Cortico-basal ganglia circuits involved in different motivation disorders in non-human primates

Impact of deep brain stimulation on urogenital function in Parkinson's disease: a systematic review and meta-analysis

Objectives

Deep Brain Stimulation (DBS) effectively treats Parkinson's motor symptoms, but its effects on the urogenital system are debated.

Methods

A research was conducted in PubMed, Embase, Cochrane Library, Web of Science, and Scopus until February 27, 2024. We primarily focused on DBS's impact on Parkinson's patients' Urine storage function, voiding function, sexual function, and quality of life.

Results

Our meta-analysis included 14 studies. The main results showed that DBS resulted in fewer instances of urinary urgency (OR = 1.85, 95% CI: 1.26 to 2.70, p = 0.002) and increased maximum bladder capacity (MD = -66.10, 95% CI: -119.37 to -12.82, p = 0.02) in terms of urinary storage function. However, there were no significant differences in first desire to void and strong desire to void. In terms of voiding function, DBS showed significant improvements in maximum flow rate (MD = -0.64, 95% CI: -1.23 to -0.05, p = 0.03), post-void residual (MD = -6.79, 95% CI: 4.54 to 9.05, P < 0.00001) and detrusor pressure during maximum flow (MD = -1.37, 95% CI: -2.73 to -0.02, p = 0.05). Additionally, there was no significant difference in sexual function between the two groups (MD = -1.41, 95% CI: -12.40 to 9.57, p = 0.80).

Conclusion

DBS has demonstrated a certain degree of efficacy in ameliorating urinary storage and voiding function in patients with Parkinson's disease. However, certain urodynamic parameters or scores do not demonstrate any statistically significant disparities. Furthermore, DBS has no significant impact on erectile function in male Parkinson's patients.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023476661, identifier CRD42023476661.

SB-258585 reduces food motivation while blocking 5-HT6 receptors in the non-human primate striatum

The interest in new 5-HT₆ agents stems from their ability to modulate cognition processing, food motivation and anxiety-like behaviors. While these findings come primarily from rodent studies, no studies on primates have been published. Furthermore, our understanding of where and how they act in the brain remains limited. Although the striatum is involved in all of these processes and expresses the highest levels of 5-HT₆ receptors, few studies have focused on it. We thus hypothesized that 5-HT6 receptor blockade would influence food motivation and modulate behavioral expression in non-human primates through striatal 5-HT6 receptors. This study thus aimed to determine the effects of acute administration of the SB-258585 selective 5-HT6 receptor antagonist on the feeding motivation and behaviors of six male macaques. Additionally, we investigated potential 5-HT6 targets using PET imaging to measure 5-HT6 receptor occupancy throughout the brain and striatal subregions. We used a food-choice task paired with spontaneous behavioral observations, checking 5-HT6 receptor occupancy with the specific PET imaging [18F]2FNQ1P radioligand. We demonstrated, for the first time in non-human primates, that modulation of 5-HT6 transmission, most likely through the striatum (the putamen and caudate nucleus), significantly reduces food motivation while exhibiting variable, weaker effects on behavior. While these results are consistent with the literature showing a decrease in food intake in rodents and proposing that 5-HT6 receptor antagonists can be used in obesity treatment, they question the antagonists' anxiolytic potential.

Cerebello-basal Ganglia Networks and Cortical Network Global Efficiency

The cerebellum (CB) and basal ganglia (BG) each have topographically distinct functional subregions that are functionally and anatomically interconnected with cortical regions through discrete thalamic loops and with each other via disynaptic connections, with previous work detailing high levels of functional connectivity between these phylogenetically ancient regions. It was posited that this CB-BG network provides support for cortical systems processing, spanning cognitive, emotional, and motor domains, implying that subcortical network measures are strongly related to cortical network measures (Bostan & Strick, 2018); however, it is currently unknown how network measures within distinct CB-BG networks relate to cortical network measures. Here, 122 regions of interest comprising cognitive and motor CB-BG networks and 7 canonical cortical resting-state were used to investigate whether the integration (quantified using global efficiency, GE) of cognitive CB-BG network (CCBN) nodes and their segregation from motor CB-BG network (MCBN) nodes is related to cortical network GE and segregation in 233 non-related, right-handed participants (Human Connectome Project-1200). CCBN GE positively correlated with GE in the default mode, motor, and auditory networks and MCBN GE positively correlated with GE in all networks, except the default mode and emotional. MCBN segregation was related to motor network segregation. These findings highlight the CB-BG network's potential role in cortical networks associated with executive function, task switching, and verbal working memory. This work has implications for understanding cortical network organization and cortical-subcortical interactions in healthy adults and may help in determining biomarkers and deciphering subcortical differences seen in disease states.

