Deep brain stimulation of the nucleus accumbens shell increases impulsive behavior and tissue levels of dopamine and serotonin

Methylphenidate, but not citalopram, decreases impulsive choice in rats performing a temporal discounting task

Introduction

Drugs targeting monoamine systems remain the most common treatment for disorders with impulse control impairments. There is a body of literature suggesting that drugs affecting serotonin reuptake and dopamine reuptake can modulate distinct aspects of impulsivity - though such tests are often performed using distinct behavioral tasks prohibiting easy comparisons.

Methods

Here, we directly compare pharmacologic agents that affect dopamine (methylphenidate) vs serotonin (citalopram) manipulations on choice impulsivity in a temporal discounting task where rats could choose between a small, immediate reward or a large reward delayed at either 2 or 10s. In control conditions, rats preferred the large reward at a small (2s) delay and discounted the large reward at a long (10s) delay.

Results

Methylphenidate, a dopamine transport inhibitor that blocks reuptake of dopamine, dose-dependently increased large reward preference in the long delay (10s) block. Citalopram, a selective serotonin reuptake inhibitor, had no effect on temporal discounting behavior. Impulsive behavior on the temporal discounting task was at least partially mediated by the nucleus accumbens shell. Bilateral lesions to the nucleus accumbens shell reduced choice impulsivity during the long delay (10s) block. Following lesions, methylphenidate did not impact impulsivity.

Discussion

Our results suggest that striatal dopaminergic systems modulate choice impulsivity via actions within the nucleus accumbens shell, whereas serotonin systems may regulate different aspects of behavioral inhibition/impulsivity.

Systematic review of rodent studies of deep brain stimulation for the treatment of neurological, developmental and neuropsychiatric disorders

Deep brain stimulation (DBS) modulates local and widespread connectivity in dysfunctional networks. Positive results are observed in several patient populations; however, the precise mechanisms underlying treatment remain unknown. Translational DBS studies aim to answer these questions and provide knowledge for advancing the field. Here, we systematically review the literature on DBS studies involving models of neurological, developmental and neuropsychiatric disorders to provide a synthesis of the current scientific landscape surrounding this topic. A systematic analysis of the literature was performed following PRISMA guidelines. 407 original articles were included. Data extraction focused on study characteristics, including stimulation protocol, behavioural outcomes, and mechanisms of action. The number of articles published increased over the years, including 16 rat models and 13 mouse models of transgenic or healthy animals exposed to external factors to induce symptoms. Most studies targeted telencephalic structures with varying stimulation settings. Positive behavioural outcomes were reported in 85.8% of the included studies. In models of psychiatric and neurodevelopmental disorders, DBS-induced effects were associated with changes in monoamines and neuronal activity along the mesocorticolimbic circuit. For movement disorders, DBS improves symptoms via modulation of the striatal dopaminergic system. In dementia and epilepsy models, changes to cellular and molecular aspects of the hippocampus were shown to underlie symptom improvement. Despite limitations in translating findings from preclinical to clinical settings, rodent studies have contributed substantially to our current knowledge of the pathophysiology of disease and DBS mechanisms. Direct inhibition/excitation of neural activity, whereby DBS modulates pathological oscillatory activity within brain networks, is among the major theories of its mechanism. However, there remain fundamental questions on mechanisms, optimal targets and parameters that need to be better understood to improve this therapy and provide more individualized treatment according to the patient's predominant symptoms.

Pramipexole restores behavioral inhibition in highly impulsive rats through a paradoxical modulation of frontostriatal networks

Impulse control disorders (ICDs), a wide spectrum of maladaptive behaviors which includes pathological gambling, hypersexuality and compulsive buying, have been recently suggested to be triggered or aggravated by treatments with dopamine D2/3 receptor agonists, such as pramipexole (PPX). Despite evidence showing that impulsivity is associated with functional alterations in corticostriatal networks, the neural basis of the exacerbation of impulsivity by PPX has not been elucidated. Here we used a hotspot analysis to assess the functional recruitment of several corticostriatal structures by PPX in male rats identified as highly (HI), moderately impulsive (MI) or with low levels of impulsivity (LI) in the 5-choice serial reaction time task (5-CSRTT). PPX dramatically reduced impulsivity in HI rats. Assessment of the expression pattern of the two immediate early genes C-fos and Zif268 by in situ hybridization subsequently revealed that PPX resulted in a decrease in Zif268 mRNA levels in different striatal regions of both LI and HI rats accompanied by a high impulsivity specific reduction of Zif268 mRNA levels in prelimbic and cingulate cortices. PPX also decreased C-fos mRNA levels in all striatal regions of LI rats, but only in the dorsolateral striatum and nucleus accumbens core (NAc Core) of HI rats. Structural equation modeling further suggested that the anti-impulsive effect of PPX was mainly attributable to the specific downregulation of Zif268 mRNA in the NAc Core. Altogether, our results show that PPX restores impulse control in highly impulsive rats by modulation of limbic frontostriatal circuits.

Dopamine in the nucleus accumbens shell controls systemic glucose metabolism via the lateral hypothalamus and hepatic vagal innervation in rodents

BACKGROUND

Growing evidence demonstrates the role of the striatal dopamine system in the regulation of glucose metabolism. Treatment with dopamine antagonists is associated with insulin resistance and hyperglycemia, while dopamine agonists are used in treatment of type 2 diabetes. The mechanism underlying striatal dopamine effects in glucose metabolism, however is not fully understood. Here, we provide mechanistic insights into the role of nucleus accumbens shell (sNAc) dopaminergic signaling in systemic glucose metabolism.

METHODS

Endogenous glucose production (EGP), blood glucose and mRNA expression in the lateral hypothalamic area (LHA) in male Wistar rats were measured following infusion of vanoxerine (VNX, dopamine reuptake inhibitor) in the sNAc. Thereafter, we analyzed projections from sNAc Drd1-expressing neurons to LHA using D1-Cre male Long-Evans rats, Cre-dependent viral tracers and fluorescence immunohistochemistry. Brain slice electrophysiology in adult mice was used to study spontaneous excitatory postsynaptic currents of sNAc Drd1-expressing neurons following VNX application. Finally, we assessed whether GABAergic LHA activity and hepatic vagal innervation were required for the effect of sNAc-VNX on glucose metabolism by combining infusion of sNAc-VNX with LHA-bicuculline, performing vagal recordings and combining infusion of sNAc-VNX with hepatic vagal denervation.

RESULTS

VNX infusion in the sNAc strongly decreased endogenous glucose production, prevented glucose increases over time, reduced Slc17A6 and Hcrt mRNA in LHA, and increased vagal activity. Furthermore, sNAc Drd1-expressing neurons increased spontaneous firing following VNX application, and viral tracing of sNAc Drd1-expressing neurons revealed direct projections to LHA with on average 67 % of orexin cells directly targeted by sNAc Drd1-expressing neurons. Importantly, the sNAc-VNX-induced effect on glucose metabolism was dependent on GABAergic signaling in the LHA and on intact hepatic vagal innervation.

CONCLUSIONS

We show that sNAc dopaminergic signaling modulates hepatic glucose metabolism through GABAergic inputs to glutamatergic LHA cells and hepatic vagal innervation. This demonstrates that striatal control of glucose metabolism involves a dopaminergic sNAc-LHA-liver axis and provides a potential explanation for the effects of dopamine agonists and antagonists on glucose metabolism.

