Search

Neurochemical recording techniques have expanded our understanding of the pathophysiology of neurological disorders, as well as the mechanisms of action of treatment modalities like deep brain stimulation (DBS). DBS is used to treat diseases such as Parkinson's disease, Tourette syndrome, and obsessive-compulsive disorder, among others. Although DBS is effective at alleviating symptoms related to these diseases and improving the quality of life of these patients, the mechanism of action of DBS is currently not fully understood. A leading hypothesis is that DBS modulates the electrical field potential by modifying neuronal firing frequencies to non-pathological rates thus providing therapeutic relief. To address this gap in knowledge, recent advances in electrochemical sensing techniques have given insight into the importance of neurotransmitters, such as dopamine, serotonin, glutamate, and adenosine, in disease pathophysiology. These studies have also highlighted their potential use in tandem with electrophysiology to serve as biomarkers in disease diagnosis and progression monitoring, as well as characterize response to treatment. Here, we provide an overview of disease-relevant neurotransmitters and their roles and implications as biomarkers, as well as innovations to the biosensors used to record these biomarkers. Furthermore, we discuss currently available neurochemical and electrophysiological recording devices, and discuss their viability to be implemented into the development of a closed-loop DBS system.

For over two decades, fast-scan cyclic voltammetry (FSCV) has served as a reliable analytical method for monitoring dopamine release in near real-time in vivo. However, contemporary FSCV techniques have been limited to measure only rapid (on the order of seconds, i.e. phasic) changes in dopamine release evoked by either electrical stimulation or elicited by presentation of behaviorally salient stimuli, and not slower changes in the tonic extracellular levels of dopamine (i.e. basal concentrations). This is because FSCV is inherently a differential method that requires subtraction of prestimulation tonic levels of dopamine to measure phasic changes relative to a zeroed baseline. Here, we describe the development and application of a novel voltammetric technique, multiple cyclic square wave voltammetry (M-CSWV), for analytical quantification of tonic dopamine concentrations in vivo with relatively high temporal resolution (10 s). M-CSWV enriches the electrochemical information by generating two dimensional voltammograms which enable high sensitivity (limit of detection, 0.17 nM) and selectivity against ascorbic acid, and 3,4-dihydroxyphenylacetic acid (DOPAC), including changes in pH. Using M-CSWV, a tonic dopamine concentration of 120 ± 18 nM (n = 7 rats, ± SEM) was determined in the striatum of urethane anethetized rats. Pharmacological treatments to elevate dopamine by selectively inhibiting dopamine reuptake and to reduce DOPAC by inhibition of monoamine oxidase supported the selective detection of dopamine in vivo. Overall, M-CSWV offers a novel voltammetric technique to quantify levels and monitor changes in tonic dopamine concentrations in the brain to further our understanding of the role of dopamine in normal behavior and neuropsychiatric disorders., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Opioids, such as morphine or heroin, increase forebrain dopamine (DA) release and locomotion, and support the acquisition of conditioned place preference (CPP) or self-administration. The most sensitive sites for these opioid effects in rodents are in the ventral tegmental area (VTA) and rostromedial tegmental nucleus (RMTg). Opioid inhibition of GABA neurons in these sites is hypothesized to lead to arousing and rewarding effects through disinhibition of VTA DA neurons. We review findings that the laterodorsal tegmental (LDTg) and pedunculopontine tegmental (PPTg) nuclei, which each contain cholinergic, GABAergic, and glutamatergic cells, are important for these effects. LDTg and/or PPTg cholinergic inputs to VTA mediate opioid-induced locomotion and DA activation via VTA M5 muscarinic receptors. LDTg and/or PPTg cholinergic inputs to RMTg also modulate opioid-induced locomotion. Lesions or inhibition of LDTg or PPTg neurons reduce morphine-induced increases in forebrain DA release, acquisition of morphine CPP or self-administration. We propose a circuit model that links VTA and RMTg GABA with LDTg and PPTg neurons critical for DA-dependent opioid effects in drug-naïve rodents., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Bioelectronic Medicines is an emerging field that capitalizes on minimally-invasive technology to stimulate the autonomic nervous system in order to evoke therapeutic biomolecular changes at the end-organ. The goal of Bioelectronic Medicines is to realize both 'precision and personalized' medicine. 'Precise' stimulation of neural circuitry creates biomolecular changes targeted exactly where needed to maximize therapeutic effects while minimizing off-target changes associated with side-effects. The therapy is then 'personalized' by utilizing implanted sensors to measure the biomolecular concentrations at, or near, the end-organ of interest and continually adjusting therapy to account for patient-specific biological changes throughout the day. To realize the promise of Bioelectronic Medicines, there is a need for minimally invasive, real-time measurement of biomarkers associated with the effects of autonomic nerve stimulation to be used for continuous titration of therapy. In this study we examine the feasibility of using fast scan cyclic voltammetry (FSCV) to measure norepinephrine levels, a neurochemical relevant to end-organ function, directly from blood. FSCV is a well-understood method for measuring electroactive neurochemicals in the central nervous system with high temporal and high spatial resolution that has yet to be adapted to the study of the autonomic nervous system. The results demonstrate that while detecting the electroactive neurochemical norepinephrine in blood is more challenging than obtaining the same FSCV measurements in a buffer solution due to biofouling of the electrode, it is feasible to utilize a minimally invasive FSCV electrode to obtain neurochemical measurements in blood.

