortex and putamen were severely disrupted by cocaine and baclofen on correct trials, while the two drugs have dramatically decreased the functional connectivity of the motor cortical-striatal network. These findings provide insight into the modulation of cortical-striatal firing related to movement with implications for therapeutic approaches to Parkinson's disease and related disorders.

Study motor skill learning by single-pellet reaching tasks in mice

Reaching for and retrieving objects require precise and coordinated motor movements in the forelimb. When mice are repeatedly trained to grasp and retrieve food rewards positioned at a specific location, their motor performance (defined as accuracy and speed) improves progressively over time, and plateaus after persistent training. Once such reaching skill is mastered, its further maintenance does not require constant practice. Here we introduce a single-pellet reaching task to study the acquisition and maintenance of skilled forelimb movements in mice. In this video, we first describe the behaviors of mice that are commonly encountered in this learning and memory paradigm, and then discuss how to categorize these behaviors and quantify the observed results. Combined with mouse genetics, this paradigm can be utilized as a behavioral platform to explore the anatomical underpinnings, physiological properties, and molecular mechanisms of learning and memory.

Changes of several brain receptor complexes in the cerebral cortex of patients with Alzheimer disease: probable new potential pharmaceutical targets

Although Alzheimer disease (AD) has been linked to defects in major brain receptors, studies thus far have been limited to the determination of receptor subunits or specific ligand binding studies. However, the availability of current technology enables the determination and quantification of brain receptor complexes. Thus, we examined levels of native receptor complexes in the brains of patients with AD. Cortical tissue was obtained from control subjects (n = 12 females and 12 males) and patients with AD (n = 12 females and 12 males) within a 3-h postmortem time period. The tissues were kept frozen until further biochemical analyses. Membrane proteins were extracted and subsequently enriched by ultracentrifugation using a sucrose gradient. Membrane proteins were then electrophoresed onto native gels and immunoblotted using antibodies against individual brain receptors. We found that the levels were comparable for complexes containing GluR2, GluR3 and GluR4 as well as 5-HT1A. Moreover, the levels of complexes containing muscarinic AChR M1, NR1 and GluR1 were significantly increased in male patients with AD. Nicotinic AChRs 4 and 7 as well as dopaminergic receptors D1 and D2 were also increased in males and females with AD. These findings reveal a pattern of altered receptor complex levels that may contribute to the deterioration of the concerted activity of these receptors and thus result in cognitive deficits observed in patients with AD. It should be emphasised that receptor complexes function as working units rather than individual subunits. Thus, the receptor deficits identified may be relevant for the design of experimental therapies. Therefore, specific pharmacological modulation of these receptors is within the pharmaceutical repertoire.

Role of movement in long-term basal ganglia changes: implications for abnormal motor responses

Abnormal involuntary movements (AIMs) and dyskinesias elicited by drugs that stimulate dopamine receptors in the basal ganglia are a major issue in the management of Parkinson’s disease (PD). Preclinical studies in dopamine-denervated animals have contributed to the modeling of these abnormal movements, but the precise neurochemical and functional mechanisms underlying these untoward effects are still elusive. It has recently been suggested that the performance of movement may itself promote the later emergence of drug-induced motor complications, by favoring the generation of aberrant motor memories in the dopamine-denervated basal ganglia. Our recent results from hemiparkinsonian rats subjected to the priming model of dopaminergic stimulation are in agreement with this. These results demonstrate that early performance of movement is crucial for the manifestation of sensitized rotational behavior, indicative of an abnormal motor response, and neurochemical modifications in selected striatal neurons following a dopaminergic challenge. Building on this evidence, this paper discusses the possible role of movement performance in drug-induced motor complications, with a look at the implications for PD management.

The effect of Parkinson's disease and levodopa on adaptation of anticipatory postural adjustments

Postural support alters anticipatory postural adjustments (APAs). Efficient adaptation to changes in postural support in reactive and centrally initiated postural synergies is impaired in Parkinson's disease (PD). This study examined whether APAs are affected differently by familiar and novel supports in people with PD, ON and OFF levodopa. The effect of PD and levodopa on the ability to immediately adapt APAs to changes in support and refine with practice was also investigated. Fourteen people with PD and 14 healthy control participants performed 20 single rapid leg lift tasks in four support conditions: unsupported, bilateral handgrip (familiar), bite plate (novel) and a combined handgrip+bite plate condition. APAs, identified from force plate data, were characterized by an increase in the vertical ground reaction force under the lifted leg as a result of a shift of weight toward the stance limb. Results showed the ability to incorporate familiar and novel external supports into the postural strategy was preserved in PD. Controls and PD patients in the OFF state further refined the postural strategy with practice as evidenced by changes in amplitude of vertical ground reaction forces and forces applied to support apparatus within conditions between the initial and final trials. In the ON state, people with PD failed to refine the use of postural supports in any condition. The results suggest that immediate postural adaptation is intact in people with PD and unaffected by levodopa administration but the ability to refine postural adaptations with task experience is compromised by dopamine therapy.