Converging circuits between pain and depression: the ventral tegmental area as a therapeutic hub

Chronic pain and depression are highly prevalent pathologies and cause a major socioeconomic burden to society. Chronic pain affects the emotional state of the individuals suffering from it, while depression worsens the prognosis of chronic pain patients and may diminish the effectiveness of pain treatments. There is a high comorbidity rate between both pathologies, which might share overlapping mechanisms. This review explores the evidence pinpointing a role for the ventral tegmental area (VTA) as a hub where both pain and emotional processing might converge. In addition, the feasibility of using the VTA as a possible therapeutic target is discussed. The role of the VTA, and the dopaminergic system in general, is highly studied in mood disorders, especially in deficits in reward-processing and motivation. Conversely, the VTA is less regarded where it concerns the study of central mechanisms of pain and its mood-associated consequences. Here, we first outline the brain circuits involving central processing of pain and mood disorders, focusing on the often-understudied role of the dopaminergic system and the VTA. Next, we highlight the state-of-the-art findings supporting the emergence of the VTA as a link where both pathways converge. Thus, we envision a promising part for the VTA as a putative target for innovative therapeutic approaches to treat chronic pain and its effects on mood. Finally, we emphasize the urge to develop and use animal models where both pain and depression-like symptoms are considered in conjunction.

Dopamine transporter blockade during adolescence increases adult dopamine function, impulsivity, and aggression

Sensitive developmental periods shape neural circuits and enable adaptation. However, they also engender vulnerability to factors that can perturb developmental trajectories. An understanding of sensitive period phenomena and mechanisms separate from sensory system development is still lacking, yet critical to understanding disease etiology and risk. The dopamine system is pivotal in controlling and shaping adolescent behaviors, and it undergoes heightened plasticity during that time, such that interference with dopamine signaling can have long-lasting behavioral consequences. Here we sought to gain mechanistic insight into this dopamine-sensitive period and its impact on behavior. In mice, dopamine transporter (DAT) blockade from postnatal (P) day 22 to 41 increases aggression and sensitivity to amphetamine (AMPH) behavioral stimulation in adulthood. Here, we refined this sensitive window to P32-41 and identified increased firing of dopaminergic neurons in vitro and in vivo as a neural correlate to altered adult behavior. Aggression can result from enhanced impulsivity and cognitive dysfunction, and dopamine regulates working memory and motivated behavior. Hence, we assessed these behavioral domains and found that P32-41 DAT blockade increases impulsivity but has no effect on cognition, working memory, or motivation in adulthood. Lastly, using optogenetics to drive dopamine neurons, we find that increased VTA but not SNc dopaminergic activity mimics the increase in impulsive behavior in the Go/NoGo task observed after adolescent DAT blockade. Together our data provide insight into the developmental origins of aggression and impulsivity that may ultimately improve diagnosis, prevention, and treatment strategies for related neuropsychiatric disorders.

Hericium erinaceus Promotes Anti-Inflammatory Effects and Regulation of Metabolites in an Animal Model of Cerebellar Ataxia

Cerebellar ataxia is a neurodegenerative disorder with no definitive treatment. Although previous study demonstrated the neuroprotective effects of Hericium erinaceus (H.E.), the mechanisms of H.E. treatment on the neuroinflammatory response, neurotransmission, and related metabolites remain largely unknown. We demonstrated that 3-AP rats treated with 25 mg/kg H.E. extracts had improved motor coordination and balance in the accelerated rotarod and rod tests. We showed that the H.E. treatment upregulated the expression of Tgfb1, Tgfb2, and Smad3 genes to levels comparable to those in the non-3-AP control group. Interestingly, we also observed a significant correlation between Tgfb2 gene expression and rod test performance in the 3-AP saline group, but not in the non-3-AP control or H.E.+3-AP groups, indicating a relationship between Tgfb2 gene expression and motor balance in the 3-AP rat model. Additionally, we also found that the H.E. treatment increased mitochondrial COX-IV protein expression and normalized dopamine-serotonin neurotransmission and metabolite levels in the cerebellum of the H.E.+3-AP group compared to the 3-AP saline group. In conclusion, our findings suggest that the H.E. treatment improved motor function in the 3-AP rat model, which was potentially mediated through neuroprotective mechanisms involving TGFB2-Smad3 signaling via normalization of neurotransmission and metabolic pathways.

Potential therapeutic mechanism of deep brain stimulation of the nucleus accumbens in obsessive-compulsive disorder

Deep brain stimulation (DBS) of the nucleus accumbens (NAc) (NAc-DBS) is an effective solution to refractory obsessive-compulsive disorder (OCD). However, evidence for the neurobiological mechanisms of OCD and the effect of NAc-DBS is still lacking. One hypothesis is that the electrophysiological activities in the NAc are modulated by DBS, and another hypothesis is that the activities of neurotransmitters in the NAc are influenced by DBS. To investigate these potential alterations, rats with quinpirole (QNP)- induced OCD were treated with DBS of the core part of NAc. Then, extracellular spikes (SPK) and local field potentials (LFP) in the NAc were recorded, and the levels of relevant neurotransmitters and related proteins were measured. Analysis of SPK revealed that the firing rate was decreased and the firing pattern was changed after NAc-DBS, and analysis of LFP showed that overall power spectral density (PSD) levels were reduced after NAc-DBS. Additionally, we found that the relative powers of the theta band, alpha band and beta band were increased in OCD status, while the relative powers of the delta band and gamma band were decreased. This pathological pattern of power distribution was reformed by NAc-DBS. Furthermore, we found that the local levels of monoamines [dopamine (DA) and serotonin (5-HT)] and amino acids [glutamate (Glu) and gamma-aminobutyric acid (GABA)] in the NAc were increased in OCD status, and that the expression of the two types of DA receptors in the NAc exhibited an opposite change. These abnormalities could be reversed by NAc-DBS. These findings provide a more comprehensive understanding about the function of the NAc in the pathophysiology of OCD and provide more detailed evidence for the potential effect of NAc-DBS.

Distribution and inter-regional relationship of amyloid-beta plaque deposition in a 5xFAD mouse model of Alzheimer’s disease

Alzheimer’s disease (AD) is the most common form of dementia. Although previous studies have selectively investigated the localization of amyloid-beta (Aβ) deposition in certain brain regions, a comprehensive characterization of the rostro-caudal distribution of Aβ plaques in the brain and their inter-regional correlation remain unexplored. Our results demonstrated remarkable working and spatial memory deficits in 9-month-old 5xFAD mice compared to wildtype mice. High Aβ plaque load was detected in the somatosensory cortex, piriform cortex, thalamus, and dorsal/ventral hippocampus; moderate levels of Aβ plaques were observed in the motor cortex, orbital cortex, visual cortex, and retrosplenial dysgranular cortex; and low levels of Aβ plaques were located in the amygdala, and the cerebellum; but no Aβ plaques were found in the hypothalamus, raphe nuclei, vestibular nucleus, and cuneate nucleus. Interestingly, the deposition of Aβ plaques was positively associated with brain inter-regions including the prefrontal cortex, somatosensory cortex, medial amygdala, thalamus, and the hippocampus. In conclusion, this study provides a comprehensive morphological profile of Aβ deposition in the brain and its inter-regional correlation. This suggests an association between Aβ plaque deposition and specific brain regions in AD pathogenesis.