Introduction: Deep brain stimulation (DBS) is a circuit-based treatment shown to relieve symptoms from multiple neurologic and neuropsychiatric disorders. In order to treat the memory deficit associated with Alzheimer's disease (AD), several clinical trials have tested the efficacy of DBS near the fornix. Early results from these studies indicated that patients who received fornix DBS experienced an improvement in memory and quality of life, yet the mechanisms behind this effect remain controversial. It is known that transmission between the medial limbic and corticolimbic circuits plays an integral role in declarative memory, and dysfunction at the circuit level results in various forms of dementia, including AD. Here, we aimed to determine the potential underlying mechanism of fornix DBS by examining the functional circuitry and brain structures engaged by fornix DBS., Methods: A multimodal approach was employed to examine global and local temporal changes that occur in an anesthetized swine model of fornix DBS. Changes in global functional activity were measured by functional MRI (fMRI), and local neurochemical changes were monitored by fast scan cyclic voltammetry (FSCV) during electrical stimulation of the fornix. Additionally, intracranial microinfusions into the nucleus accumbens (NAc) were performed to investigate the global activity changes that occur with dopamine and glutamate receptor-specific antagonism., Results: Hemodynamic responses in both medial limbic and corticolimbic circuits measured by fMRI were induced by fornix DBS. Additionally, fornix DBS resulted in increases in dopamine oxidation current (corresponding to dopamine efflux) monitored by FSCV in the NAc. Finally, fornix DBS-evoked hemodynamic responses in the amygdala and hippocampus decreased following dopamine and glutamate receptor antagonism in the NAc., Conclusions: The present findings suggest that fornix DBS modulates dopamine release on presynaptic dopaminergic terminals in the NAc, involving excitatory glutamatergic input, and that the medial limbic and corticolimbic circuits interact in a functional loop., (Copyright © 2016 Elsevier Inc. All rights reserved.)