Changes in striatal dopamine release associated with human motor-skill acquisition

The acquisition of new motor skills is essential throughout daily life and involves the processes of learning new motor sequence and encoding elementary aspects of new movement. Although previous animal studies have suggested a functional importance for striatal dopamine release in the learning of new motor sequence, its role in encoding elementary aspects of new movement has not yet been investigated. To elucidate this, we investigated changes in striatal dopamine levels during initial skill-training (Day 1) compared with acquired conditions (Day 2) using ¹¹C-raclopride positron-emission tomography. Ten volunteers learned to perform brisk contractions using their non-dominant left thumbs with the aid of visual feedback. On Day 1, the mean acceleration of each session was improved through repeated training sessions until performance neared asymptotic levels, while improved motor performance was retained from the beginning on Day 2. The ¹¹C-raclopride binding potential (BP) in the right putamen was reduced during initial skill-training compared with under acquired conditions. Moreover, voxel-wise analysis revealed that ¹¹C-raclopride BP was particularly reduced in the right antero-dorsal to the lateral part of the putamen. Based on findings from previous fMRI studies that show a gradual shift of activation within the striatum during the initial processing of motor learning, striatal dopamine may play a role in the dynamic cortico-striatal activation during encoding of new motor memory in skill acquisition.

Subcellular location of PKA controls striatal plasticity: stochastic simulations in spiny dendrites

Dopamine release in the striatum has been implicated in various forms of reward dependent learning. Dopamine leads to production of cAMP and activation of protein kinase A (PKA), which are involved in striatal synaptic plasticity and learning. PKA and its protein targets are not diffusely located throughout the neuron, but are confined to various subcellular compartments by anchoring molecules such as A-Kinase Anchoring Proteins (AKAPs). Experiments have shown that blocking the interaction of PKA with AKAPs disrupts its subcellular location and prevents LTP in the hippocampus and striatum; however, these experiments have not revealed whether the critical function of anchoring is to locate PKA near the cAMP that activates it or near its targets, such as AMPA receptors located in the post-synaptic density. We have developed a large scale stochastic reaction-diffusion model of signaling pathways in a medium spiny projection neuron dendrite with spines, based on published biochemical measurements, to investigate this question and to evaluate whether dopamine signaling exhibits spatial specificity post-synaptically. The model was stimulated with dopamine pulses mimicking those recorded in response to reward. Simulations show that PKA colocalization with adenylate cyclase, either in the spine head or in the dendrite, leads to greater phosphorylation of DARPP-32 Thr34 and AMPA receptor GluA1 Ser845 than when PKA is anchored away from adenylate cyclase. Simulations further demonstrate that though cAMP exhibits a strong spatial gradient, diffusible DARPP-32 facilitates the spread of PKA activity, suggesting that additional inactivation mechanisms are required to produce spatial specificity of PKA activity.

The striatum is a part of the basal ganglia which plays a role in addiction and reward learning. Its importance is underscored by pathologies such as Parkinson's disease and Huntington's disease in which degeneration of the dopamine inputs to the striatum or degeneration of neurons in the striatum, respectively, produces motor dysfunction. Dopamine in the striatum activates cascades of signaling molecules, ultimately producing an activity dependent change in the strength of connections between neurons. However, the dispersive movement of signaling molecules seems incompatible with the strengthening of specific subsets of connections, which is required for formation of distinct memories. Anchoring proteins, which restrict molecules to particular compartments within the neuron, are proposed to achieve specificity. We develop a reaction-diffusion model of dopamine activated signaling pathways to explore mechanisms whereby anchoring proteins can produce specificity. We use an efficient Monte-Carlo simulator to implement the cascades of signaling molecules in a neuronal dendrite with multiple dendritic spines. Simulations demonstrate that spatial specificity requires both anchoring proteins and inactivation mechanisms that limit the diffusion of signaling molecules.