A Role for Serotonin in Modulating Opposing Drive and Brake Circuits of Impulsivity

Impulsivity generally refers to a deficit in inhibition, with a focus on understanding the neural circuits which constitute the “brake” on actions and gratification. It is likely that increased impulsivity can arise not only from reduced inhibition, but also from a heightened or exaggerated excitatory “drive.” For example, an action which has more vigor, or is fueled by either increased incentive salience or a stronger action-outcome association, may be harder to inhibit. From this perspective, this review focuses on impulse control as a competition over behavioral output between an initially learned response-reward outcome association, and a subsequently acquired opposing inhibitory association. Our goal is to present a synthesis of research from humans and animal models that supports this dual-systems approach to understanding the behavioral and neural substrates that contribute to impulsivity, with a focus on the neuromodulatory role of serotonin. We review evidence for the role of serotonin signaling in mediating the balance of the “drive” and “brake” circuits. Additionally, we consider parallels of these competing instrumental systems in impulsivity within classical conditioning processes (e.g., extinction) in order to point us to potential behavioral and neural mechanisms that may modulate the competing instrumental associations. Finally, we consider how the balance of these competing associations might contribute to, or be extracted from, our experimental assessments of impulsivity. A careful understanding of the underlying behavioral and circuit level contributions to impulsivity is important for understanding the pathogenesis of increased impulsivity present in a number of psychiatric disorders. Pathological levels of impulsivity in such disorders are likely subserved by deficits in the balance of motivational and inhibitory processes.

Dissociation of impulsive traits by subthalamic metabotropic glutamate receptor 4

Behavioral strategies require gating of premature responses to optimize outcomes. Several brain areas control impulsive actions, but the neuronal basis of natural variation in impulsivity between individuals remains largely unknown. Here, by combining a Go/No-Go behavioral assay with resting-state (rs) functional MRI in mice, we identified the subthalamic nucleus (STN), a known gate for motor control in the basal ganglia, as a major hotspot for trait impulsivity. In vivo recorded STN neural activity encoded impulsive action as a separable state from basic motor control, characterized by decoupled STN/substantia nigra pars reticulata (SNr) mesoscale networks. Optogenetic modulation of STN activity bidirectionally controlled impulsive behavior. Pharmacological and genetic manipulations showed that these impulsive actions are modulated by metabotropic glutamate receptor 4 (mGlu4) function in STN and its coupling to SNr in a behavioral trait-dependent manner, and independently of general motor function. In conclusion, STN circuitry multiplexes motor control and trait impulsivity, which are molecularly dissociated by mGlu4. This provides a potential mechanism for the genetic modulation of impulsive behavior, a clinically relevant predictor for developing psychiatric disorders associated with impulsivity.

A narrative review on invasive brain stimulation for treatment-resistant depression

While most patients with depression respond to pharmacotherapy and psychotherapy, about one-third will present treatment resistance to these interventions. For patients with treatment-resistant depression (TRD), invasive neurostimulation therapies such as vagus nerve stimulation, deep brain stimulation, and epidural cortical stimulation may be considered. We performed a narrative review of the published literature to identify papers discussing clinical studies with invasive neurostimulation therapies for TRD. After a database search and title and abstract screening, relevant English-language articles were analyzed. Vagus nerve stimulation, approved by the U.S. Food and Drug Administration as a TRD treatment, may take several months to show therapeutic benefits, and the average response rate varies from 15.2-83%. Deep brain stimulation studies have shown encouraging results, including rapid response rates (> 30%), despite conflicting findings from randomized controlled trials. Several brain regions, such as the subcallosal-cingulate gyrus, nucleus accumbens, ventral capsule/ventral striatum, anterior limb of the internal capsule, medial-forebrain bundle, lateral habenula, inferior-thalamic peduncle, and the bed-nucleus of the stria terminalis have been identified as key targets for TRD management. Epidural cortical stimulation, an invasive intervention with few reported cases, showed positive results (40-60% response), although more extensive trials are needed to confirm its potential in patients with TRD.

Mapping Large-Scale Networks Associated with Action, Behavioral Inhibition and Impulsivity

A key aspect of behavioral inhibition is the ability to wait before acting. Failures in this form of inhibition result in impulsivity and are commonly observed in various neuropsychiatric disorders. Prior evidence has implicated medial frontal cortex, motor cortex, orbitofrontal cortex (OFC), and ventral striatum in various aspects of inhibition. Here, using distributed recordings of brain activity [with local-field potentials (LFPs)] in rodents, we identified oscillatory patterns of activity linked with action and inhibition. Low-frequency (δ) activity within motor and premotor circuits was observed in two distinct networks, the first involved in cued, sensory-based responses and the second more generally in both cued and delayed actions. By contrast, θ activity within prefrontal and premotor regions (medial frontal cortex, OFC, ventral striatum, and premotor cortex) was linked with inhibition. Connectivity at θ frequencies was observed within this network of brain regions. Interestingly, greater connectivity between primary motor cortex (M1) and other motor regions was linked with greater impulsivity, whereas greater connectivity between M1 and inhibitory brain regions (OFC, ventral striatum) was linked with improved inhibition and diminished impulsivity. We observed similar patterns of activity on a parallel task in humans: low-frequency activity in sensorimotor cortex linked with action, θ activity in OFC/ventral prefrontal cortex (PFC) linked with inhibition. Thus, we show that δ and θ oscillations form distinct large-scale networks associated with action and inhibition, respectively.

Basal impulses: findings from the last twenty years on impulsivity and reward pathways using deep brain stimulation

INTRODUCTION

Deep brain stimulation (DBS) is an important treatment modality for movement disorders. Its role in tasks and processes of higher cortical function continues to increase in importance and relevance. This systematic review investigates the impact of DBS on measures of impulsivity.

EVIDENCE ACQUISITION

A total of 45 studies were collated from PubMed (30 prospective, 8 animal, 4 questionnaire-based, and 3 computational models), excluding case reports and review articles. Two areas extensively studied are the subthalamic nucleus (STN) and nucleus accumbens (NAc).

EVIDENCE SYNTHESIS

While both are part of the basal ganglia, the STN and NAc have extensive connections to the prefrontal cortex, cingulate cortex, and limbic system. Therefore, understanding cause and treatment of impulsivity requires understanding motor pathways, learning, memory, and emotional processing. DBS of the STN and NAc shell can increase objective measures of impulsivity, as measured by reaction times or reward-based learning, independent from patient insight. The ability for DBS to treat impulse control disorders, and also cause and/or worsen impulsivity in Parkinson's disease, may be explained by the affected closely-related neuroanatomical areas with discrete and sometimes opposing functions.

CONCLUSIONS

As newer, more refined DBS technology emerges, large-scale prospective studies specifically aimed at treatment of impulsivity disorders are needed.

Nucleus Accumbens as a Novel Target for Deep Brain Stimulation in the Treatment of Addiction: A Hypothesis on the Neurochemical and Morphological Basis

Addiction is a major cause of mortality and morbidity. Apart from psychotropic substances, alcohol and nicotine remain the common addictive materials responsible for the majority of deaths. Conventional conservative therapies are beneficial to certain populations, but the majority may require interventional treatments such as deep brain stimulation (DBS) in view of increasing mortality from drug abuse in recent years. We present a brief review on a novel neuromodulation target of the nucleus accumbens (NA) and its promising role in the management of addiction. The three stages of the addiction cycle are known to be mediated by dopaminergic pathways located in the mesolimbic dopamine system with connections to dorsal striatum, extended amygdala, cingulate gyrus, orbitofrontal cortex, prefrontal cortex, and ventral tegmental area. Recent advanced neuroimaging in humans and several animal studies demonstrated NA to be a vital anatomical area modulating this network. DBS of NA in animals reduced addictive behavior to alcohol, cocaine, and other narcotics significantly. The accidental observation that DBS of NA for psychiatric illnesses induced relief from addiction to alcohol and smoking has encouraged further research of late. Bilateral NA ablative surgery had shown nonrelapse in more than 50% of cases. Small series of patients have benefited so far from DBS of NA, but larger numbers are required to provide evidence-based treatment. The modulation of dopaminergic pathways through DBS of NA as a valid treatment for addiction is substantiated extensively by animal studies and also in a few clinical studies. However, this needs to be validated by a well-structured, multicenter controlled study in a large group of patients suffering from substance abuse.