This review presents state-of-the-art knowledge about the roles of the basal ganglia (BG) in action-selection, cognition, and motivation, and how this knowledge has been used to improve deep brain stimulation (DBS) treatment of neurological and psychiatric disorders. Such pathological conditions include Parkinson's disease, Huntington's disease, Tourette syndrome, depression, and obsessive-compulsive disorder. The first section presents evidence supporting current hypotheses of how the cortico-BG circuitry works to select motor and emotional actions, and how defects in this circuitry can cause symptoms of the BG diseases. Emphasis is given to the role of striatal dopamine on motor performance, motivated behaviors and learning of procedural memories. Next, the use of cutting-edge electrochemical techniques in animal and human studies of BG functioning under normal and disease conditions is discussed. Finally, functional neuroimaging studies are reviewed; these works have shown the relationship between cortico-BG structures activated during DBS and improvement of disease symptoms., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Rationale: Alcohol use in adolescence is one of the most significant predictors of alcohol dependence in adulthood, yet the neurochemical mechanisms underlying this heightened vulnerability remain unknown. Whereas research has focused on characterizing adaptations in the mesolimbic dopamine (DA) system following ethanol exposure in adolescence, whether these changes persist into adulthood has yet to be determined., Objectives: The objective of this study is to investigate the effects of binge-intermittent ethanol administration in adolescence (P30-50) or early adulthood (P60-80) on DA in the nucleus accumbens (NAc) core after an ethanol challenge in adulthood following a period of abstinence., Methods: Male Sprague Dawley rats (n = 160) were administered intermittent ethanol injections, 1 or 3 g/kg, intraperitoneally (i.p.) every other day for 20 days starting on either P30 or 60. Following an ethanol-free period of either 7, 14, or 28 days, we measured DA efflux following an ethanol challenge (3 g/kg, i.p.) using electrochemical recording electrodes bilaterally implanted into the NAc core., Results: Moderate-dose ethanol administration (1 g/kg, i.p.) during adolescence significantly decreased ethanol-evoked DA release in adulthood at 7 and 14 days, but not 28 days, following pretreatment exposure compared to saline controls. Relative to rats pretreated with ethanol in adulthood, moderate-dose ethanol in adolescence significantly reduced DA efflux at all time points measured. Additionally, adult rats pretreated with high dose ethanol administration (3 g/kg, i.p.) displayed significantly decreased DA compared to adolescents after 28 days of withdrawal., Conclusions: Binge-intermittent ethanol administration during adolescence may induce age-dependent neuroadaptations in the mesolimbic DA system compared to ethanol-treated adults during protracted ethanol withdrawal.

Neural abnormalities commonly associated with autism spectrum disorders include prefrontal cortex (PFC) dysfunction and cerebellar pathology in the form of Purkinje cell loss and cerebellar hypoplasia. It has been reported that loss of cerebellar Purkinje cells results in aberrant dopamine neurotransmission in the PFC which occurs via dysregulation of multisynaptic efferents from the cerebellum to the PFC. Using a mouse model, we investigated the possibility that developmental cerebellar Purkinje cell loss could disrupt glutamatergic cerebellar projections to the PFC that ultimately modulate DA release. We measured glutamate release evoked by local electrical stimulation using fixed-potential amperometry in combination with glutamate selective enzyme-based recording probes in urethane-anesthetized Lurcher mutant and wildtype mice. Target sites included the mediodorsal and ventrolateral thalamic nuclei, reticulotegmental nuclei, pedunculopontine nuclei, and ventral tegmental area. With the exception of the ventral tegmental area, the results indicated that in comparison to wildtype mice, evoked glutamate release was reduced in Lurcher mutants by between 9 and 72% at all stimulated sites. These results are consistent with the notion that developmental loss of cerebellar Purkinje cells drives reductions in evoked glutamate release in cerebellar efferent pathways that ultimately influence PFC dopamine release. Possible mechanisms whereby reductions in glutamate release could occur are discussed.