Preferential Modulatory Action of 5-HT2A Receptors on the Dynamic Regulation of Basal Ganglia Circuits

In rodents, cortical information is transferred to the substantia nigra pars reticulata (SNr) through motor and medial prefrontal (mPF) basal ganglia (BG) circuits implicated in motor and cognitive/motivational behaviors, respectively. The serotonergic 5-HT_2A receptors are located in both of these neuronal networks, displaying topographical differences with a high expression in the associative/limbic territories, and a very low expression in the subthalamic nucleus. This study investigated whether the stimulation of 5-HT_2A receptors could have a specific signature on the dynamic regulation of BG circuits, preferentially modulating the mPF information processing through trans-striatal pathways. We performed in vivo single-unit extracellular recordings to assess the effect of the 5-HT_2A agonist TCB-2 on the spontaneous and cortically evoked activity of lateral and medial SNr neurons in male rats (involved in motor and mPF circuits, respectively). TCB-2 (50-200 µg/kg, i.v.) increased the basal firing rate and enhanced the cortically evoked inhibitory response of medial SNr neurons (transmission through the direct striato-nigral pathway). A prior administration of the preferential 5-HT_2A receptor antagonist MDL11939 (200 µg/kg, i.v.) did not modify any electrophysiological parameter, but occluded TCB-2-induced effects. In animals treated with the 5-HT synthesis inhibitor pCPA (4-chloro-dl-phenylalanine methyl ester hydrochloride), TCB-2 failed to induce the above-mentioned effects, thus suggesting the contribution of endogenous 5-HT. However, the mobilization of 5-HT induced by the acute administration of fluoxetine (10 mg/kg, i.p.) did not mimic the effects triggered by TCB-2. Overall, these data suggest that 5-HT_2A receptors have a preferential modulatory action on the dynamic regulation of BG circuitry.SIGNIFICANCE STATEMENT Motor and medial prefrontal (mPF) basal ganglia (BG) circuits play an important role in integrative brain functions like movement control or cognitive/motivational behavior, respectively. Although these neuronal networks express 5-HT_2A receptors, the expression is higher in associative/limbic structures than in the motor ones. We show a topographical-dependent dissociation in the effects triggered by the 5HT_2A agonist TCB-2, which specifically increases the medial substantia nigra pars reticulata neuron activity and has a preferential action on mPF information processing through the striato-nigral direct pathway. These are very likely to be 5-HT_2A receptor-mediated effects that require mobilization of the endogenous 5-HT system. These findings provide evidence about the specific signature of 5-HT_2A receptors on the dynamic regulation of BG circuits.

Impulsive and compulsive behaviors can be induced by opposite GABAergic dysfunctions inside the primate ventral pallidum