Parkinsonism and subthalamic deep brain stimulation dysregulate behavioral motivation in a rodent model

BACKGROUND

Apathy and impulsivity constitute opposite poles of a behavioral motivation spectrum often disrupted by both the symptoms and therapies for Parkinson's Disease (PD). Upwards of 70% of PD patients experience symptoms of apathy, frequently unresolved or worsened by deep brain stimulation (DBS) of the subthalamic nucleus (STN). Worse, more than half of patients receiving DBS for PD experience new-onset impulse control disorders of varying severity following therapy initiation. While these symptoms and side-effects have been widely reported in clinical studies, they are largely unexplored in animal models.

METHODS

We applied high-frequency DBS in a 6-OHDA hemiparkinsonian rat model. We trained rats on a series of go/stop and go/no-go behavioral paradigms and examined how parkinsonism and DBS modulated task responses.

RESULTS

STN DBS in healthy rodents drove impulsive behavior in the form of stop and no-go task failure, impulsive reward seeking, and noninstructed task attempts. While trained rats without DBS only tended to fail stop and no-go cues very shortly after the cue, DBS led to failures at significantly later time points. Hemiparkinsonism slowed response times and reduced response rates, not alleviated by effective DBS.

INTERPRETATIONS

PD interrupts neural signaling responsible for healthy action selection, not restored by DBS. PD may be associated with a dearth of action commands, manifesting as apathy. Conversely, effective DBS may bias the system toward the impulsive end of the behavioral motivation spectrum without restoring behaviorally reasonable actions, mis-weighting reward-based action selection and manifesting as impulsivity, aided by DBS interfering with stop signaling.

The Paradoxical Effect of Deep Brain Stimulation on Memory

Deep brain stimulation (DBS) is a promising treatment for many memory-related disorders including dementia, anxiety, and addiction. However, the use of DBS can be a paradoxical conundrum-dementia treatments aim to improve memory, whereas anxiety or addiction treatments aim to suppress maladaptive memory. In this review, the key hypotheses on how DBS affects memory are highlighted. We consolidate the findings and conclusions from the current research on the effects of DBS on memory in attempt to make sense of the bidirectional nature of DBS in disrupting and enhancing memory. Based on the current literature, we hypothesize that the timing of DBS plays a key role in its contradictory effects, and therefore, we propose a consolidated model of how DBS can both disrupt and enhance memory.

Cognitive Task Performance During Titration Predicts Deep Brain Stimulation Treatment Efficacy: Evidence From a Case Study

Device titration is a major challenge when using deep brain stimulation (DBS) to treat behavioral disorders. Unlike in movement disorders, there is no reliable real-time clinical feedback for changes in complex behaviors resulting from DBS. Here, a female patient receiving DBS of the nucleus accumbens for the treatment of morbid obesity underwent cognitive testing via the flanker task alongside traditional methods of device titration. One set of stimulation parameters administered during titration resulted in acute cognitive improvement (p = 0.033) and increased frontal engagement as measured by electroencephalography (left anterior: p = 0.007, right anterior: p = 0.005) relative to DBS-OFF. The same parameters resulted in the most weight-loss during long-term continuous stimulation (47.8 lbs lost in 129 days) compared to the results of other stimulation settings. Diffusion tensor imaging analyses showed increased connectivity to dorsal attention networks and decreased connectivity to the default mode network for optimal parameters (p < 0.01). Our results provide evidence that targeted cognitive testing is a potentially useful tool for capturing acute effects of DBS stimulation during titration and predicting long-term treatment outcomes.

CLINICAL TRIAL REGISTRATION

www.ClinicalTrials.gov, identifier: NCT01512134.

Severe seizures as a side effect of deep brain stimulation in the dorsal peduncular cortex in a rat model of depression

Deep brain stimulation (DBS) has shown to have antidepressant effects in both human trials and animal studies. However, the optimal target and the underlying therapeutic mechanisms remain to be determined. In this study, we investigated if high frequency (HF) DBS in the dorsal peduncular cortex (DPC) alleviates depressive-like behavior in an experimental model of depression. Surprisingly, HF DBS in the DPC caused acute induction of seizures in ~40% of animals stimulated with clinically relevant stimulation parameters. Reducing the stimulation's amplitude by 50% did not alter seizure occurrence. Electroencephalographic (EEG) recordings showed seizures up to Racine stage IV lasting up to 4 min after cessation of stimulation. We conclude that HF DBS in the DPC is not suitable for mood-related experiments in rats but could be a potential model for seizure induction.

Nucleus Accumbens Deep Brain Stimulation for Obsessive-Compulsive Disorder and Aggression in an Autistic Patient: A Case Report and Hypothesis of the Role of Nucleus Accumbens in Autism and Comorbid Symptoms

BACKGROUND

Autism spectrum disorder represents a set of developmental disorders characterized by lack of social interaction and verbal and nonverbal communication in the first 3 years of life. It is also associated with several comorbidities, including epilepsy, aggression, self-mutilating behavior, and obsessive-compulsive behavior. In some cases, obsessive-compulsive disorder (OCD) develops. The nucleus accumbens (NAc) plays a key role in reward circuitry and is involved in the control of OCD and aggression.

CASE DESCRIPTION

A 42-year-old woman with autism was offered NAc deep brain stimulation for her comorbidities of OCD and aggression. The NAc was targeted using standard stereotactic methods, and postoperative scans confirmed the position of the active electrode to be within the NAc. The patient experienced significant symptom relief. At 1-year follow-up, the Yale-Brown Obsessive Compulsive Scale score for OCD, excluding items 1-5 of the scale, improved from 19 to 5. Hamilton Depression Scale and Hamilton Anxiety Scale scores similarly improved from 20 to 15 and from 30 to 18, respectively. Social Communication Questionnaire Current version for autism score improved from 26 to 16. Subscores for reciprocal social interactionimproved from 13 to 8; for communication improved from 5 to 4; and for restricted, repetitive, and stereotyped patterns of behavior improved from 6 to 3.

CONCLUSIONS

This case report illustrated the role of the NAc in OCD and aggression in an autistic patient. We discussed the role of the NAc as a target to explain the outcome of this case.

Efficacy of Invasive and Non-Invasive Brain Modulation Interventions for Addiction

It is important to find new treatments for addiction due to high relapse rates despite current interventions and due to expansion of the field with non-substance related addictive behaviors. Neuromodulation may provide a new type of treatment for addiction since it can directly target abnormalities in neurocircuits. We review literature on five neuromodulation techniques investigated for efficacy in substance related and behavioral addictions: transcranial direct current stimulation (tDCS), (repetitive) transcranial magnetic stimulation (rTMS), EEG, fMRI neurofeedback and deep brain stimulation (DBS) and additionally report on effects of these interventions on addiction-related cognitive processes. While rTMS and tDCS, mostly applied at the dorsolateral prefrontal cortex, show reductions in immediate craving for various addictive substances, placebo-responses are high and long-term outcomes are understudied. The lack in well-designed EEG-neurofeedback studies despite decades of investigation impedes conclusions about its efficacy. Studies investigating fMRI neurofeedback are new and show initial promising effects on craving, but future trials are needed to investigate long-term and behavioral effects. Case studies report prolonged abstinence of opioids or alcohol with ventral striatal DBS but difficulties with patient inclusion may hinder larger, controlled trials. DBS in neuropsychiatric patients modulates brain circuits involved in reward processing, extinction and negative-reinforcement that are also relevant for addiction. To establish the potential of neuromodulation for addiction, more randomized controlled trials are needed that also investigate treatment duration required for long-term abstinence and potential synergy with other addiction interventions. Finally, future advancement may be expected from tailoring neuromodulation techniques to specific patient (neurocognitive) profiles.