This study examined the effects of bilateral excitotoxic lesions of the nucleus accumbens core (NAc-co), dorsomedial striatum (DMS) or dorsolateral striatum (DLS) of rats on the learning and extinction of Pavlovian and instrumental components of conditioned avoidance responses (CARs). None of the lesions caused sensorimotor deficits that could affect locomotion. Lesions of the NAc-co, but not DMS or DLS, decreased unconditioned and conditioned freezing. The NAc-co and DLS lesioned rats learned the 2-way active avoidance task more slowly. These results suggest: (i) CARs depend on both Pavlovian and instrumental learning; (ii) learning the Pavlovian component of CARs depends on the NAc-co; learning the instrumental component of CARs depends on the DLS, NAc and DMS; (iii) although the NAc-co is also needed for learning the instrumental component, it is not clear whether it plays a role in learning the instrumental component per se or if it simply allows learning of the Pavlovian component which is a pre-condition for learning the instrumental component; (iv) we did not find evidence that the DMS and DLS play the same roles in habit and goal-directed aspects of the instrumental component of CARs as observed in appetitive motivated instrumental responding., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Objective: Seizures are currently defined by their electrographic features. However, neuronal networks are intrinsically dependent on neurotransmitters of which little is known regarding their periictal dynamics. Evidence supports adenosine as having a prominent role in seizure termination, as its administration can terminate and reduce seizures in animal models. Furthermore, microdialysis studies in humans suggest that adenosine is elevated periictally, but the relationship to the seizure is obscured by its temporal measurement limitations. Because electrochemical techniques can provide vastly superior temporal resolution, we test the hypothesis that extracellular adenosine concentrations rise during seizure termination in an animal model and humans using electrochemistry., Methods: White farm swine (n = 45) were used in an acute cortical model of epilepsy, and 10 human epilepsy patients were studied during intraoperative electrocorticography (ECoG). Wireless Instantaneous Neurotransmitter Concentration Sensor (WINCS)-based fast scan cyclic voltammetry (FSCV) and fixed potential amperometry were obtained utilizing an adenosine-specific triangular waveform or biosensors, respectively., Results: Simultaneous ECoG and electrochemistry demonstrated an average adenosine increase of 260% compared to baseline, at 7.5 ± 16.9 s with amperometry (n = 75 events) and 2.6 ± 11.2 s with FSCV (n = 15 events) prior to electrographic seizure termination. In agreement with these animal data, adenosine elevation prior to seizure termination in a human patient utilizing FSCV was also seen., Significance: Simultaneous ECoG and electrochemical recording supports the hypothesis that adenosine rises prior to seizure termination, suggesting that adenosine itself may be responsible for seizure termination. Future work using intraoperative WINCS-based FSCV recording may help to elucidate the precise relationship between adenosine and seizure termination., (Wiley Periodicals, Inc. © 2014 International League Against Epilepsy.)

Studies of adolescent drug use show (1) a pattern in which the use of tobacco precedes the use of other drugs and (2) a positive relationship between adolescent tobacco use and later drug use. These observations have led to the hypothesis that a causal relationship exists between early exposure to nicotine and the later use of hard drugs such as cocaine. Using male C57BL/6J mice, we tested the hypothesis that nicotine exposure in adolescence leads to increased intravenous self-administration (IVSA) of cocaine in adulthood. Using miniature osmotic pumps, we exposed mice and their littermate controls to nicotine (24 mg/kg/day) or vehicle, respectively, over the entire course of adolescence [postnatal days (P) 28-56]. Nicotine exposure was terminated on P56 and mice were not exposed to nicotine again during the experiment. On P73, mice were allowed to acquire cocaine IVSA (1.0 mg/kg/infusion) and a dose-response curve was generated (0.18, 0.32, 0.56, 1.0, 1.8 mg/kg/infusion). Lever pressing during extinction conditions was also evaluated. All mice rapidly learned to lever press for the combination of cocaine infusions and non-drug stimuli. Analysis of the dose-response curve revealed that adolescent nicotine-exposed mice self-administered significantly more (P < 0.05) cocaine than controls at all but the highest dose. No significant differences were observed between adolescent nicotine-exposed and control mice during the acquisition or extinction stages. These results indicate that adolescent nicotine exposure can increase cocaine IVSA in mice, which suggests the possibility of a causal link between adolescent tobacco use and later cocaine use in humans., (© 2012 The Authors, Addiction Biology © 2012 Society for the Study of Addiction.)