Interactions between Procedural Learning and Cocaine Exposure Alter Spontaneous and Cortically Evoked Spike Activity in the Dorsal Striatum

We have previously shown that cocaine enhances gene regulation in the sensorimotor striatum associated with procedural learning in a running-wheel paradigm. Here we assessed whether cocaine produces enduring modifications of learning-related changes in striatal neuron activity, using single-unit recordings in anesthetized rats 1 day after the wheel training. Spontaneous and cortically evoked spike activity was compared between groups treated with cocaine or vehicle immediately prior to the running-wheel training or placement in a locked wheel (control conditions). We found that wheel training in vehicle-treated rats increased the average firing rate of spontaneously active neurons without changing the relative proportion of active to quiescent cells. In contrast, in rats trained under the influence of cocaine, the proportion of spontaneously firing to quiescent cells was significantly greater than in vehicle-treated, trained rats. However, this effect was associated with a lower average firing rate in these spontaneously active cells, suggesting that training under the influence of cocaine recruited additional low-firing cells. Measures of cortically evoked activity revealed a second interaction between cocaine treatment and wheel training, namely, a cocaine-induced decrease in spike onset latency in control rats (locked wheel). This facilitatory effect of cocaine was abolished when rats trained in the running wheel during cocaine action. These findings highlight important interactions between cocaine and procedural learning, which act to modify population firing activity and the responsiveness of striatal neurons to excitatory inputs. Moreover, these effects were found 24 h after the training and last drug exposure indicating that cocaine exposure during the learning phase triggers long-lasting changes in synaptic plasticity in the dorsal striatum. Such changes may contribute to the transition from recreational to habitual or compulsive drug taking behavior.

Activation of calcium/calmodulin-dependent protein kinase IIalpha in the striatum by the heteromeric D1-D2 dopamine receptor complex

Synaptic plasticity in the striatum is a key mechanism that underlies processes such as reward related incentive learning and behavioral habit formation resulting from drugs of abuse. Key aspects of these functions are dependent on dopamine transmission as well as activation of calcium/calmodulin-dependent protein kinase IIalpha (CaMKIIalpha). In this study, we examined the ability of a recently identified heteromeric complex composed of D1 and D2 dopamine receptors coupled to Gq/11 to activate striatal CaMKIIalpha. Using the dopaminergic agonist SKF83959, which selectively activates the D1-D2 complex, we demonstrated phosphorylation of CaMKIIalpha at threonine 286, both in heterologous cells and in the murine striatum in vivo. Phosphorylation of CaMKIIalpha by activation of the receptor complex required concurrent agonism of both D1 and D2 receptors and was independent of receptor pathways that modulated adenylyl cyclase. The identification of this novel mechanism by which dopamine may modulate synaptic plasticity has implications for our understanding of striatal-mediated reward and motor function, as well as neuronal disorders in which striatal dopaminergic neurotransmission is involved.

Dopamine signaling in the nucleus accumbens of animals self-administering drugs of abuse

Abuse of psychoactive substances can lead to drug addiction. In animals, addiction is best modeled by drug self-administration paradigms. It has been proposed that the crucial common denominator for the development of drug addiction is the ability of drugs of abuse to increase extracellular concentrations of dopamine in the nucleus accumbens (NAcc). Studies using in vivo microdialysis and chronoamperometry in the behaving animal have demonstrated that drugs of abuse increase tonic dopamine concentrations in the NAcc. However, it is known that dopamine neurons respond to reward-related stimuli on a subsecond timescale. Thus, it is necessary to collect neurochemical information with this level of temporal resolution, as achieved with in vivo fast-scan cyclic voltammetry (FSCV), to fully understand the role of phasic dopamine release in normal behavior and drug addiction. We review studies that investigated the effects of drugs of abuse on NAcc dopamine levels in freely moving animals using in vivo microdialysis, chronoamperometry, and FSCV. After a brief introduction of dopamine signal transduction and anatomy and a section on current theories on the role of dopamine in natural goal-directed behavior, a discussion of techniques for the in vivo assessment of extracellular dopamine in behaving animals is presented. Then, we review studies using these techniques to investigate changes in phasic and tonic dopamine signaling in the NAcc during (1) response-dependent and -independent administration of abused drugs, (2) the presentation of drug-conditioned stimuli and operant behavior in self-administration paradigms, (3) drug withdrawal, and (4) cue-induced reinstatement of drug seeking. These results are then integrated with current ideas on the role of dopamine in addiction with an emphasis on a model illustrating phasic and tonic NAcc dopamine signaling during different stages of drug addiction. This model predicts that phasic dopamine release in response to drug-related stimuli will be enhanced over stimuli associated with natural reinforcers, which may result in aberrant goal-directed behaviors contributing to drug addiction.