Circuit Mechanisms of Reward, Anhedonia, and Depression

Pleasure and motivation are important factors for goal-directed behavior and well-being in both animals and humans. Intact hedonic capacity requires an undisturbed interplay between a number of different brain regions and transmitter systems. Concordantly, dysfunction of networks encoding for reward have been shown in depression and other psychiatric disorders. The development of technological possibilities to investigate connectivity on a functional level in humans and to directly influence networks in animals using optogenetics among other techniques has provided new important insights in this field of research.In this review, we aim to provide an overview on the neurobiological substrates of anhedonia on a network level. For this purpose, definition of anhedonia and the involved reward components are described first, then current data on reward networks in healthy individuals and in depressed patients are summarized, and the roles of different neurotransmitter systems involved in reward processing are specified. Based on this information, the impact of different therapeutic approaches on reward processing is described with a particular focus on deep brain stimulation (DBS) as a possibility for a direct modulation of human brain structures in vivo.Overall, results of current studies emphasize the importance of anhedonia in psychiatric disorders and the relevance of targeting this phenotype for a successful psychiatric treatment. However, more data incorporating these results for the refinement of methodological approaches are needed to be able to develop individually tailored therapeutic concepts based on both clinical and neurobiological profiles of patients.

Deep brain stimulation for treatment-resistant depression: an integrative review of preclinical and clinical findings and translational implications

Although deep brain stimulation (DBS) is an established treatment choice for Parkinson's disease (PD), essential tremor and movement disorders, its effectiveness for the management of treatment-resistant depression (TRD) remains unclear. Herein, we conducted an integrative review on major neuroanatomical targets of DBS pursued for the treatment of intractable TRD. The aim of this review article is to provide a critical discussion of possible underlying mechanisms for DBS-generated antidepressant effects identified in preclinical studies and clinical trials, and to determine which brain target(s) elicited the most promising outcomes considering acute and maintenance treatment of TRD. Major electronic databases were searched to identify preclinical and clinical studies that have investigated the effects of DBS on depression-related outcomes. Overall, 92 references met inclusion criteria, and have evaluated six unique DBS targets namely the subcallosal cingulate gyrus (SCG), nucleus accumbens (NAc), ventral capsule/ventral striatum or anterior limb of internal capsule (ALIC), medial forebrain bundle (MFB), lateral habenula (LHb) and inferior thalamic peduncle for the treatment of unrelenting TRD. Electrical stimulation of these pertinent brain regions displayed differential effects on mood transition in patients with TRD. In addition, 47 unique references provided preclinical evidence for putative neurobiological mechanisms underlying antidepressant effects of DBS applied to the ventromedial prefrontal cortex, NAc, MFB, LHb and subthalamic nucleus. Preclinical studies suggest that stimulation parameters and neuroanatomical locations could influence DBS-related antidepressant effects, and also pointed that modulatory effects on monoamine neurotransmitters in target regions or interconnected brain networks following DBS could have a role in the antidepressant effects of DBS. Among several neuromodulatory targets that have been investigated, DBS in the neuroanatomical framework of the SCG, ALIC and MFB yielded more consistent antidepressant response rates in samples with TRD. Nevertheless, more well-designed randomized double-blind, controlled trials are warranted to further assess the efficacy, safety and tolerability of these more promising DBS targets for the management of TRD as therapeutic effects have been inconsistent across some controlled studies.

Deep brain stimulation as a therapeutic option for obesity: A critical review

Despite a better understanding of obesity pathophysiology, treating this disease remains a challenge. New therapeutic options are needed. Targeting the brain is a promising way, considering both the brain abnormalities in obesity and the effects of bariatric surgery on the gut-brain axis. Deep brain stimulation could be an alternative treatment for obesity since this safe and reversible neurosurgical procedure modulates neural circuits for therapeutic purposes. We aimed to provide a critical review of published clinical and preclinical studies in this field. Owing to the physiology of eating and brain alterations in people with obesity, two brain areas, namely the hypothalamus and the nucleus accumbens are putative targets. Preclinical studies with animal models of obesity showed that deep brain stimulation of hypothalamus or nucleus accumbens induces weight loss. The mechanisms of action remain to be fully elucidated. Preclinical data suggest that stimulation of nucleus accumbens reduces food intake, while stimulation of hypothalamus could increase resting energy expenditure. Clinical experience with deep brain stimulation for obesity remains limited to six patients with mixed results, but some clinical trials are ongoing. Thus, drawing clear conclusions about the effectiveness of this treatment is not yet possible, even if the results of preclinical studies are encouraging. Future clinical studies should examine its efficacy and safety, while preclinical studies could help understand its mechanisms of action. We hope that our review will provide ways to design further studies.

Nucleus Accumbens Deep Brain Stimulation in Patients with Substance Use Disorders and Delay Discounting

Deep brain stimulation (DBS) of the nucleus accumbens (NAc) shows first promising results in patients with severe substance use disorder (SUD), a patient group known to have deficits in self-control. One facet of self-control is the ability to forego smaller sooner rewards in favor of larger later rewards (delay discounting, DD). The NAc has been suggested to integrate motivational information to guide behavior while the consequences of NAc-DBS on DD are unknown. To this end, nine patients with SUD performed a DD task with DBS on and after a 24 h DBS off period. Furthermore, 18 healthy controls were measured to assess possible alterations in DD in patients with SUD. Our findings implicate that DD was not significantly modulated by NAc-DBS and also that patients with SUD did not differ from healthy controls. While null results must be interpreted with caution, the commonly observed association of impaired DD in SUD might suggest a long-term effect of NAc-DBS that was not sufficiently modulated by a 24 h DBS off period.

Increased dopamine receptor expression and anti-depressant response following deep brain stimulation of the medial forebrain bundle

BACKGROUND

Among several potential neuroanatomical targets pursued for deep brain stimulation (DBS) for treating those with treatment-resistant depression (TRD), the superolateral-branch of the medial forebrain bundle (MFB) is emerging as a privileged location. We investigated the antidepressant-like phenotypic and chemical changes associated with reward-processing dopaminergic systems in rat brains after MFB-DBS.

METHODS

Male Wistar rats were divided into three groups: sham-operated, DBS-Off, and DBS-On. For DBS, a concentric bipolar electrode was stereotactically implanted into the right MFB. Exploratory activity and depression-like behavior were evaluated using the open-field and forced-swimming test (FST), respectively. MFB-DBS effects on the dopaminergic system were evaluated using immunoblotting for tyrosine hydroxylase (TH), dopamine transporter (DAT), and dopamine receptors (D1-D5), and high-performance liquid chromatography for quantifying dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) in brain homogenates of prefrontal cortex (PFC), hippocampus, amygdala, and nucleus accumbens (NAc).

RESULTS

Animals receiving MFB-DBS showed a significant increase in swimming time without alterations in locomotor activity, relative to the DBS-Off (p<0.039) and sham-operated groups (p<0.014), indicating an antidepressant-like response. MFB-DBS led to a striking increase in protein levels of dopamine D2 receptors and DAT in the PFC and hippocampus, respectively. However, we did not observe appreciable differences in the expression of other dopamine receptors, TH, or in the concentrations of dopamine, DOPAC, and HVA in PFC, hippocampus, amygdala, and NAc.

LIMITATIONS

This study was not performed on an animal model of TRD.

CONCLUSION

MFB-DBS rescues the depression-like phenotypes and selectively activates expression of dopamine receptors in brain regions distant from the target area of stimulation.