Exposure to polychlorinated biphenyls (PCBs) alters brain dopamine (DA) concentrations and DA receptor/transporter function, suggesting the reinforcing properties of drugs of abuse acting on the DA system may be affected by PCB exposure. Female Long-Evans rats were orally exposed to 0, 3, or 6 mg/kg/day PCBs from 4 weeks prior to breeding until litters were weaned on postnatal day 21. In vivo fixed potential amperometry (FPA) was used in adult anesthetized offspring to determine whether perinatal PCB exposure altered (1) presynaptic DA autoreceptor (DAR) sensitivity, (2) electrically evoked nucleus accumbens (NAc) DA efflux following administration of cocaine, and (3) the rate of depletion of presynaptic DA stores. One adult male and female littermate were tested using FPA following a single injection of cocaine (20 mg/kg ip), whereas a second adult male and female littermate were tested following the last of seven daily cocaine injections of the same dose. The carbon fiber recording microelectrode was positioned in the NAc core, and DA oxidation currents (i.e., DA release) evoked by brief stimulation of the medial forebrain bundle (MFB) were quantified before and after administration of cocaine. PCB-exposed rats exhibited enhanced stimulation-evoked DA release (relative to baseline) following a single injection of cocaine. Although nonexposed controls exhibited typical DA sensitization following repeated cocaine administration, this effect was attenuated in PCB-exposed rats. In addition, DAR sensitivity was higher (males only), and the rate of depletion of presynaptic DA stores was greater in PCB-exposed animals relative to nonexposed controls. These results indicate that perinatal PCB exposure can modify DA synaptic transmission in the NAc in a manner previously shown to alter the reinforcing properties of cocaine.

Fragile X syndrome (FXS) is the most common inherited form of intellectual disability in males and the most common genetic cause of autism. Although executive dysfunction is consistently found in humans with FXS, evidence of executive dysfunction in Fmr1 KO mice, a mouse model of FXS, has been inconsistent. One possible explanation for this is that executive dysfunction in Fmr1 KO mice, similar to humans with FXS, is only evident when cognitive demands are high. Using touchscreen operant conditioning chambers, male Fmr1 KO mice and their male wildtype littermates were tested on the acquisition of a pairwise visual discrimination followed by four serial reversals of the response rule. We assessed reversal learning performance under two different conditions. In the first, the correct stimulus was salient and the incorrect stimulus was non-salient. In the second and more challenging condition, the incorrect stimulus was salient and the correct stimulus was non-salient; this increased cognitive load by introducing conflict between sensory-driven (i.e., bottom-up) and task-dependent (i.e., top-down) signals. Fmr1 KOs displayed two distinct impairments relative to wildtype littermates. First, Fmr1 KOs committed significantly more learning-type errors during the second reversal stage, but only under high cognitive load. Second, during the first reversal stage, Fmr1 KOs committed significantly more attempts to collect a reward during the timeout following an incorrect response. These findings indicate that Fmr1 KO mice display executive dysfunction that, in some cases, is only evident under high cognitive load., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Imaging, clinical, and pre-clinical studies have provided ample evidence for a cerebellar involvement in cognitive brain function including cognitive brain disorders, such as autism and schizophrenia. We previously reported that cerebellar activity modulates dopamine release in the mouse medial prefrontal cortex (mPFC) via two distinct pathways: (1) cerebellum to mPFC via dopaminergic projections from the ventral tegmental area (VTA) and (2) cerebellum to mPFC via glutamatergic projections from the mediodorsal and ventrolateral thalamus (ThN md and vl). The present study compared functional adaptations of cerebello-cortical circuitry following developmental cerebellar pathology in a mouse model of developmental loss of Purkinje cells (Lurcher) and a mouse model of fragile X syndrome (Fmr1 KO mice). Fixed potential amperometry was used to measure mPFC dopamine release in response to cerebellar electrical stimulation. Mutant mice of both strains showed an attenuation in cerebellar-evoked mPFC dopamine release compared to respective wildtype mice. This was accompanied by a functional reorganization of the VTA and thalamic pathways mediating cerebellar modulation of mPFC dopamine release. Inactivation of the VTA pathway by intra-VTA lidocaine or kynurenate infusions decreased dopamine release by 50 % in wildtype and 20-30 % in mutant mice of both strains. Intra-ThN vl infusions of either drug decreased dopamine release by 15 % in wildtype and 40 % in mutant mice of both strains, while dopamine release remained relatively unchanged following intra-ThN md drug infusions. These results indicate a shift in strength towards the thalamic vl projection, away from the VTA. Thus, cerebellar neuropathologies associated with autism spectrum disorders may cause a reduction in cerebellar modulation of mPFC dopamine release that is related to a reorganization of the mediating neuronal pathways.

