Abnormal synaptic plasticity in the striatum of mice lacking dopamine D2 receptors

The dose-dependent effect of the D2R agonist quinpirole microinjected into the ventral pallidum on information flow in the limbic system

The ventral pallidum (VP) receives its primary inputs from the nucleus accumbens (NAC) and the basolateral amygdala (BLA). We demonstrated recently that in the VP, the D2 DA receptor (D2R) agonist quinpirole dose-dependently facilitates memory consolidation in inhibitory avoidance and spatial learning. In the VP, D2R can be found both on NAC and BLA terminals. According to our hypothesis, quinpirole microinjected into the VP can facilitate memory consolidation via modulation of synaptic plasticity on NAC and/or BLA terminals. The effect of intra-VP quinpirole on BLA-VP and NAC shell-VP synapses was investigated via a high frequency stimulation (HFS) protocol. Quinpirole was administered in three doses into the VP of male Sprague-Dawley rats after HFS; controls received vehicle. To examine whether an interaction between the NAC shell and the BLA at the level of the VP was involved, tetrodotoxin (TTX) was microinjected into one of the nuclei while stimulating the other nucleus. Our results showed that quinpirole dose-dependently modulates BLA-VP and NAC shell-VP synapses, similar to those observed in inhibitory avoidance and spatial learning, respectively. The lower dose inhibits BLA inputs, while the larger doses facilitates NAC shell inputs. The experiments with TTX demonstrates that the two nuclei do not influence each others' evoked responses in the VP. Power spectral density analysis demonstrated that independent from the synaptic facilitation, intra-VP quinpirole increases the amplitude of gamma frequency band after NAC HFS, and BLA tonically suppresses the NAC's HFS-induced gamma facilitation. In contrast, HFS of the BLA results in a delayed, transient increase in the amplitude of the gamma frequency band correlating with the LTP of the P1 component of the VP response to BLA stimulation. Furthermore, our results demonstrate that the BLA plays a prominent role in the generation of the delta oscillations: HFS of the BLA leads to a gradually increasing delta frequency band facilitation over time, while BLA inhibition blocks the NAC's HFS induced strong delta facilitation. These findings demonstrate that there is a complex interaction between the NAC shell region and the VP, as well as the BLA and the VP, and support the important role of VP D2Rs in the regulation of limbic information flow.

Dopaminergic Input Regulates the Sensitivity of Indirect Pathway Striatal Spiny Neurons to Brain-Derived Neurotrophic Factor

Motor dysfunction in Parkinson's disease (PD) is closely linked to the dopaminergic depletion of striatal neurons and altered synaptic plasticity at corticostriatal synapses. Dopamine receptor D1 (DRD1) stimulation is a crucial step in the formation of long-term potentiation (LTP), whereas dopamine receptor D2 (DRD2) stimulation is needed for the formation of long-term depression (LTD) in striatal spiny projection neurons (SPNs). Tropomyosin receptor kinase B (TrkB) and its ligand brain-derived neurotrophic factor (BDNF) are centrally involved in plasticity regulation at the corticostriatal synapses. DRD1 activation enhances TrkB's sensitivity for BDNF in direct pathway spiny projection neurons (dSPNs). In this study, we showed that the activation of DRD2 in cultured striatal indirect pathway spiny projection neurons (iSPNs) and cholinergic interneurons causes the retraction of TrkB from the plasma membrane. This provides an explanation for the opposing synaptic plasticity changes observed upon DRD1 or DRD2 stimulation. In addition, TrkB was found within intracellular structures in dSPNs and iSPNs from Pitx3-/- mice, a genetic model of PD with early onset dopaminergic depletion in the dorsolateral striatum (DLS). This dysregulated BDNF/TrkB signaling might contribute to the pathophysiology of direct and indirect pathway striatal projection neurons in PD.

The Dysfunctional Mechanisms Throwing Tics: Structural and Functional Changes in Tourette Syndrome

Tourette Syndrome (TS) is a high-incidence multifactorial neuropsychiatric disorder characterized by motor and vocal tics co-occurring with several diverse comorbidities, including obsessive-compulsive disorder and attention-deficit hyperactivity disorder. The origin of TS is multifactorial, with strong genetic, perinatal, and immunological influences. Although almost all neurotransmettitorial systems have been implicated in TS pathophysiology, a comprehensive neurophysiological model explaining the dynamics of expression and inhibition of tics is still lacking. The genesis and maintenance of motor and non-motor aspects of TS are thought to arise from functional and/or structural modifications of the basal ganglia and related circuitry. This complex wiring involves several cortical and subcortical structures whose concerted activity controls the selection of the most appropriate reflexive and habitual motor, cognitive and emotional actions. Importantly, striatal circuits exhibit bidirectional forms of synaptic plasticity that differ in many respects from hippocampal and neocortical plasticity, including sensitivity to metaplastic molecules such as dopamine. Here, we review the available evidence about structural and functional anomalies in neural circuits which have been found in TS patients. Finally, considering what is known in the field of striatal plasticity, we discuss the role of exuberant plasticity in TS, including the prospect of future pharmacological and neuromodulation avenues.

D2R signaling in striatal spiny neurons modulates L-DOPA induced dyskinesia

Degeneration of dopaminergic neurons leads to Parkinson’s disease (PD), characterized by reduced levels of striatal dopamine (DA) and impaired voluntary movements. DA replacement is achieved by levodopa treatment which in long-term causes involuntary movements or dyskinesia. Dyskinesia is linked to the pulsatile activation of D1 receptors of the striatal medium spiny neurons (MSNs) forming the direct output pathway (dMSNs). The contribution of DA stimulation of D2R in MSNs of the indirect pathway (iMSNs) is less clear. Using the 6-hydroxydopamine model of PD, here we show that loss of DA-mediated inhibition of these neurons intensifies levodopa-induced dyskinesia (LID) leading to reprogramming of striatal gene expression. We propose that the motor impairments characteristic of PD and of its therapy are critically dependent on D2R-mediated iMSNs activity. D2R signaling not only filters inputs to the striatum but also indirectly regulates dMSNs mediated responses.