Deep Brain Stimulation of the Nucleus Accumbens Core Affects Trait Impulsivity in a Baseline-Dependent Manner

Deep brain stimulation (DBS) of the nucleus accumbens (NA) is explored as a treatment for refractory psychiatric disorders, such as obsessive-compulsive disorder (OCD), depressive disorder (MDD), and substance use disorder (SUD). A common feature of some of these disorders is pathological impulsivity. Here, the effects of NAcore DBS on impulsive choice and impulsive action, two distinct forms of impulsive behavior, were investigated in translational animal tasks, the delayed reward task (DRT) and five-choice serial reaction time task (5-CSRTT), respectively. In both tasks, the effects of NAcore DBS were negatively correlated with baseline impulsive behavior, with more pronounced effects in the 5-CSRTT. To further examine the effects of DBS on trait impulsive action, rats were screened for high (HI) and low (LI) impulsive responding in the 5-CSRTT. NAcore DBS decreased impulsive, premature responding in HI rats under conventional conditions. However, upon challenged conditions to increase impulsive responding, NAcore DBS did not alter impulsivity. These results strongly suggest a baseline-dependent effect of DBS on impulsivity, which is in line with clinical observations.

Cellular and molecular mechanisms triggered by Deep Brain Stimulation in depression: A preclinical and clinical approach

Deep Brain Stimulation (DBS) was originally developed as a therapeutic approach to manage movement disorders, in particular Parkinson's Disease. However, DBS also seems to be an effective treatment against refractory depression when patients fail to respond satisfactorily to conventional therapies. Thus, DBS targeting specific brain areas can produce an antidepressant response that improves depressive symptomatology, these areas including the subcallosal cingulate region, nucleus accumbens, ventral capsule/ventral striatum, medial forebrain bundle, the inferior thalamic peduncle and lateral habenula. Although the efficacy and safety of this therapy has been demonstrated in some clinical trials and preclinical studies, the intrinsic mechanisms underlying its antidepressant effect remain poorly understood. This review aims to provide a comprehensive overview of DBS, focusing on the molecular and cellular changes reported after its use that could shed light on the mechanisms underpinning its antidepressant effect. Several potential mechanisms of action of DBS are considered, including monoaminergic and glutamatergic neurotransmission, neurotrophic and neuroinflammatory mechanisms, as well as potential effects on certain intracellular signaling pathways. Although future studies will be necessary to determine the key molecular events underlying the antidepressant effect of DBS, the findings presented provide an insight into some of its possible modes of action.

Testing different paradigms to optimize antidepressant deep brain stimulation in different rat models of depression

Deep brain stimulation (DBS) of several targets induces beneficial responses in approximately 60% of patients suffering from treatment-resistant depression (TRD). The remaining 40% indicate that these stimulation sites do not bear therapeutic relevance for all TRD patients and consequently DBS-targets should be selected according to individual symptom profiles. We here used two animal models of depression known to have different genetic backgrounds and behavioral responses: the therapy-responsive Flinders sensitive line (FSL) and the therapy-refractory congenitally learned helpless rats (cLH) to study symptom-specific DBS effects i) of different brain sites ii) at different stimulation parameters, and iii) at different expressions of the disease. Sham-stimulation/DBS was applied chronic-intermittently or chronic-continuously to either the ventromedial prefrontal cortex (vmPFC, rodent equivalent to subgenual cingulate), nucleus accumbens (Nacc) or subthalamic nucleus (STN), and effects were studied on different depression-associated behaviors, i.e. anhedonia, immobility/behavioral despair and learned helplessness. Biochemical substrates of behaviorally effective versus ineffective DBS were analyzed using in-vivo microdialysis and post-mortem high-performance liquid chromatography (HPLC). We found that i) vmPFC-DBS outperforms Nacc-DBS, ii) STN-DBS increases depressive states, iii) chronic-continuous DBS does not add benefits compared to chronic-intermittent DBS, iv) DBS-efficacy depends on the disease expression modeled and iv) antidepressant DBS is associated with an increase in serotonin turnover alongside site-specific reductions in serotonin contents. The reported limited effectiveness of vmPFC DBS suggests that future research may consider the specific disease expression, investigation of different DBS-targets and alternative parameter settings.

Effects of deep brain stimulation on prepulse inhibition in obsessive-compulsive disorder

Owing to a high response rate, deep brain stimulation (DBS) of the ventral striatal area has been approved for treatment-refractory obsessive-compulsive disorder (tr-OCD). Many basic issues regarding DBS for tr-OCD are still not understood, in particular, the mechanisms of action and the origin of side effects. We measured prepulse inhibition (PPI) in treatment-refractory OCD patients undergoing DBS of the nucleus accumbens (NAcc) and matched controls. As PPI has been used in animal DBS studies, it is highly suitable for translational research. Eight patients receiving DBS, eight patients with pharmacological treatment and eight age-matched healthy controls participated in our study. PPI was measured twice in the DBS group: one session with the stimulator switched on and one session with the stimulator switched off. OCD patients in the pharmacologic group took part in a single session. Controls were tested twice, to ensure stability of data. Statistical analysis revealed significant differences between controls and (1) patients with pharmacological treatment and (2) OCD DBS patients when the stimulation was switched off. Switching the stimulator on led to an increase in PPI at a stimulus-onset asynchrony of 200 ms. There was no significant difference in PPI between OCD patients being stimulated and the control group. This study shows that NAcc-DBS leads to an increase in PPI in tr-OCD patients towards a level seen in healthy controls. Assuming that PPI impairments partially reflect the neurobiological substrates of OCD, our results show that DBS of the NAcc may improve sensorimotor gating via correction of dysfunctional neural substrates. Bearing in mind that PPI is based on a complex and multilayered network, our data confirm that DBS most likely takes effect via network modulation.

Electrical stimulation alleviates depressive-like behaviors of rats: investigation of brain targets and potential mechanisms

Deep brain stimulation (DBS) is a promising therapy for patients with refractory depression. However, key questions remain with regard to which brain target(s) should be used for stimulation, and which mechanisms underlie the therapeutic effects. Here, we investigated the effect of DBS, with low- and high-frequency stimulation (LFS, HFS), in different brain regions (ventromedial prefrontal cortex, vmPFC; cingulate cortex, Cg; nucleus accumbens (NAc) core or shell; lateral habenula, LHb; and ventral tegmental area) on a variety of depressive-like behaviors using rat models. In the naive animal study, we found that HFS of the Cg, vmPFC, NAc core and LHb reduced anxiety levels and increased motivation for food. In the chronic unpredictable stress model, there was a robust depressive-like behavioral phenotype. Moreover, vmPFC HFS, in a comparison of all stimulated targets, produced the most profound antidepressant effects with enhanced hedonia, reduced anxiety and decreased forced-swim immobility. In the following set of electrophysiological and histochemical experiments designed to unravel some of the underlying mechanisms, we found that vmPFC HFS evoked a specific modulation of the serotonergic neurons in the dorsal raphe nucleus (DRN), which have long been linked to mood. Finally, using a neuronal mapping approach by means of c-Fos expression, we found that vmPFC HFS modulated a brain circuit linked to the DRN and known to be involved in affect. In conclusion, HFS of the vmPFC produced the most potent antidepressant effects in naive rats and rats subjected to stress by mechanisms also including the DRN.