Introduction: The ventral pallidum (VP) is central in the limbic Basal Ganglia circuit, controlling both appetitive (approach) and aversive (avoidance) motivated behaviors. Nevertheless, VP involvement in pathological aspects remains unclear, especially in the behavioral expression of different motivational dysfunctions. This study aimed to investigate how the VP contributes to the expression of abnormal behaviors via opposite GABAergic dysfunctions. Methods: Opposite GABAergic dysfunctions were induced by injecting muscimol (a GABA_A agonist) and bicuculline (a GABA_A antagonist) into monkeys. We determined the effects of both substances on self-initiated behaviors in lab-chair and in free-moving home-cage contexts in six monkeys, and in two animals performing an approach-avoidance task in appetitive and aversive contexts. Results: While the self-initiated behaviors induced by bicuculline injections in VP were characterized by compulsive behaviors such as repetitive grooming and self-biting, muscimol injections induced impulsive behaviors including limb movements in a lab-chair context and exploration behaviors in a free-moving context. More specific behavioral effects were observed in the approach-avoidance task. The muscimol injections induced premature responses and erroneous screen touches, which characterize impulsive and attention disorders, while the bicuculline injections into the VP increased passive avoidance (non-initiated action) and task-escape in an aversive context, suggesting an anxiety disorder. Conclusions: These results show that activating or blocking GABAergic transmission in the VP impairs motivated behaviors. Furthermore, the behavioral expressions produced by these opposite disturbances show that the VP could be involved in anxiety-driven compulsive disorders, such as OCD, as well as in impulsive disorders motivated by attention deficits or reward-seeking, as seen in ADHD or impulse control disorders.

Cerebellar and basal ganglia motor network predicts trait depression and hyperactivity

In the human brain, the cerebellum (CB) and basal ganglia (BG) are implicated in cognition-, emotion-, and motor-related cortical processes and are highly interconnected, both to cortical regions via separate, trans-thalamic pathways and to each other via subcortical disynaptic pathways. We previously demonstrated a distinction between cognitive and motor CB-BG networks (CCBN, MCBN, respectively) as it relates to cortical network integration in healthy young adults, suggesting the subcortical networks separately support cortical networks. The CB and BG are also implicated in the pathophysiology of schizophrenia, Parkinson's, and compulsive behavior; thus, integration within subcortical CB-BG networks may be related to transdiagnostic symptomology. Here, we asked whether CCBN or MCBN integration predicted Achenbach Self-Report scores for anxiety, depression, intrusive thoughts, hyperactivity and inactivity, and cognitive performance in a community sample of young adults. We computed global efficiency for each CB-BG network and 7 canonical resting-state networks for all right-handed participants in the Human Connectome Project 1200 release with a complete set of preprocessed resting-state functional MRI data (N = 783). We used multivariate regression to control for substance abuse and age, and permutation testing with exchangeability blocks to control for family relationships. MCBN integration negatively predicted depression and hyperactivity, and positively predicted cortical network integration. CCBN integration predicted cortical network integration (except for the emotional network) and marginally predicted a positive relationship with hyperactivity, indicating a potential dichotomy between cognitive and motor CB-BG networks and hyperactivity. These results highlight the importance of CB-BG interactions as they relate to motivation and symptoms of depression.

Repetitive and Inflexible Active Coping and Addiction-like Neuroplasticity in Stressed Mice of a Helplessness-Resistant Inbred Strain

Dysfunctional coping styles are involved in the development, persistence, and relapse of psychiatric diseases. Passive coping with stress challenges (helplessness) is most commonly used in animal models of dysfunctional coping, although active coping strategies are associated with generalized anxiety disorder, social anxiety disorder, panic, and phobias as well as obsessive-compulsive and post-traumatic stress disorder. This paper analyzes the development of dysfunctional active coping strategies of mice of the helplessness–resistant DBA/2J (D2) inbred strain, submitted to temporary reduction in food availability in an uncontrollable and unavoidable condition. The results indicate that food-restricted D2 mice developed a stereotyped form of food anticipatory activity and dysfunctional reactive coping in novel aversive contexts and acquired inflexible and perseverant escape strategies in novel stressful situations. The evaluation of FosB/DeltaFosB immunostaining in different brain areas of food-restricted D2 mice revealed a pattern of expression typically associated with behavioral sensitization to addictive drugs and compulsivity. These results support the conclusion that an active coping style represents an endophenotype of mental disturbances characterized by perseverant and inflexible behavior.