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D2RKO in iMSNs increases L-DOPA-induced dyskinesia (LID)

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D2R signaling in iMSNs inhibits striatal gene and PD-associated genes

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Unopposed M1R signaling is responsible for the increased LID in iMSN-D2RKO mice

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Simultaneous modulation of M1R and M4R signaling on MSNs drastically reduces LID

Basic mechanisms of plasticity and learning

The last century was characterized by a significant scientific effort aimed at unveiling the neurobiological basis of learning and memory. Thanks to the characterization of the mechanisms regulating the long-term changes of neuronal synaptic connections, it was possible to understand how specific neural networks shape themselves during the acquisition of memory traces or complex motor tasks. In this chapter, we will summarize the mechanisms underlying the main forms of synaptic plasticity taking advantage of the studies performed in the hippocampus and in the nucleus striatum, key brain structures that play a crucial role in cognition. Moreover, we will discuss how the molecular pathways involved in the induction of physiologic synaptic long-term changes could be disrupted during neurodegenerative and neuroinflammatory disorders, highlighting the translational relevance of this intriguing research field.

Spike-Timing-Dependent Plasticity Mediated by Dopamine and its Role in Parkinson's Disease Pathophysiology

Parkinson's disease (PD) is a multi-systemic neurodegenerative brain disorder. Motor symptoms of PD are linked to the significant dopamine (DA) loss in substantia nigra pars compacta (SNc) followed by basal ganglia (BG) circuit dysfunction. Increasing experimental and computational evidence indicates that (synaptic) plasticity plays a key role in the emergence of PD-related pathological changes following DA loss. Spike-timing-dependent plasticity (STDP) mediated by DA provides a mechanistic model for synaptic plasticity to modify synaptic connections within the BG according to the neuronal activity. To shed light on how DA-mediated STDP can shape neuronal activity and synaptic connectivity in the PD condition, we reviewed experimental and computational findings addressing the modulatory effect of DA on STDP as well as other plasticity mechanisms and discussed their potential role in PD pathophysiology and related network dynamics and connectivity. In particular, reshaping of STDP profiles together with other plasticity-mediated processes following DA loss may abnormally modify synaptic connections in competing pathways of the BG. The cascade of plasticity-induced maladaptive or compensatory changes can impair the excitation-inhibition balance towards the BG output nuclei, leading to the emergence of pathological activity-connectivity patterns in PD. Pre-clinical, clinical as well as computational studies reviewed here provide an understanding of the impact of synaptic plasticity and other plasticity mechanisms on PD pathophysiology, especially PD-related network activity and connectivity, after DA loss. This review may provide further insights into the abnormal structure-function relationship within the BG contributing to the emergence of pathological states in PD. Specifically, this review is intended to provide detailed information for the development of computational network models for PD, serving as testbeds for the development and optimization of invasive and non-invasive brain stimulation techniques. Computationally derived hypotheses may accelerate the development of therapeutic stimulation techniques and potentially reduce the number of related animal experiments.

Cell-type-specific disruption of PERK-eIF2α signaling in dopaminergic neurons alters motor and cognitive function

Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) has been shown to activate the eIF2α kinase PERK to directly regulate translation initiation. Tight control of PERK-eIF2α signaling has been shown to be necessary for normal long-lasting synaptic plasticity and cognitive function, including memory. In contrast, chronic activation of PERK-eIF2α signaling has been shown to contribute to pathophysiology, including memory impairments, associated with multiple neurological diseases, making this pathway an attractive therapeutic target. Herein, using multiple genetic approaches we show that selective deletion of the PERK in mouse midbrain dopaminergic (DA) neurons results in multiple cognitive and motor phenotypes. Conditional expression of phospho-mutant eIF2α in DA neurons recapitulated the phenotypes caused by deletion of PERK, consistent with a causal role of decreased eIF2α phosphorylation for these phenotypes. In addition, deletion of PERK in DA neurons resulted in altered de novo translation, as well as changes in axonal DA release and uptake in the striatum that mirror the pattern of motor changes observed. Taken together, our findings show that proper regulation of PERK-eIF2α signaling in DA neurons is required for normal cognitive and motor function in a non-pathological state, and also provide new insight concerning the onset of neuropsychiatric disorders that accompany UPR failure.

In Parkinson's patient-derived dopamine neurons, the triplication of α-synuclein locus induces distinctive firing pattern by impeding D2 receptor autoinhibition

Pathophysiological changes in dopamine neurons precede their demise and contribute to the early phases of Parkinson's disease (PD). Intracellular pathological inclusions of the protein α-synuclein within dopaminergic neurons are a cardinal feature of PD, but the mechanisms by which α-synuclein contributes to dopaminergic neuron vulnerability remain unknown. The inaccessibility to diseased tissue has been a limitation in studying progression of pathophysiology prior to degeneration of dopamine neurons. To address these issues, we differentiated induced pluripotent stem cells (iPSCs) from a PD patient carrying the α-synuclein triplication mutation (AST) and an unaffected first-degree relative (NAS) into dopaminergic neurons. In human-like dopamine neurons α-synuclein overexpression reduced the functional availability of D2 receptors, resulting in a stark dysregulation in firing activity, dopamine release, and neuronal morphology. We back-translated these findings into primary mouse neurons overexpressing α-synuclein and found a similar phenotype, supporting the causal role for α-synuclein. Importantly, application of D2 receptor agonist, quinpirole, restored the altered firing activity of AST-derived dopaminergic neurons to normal levels. These results provide novel insights into the pre-degenerative pathophysiological neuro-phenotype induced by α-synuclein overexpression and introduce a potential mechanism for the long-established clinical efficacy of D2 receptor agonists in the treatment of PD.

Neuro-Immune Cross-Talk in the Striatum: From Basal Ganglia Physiology to Circuit Dysfunction

The basal ganglia network is represented by an interconnected group of subcortical nuclei traditionally thought to play a crucial role in motor learning and movement execution. During the last decades, knowledge about basal ganglia physiology significantly evolved and this network is now considered as a key regulator of important cognitive and emotional processes. Accordingly, the disruption of basal ganglia network dynamics represents a crucial pathogenic factor in many neurological and psychiatric disorders. The striatum is the input station of the circuit. Thanks to the synaptic properties of striatal medium spiny neurons (MSNs) and their ability to express synaptic plasticity, the striatum exerts a fundamental integrative and filtering role in the basal ganglia network, influencing the functional output of the whole circuit. Although it is currently established that the immune system is able to regulate neuronal transmission and plasticity in specific cortical areas, the role played by immune molecules and immune/glial cells in the modulation of intra-striatal connections and basal ganglia activity still needs to be clarified. In this manuscript, we review the available evidence of immune-based regulation of synaptic activity in the striatum, also discussing how an abnormal immune activation in this region could be involved in the pathogenesis of inflammatory and degenerative central nervous system (CNS) diseases.