Strain dependence of adolescent Cannabis influence on heroin reward and mesolimbic dopamine transmission in adult Lewis and Fischer 344 rats

Adolescent Cannabis exposure has been hypothesized to act as a gateway to opiate abuse. In order to investigate the role of genetic background in cannabinoid-opiate interactions, we studied the effect of Δ(9) -tetrahydrocannabinol (THC) exposure of adolescent Lewis and Fischer 344 rats on the responsiveness of accumbens shell and core dopamine (DA), as monitored by microdialysis, to THC and heroin at adulthood. Heroin reward and reinstatement by heroin priming were studied by conditioned place preference (CPP) and cognitive and emotional functions by object recognition, Y maze and elevated plus maze paradigms. THC stimulated shell DA in Lewis but not in Fischer 344 rats. Adolescent THC exposure potentiated DA stimulant effects of heroin in the shell and core of Lewis and only in the core of Fischer 344 rats. Control Lewis rats developed stronger CPP to heroin and resistance to extinction compared with Fischer 344 strain. In Lewis rats, THC exposure did not affect heroin CPP but potentiated the effect of heroin priming. In Fischer 344 rats, THC exposure increased heroin CPP and made it resistant to extinction. Lewis rats showed seeking reactions during extinction and hedonic reactions in response to heroin priming. Moreover, adolescent THC exposure affected emotional function only in Lewis rats. These observations suggest that long-term effects of Cannabis exposure on heroin addictive liability and emotionality are dependent on individual genetic background.

Translatable and Back-Translatable Measurement of Impulsivity and Compulsivity: Convergent and Divergent Processes

Impulsivity and compulsivity have emerged as important dimensional constructs that challenge traditional psychiatric classification systems. Both are present in normal healthy populations where the need to act quickly and repeatedly without hesitation can be highly advantageous. However, when excessively expressed, impulsive and compulsive behavior can lead to adverse consequences and spectrum disorders exemplified by attention-deficit/hyperactivity disorder (ADHD), obsessive compulsive disorder (OCD), autism, and drug addiction. Impulsive individuals have difficulty in deferring gratification and are inclined to 'jump the gun' and respond prematurely before sufficient information is gathered. Compulsivity involves repetitive behavior often motivated by the need to reduce or prevent anxiety, thus leading to the maladaptive perseveration of behavior. Defined in this way, impulsivity and compulsivity could be viewed as separate entities or 'traits' but overwhelming evidence indicates that both may be present in the same disorder, either concurrently or even separately at different time points. Herein we discuss the neural and cognitive heterogeneity of impulsive and compulsive endophenotypes. These constructs map onto distinct fronto-striatal neural and neurochemical structures interacting both at nodal convergent points and as opponent processes highlighting both the heterogeneity and the commonalities of function. We focus on discoveries made using both translational research methodologies and studies exclusively in humans, and implications for treatment intervention in disorders in which impulsive and compulsive symptoms prevail. We emphasize the relevance of these constructs for understanding dimensional psychiatry.

Nucleus accumbens core and shell inactivation differentially affects impulsive behaviours in rats

Impulsivity is a multifactorial phenomenon, determined by deficits in decision-making (impulsive choice) and impulse control (impulsive action). Recent findings indicate that impulsive behaviour is not only top-down controlled by cortical areas, but also modulated at subcortical level. The nucleus accumbens (NAc) might be a key substrate in cortico-limbic-striatal circuits involved in impulsive behaviour. Dissociable effects of the NAc subregions in various behavioural paradigms point to a potential functional distinction between NAc core and shell concerning different types of impulsivity. The present study used reversible inactivation of the rats' NAc core and shell via bilateral microinfusion of the GABAA receptor agonist muscimol (0.05μg/0.3μl) and fluorophore-conjugated muscimol (FCM, 0.27μg/0.3μl) in order to study their contribution to different aspects of impulse control in a 5-choice serial reaction time task (5-CSRTT) and impulsive choice in a delay-based decision-making T-maze task. Acute inactivation of NAc core as well as shell by muscimol increased impulsive choice, with higher impairments of the rats' waiting capacity in the T-maze following core injections compared to shell. Intra-NAc shell infusion of muscimol also induced specific impulse control deficits in the 5-CSRTT, while deactivation of the core caused severe general impairments in task performance. FCM did not affect animal behaviour. Our findings reveal clear involvement of NAc shell in both forms of impulsivity. Both subareas play a key role in the regulation of impulsive decision-making, but show functional dichotomy regarding impulse control with the core being more implicated in motivational and motor aspects.

Deep brain stimulation induces striatal dopamine release in obsessive-compulsive disorder

BACKGROUND

Obsessive-compulsive disorder is a chronic psychiatric disorder related to dysfunctional dopaminergic neurotransmission. Deep brain stimulation (DBS) targeted at the nucleus accumbens (NAc) has recently become an effective treatment for therapy-refractory obsessive-compulsive disorder, but its effect on dopaminergic transmission is unknown.

METHODS

We measured the effects of NAc DBS in 15 patients on the dopamine D2/3 receptor availability in the striatum with [(123)I]iodobenzamide ([(123)I]IBZM) single photon emission computed tomography. We correlated changes in [(123)I]IBZM binding potential (BP) with plasma levels of homovanillic acid (HVA) and clinical symptoms.

RESULTS

Acute (1-hour) and chronic (1-year) DBS decreased striatal [(123)I]IBZM BP compared with the nonstimulated condition in the putamen. BP decreases were observed after 1 hour of stimulation, and chronic stimulation was related to concurrent HVA plasma elevations, implying DBS-induced dopamine release. BP decreases in the area directly surrounding the electrodes were significantly correlated with changes in clinical symptoms (45% symptom decrease).

CONCLUSIONS

NAc DBS induced striatal dopamine release, which was associated with increased HVA plasma levels and improved clinical symptoms, suggesting that DBS may compensate for a defective dopaminergic system.

Effect of deep brain stimulation in rats selectively bred for reduced prepulse inhibition

BACKGROUND

Sensorimotor gating, measured as prepulse inhibition (PPI) of the acoustic startle reaction (ASR), is disturbed in certain neuropsychiatric disorders, such as schizophrenia, obsessive compulsive disorder, and Tourette's syndrome (TS). Deep brain stimulation (DBS) of the centromedian-parafascicular complex (CM-Pf), globus pallidus internus (in rats the entopeduncular nucleus - EPN), and the ventral striatum (in rats the nucleus accumbens - NAC) has been used for treatment in TS.

OBJECTIVE

We tested whether DBS of these regions would alleviate breeding-induced low PPI in rats.

METHODS

Rats with breeding-induced low and high PPI were bilaterally implanted with electrodes in the CM-Pf, the EPN, or the NAC. After two weeks, they were stimulated or sham stimulated for epochs of 6 days (in the EPN with a current of 20% below the individual threshold for stimulation-induced side effects, in the NAC or CM-Pf with 100 μA and 150 μA). On the 6th day the rats were tested for PPI of ASR.

RESULTS

Stimulation in the CM-Pf with 150 μA significantly alleviated PPI, while NAC stimulation was less effective. In PPI low rats electrode implantation in the EPN already improved PPI, while subsequent stimulation had no additional effect. Startle reaction of PPI low rats was not affected by stimulation of either region.

CONCLUSION

The CM-Pf and the EPN are important for the modulation of sensorimotor gating in rats with breeding-induced low PPI. These rats may therefore be useful to further investigate the pathophysiological mechanisms of deficient sensorimotor gating and also mechanisms of action of DBS in these circumstances.