Selective serotonin reuptake inhibitor treatment retunes emotional valence in primate ventral striatum

Selective serotonin reuptake inhibitors (SSRIs) are widely used to treat psychiatric disorders with affective biases such as depression and anxiety. How SSRIs exert a beneficial action on emotions associated with life events is still unknown. Here we ask whether and how the effectiveness of the SSRI fluoxetine is underpinned by neural mechanisms in the ventral striatum. To address these issues, we studied the spiking activity of neurons in the ventral striatum of monkeys during an approach-avoidance task in which the valence assigned to sensory stimuli was manipulated. Neural responses to positive and negative events were measured before and during a 4-week treatment with fluoxetine. We conducted PET scans to confirm that fluoxetine binds within the ventral striatum at a therapeutic dose. In our monkeys, fluoxetine facilitated approach of rewards and avoidance of punishments. These beneficial effects were associated with changes in tonic and phasic activities of striatal neurons. Fluoxetine increased the spontaneous firing rate of striatal neurons and amplified the number of cells responding to rewards versus punishments, reflecting a drug-induced positive shift in the processing of emotionally valenced information. These findings reveal how SSRI treatment affects ventral striatum neurons encoding positive and negative valence and striatal signaling of emotional information. In addition to a key role in appetitive processing, our results shed light on the involvement of the ventral striatum in aversive processing. Together, the ventral striatum appears to play a central role in the action of SSRIs on emotion processing biases commonly observed in psychiatric disorders.

Causal Evidence for Induction of Pessimistic Decision-Making in Primates by the Network of Frontal Cortex and Striosomes

Clinical studies have shown that patients with anxiety disorders exhibited coactivation of limbic cortices and basal ganglia, which together form a large-scale brain network. The mechanisms by which such a large-scale network could induce or modulate anxiety-like states are largely unknown. This article reviews our experimental program in macaques demonstrating a causal involvement of local striatal and frontal cortical sites in inducing pessimistic decision-making that underlies anxiety. Where relevant, we related these findings to the wider literature. To identify such sites, we have made a series of methodologic advances, including the combination of causal evidence for behavioral modification of pessimistic decisions with viral tracing methods. Critically, we introduced a version of the classic approach-avoidance (Ap-Av) conflict task, modified for use in non-human primates. We performed microstimulation of limbic-related cortical regions and the striatum, focusing on the pregenual anterior cingulate cortex (pACC), the caudal orbitofrontal cortex (cOFC), and the caudate nucleus (CN). Microstimulation of localized sites within these regions induced pessimistic decision-making by the monkeys, supporting the idea that the focal activation of these regions could induce an anxiety-like state, which subsequently influences decision-making. We further performed combined microstimulation and tract-tracing experiments by injecting anterograde viral tracers into focal regions, at which microstimulation induced increased avoidance. We found that effective stimulation sites in both pACC and cOFC zones projected preferentially to striosomes in the anterior striatum. Experiments in rodents have shown that the striosomes in the anterior striatum project directly to the dopamine-containing cells in the substantia nigra, and we have found evidence for a functional connection between striosomes and the lateral habenular region in which responses to reward are inhibitory. We present here further evidence for network interactions: we show that the pACC and cOFC project to common structures, including not only the anterior parts of the striosome compartment but also the tail of the CN, the subgenual ACC, the amygdala, and the thalamus. Together, our findings suggest that networks having pACC and cOFC as nodes share similar features in their connectivity patterns. We here hypothesize, based on these results, that the brain sites related to pessimistic judgment are mediated by a large-scale brain network that regulates dopaminergic functions and includes striosomes and striosome-projecting cortical regions.

Common and distinct neural correlates of music and food-induced pleasure: A coordinate-based meta-analysis of neuroimaging studies

Neuroimaging studies have shown that, despite the abstractness of music, it may mimic biologically rewarding stimuli (e.g., food) in its ability to engage the brain's reward circuitry. However, due to the lack of research comparing music and other types of reward, it is unclear to what extent the recruitment of reward-related structures overlaps among domains. To achieve this goal, we performed a coordinate-based meta-analysis of 38 neuroimaging studies (703 subjects) comparing the brain responses specifically to music and food-induced pleasure. Both engaged a common set of brain regions, including the ventromedial prefrontal cortex, ventral striatum, and insula. Yet, comparative analyses indicated a partial dissociation in the engagement of the reward circuitry as a function of the type of reward, as well as additional reward type-specific activations in brain regions related to perception, sensory processing, and learning. These results support the idea that hedonic reactions rely on the engagement of a common reward network, yet through specific routes of access depending on the modality and nature of the reward.