We conducted an experiment in which hedonia, salience and prediction error hypotheses predicted different patterns of dopamine (DA) release in the striatum during learning of conditioned avoidance responses (CARs). The data strongly favor the latter hypothesis. It predicts that during learning of the 2-way active avoidance CAR task, positive prediction errors generated when rats do not receive an anticipated footshock (which is better than expected) cause DA release that reinforces the instrumental avoidance action. In vivo microdialysis in the rat striatum showed that extracellular DA concentration increased during early CAR learning and decreased throughout training returning to baseline once the response was well learned. In addition, avoidance learning was proportional to the degree of DA release. Critically, exposure of rats to the same stimuli but in an unpredictable, unavoidable, and inescapable manner, did not produce alterations from baseline DA levels as predicted by the prediction error but not hedonic or salience hypotheses. In addition, rats with a partial lesion of substantia nigra DA neurons, which did not show increased DA levels during learning, failed to learn this task. These data represent clear and unambiguous evidence that it was the factor positive prediction error, and not hedonia or salience, which caused increase in the tonic level of striatal DA and which reinforced learning of the instrumental avoidance response., (Copyright © 2012. Published by Elsevier B.V.)

The combination of deep brain stimulation (DBS) and functional MRI (fMRI) is a powerful means of tracing brain circuitry and testing the modulatory effects of electrical stimulation on a neuronal network in vivo. The goal of this study was to trace DBS-induced global neuronal network activation in a large animal model by monitoring the blood oxygenation level-dependent (BOLD) response on fMRI. We conducted DBS in normal anesthetized pigs, targeting the subthalamic nucleus (STN) (n=7) and the entopeduncular nucleus (EN), the non-primate analog of the primate globus pallidus interna (n=4). Using a normalized functional activation map for group analysis and the application of general linear modeling across subjects, we found that both STN and EN/GPi DBS significantly increased BOLD activation in the ipsilateral sensorimotor network (FDR<0.001). In addition, we found differential, target-specific, non-motor network effects. In each group the activated brain areas showed a distinctive correlation pattern forming a group of network connections. Results suggest that the scope of DBS extends beyond an ablation-like effect and that it may have modulatory effects not only on circuits that facilitate motor function but also on those involved in higher cognitive and emotional processing. Taken together, our results show that the swine model for DBS fMRI, which conforms to human implanted DBS electrode configurations and human neuroanatomy, may be a useful platform for translational studies investigating the global neuromodulatory effects of DBS., (Copyright © 2012 Elsevier Inc. All rights reserved.)

There has been significant advancement in various aspects of scientific knowledge concerning the role of cerebellum in the etiopathogenesis of autism. In the current consensus paper, we will observe the diversity of opinions regarding the involvement of this important site in the pathology of autism. Recent emergent findings in literature related to cerebellar involvement in autism are discussed, including: cerebellar pathology, cerebellar imaging and symptom expression in autism, cerebellar genetics, cerebellar immune function, oxidative stress and mitochondrial dysfunction, GABAergic and glutamatergic systems, cholinergic, dopaminergic, serotonergic, and oxytocin-related changes in autism, motor control and cognitive deficits, cerebellar coordination of movements and cognition, gene-environment interactions, therapeutics in autism, and relevant animal models of autism. Points of consensus include presence of abnormal cerebellar anatomy, abnormal neurotransmitter systems, oxidative stress, cerebellar motor and cognitive deficits, and neuroinflammation in subjects with autism. Undefined areas or areas requiring further investigation include lack of treatment options for core symptoms of autism, vermal hypoplasia, and other vermal abnormalities as a consistent feature of autism, mechanisms underlying cerebellar contributions to cognition, and unknown mechanisms underlying neuroinflammation.