Prenatal Stress Leads to the Altered Maturation of Corticostriatal Synaptic Plasticity and Related Behavioral Impairments Through Epigenetic Modifications of Dopamine D2 Receptor in Mice

Prenatal stress (PRS) had a long-term adverse effect on motor behaviors. Corticostriatal synaptic plasticity, a cellular basis for motor controlling, has been proven to participate in the pathogenesis of many behavior disorders. Based on the reports about the involvement of epigenetic DNA alterations in PRS-induced long-term effects, this research investigated the influence of PRS on the development and maturation of corticostriatal synaptic plasticity and related behaviors and explored the underlying epigenetic mechanism. Subjects were male offspring of dams that were exposed to stress three times per day from the 10th day of pregnancy until delivery. The development and maturation of plasticity at corticostriatal synapses, dopamine signaling, behavioral habituation, and DNA methylation were examined and analyzed. Control mice expressed long-term potentiation (LTP) at corticostriatal synapses during postnatal days (PD) 12-14 and produced long-term depression (LTD) during PD 20-60. However, PRS mice exhibited sustained LTP during PD 12-60. The treatment with dopamine 2 receptor (D2R) agonist quinpirole recovered striatal LTD and improved the impaired behavioral habituation in PD 45 adult PRS mice. Additionally, adult PRS mice showed reduced D2R, excess DNA methyltransferase 1 (DNMT1), increased binding of DNMT1 to D2R promoter, and hypermethylation at D2R promoter in the striatum. The DNMT1 inhibitor 5-aza-deoxycytidine restored striatal synaptic plasticity and improved behavioral habituation in adult PRS mice via D2R-mediated dopamine signaling. DNMT1-associated D2R hypermethylation is responsible for altering the maturation of plasticity at corticostriatal synapses and impairing the behavioral habituation in PRS mice.

SCH23390 Reduces Methamphetamine Self-Administration and Prevents Methamphetamine-Induced Striatal LTD

Extended-access methamphetamine self-administration results in unregulated intake of the drug; however, the role of dorsal striatal dopamine D1-like receptors (D1Rs) in the reinforcing properties of methamphetamine under extended-access conditions is unclear. Acute (ex vivo) and chronic (in vivo) methamphetamine exposure induces neuroplastic changes in the dorsal striatum, a critical region implicated in instrumental learning. For example, methamphetamine exposure alters high-frequency stimulation (HFS)-induced long-term depression in the dorsal striatum; however, the effect of methamphetamine on HFS-induced long-term potentiation (LTP) in the dorsal striatum is unknown. In the current study, dorsal striatal infusion of SCH23390, a D1R antagonist, prior to extended-access methamphetamine self-administration reduced methamphetamine addiction-like behavior. Reduced behavior was associated with reduced expression of PSD-95 in the dorsal striatum. Electrophysiological findings demonstrate that superfusion of methamphetamine reduced basal synaptic transmission and HFS-induced LTP in dorsal striatal slices, and SCH23390 prevented this effect. These results suggest that alterations in synaptic transmission and synaptic plasticity induced by acute methamphetamine via D1Rs could assist with methamphetamine-induced modification of corticostriatal circuits underlying the learning of goal-directed instrumental actions and formation of habits, mediating escalation of methamphetamine self-administration and methamphetamine addiction-like behavior.

Mathematical modeling and parameter estimation of levodopa motor response in patients with parkinson disease

Parkinson disease (PD) is characterized by a clear beneficial motor response to levodopa (LD) treatment. However, with disease progression and longer LD exposure, drug-related motor fluctuations usually occur. Recognition of the individual relationship between LD concentration and its effect may be difficult, due to the complexity and variability of the mechanisms involved. This work proposes an innovative procedure for the automatic estimation of LD pharmacokinetics and pharmacodynamics parameters, by a biologically-inspired mathematical model. An original issue, compared with previous similar studies, is that the model comprises not only a compartmental description of LD pharmacokinetics in plasma and its effect on the striatal neurons, but also a neurocomputational model of basal ganglia action selection. Parameter estimation was achieved on 26 patients (13 with stable and 13 with fluctuating LD response) to mimic plasma LD concentration and alternate finger tapping frequency along four hours after LD administration, automatically minimizing a cost function of the difference between simulated and clinical data points. Results show that individual data can be satisfactorily simulated in all patients and that significant differences exist in the estimated parameters between the two groups. Specifically, the drug removal rate from the effect compartment, and the Hill coefficient of the concentration-effect relationship were significantly higher in the fluctuating than in the stable group. The model, with individualized parameters, may be used to reach a deeper comprehension of the PD mechanisms, mimic the effect of medication, and, based on the predicted neural responses, plan the correct management and design innovative therapeutic procedures.

Striatal Dopamine D2 Receptors Regulate Cost Sensitivity and Behavioral Thrift

The role of the dopamine D2 receptor (D2R) in regulating appetitive behavior continues to be controversial. Earlier literature suggests that reduced D2R signaling diminishes motivated behavior while more recent theories suggest that reduced D2R, as has been putatively observed in obesity, facilitates compulsive appetitive behavior and promotes overeating. Using a homecage foraging paradigm with mice, we revisit classic neuroleptic pharmacological studies from the 1970s that led to the 'extinction mimicry' hypothesis: that dopamine blockade reduces reinforcement leading to an extinction-like reduction in a learned, motivated behavior. We complement this with a selective genetic deletion of D2R in indirect pathway medium spiny neurons (iMSNs). Administration of haloperidol shifts foraging strategy toward less effortful, more thrifty pursuit of food without altering consumption or bodyweight. D2R deletion in iMSNs also reduces effort and energy expended toward food pursuit, but without a compensatory shift in foraging strategy, resulting in loss of body weight, an effect more pronounced under conditions of escalating costs as the knockouts fail to adequately increase effort. The selective knockouts exhibit no change in sucrose preference or sucrose reinforcement. These data suggest that striatal D2R regulates effort in response to costs, mediating cost sensitivity and behavioral thrift. In the context of obesity, these data suggest that reduced D2R is more likely to diminish effort and behavioral energy expenditure rather than increase appetitive motivation and consumption, possibly contributing to reduced physical activity commonly observed in obesity.