Neuropsychiatric Disorders in Parkinson's Disease: What Do We Know About the Role of Dopaminergic and Non-dopaminergic Systems?

Besides the hallmark motor symptoms (rest tremor, hypokinesia, rigidity, and postural instability), patients with Parkinson’s disease (PD) have non-motor symptoms, namely neuropsychiatric disorders. They are frequent and may influence the other symptoms of the disease. They have also a negative impact on the quality of life of patients and their caregivers. In this article, we will describe the clinical manifestations of the main PD-related behavioral disorders (depression, anxiety disorders, apathy, psychosis, and impulse control disorders). We will also provide an overview of the clinical and preclinical literature regarding the underlying mechanisms with a focus on the role of the dopaminergic and non-dopaminergic systems.

Ventral striatum supports Methylphenidate therapeutic effects on impulsive choices expressed in temporal discounting task

Methylphenidate (MPH) is a dopamine transporter (DAT) inhibitor used to treat attention-deficit/hyperactivity-disorder (ADHD). ADHD patients make impulsive choices in delay discounting tasks (DDT) and MPH reduces such impulsivity, but its therapeutic site of action remains unknown. Based on the high density of DAT in the striatum, we hypothesized that the striatum, especially the ventral striatum (VS) and caudate nucleus which both encode temporal discounting, can be preferential MPH action sites. To determine whether one of these striatal territories is predominantly involved in the effect of MPH, we trained monkeys to make choices during DDT. First, consistent with clinical observations, we found an overall reduction of impulsive choices with a low dose of MPH administered via intramuscular injections, whereas we reported sedative-like effects with a higher dose. Then, using PET-imaging, we found that the therapeutic reduction of impulsive choices was associated with selective DAT occupancy of MPH in the VS. Finally, we confirmed the selective involvement of the VS in the effect of MPH by testing the animals’ impulsivity with microinjections of the drug in distinct striatal territories. Together, these results show that the therapeutic effect of MPH on impulsive decisions is mainly restricted to its action in the VS.

The anterior caudate nucleus supports impulsive choices triggered by pramipexole

BACKGROUND

Pramipexole is a dopamine agonist used as a treatment in PD and restless legs syndrome to reduce motor symptoms, but it often induces impulse control disorders. In particular, patients with impulse control disorders tend to make more impulsive choices in the delay discounting task, that is, they choose small immediate rewards over larger delayed ones more often than patients without impulse control disorders and healthy subjects do. Yet the site of action of pramipexole that produces these impulsive choices remains unknown. Based on the heterogeneity of corticostriatal projections and the massive dopamine innervation of the striatum, we hypothesized that impulsive choices triggered by dopamine treatments may be supported by a specific striatal territory.

OBJECTIVES

This study aims to determine by which anteriorstriatum territory the Pramipexole trigger impulsive choices; the caudate nucleus, the ventral striatum or the putamen.

METHODS

We compared pramipexole intramuscular injections to intracerebral microinjections within the three striatal territories in healthy monkeys trained to execute the delay discounting task, a behavioral paradigm typically used to evaluate impulsive choices.

RESULTS

We found that pramipexole intramuscular injections induced impulsive choices in all monkeys. Local microinjections were performed inside the anterior caudate nucleus, ventral striatum, and anterior putamen and reproduced those impulsive choices when pramipexole was directly injected into the caudate nucleus, whereas injections into the ventral striatum or putamen had no effect on monkeys' choices.

CONCLUSIONS

These results, consistent with clinical studies, suggest that impulsive choices triggered by pramipexole are supported by the caudate nucleus, allowing us to emphasize the importance of dopamine modulation inside this striatal territory in decision processes underlying impulsive behaviors. © 2019 International Parkinson and Movement Disorder Society.