The role of granulocyte-colony stimulating factor (G-CSF) in the healthy brain: a characterization of G-CSF-deficient mice

Granulocyte-colony stimulating factor (G-CSF) is a hematopoietic growth factor that controls proliferation and differentiation of neural stem cells. Although recent studies have begun to explore G-CSF-related mechanisms of action in various disease models, little is known about its function in the healthy brain. In the present study, the effect of G-CSF deficiency on memory formation and motor skills was investigated. The impact of G-CSF deficiency on the structural integrity of the hippocampus was evaluated by analyzing the generation of doublecortin-expressing cells, the amount of bromodeoxyurine-labeled cells, the dendritic complexity in hippocampal neurons, the binding densities of NMDA and GABA(A) receptors and the induction of long-term potentiation (LTP). G-CSF deficiency caused a disruption in memory formation and in the development of motor skills. These impairments were associated with reduced ligand binding densities of NMDA receptors in hippocampal subfields CA3 and the dentate gyrus. The reduced excitation was potentiated by increased ligand binding densities of GABA(A) receptors resulting in a relative shift in favor of inhibition and impaired behavioral performance. These alterations were accompanied by impaired induction of LTP in the CA1 region. Moreover, G-CSF deficiency led to decreased dendritic complexity in hippocampal neurons in the dentate gyrus and the CA1 region. G-CSF deficiency also caused a reduction of neuronal precursor cells in the dentate gyrus. These findings confirm G-CSF as an essential neurotrophic factor, and point to a role in the proliferation, differentiation and functional integration of neural cells necessary for the structural and functional integrity of the hippocampal formation.

Partial ablation of mu-opioid receptor rich striosomes produces deficits on a motor-skill learning task

Basal ganglia striosomes, or patches, are rich in mu opioid receptors (MOR) and form a three-dimensional labyrinth of cells that extend throughout the mid- and anterior striatum in mice. Though previous studies have suggested that striosomes could affect drug-induced motor output in rodents, the functional role of these compartmentalized MOR-rich striosomes is not well understood. To investigate any relationship between the striosomes and motor behavior we used the toxin dermorphin-saporin (DS) to selectively ablate MOR-rich striosomal cells. FVB mice were bilaterally infused with DS in the midstriatum alone or in the mid- and anterior striatum, and were tested on three motor tasks and in an open field. Two volume measurement procedures and stereological cell counts were used to confirm the induced pathology. Mice that received DS injections showed significantly smaller volumes (-26% to -44%) and fewer cells (-30% to -49%) in the striosome compartment compared to mice that received control injections of saline or saporin. Striosome pathology was greatest in the dorsolateral striatum. The extrastriosomal matrix was not significantly affected, resulting in an imbalance in the ratio of striosome-to-matrix cells. Behaviorally, toxin injections caused deficits on an accelerating rotarod task and the deficit was worse in mice that received mid and anterior injections than those that received midstriatal injections alone. However, DS-injected mice did not differ from control mice on other motor tasks. We conclude that the MOR-rich cells of the striosomes are necessary for optimal rotarod performance, including learning and/or improvement on the task.

Common key-signals in learning and neurodegeneration: focus on excito-amino acids, beta-amyloid peptides and alpha-synuclein

In this paper a hypothesis that some special signals ("key-signals" excito-amino acids, beta-amyloid peptides and alpha-synuclein) are not only involved in information handling by the neuronal circuits, but also trigger out substantial structural and/or functional changes in the Central Nervous System (CNS) is introduced. This forces the neuronal circuits to move from one stable state towards a new state, but in doing so these signals became potentially dangerous. Several mechanisms are put in action to protect neurons and glial cells from these potentially harmful signals. However, in agreement with the Red Queen Theory of Ageing (Agnati et al. in Acta Physiol Scand 145:301-309, 1992), it is proposed that during ageing these neuroprotective processes become less effective while, in the meantime, a shortage of brain plasticity occurs together with an increased need of plasticity for repairing the wear and tear of the CNS. The paper presents findings supporting the concept that such key-signals in instances such as ageing may favour neurodegenerative processes in an attempt of maximizing neuronal plasticity.