Corticostriatal synaptic plasticity alterations in the R6/1 transgenic mouse model of Huntington's disease

Huntington's disease (HD) is a genetic neurodegenerative condition characterized by abnormal dopamine (DA)-glutamate interactions, severe alterations in motor control, and reduced behavioral flexibility. Experimental models of disease show that during symptomatic phases, HD shares with other hyperkinetic disorders the loss of synaptic depotentiation in the striatal spiny projection neurons (SPNs). Here we test the hypothesis that corticostriatal long-term depression (LTD), a well-conserved synaptic scaling down response to environmental stimuli, is also altered in symptomatic male R6/1 mice, a HD model with gradual development of symptoms. In vitro patch-clamp and intracellular recordings of corticostriatal slices from R6/1 mice confirm that, similar to other models characterized by hyperkinesia and striatal DA D1 receptor pathway dysregulation, once long-term potentiation (LTP) is induced, synaptic depotentiation is lost. Our new observations show that activity-dependent LTD was abolished in SPNs of mutant mice. In an experimental condition in which N-methyl-d-aspartate (NMDA) receptors are normally not recruited, in vitro bath application of DA revealed an abnormal response of D1 receptors that caused a shift in synaptic plasticity direction resulting in an NMDA-dependent LTP. Our results demonstrate that corticostriatal LTD is lost in R6/1 mouse model and confirm the role of aberrant DA-glutamate interactions in the alterations of synaptic scaling down associated with HD symptoms.

Compensatory Relearning Following Stroke: Cellular and Plasticity Mechanisms in Rodents

von Monakow’s theory of diaschisis states the functional ‘standstill’ of intact brain regions that are remote from a damaged area, often implied in recovery of function. Accordingly, neural plasticity and activity patterns related to recovery are also occurring at the same regions. Recovery relies on plasticity in the periinfarct and homotopic contralesional regions and involves relearning to perform movements. Seeking evidence for a relearning mechanism following stroke, we found that rodents display many features that resemble classical learning and memory mechanisms. Compensatory relearning is likely to be accompanied by gradual shaping of these regions and pathways, with participating neurons progressively adapting cortico-striato-thalamic activity and synaptic strengths at different cortico-thalamic loops – adapting function relayed by the striatum. Motor cortex functional maps are progressively reinforced and shaped by these loops as the striatum searches for different functional actions. Several cortical and striatal cellular mechanisms that influence motor learning may also influence post-stroke compensatory relearning. Future research should focus on how different neuromodulatory systems could act before, during or after rehabilitation to improve stroke recovery.

Metaplasticity at the addicted tetrapartite synapse: A common denominator of drug induced adaptations and potential treatment target for addiction

In light of the current worldwide addiction epidemic, the need for successful therapies is more urgent than ever. Although we made substantial progress in our basic understanding of addiction, reliable therapies are lacking. Since 40-60% of patients treated for substance use disorder return to active substance use within a year following treatment discharge, alleviating the vulnerability to relapse is regarded as the most promising avenue for addiction therapy. Preclinical addiction research often focuses on maladaptive synaptic plasticity within the reward pathway. However, drug induced neuroadaptations do not only lead to a strengthening of distinct drug associated cues and drug conditioned behaviors, but also seem to increase plasticity thresholds for environmental stimuli that are not associated with the drug. This form of higher order plasticity, or synaptic metaplasticity, is not expressed as a change in the efficacy of synaptic transmission but as a change in the direction or degree of plasticity induced by a distinct stimulation pattern. Experimental addiction research has demonstrated metaplasticity after exposure to multiple classes of addictive drugs. In this review we will focus on the concept of synaptic metaplasticity in the context of preclinical addiction research. We will take a closer look at the tetrapartite glutamatergic synapse and outline forms of metaplasticity that have been described at the addicted synapse. Finally we will discuss the different potential avenues for pharmacotherapies that target glutamatergic synaptic plasticity and metaplasticity. Here we will argue that aberrant metaplasticity renders the reward seeking circuitry more rigid and hence less able to adapt to changing environmental contingencies. An understanding of the molecular mechanisms that underlie this metaplasticity is crucial for the development of new strategies for addiction therapy. The correction of drug-induced metaplasticity could be used to support behavioral and pharmacotherapies for the treatment of addiction.

Functional Relevance of Endocannabinoid-Dependent Synaptic Plasticity in the Central Nervous System

The endocannabinoid (eCB) signaling system plays a key role in short-term and long-term synaptic plasticity in brain regions involved in various neural functions ranging from action selection to appetite control. This review will explore the role of eCBs in shaping neural circuit function to regulate behaviors. In particular, we will discuss the behavioral consequences of eCB mediated long-term synaptic plasticity in different brain regions. This review brings together evidence from in vitro and ex vivo studies and points out the need for more in vivo studies.

Dual Dopaminergic Regulation of Corticostriatal Plasticity by Cholinergic Interneurons and Indirect Pathway Medium Spiny Neurons

Endocannabinoid (eCB)-mediated long-term depression (LTD) requires dopamine (DA) D2 receptors (D2Rs) for eCB mobilization. The cellular locus of the D2Rs involved in LTD induction remains highly debated. We directly examined the role in LTD induction of D2Rs expressed by striatal cholinergic interneurons (Chls) and indirect pathway medium spiny neurons (iMSNs) using neuron-specific targeted deletion of D2Rs. Deletion of Chl-D2Rs (Chl-Drd2KO) impaired LTD induction in both subtypes of MSNs. LTD induction was restored in the Chl-Drd2KO mice by an M1-selective muscarinic acetylcholine receptor antagonist. In contrast, after the deletion of iMSN-D2Rs (iMSN-Drd2KO), LTD induction was intact in MSNs. Separate interrogation of direct pathway and iMSNs revealed a deficit in LTD induction only at synapses onto iMSNs that lack D2Rs. LTD induction in iMSNs was restored by D2R agonist application. Our findings suggest that Chl D2Rs strongly modulate LTD induction in MSNs, with iMSN-D2Rs having a weaker, iMSN-specific, modulatory effect.

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.