Pathophysiology of dyskinesia and behavioral disorders in non-human primates: the role of serotonergic fibers

The MPTP monkey model of Parkinson's disease (PD) has allowed huge advances regarding the understanding of the pathological mechanisms of PD and L-DOPA-induced adverse effects. Among the main findings were the imbalance between the efferent striatal pathways in opposite directions between the hypokinetic and hyperkinetic states of PD. In both normal and parkinsonian monkeys, the combination of behavioral and anatomical studies has allowed the deciphering of the cortico-basal ganglia circuits involved in both movement and behavioral disorders. A major breakthrough has then been made regarding the hypothesis of the involvement of serotonergic fibers in the conversion of L-DOPA to dopamine when dopaminergic neurons are dying and to release it, in an uncontrolled manner, as serotonergic neurons are deprived from the machinery required for buffering dopamine from the synaptic cleft. The crucial involvement of serotonergic fibers underlying L-DOPA-induced dyskinesia (LID) has been demonstrated in both rodent and monkey models of PD, in which dyskinesia induced by L-DOPA is abolished following lesion of the serotonergic system. Moreover, the role of serotonergic fibers goes well beyond dyskinesia, as lesioning of such serotonergic fibers by MDMA in the monkey also decreased other L-DOPA-induced adverse effects such as impulsive compulsive behaviors and visual hallucinations. The same pathological mechanism, i.e., an imbalance between serotonin and dopamine terminals may, therefore, favor L-DOPA-induced adverse effects according to the basal ganglia territory it inhabits. Further non-human primate studies will be needed to demonstrate the role of such a pathological mechanism in both movement and behavioral disorders driven by L-DOPA therapy but also to determine the causal link between serotonin lesions and the expression of non-motor symptoms like apathy, depression and anxiety, frequently observed in PD patients.

Characterization and Reliability of [18F]2FNQ1P in Cynomolgus Monkeys as a PET Radiotracer for Serotonin 5-HT6 Receptors

Brain serotonin-6 receptor (5-HT₆R) is the one of the most recently identified serotonin receptors. Accumulating evidence suggests that it is a potent therapeutic target for psychiatric and neurological diseases. Since [¹⁸F]2FNQ1P was recently proposed as the first fluorinated positron emission tomography (PET) radioligand for this receptor, the objective of the present study was to demonstrate its suitability for 5-HT₆R neuroimaging in primates. [¹⁸F]2FNQ1P was characterized by in vitro autoradiography and in vivo PET imaging in cynomolgus monkeys. Following in vivo PET imaging, tracer binding indices were computed using the simplified reference tissue model and Logan graphical model, with cerebellum as reference region. The tracer binding reproducibility was assessed by test–retest in five animals. Finally, specificity was assessed by pre-injection of a 5-HT₆R antagonist, SB258585. In vitro, results showed wide cerebral distribution of the tracer with specificity toward 5-HT₆Rs as binding was effectively displaced by SB258585. In vivo brain penetration was good with reproducible distribution at cortical and subcortical levels. The automated method gave the best spatial normalization. The Logan graphical model showed the best tracer binding indices, giving the highest magnitude, lowest standard deviation and best reproducibility and robustness. Finally, 5-HT₆R antagonist pre-injection significantly decreased [¹⁸F]2FNQ1P binding mainly in the striatum and sensorimotor cortex. Taken together, these preclinical results show that [¹⁸F]2FNQ1P is a good candidate to address 5-HT6 receptors in clinical studies.

Altered putamen functional connectivity is associated with anxiety disorder in Parkinson's disease

In this study, we used resting state-functional magnetic resonance imaging (rs-fMRI) to explore altered putamen functional connectivity (FC) in Parkinson's disease patients with anxiety disorder. We divided 65 Parkinson's disease patients into anxiety (PD-A; n=18) and non-anxiety (PD-NA; n=45) groups based on a Hamilton Anxiety Rating Scale cutoff score of 12. The PD-A patients exhibited altered putamen FC with cortical and subcortical regions. The PD-A patients showed enhanced putamen FC with the caudatum, which correlated with increased emotional processing during anxiety. Decreased putamen FC with the orbitofrontal gyrus and cerebellum also correlated with increased anxiety in Parkinson's disease. Our findings demonstrate that anxiety disorder in Parkinson's disease is associated with abnormal putamen FC networks, especially with caudatum, orbitofrontal gyrus and cerebellum.