Nucleus accumbens high-frequency stimulation selectively impacts nigrostriatal dopaminergic neurons

High-frequency stimulation of the nucleus accumbens, also known as deep brain stimulation (DBS), is currently used to alleviate obsessive compulsive symptoms when pharmacotherapy is ineffective. However, the mechanism by which DBS achieves its therapeutic actions is not understood. Imaging studies and the actions of dopaminergic drugs in untreated patients suggest that the dopamine (DA) system likely plays a role in the pathophysiology of obsessive compulsive disorder. Therefore, we examined whether DBS would impact the DA system as a potential component of its therapeutic actions. The activity of DA neurons in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) were recorded in anesthetized rats under high-frequency stimulation. DA neuron activity was measured in terms of number of neurons firing, average firing rate and firing pattern. DBS of the nucleus accumbens core did not significantly affect VTA activity or discharge pattern. On the other hand, DBS caused a potent decrease in the number of SNc DA neurons firing spontaneously. Such an effect could contribute to the disruption of pathological habit formation in the SNc-dorsal striatal projection system that may have therapeutic implications for the treatment of obsessive compulsive disorder.

Chronic deep brain stimulation of the hypothalamic nucleus in wistar rats alters circulatory levels of corticosterone and proinflammatory cytokines

Deep brain stimulation (DBS) is a therapeutic option for several diseases, but its effects on HPA axis activity and systemic inflammation are unknown. This study aimed to detect circulatory variations of corticosterone and cytokines levels in Wistar rats, after 21 days of DBS-at the ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl), unilateral cervical vagotomy (UCVgX), or UCVgX plus DBS. We included the respective control (C) and sham (S) groups (n = 6 rats per group). DBS treated rats had higher levels of TNF-α (120%; P < 0.01) and IFN-γ (305%; P < 0.001) but lower corticosterone concentration (48%; P < 0.001) than C and S. UCVgX animals showed increased corticosterone levels (154%; P < 0.001) versus C and S. UCVgX plus DBS increased IL-1β (402%; P < 0.001), IL-6 (160%; P < 0.001), and corsticosterone (178%; P < 0.001 versus 48%; P < 0.001) compared with the C and S groups. Chronic DBS at VMHvl induced a systemic inflammatory response accompanied by a decrease of HPA axis function. UCVgX rats experienced HPA axis hyperactivity as result of vagus nerve injury; however, DBS was unable to block the HPA axis hyperactivity induced by unilateral cervical vagotomy. Further studies are necessary to explore these findings and their clinical implication.

Amelioration of binge eating by nucleus accumbens shell deep brain stimulation in mice involves D2 receptor modulation

Hedonic overconsumption contributing to obesity involves altered activation within the mesolimbic dopamine system. Dysregulation of dopamine signaling in the nucleus accumbens shell (NAS) has been implicated in reward-seeking behaviors, such as binge eating, which contributes to treatment resistance in obesity (Wise, 2012). Direct modulation of the NAS with deep brain stimulation (DBS), a surgical procedure currently under investigation in humans for the treatment of major depression, obsessive-compulsive disorder, and addiction, may also be effective in ameliorating binge eating. Therefore, we examined the ability of DBS of the NAS to block this behavior in mice. c-Fos immunoreactivity was assessed as a marker of DBS-mediated neuronal activation. NAS DBS was found to reduce binge eating and increased c-Fos levels in this region. DBS of the dorsal striatum had no influence on this behavior, demonstrating anatomical specificity for this effect. The dopamine D2 receptor antagonist, raclopride, attenuated the action of DBS, whereas the D1 receptor antagonist, SCH-23390, was ineffective, suggesting that dopamine signaling involving D2 receptors underlies the effect of NAS DBS. To determine the potential translational relevance to the obese state, chronic NAS DBS was also examined in diet-induced obese mice and was found to acutely reduce caloric intake and induce weight loss. Together, these findings support the involvement of the mesolimbic dopamine pathways in the hedonic mechanisms contributing to obesity, and the efficacy of NAS DBS to modulate this system.

Dopamine-rich grafts alleviate deficits in contralateral response space induced by extensive dopamine depletion in rats

Unilateral infusion of 6-hydroxydopamine into the nigro-striatal pathway in the rat is the most common dopamine lesion model of Parkinson's disease. In the present study, we explore the impact of near complete unilateral loss of dopamine along the nigro-striatal pathway and subsequent cell replacement therapy in a choice reaction time task in rats, with assessment of spatial responding towards either side of the body (ipsilateral or contralateral to the lesion) on alternate days. Results indicated a stable contralateral deficit in response accuracy, reaction times and motor function for 50 consecutive days of testing, with no signs of recovery or compensation. All lesioned rats developed a near-hole bias and displayed prolonged movement and reaction times when responses had to be directed towards a distal response location on the side of the body contralateral to the lesion, as well as a smaller ipsilateral impairment in response accuracy and movement times. Grafts of dopamine-rich tissue into the denervated striatum improved some, but not all, of the deficits induced by the lesion. Specifically, grafted rats performed at a similar level to control animals when assessed on the ipsilateral side, they demonstrated a partial restitution of their ability to respond to far contralateral stimuli, and they exhibited a marked reduction in the time to complete all lateralised responses on both sides. The present characterisation of the task and the effects of cell replacement via primary fetal mesencephalic tissue demonstrate restorative properties in alleviating the marked spatial response bias induced by unilateral loss of dopamine.

Deep brain stimulation of the accumbens increases dopamine, serotonin, and noradrenaline in the prefrontal cortex

Deep brain stimulation (DBS) of the nucleus accumbens (NAc) is effective in treatment-refractory obsessive-compulsive disorder and major depressive disorder. However, little is known about the neurobiological mechanisms underlying the rapid and effective changes of DBS. One of the hypotheses is that DBS modulates activity of monoamine neurotransmitters. In this study, we evaluated the effects of DBS in the NAc core on the extracellular concentration of monoaminergic neurotransmitters in the medial (mPFC) and orbital prefrontal cortex (OFC). Freely moving rats were bilaterally stimulated in the NAc core for 2 h while dopamine, serotonin, and noradrenaline were measured using in vivo microdialysis in the mPFC and the OFC. We report rapid increases in the release of dopamine and serotonin to a maximum of 177% and 127% in the mPFC and an increase up to 171% and 166% for dopamine and noradrenaline in the OFC after onset of stimulation in the NAc core. These results provide further evidence for the distal effects of DBS and corroborate previous clinical and pre-clinical findings of altered neuronal activity in prefrontal areas.

Long-term high frequency deep brain stimulation of the nucleus accumbens drives time-dependent changes in functional connectivity in the rodent limbic system

Deep brain stimulation of the ventral striatum is an effective treatment for a variety of treatment refractory psychiatric disorders yet the mechanism of action remains elusive. We examined how five days of stimulation affected rhythmic brain activity in freely moving rats in terms of oscillatory power within, and coherence between, selected limbic regions bilaterally. Custom made bipolar stimulating/recording electrodes were implanted, bilaterally, in the nucleus accumbens core. Local field potential (LFP) recording electrodes were implanted, bilaterally in the prelimbic and orbitofrontal cortices and mediodorsal thalamic nucleus. Stimulation was delivered bilaterally with 100 μs duration constant current pulses at a frequency of 130 Hz delivered at an amplitude of 100 μA using a custom-made stimulation device. Synchronized video and LFP data were collected from animals in their home cages before, during and after stimulation. Signals were processed to remove movement and stimulation artifacts, and analyzed to determine changes in spectral power within, and coherence between regions. Five days stimulation of the nucleus accumbens core yielded temporally dynamic modulation of LFP power in multiple bandwidths across multiple brain regions. Coherence was seen to decrease in the alpha band between the mediodorsal thalamic nucleus and core of the nucleus accumbens. Coherence between each core of the nucleus accumbens bilaterally showed rich temporal dynamics throughout the five day stimulation period. Stimulation cessation revealed significant "rebound" effects in both power and coherence in multiple brain regions. Overall, the initial changes in power observed with short-term stimulation are replaced by altered coherence, which may reflect the functional action of DBS.