Basal ganglia mechanisms in action selection, plasticity, and dystonia

Basal ganglia circuits are organized to selected desired actions and to inhibit potentially competing unwanted actions. This is accomplished through a complex circuitry that is modified through development and learning. Mechanisms of neural plasticity underlying these modifications are increasingly understood, but new mechanisms continue to be discovered. Dystonia, a movement disorder characterized by involuntary muscle contractions that cause abnormal postures and movements. Emerging evidence points to important links between mechanisms of plasticity and the manifestations of dystonia. Investigation of these mechanisms has improved understanding of the action of currently used medication and is informing the development of new treatments.

To Do or Not to Do: Dopamine, Affordability and the Economics of Opportunity

Five years ago, we introduced the thrift hypothesis of dopamine (DA), suggesting that the primary role of DA in adaptive behavior is regulating behavioral energy expenditure to match the prevailing economic conditions of the environment. Here we elaborate that hypothesis with several new ideas. First, we introduce the concept of affordability, suggesting that costs must necessarily be evaluated with respect to the availability of resources to the organism, which computes a value not only for the potential reward opportunity, but also the value of resources expended. Placing both costs and benefits within the context of the larger economy in which the animal is functioning requires consideration of the different timescales against which to compute resource availability, or average reward rate. Appropriate windows of computation for tracking resources requires corresponding neural substrates that operate on these different timescales. In discussing temporal patterns of DA signaling, we focus on a neglected form of DA plasticity and adaptation, changes in the physical substrate of the DA system itself, such as up- and down-regulation of receptors or release probability. We argue that changes in the DA substrate itself fundamentally alter its computational function, which we propose mediates adaptations to longer temporal horizons and economic conditions. In developing our hypothesis, we focus on DA D2 receptors (D2R), arguing that D2R implements a form of “cost control” in response to the environmental economy, serving as the “brain’s comptroller”. We propose that the balance between the direct and indirect pathway, regulated by relative expression of D1 and D2 DA receptors, implements affordability. Finally, as we review data, we discuss limitations in current approaches that impede fully investigating the proposed hypothesis and highlight alternative, more semi-naturalistic strategies more conducive to neuroeconomic investigations on the role of DA in adaptive behavior.

The Altered Supramolecular Structure of Dopamine D2 Receptors in Disc1-deficient Mice

Disc1 is a susceptibility gene for psychiatric disorders including schizophrenia. It has been suggested that excess transmission through dopamine type 2 receptors (D2Rs) in the striatum is an underlying mechanism of pathogenesis. In this study, we used super-resolution microscopy to study the distribution of D2Rs at the nanoscale in mice lacking exons 2 and 3 of Disc1 (Disc1-deficient mice). We found that D2Rs in the nucleus accumbens (NAc) of wild-type mice form nanoclusters (~ 20,000 nm²), and that Disc1-deficient mice have larger and more D2R nanoclusters than wild-type mice. Interestingly, administration of clozapine reduced the size and spatial distribution of the nanoclusters only in Disc1-deficient mice. Moreover, we observed that medium spiny neurons in the NAc of Disc1-deficient mice had reduced spine density on their dendrites than did wild-type mice, and this was also reversed by clozapine administration. The altered D2R nanoclusters might be morphological representations of the altered dopaminergic transmission in disease states such as schizophrenia.

Regulation of Striatal Neuron Activity by Cyclic Nucleotide Signaling and Phosphodiesterase Inhibition: Implications for the Treatment of Parkinson's Disease

Cyclic nucleotide phosphodiesterase (PDE) enzymes catalyze the hydrolysis and inactivation of cyclic nucleotides (cAMP/cGMP) in the brain. Several classes of PDE enzymes with distinct tissue distributions, cyclic nucleotide selectivity, and regulatory factors are highly expressed in brain regions subserving cognitive and motor processes known to be disrupted in neurodegenerative diseases such as Parkinson's disease (PD). Furthermore, small-molecule inhibitors of several different PDE family members alter cyclic nucleotide levels and favorably enhance motor performance and cognition in animal disease models. This chapter will explore the roles and therapeutic potential of non-selective and selective PDE inhibitors on neural processing in fronto-striatal circuits in normal animals and models of DOPA-induced dyskinesias (LIDs) associated with PD. The impact of selective PDE inhibitors and augmentation of cAMP and cGMP signaling on the membrane excitability of striatal medium-sized spiny projection neurons (MSNs) will be discussed. The effects of cyclic nucleotide signaling and PDE inhibitors on synaptic plasticity of striatonigral and striatopallidal MSNs will be also be reviewed. New data on the efficacy of PDE10A inhibitors for reversing behavioral and electrophysiological correlates of L-DOPA-induced dyskinesias in a rat model of PD will also be presented. Together, these data will highlight the potential of novel PDE inhibitors for treatment of movement disorders such as PD which are associated with abnormal corticostriatal transmission.

Chronic Nicotine Alters Corticostriatal Plasticity in the Striatopallidal Pathway Mediated By NR2B-Containing Silent Synapses

Smoking is the leading cause of preventable death in the United States and success rates for quitting remain low. High relapse rates are attributed to pervasive nicotine-reinforced associative learning of incentive cues that is highly resistant to extinction. Why such learning is so persistent is poorly understood but may arise as a consequence of neuroadaptations in synaptic plasticity induced by chronic nicotine. We used whole-cell patch clamp recording to investigate the effect of chronic nicotine (cNIC) on synaptic plasticity in dopamine D2 receptor-expressing medium-spiny neurons in the indirect, striatopallidal pathway in dorsolateral striatum. Mice exposed to cNIC exhibited long-term potentiation in response to high-frequency stimulation instead of the expected depression. cNIC decreased baseline AMPA/NMDA ratio, arising from increased NMDA currents enriched in the NR2B subunit with a concomitant upregulation of NMDA-only, silent synapses. These data demonstrate that cNIC can increase silent synapses in MSNs, as observed with cocaine and opiates, and alter the regulation of corticostriatal plasticity. Prior work has characterized cocaine- and morphine-induced upregulation of silent synapses in the ventral striatum; we show it can occur in the dorsal striatum, a region associated with later stages of addiction, craving, and cue-induced relapse.