Serotonergic Approaches in Parkinson's Disease: Translational Perspectives, an Update

Parkinson's disease (PD) has long been seen as a disorder caused by degeneration of the dopaminergic system, leading to the classic motor manifestations of the disease. However, there is now overwhelming evidence that PD is more than a disease merely caused by dopamine depletion. It is well-known that a myriad of other neurotransmitters are affected by the disease process. One such neurotransmitter is serotonin (5-HT). 5-HT has been shown to play a role in several motor and nonmotor manifestations of PD, including tremor, cognition, depression and psychosis. 5-HT also seems to play a critical role in L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia. A breadth of preclinical studies and clinical trials have been conducted that aimed at modulating the 5-HT system in order to alleviate depression, cognitive deficits, psychosis, and dyskinesia. In this Review, we summarize recent advances in the 5-HT field in PD, but with a translational emphasis. We start by presenting a novel nonhuman primate model of PD that presents with dual dopamine and 5-HT lesions. We then present preclinical and clinical data that introduce new concepts, such as the use of biased and partial agonists, as well as molecules recently introduced to the field of PD, such as eltoprazine, pimavanserin, nelotanserin, and SYN-120, to enhance therapeutic benefit while minimizing adverse events, notably on parkinsonian disability.

Roles of Multiple Globus Pallidus Territories of Monkeys and Humans in Motivation, Cognition and Action: An Anatomical, Physiological and Pathophysiological Review

The globus pallidus (GP) communicates with widespread cortical areas that support various functions, including motivation, cognition and action. Anatomical tract-tracing studies revealed that the anteroventral GP communicates with the medial prefrontal and orbitofrontal cortices, which are involved in motivational control; the anterodorsal GP communicates with the lateral prefrontal cortex, which is involved in cognitive control; and the posterior GP communicates with the frontal motor cortex, which is involved in action control. This organization suggests that distinct subdivisions within the GP play specific roles. Neurophysiological studies examining GP neurons in monkeys during behavior revealed that the types of information coding performed within these subdivisions differ greatly. The anteroventral GP is characterized by activities related to motivation, such as reward seeking and aversive avoidance; the anterodorsal GP is characterized by activity that reflects cognition, such as goal decision and action selection; and the posterior GP is characterized by activity associated with action preparation and execution. Pathophysiological studies have shown that GABA-related substances or GP lesions result in abnormal activity in the GP, which causes site-specific behavioral and motor symptoms. The present review article discusses the anatomical organization, physiology and pathophysiology of the three major GP territories in nonhuman primates and humans.

Dopamine and serotonin modulation of motor and non-motor functions of the non-human primate striato-pallidal circuits in normal and pathological states

Thanks to the non-human primate (NHP), we have shown that the pharmacological disturbance of the anterior striatum or of external globus pallidus triggers a set of motivation and movement disorders, depending on the functional subterritory involved. One can, therefore, assume that the aberrant activity of the different subterritories of basal ganglia (BG) could lead to different behavioral disorders in neuropsychiatric disorders as Tourette's syndrome and Parkinson's disease. We are now addressing in the NHP the impact of modulating dopamine or serotonin within the BG on behavioral disorders. Indeed, we have shown a prominent role of serotonergic degeneration within the ventral striatum and caudate nucleus in neuropsychiatric symptoms in de novo PD patients. Of note, the serotonergic modulation of these BG regions in the NHP plays also a critical role in the induction or treatment of behavioral disorders. Given that both dopamine and serotonin are targeted to treat neuropsychiatric disorders, we are studying the effects of modulating dopamine and serotonin transporters in the different territories of the striatum, and more particularly within the ventral striatum on decision-making processing at both behavioral and neuronal levels. Finally, we evidence the need to extend the pharmacological approach to the receptors of these two neuromodulator systems as the use of substances targeting receptor subtypes preferentially localized in the associative and limbic territories of BG could be very effective to specifically improve the behavioral disorders in Parkinson's disease, Gilles de la Tourette syndrome but also in several psychiatric disorders such as depression, anxiety, anorexia, or impulse control disorders.