Priming of rotational behavior by a dopamine receptor agonist in Hemiparkinsonian rats: movement-dependent induction

Repetitive stimulation of dopamine receptors located in the basal ganglia may lead to the manifestation of sensitized, abnormal, motor responses in dopamine-denervated rats. In order to study the role of motor behavior execution on the expression of these altered motor responses, we evaluated how "priming", a phenomenon displaying neurochemical and behavioral features peculiar to a sensitized abnormal motor response in dopamine-denervated rats, depends on actual movement performance. To this end, unilaterally 6-hydroxydopamine-lesioned rats received apomorphine (0.2 mg/kg s.c.), being either allowed to move or immobilized (1 h) before, concomitantly to, or after its administration, respectively. Three days after apomorphine, the dopamine D(1) receptor agonist 1-Phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol (SKF 38393, 3 mg/kg s.c.) was administered to all animals. Rats that had performed rotational behavior following apomorphine administration displayed robust contraversive rotational behavior in response to SKF 38393, whereas rats that had been immobilized concomitantly to, but neither before nor after apomorphine, did not. To clarify whether stress, which may be increased by immobilization, mediated the results observed, additional rats received apomorphine paired with immobilization plus the corticosterone-synthesis inhibitor metyrapone (100 mg/kg i.p.), or apomorphine paired with a tail stressor, being not immobilized. Metyrapone did not affect the capacity of immobilization to prevent priming and tail stressor imposition did not affect priming magnitude, suggesting that stress has minimal or no effect on the results observed. This study demonstrates how movement performance following initial dopaminergic stimulation governs the occurrence of a sensitized, abnormal, motor response to a subsequent dopaminergic challenge in dopamine-denervated rats.

Motor sequence learning in primate: role of the D2 receptor in movement chunking during consolidation

Motor learning disturbances have been shown in diseases involving dopamine insufficiency such as Parkinson's disease and schizophrenic patients under antipsychotic drug treatment. In non-human primates, motor learning deficits have also been observed following systemic administration of raclopride, a selective D2-receptor antagonist. These deficits were characterized by persistent fluctuations of performance from trial to trial, and were described as difficulties in consolidating movements following a learning period. Moreover, it has been suggested that these raclopride-induced fluctuations can result from impediments in grouping separate movements into one fluent sequence. In the present study, we explore the hypothesis that such fluctuations during movement consolidation can be prevented through the use of sumanirole - a highly selective D2 agonist - if administered before raclopride. Two monkeys were trained to execute a well known sequence of movements, which was later recalled under three pharmacological conditions: (1) no drug, (2) raclopride, and (3) sumanirole+raclopride. The same three pharmacological conditions were repeated with the two monkeys, trained this time to learn new sequences of movements. Results show that raclopride has no deleterious effect on the well known sequence, nor the sumanirole+raclopride co-administration. However, results on the new sequence to be learned revealed continuous fluctuations of performances in the raclopride condition, but not in the sumanirole+raclopride condition. These fluctuations occurred concurrently with a difficulty in merging separate movement components, known as a "chunking deficit". D2 receptors seem therefore to be involved in the consolidation of new motor skills, and this might involve the chunking of separate movements into integrated motor sequences.

Skill-memory consolidation in the striatum: critical for late but not early long-term memory and stabilized by cocaine

The sensorimotor striatum is important for procedural learning, including skill learning. Our previous findings indicate that this part of the striatum mediates the acquisition of a motor skill in a running-wheel task and that this skill learning is dependent on striatal D1 dopamine receptors. Here, we investigated whether the sensorimotor striatum is also involved in the consolidation of this skill memory and whether this consolidation is modified by the indirect dopamine receptor agonist cocaine. Rats were trained on a running wheel for 2 days (40 min/day) to learn a new motor skill, that is, the ability to control the movement of the wheel. Before each training session, the animals received an injection of vehicle or cocaine (25mg/kg, i.p.). Immediately following the training session, an intrastriatal infusion of 2% lidocaine (1 microl) or a sham infusion were administered. Wheel-skill performance was tested before and repeatedly after the training. Our results show that post-trial intrastriatal infusion of lidocaine disrupted late-stage long-term skill memory (post-training days 6-26), but spared early long-term memory (1 day after the training). Skill consolidation was more susceptible to such disruption in animals that practiced less during the training. Cocaine given pre-trial prevented this post-trial disruption of skill consolidation. These findings indicate that the sensorimotor striatum is critical for the consolidation of late but not early long-term skill memory. Furthermore, cocaine appeared to stabilize motor-memory formation by protecting consolidation processes after the training.