The leukotriene B4 receptors BLT1 and BLT2 form an antagonistic sensitizing system in peripheral sensory neurons

Sensitization of the heat-activated ion channel transient receptor potential vanilloid 1 (TRPV1) through lipids is a fundamental mechanism during inflammation-induced peripheral sensitization. Leukotriene B4 is a proinflammatory lipid mediator whose role in peripheral nociceptive sensitization is not well understood to date. Two major G-protein-coupled receptors for leukotriene B4 have been identified: the high-affinity receptor BLT1 and the low-affinity receptor BLT2. Transcriptional screening for the expression G-protein-coupled receptors in murine dorsal root ganglia showed that both receptors were among the highest expressed in dorsal root ganglia. Calcium imaging revealed a sensitization of TRPV1-mediated calcium increases in a relative narrow concentration range for leukotriene B4 (100-200 nm). Selective antagonists and neurons from knock-out mice demonstrated a BLT1-dependent sensitization of TRPV1-mediated calcium increases. Accordingly, leukotriene B4-induced thermal hyperalgesia was mediated through BLT1 and TRPV1 as shown using the respective knock-out mice. Importantly, higher leukotriene B4 concentrations (>0.5 μm) and BLT2 agonists abolished sensitization of the TRPV1-mediated calcium increases. Also, BLT2 activation inhibited protein kinase C- and protein kinase A-mediated sensitization processes through the phosphatase calcineurin. Consequently, a selective BLT2-receptor agonist increased thermal and mechanical withdrawal thresholds during zymosan-induced inflammation. In accordance with these data, immunohistochemical analysis showed that both leukotriene B4 receptors were expressed in peripheral sensory neurons. Thus, the data show that the two leukotriene B4 receptors have opposing roles in the sensitization of peripheral sensory neurons forming a self-restricting system.

Impaired novelty acquisition and synaptic plasticity in congenital hyperammonemia caused by hepatic glutamine synthetase deficiency

Genetic defects in ammonia metabolism can produce irreversible damage of the developing CNS causing an impairment of cognitive and motor functions. We investigated alterations in behavior, synaptic plasticity and gene expression in the hippocampus and dorsal striatum of transgenic mice with systemic hyperammonemia resulting from conditional knockout of hepatic glutamine synthetase (LGS-ko). These mice showed reduced exploratory activity and delayed habituation to a novel environment. Field potential recordings from LGS-ko brain slices revealed significantly reduced magnitude of electrically-induced long-term potentiation (LTP) in both CA3-CA1 hippocampal and corticostriatal synaptic transmission. Corticostriatal but not hippocampal slices from LGS-ko brains demonstrated also significant alterations in long-lasting effects evoked by pharmacological activation of glutamate receptors. Real-time RT-PCR revealed distinct patterns of dysregulated gene expression in the hippocampus and striatum of LGS-ko mice: LGS-ko hippocampus showed significantly modified expression of mRNAs for mGluR1, GluN2B subunit of NMDAR, and A1 adenosine receptors while altered expression of mRNAs for D1 dopamine receptors, the M1 cholinoreceptor and the acetylcholine-synthetizing enzyme choline-acetyltransferase was observed in LGS-ko striatum. Thus, inborn systemic hyperammonemia resulted in significant deficits in novelty acquisition and disturbed synaptic plasticity in corticostriatal and hippocampal pathways involved in learning and goal-directed behavior.

Neural plasticity and network remodeling: From concepts to pathology

Neuroplasticity has been subject to a great deal of research in the last century. Recently, significant emphasis has been placed on the global effect of localized plastic changes throughout the central nervous system, and on how these changes integrate in a pathological context. Specifically, alterations of network functionality have been described in various pathological contexts to which corresponding structural alterations have been proposed. However, considering the amount of literature and the different pathological contexts, an integration of this information is still lacking. In this paper we will review the concepts of neural plasticity as well as their repercussions on network remodeling and provide a possible explanation to how these two concepts relate to each other. We will further examine how alterations in different pathological contexts may relate to each other and will discuss the concept of plasticity diseases, its models and implications.

Caspr3-Deficient Mice Exhibit Low Motor Learning during the Early Phase of the Accelerated Rotarod Task

Caspr3 (Contactin-associated protein-like 3, Cntnap3) is a neural cell adhesion molecule belonging to the Caspr family. We have recently shown that Caspr3 is expressed abundantly between the first and second postnatal weeks in the mouse basal ganglia, including the striatum, external segment of the globus pallidus, subthalamic nucleus, and substantia nigra. However, its physiological role remains largely unknown. In this study, we conducted a series of behavioral analyses on Capsr3-knockout (KO) mice and equivalent wild-type (WT) mice to investigate the role of Caspr3 in brain function. No significant differences were observed in most behavioral traits between Caspr3-KO and WT mice, but we found that Caspr3-KO mice performed poorly during the early phase of the accelerated rotarod task in which latency to falling off a rod rotating with increasing velocity was examined. In the late phase, the performance of the Caspr3-KO mice caught up to the level of WT mice, suggesting that the deletion of Caspr3 caused a delay in motor learning. We then examined changes in neural activity after training on the accelerated rotarod by conducting immunohistochemistry using antibody to c-Fos, an indirect marker for neuronal activity. Experience of the accelerated rotarod task caused increases in the number of c-Fos-positive cells in the dorsal striatum, cerebellum, and motor cortex in both Caspr3-KO and WT mice, but the number of c-Fos-positive cells was significantly lower in the dorsal striatum of Caspr3-KO mice than in that of WT mice. The expression of c-Fos in the ventral striatum of Caspr3-KO and WT mice was not altered by the training. Our findings suggest that reduced activation of neural cells in the dorsal striatum in Caspr3-KO mice leads to a decline in motor learning in the accelerated rotarod task.

Differential CaMKII regulation by voltage-gated calcium channels in the striatum

Calcium signaling regulates synaptic plasticity and many other functions in striatal medium spiny neurons to modulate basal ganglia function. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is a major calcium-dependent signaling protein that couples calcium entry to diverse cellular changes. CaMKII activation results in autophosphorylation at Thr286 and sustained calcium-independent CaMKII activity after calcium signals dissipate. However, little is known about the mechanisms regulating striatal CaMKII. To address this, mouse brain slices were treated with pharmacological modulators of calcium channels and punches of dorsal striatum were immunoblotted for CaMKII Thr286 autophosphorylation as an index of CaMKII activation. KCl depolarization increased levels of CaMKII autophosphorylation ~2-fold; this increase was blocked by an LTCC antagonist and was mimicked by treatment with pharmacological LTCC activators. The chelation of extracellular calcium robustly decreased basal CaMKII autophosphorylation within 5min and increased levels of total CaMKII in cytosolic fractions, in addition to decreasing the phosphorylation of CaMKII sites in the GluN2B subunit of NMDA receptors and the GluA1 subunit of AMPA receptors. We also found that the maintenance of basal levels of CaMKII autophosphorylation requires low-voltage gated T-type calcium channels, but not LTCCs or R-type calcium channels. Our findings indicate that CaMKII activity is dynamically regulated by multiple calcium channels in the striatum thus coupling calcium entry to key downstream substrates.

Dopaminergic Modulation of Striatal Inhibitory Transmission and Long-Term Plasticity

Dopamine (DA) modulates glutamatergic synaptic transmission and its plasticity in the striatum; however it is not well known how DA modulates long-term plasticity of striatal GABAergic inhibitory synapses. This work focused on the analysis of both dopaminergic modulation of inhibitory synapses and the synaptic plasticity established between GABAergic afferents to medium spiny neurons (MSNs). Our results showed that low and high DA concentrations mainly reduced the amplitude of inhibitory synaptic response; however detailed analysis of the D1 and D2 participation in this modulation displayed a wide variability in synaptic response. Analyzing DA participation in striatal GABAergic plasticity we observed that high frequency stimulation (HFS) of GABAergic interneurons in the presence of DA at a low concentration (200 nM) favored the expression of inhibitory striatal LTD, whereas higher concentration of DA (20 μM) primarily induced LTP. Interestingly, the plasticity induced in an animal model of striatal degeneration mimicked that induced in the presence of DA at a high concentration, which was not abolished with D2 antagonist but was prevented by PKA blocker.

Rhes influences striatal cAMP/PKA-dependent signaling and synaptic plasticity in a gender-sensitive fashion

Mechanisms of gender-specific synaptic plasticity in the striatum, a brain region that controls motor, cognitive and psychiatric functions, remain unclear. Here we report that Rhes, a GTPase enriched in medium spiny neurons (MSNs) of striatum, alters the striatal cAMP/PKA signaling cascade in a gender-specific manner. While Rhes knockout (KO) male mice, compared to wild-type (WT) mice, had a significant basal increase of cAMP/PKA signaling pathway, the Rhes KO females exhibited a much stronger response of this pathway, selectively under the conditions of dopamine/adenosine-related drug challenge. Corticostriatal LTP defects are exclusively found in A2AR/D2R-expressing MSNs of KO females, compared to KO males, an effect that is abolished by PKA inhibitors but not by the removal of circulating estrogens. This suggests that the synaptic alterations found in KO females could be triggered by an aberrant A2AR/cAMP/PKA activity, but not due to estrogen-mediated effect. Consistent with increased cAMP signaling, D1R-mediated motor stimulation, haloperidol-induced catalepsy and caffeine-evoked hyper-activity are robustly enhanced in Rhes KO females compared to mutant males. Thus Rhes, a thyroid hormone-target gene, plays a relevant role in gender-specific synaptic and behavioral responses.

Presynaptic D2 dopamine receptors control long-term depression expression and memory processes in the temporal hippocampus

BACKGROUND

Dysfunctional mesocorticolimbic dopamine signaling has been linked to alterations in motor and reward-based functions associated with psychiatric disorders. Converging evidence from patients with psychiatric disorders and use of antipsychotics suggests that imbalance of dopamine signaling deeply alters hippocampal functions. However, given the lack of full characterization of a functional mesohippocampal pathway, the precise role of dopamine transmission in memory deficits associated with these disorders and their dedicated therapies is unknown. In particular, the positive outcome of antipsychotic treatments, commonly antagonizing D2 dopamine receptors (D2Rs), on cognitive deficits and memory impairments remains questionable.

METHODS

Following pharmacologic and genetic manipulation of dopamine transmission, we performed anatomic, neurochemical, electrophysiologic, and behavioral investigations to uncover the role of D2Rs in hippocampal-dependent plasticity and learning. Naïve mice (n = 4-21) were used in the different procedures.

RESULTS

Dopamine modulated both long-term potentiation and long-term depression in the temporal hippocampus as well as spatial and recognition learning and memory in mice through D2Rs. Although genetic deletion or pharmacologic blockade of D2Rs led to the loss of long-term potentiation expression, the specific genetic removal of presynaptic D2Rs impaired long-term depression and performances on spatial memory tasks.

CONCLUSIONS

Presynaptic D2Rs in dopamine fibers of the temporal hippocampus tightly modulate long-term depression expression and play a major role in the regulation of hippocampal learning and memory. This direct role of mesohippocampal dopamine input as uncovered here adds a new dimension to dopamine involvement in the physiology underlying deficits associated with neuropsychiatric disorders.

Long-term depression at distinct glutamatergic synapses in the basal ganglia

Long-term adaptations of synaptic transmission are believed to be the cellular basis of information storage in the brain. In particular, long-term depression of excitatory neurotransmission has been under intense investigation since convergent lines of evidence support a crucial role for this process in learning and memory. Within the basal ganglia, a network of subcortical nuclei forming a key part of the extrapyramidal motor system, plasticity at excitatory synapses is essential to the regulation of motor, cognitive, and reward functions. The striatum, the main gateway of the basal ganglia, receives convergent excitatory inputs from cortical areas and transmits information to the network output structures and is a major site of activity-dependent plasticity. Indeed, long-term depression at cortico-striatal synapses modulates the transfer of information to basal ganglia output structures and affects voluntary movement execution. Cortico-striatal plasticity is thus considered as a cellular substrate for adaptive motor control. Downstream in this network, the subthalamic nucleus and substantia nigra nuclei also receive glutamatergic innervation from the cortex and the subthalamic nucleus, respectively. Although these connections have been less investigated, recent studies have started to unravel the molecular mechanisms that contribute to adjustments in the strength of cortico-subthalamic and subthalamo-nigral transmissions, revealing that adaptations at these synapses governing the output of the network could also contribute to motor planning and execution. Here, we review our current understanding of long-term depression mechanisms at basal ganglia glutamatergic synapses and emphasize the common and unique plastic features observed at successive levels of the network in healthy and pathological conditions.

Electroacupuncture-Induced Neuroprotection against Cerebral Ischemia in Rats: Role of the Dopamine D2 Receptor

Background. Cerebral ischemia is known to produce brain damage and related behavioural deficits, including memory deficits and motor disorders. Evidence shows that EA significantly promotes recovery of neurological function and thus improves quality of life. Objective. Evidence exists for the involvement of catecholamines in human neuroplasticity. A better understanding of dopaminergic (DAergic) modulation in this process will be important. Methods. A total of 72 adult male Sprague-Dawley (SD) rats were divided into 6 groups: normal, model, EA, spiperone group, EA + spiperone group, and pergolide. The middle cerebral artery occlusion (MCAO) model was used in all 6 groups except the normal group. A behavioural assessment was conducted at 1, 3, 5, and 7 days after MCAO. The percent of brain infarct area was also determined 7 days after MCAO. Tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP-43) fluorescence double labeling was performed in the striatum. Results. In this study, we found that EA at Fengchi (GB20) acupoints resulted in marked improvements based on a behavioural assessment. Both TTC staining and GAP-43 immunofluorescence labeling results showed that EA treatment reduced ischemia injury and promoted neuroplasticity compared with the model group. The D2R-selective agonist, pergolide, showed similar results, but these results were reversed by the D2R-selective antagonist, spiperone. We also found that there were more colocalization and expression of GAP-43 and TH in the EA and pergolide groups than those in the other groups. Conclusion. These results suggest that the neuroplasticity induced by EA was mediated by D2 autoreceptors in DAergic neurons.

Molecular and cellular mechanisms of dopamine-mediated behavioral plasticity in the striatum

The striatum is the input structure of the basal ganglia system. By integrating glutamatergic signals from cortical and subcortical regions and dopaminergic signals from mesolimbic nuclei the striatum functions as an important neural substrate for procedural and motor learning as well as for reward-guided behaviors. In addition, striatal activity is significantly altered in pathological conditions in which either a loss of dopamine innervation (Parkinson's disease) or aberrant dopamine-mediated signaling (drug addiction and L-DOPA induced dyskinesia) occurs. Here we discuss cellular mechanisms of striatal synaptic plasticity and aspects of cell signaling underlying striatum-dependent behavior, with a major focus on the neuromodulatory action of the endocannabinoid system and on the role of the Ras-ERK cascade.

A comparison of the subsecond dynamics of neurotransmission of dopamine and serotonin

The neuromodulators dopamine (DA) and serotonin (5-hydroxytryptamine; 5-HT) are similar in a number of ways. Both monoamines can act by volume transmission at metabotropic receptors to modulate synaptic transmission in brain circuits. Presynaptic regulation of 5-HT and DA is governed by parallel processes, and behaviorally, both exert control over emotional processing. However, differences are also apparent: more than twice as many 5-HT receptor subtypes mediate postsynaptic effects than DA receptors and different presynaptic regulation is also emerging. Monoamines are amenable to real-time electrochemical detection using fast scan cyclic voltammetry (FSCV), which allows resolution of the subsecond dynamics of release and reuptake in response to a single action potential. This approach has greatly enriched understanding of DA transmission and has facilitated an integrated view of how DA mediates behavioral control. However, technical challenges are associated with FSCV measurement of 5-HT and understanding of 5-HT transmission at subsecond resolution has not advanced at the same rate. As a result, how the actions of 5-HT at the level of the synapse translate into behavior is poorly understood. Recent technical advances may aid the study of 5-HT in real-time. It is timely, therefore, to compare and contrast what is currently understood of the subsecond characteristics of transmission for DA and 5-HT. In doing so, a number of areas are highlighted as being worthy of exploration for 5-HT.

A role for dopamine-mediated learning in the pathophysiology and treatment of Parkinson's disease

Dopamine contributes to corticostriatal plasticity and motor learning. Dopamine denervation profoundly alters motor performance, as in Parkinson's disease (PD); however, the extent to which these symptoms reflect impaired motor learning is unknown. Here, we demonstrate a D2 receptor blockade-induced aberrant learning that impedes future motor performance when dopamine signaling is restored, an effect diminished by coadministration of adenosine antagonists during blockade. We hypothesize that an inappropriate corticostriatal potentiation in striatopallidal cells of the indirect pathway underlies aberrant learning. We demonstrate synaptic potentiation in striatopallidal neurons induced by D2 blockade and diminished by application of an adenosine antagonist, consistent with behavioral observations. A neurocomputational model of the basal ganglia recapitulates the behavioral pattern and further links aberrant learning to plasticity in the indirect pathway. Thus, D2-mediated aberrant learning may contribute to motor deficits in PD, suggesting new avenues for the development of therapeutics.

Distinct roles of dopamine and subthalamic nucleus in learning and probabilistic decision making

Even simple behaviour requires us to make decisions based on combining multiple pieces of learned and new information. Making such decisions requires both learning the optimal response to each given stimulus as well as combining probabilistic information from multiple stimuli before selecting a response. Computational theories of decision making predict that learning individual stimulus–response associations and rapid combination of information from multiple stimuli are dependent on different components of basal ganglia circuitry. In particular, learning and retention of memory, required for optimal response choice, are significantly reliant on dopamine, whereas integrating information probabilistically is critically dependent upon functioning of the glutamatergic subthalamic nucleus (computing the ‘normalization term’ in Bayes’ theorem). Here, we test these theories by investigating 22 patients with Parkinson’s disease either treated with deep brain stimulation to the subthalamic nucleus and dopaminergic therapy or managed with dopaminergic therapy alone. We use computerized tasks that probe three cognitive functions—information acquisition (learning), memory over a delay and information integration when multiple pieces of sequentially presented information have to be combined. Patients performed the tasks ON or OFF deep brain stimulation and/or ON or OFF dopaminergic therapy. Consistent with the computational theories, we show that stopping dopaminergic therapy impairs memory for probabilistic information over a delay, whereas deep brain stimulation to the region of the subthalamic nucleus disrupts decision making when multiple pieces of acquired information must be combined. Furthermore, we found that when participants needed to update their decision on the basis of the last piece of information presented in the decision-making task, patients with deep brain stimulation of the subthalamic nucleus region did not slow down appropriately to revise their plan, a pattern of behaviour that mirrors the impulsivity described clinically in some patients with subthalamic nucleus deep brain stimulation. Thus, we demonstrate distinct mechanisms for two important facets of human decision making: first, a role for dopamine in memory consolidation, and second, the critical importance of the subthalamic nucleus in successful decision making when multiple pieces of information must be combined.