Essential tremor is often markedly reduced during deep brain stimulation simply by implanting the stimulating electrode before activating neurostimulation. Referred to as the microthalamotomy effect, the mechanisms of this unexpected consequence are thought to be related to microlesioning targeted brain tissue, that is, a microscopic version of tissue ablation in thalamotomy. An alternate possibility is that implanting the electrode induces immediate neurochemical release. Herein, we report the experiment performing with real-time fast-scan cyclic voltammetry to quantify neurotransmitter concentrations in human subjects with essential tremor during deep brain stimulation. The results show that the microthalamotomy effect is accompanied by local neurochemical changes, including adenosine release., (Copyright © 2012 Mayo Foundation for Medical Education and Research. Published by Elsevier Inc. All rights reserved.)

Preclinical and clinical evidence suggest an association between alcoholism and the primary regulator of extracellular dopamine concentrations, the dopamine transporter (DAT). However, the nature of this association is unclear. We determined if 10 days of voluntary alcohol self-administration followed by withdrawal could directly alter DAT function, or if genetically mediated changes in DAT function and/or availability could influence vulnerability to alcohol abuse. Heterozygous (DAT+/-) and homozygous mutant (DAT-/-) and wild-type (DAT+/+) mice were allowed to consume 5% alcohol in a schedule-induced polydipsia (SIP) task. In vivo fixed potential amperometry in anesthetized mice was used to (1) identify functional characteristics of mesoaccumbens dopamine neurons related to genotype, including dopamine autoreceptor (DAR) sensitivity, DAT efficiency, and DAT capacity, (2) determine if any of these characteristics correlated with alcohol drinking observed in DAT+/+ and DAT+/- animals, and (3) determine if SIP-alcohol self-administration altered DAR sensitivity, DAT efficiency, and DAT capacity by comparing these characteristics in wild-type (DAT+/+) mice that were SIP-alcohol naïve, with those that had undergone SIP-alcohol testing. DAT-/- mice consumed significantly less alcohol during testing and this behavioral difference was related to significant differences in DAR sensitivity, DAT efficiency, and DAT capacity. These functional characteristics were correlated to varying degrees with g/kg alcohol consumption in DAT+/+ and DAT+/- mice. DAR sensitivity was consistently reduced and DAT efficiency was enhanced in SIP-alcohol-experienced DAT+/+ mice when compared with naïve animals. These results indicate that DAR sensitivity is reduced by SIP-alcohol consumption and that DAT efficiency is modified by genotype and SIP-alcohol exposure. DAT capacity appeared to be strictly associated with SIP-alcohol consumption., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Rationale: The tendency to use cocaine is determined by genetic and environmental effects across the lifespan. One critical environmental effect is early drug exposure, which is both driven by and interacts with genetic background. The mesoaccumbens dopamine system, which is critically involved in the rewarding properties of drugs of abuse, undergoes significant development during adolescence, and thus may be at particular risk to repeated nicotine exposure during this period, thereby establishing vulnerability for subsequent adult psychostimulant use., Objectives: We tested the hypotheses that adolescent nicotine exposure results in attenuation of the enhancing effects of cocaine on medial forebrain bundle (MFB) electrical stimulation-evoked dopamine release in the nucleus accumbens shell (AcbSh) in adulthood and that this effect is significantly influenced by genotype., Methods: Mice from the progenitor strains C57BL/6J and DBA/2J and those from the BXD20/TyJ and BXD86/RwwJ recombinant inbred lines were exposed to nicotine via osmotic minipumps from postnatal day (P) 28 to P56. When mice reached P70, dopamine functional dynamics in AcbSh was evaluated by means of in vivo fixed potential amperometry in combination with electrical stimulation of mesoaccumbens dopaminergic axons in the MFB., Results: Adolescent exposure to nicotine in all strains dose-dependently reduced the ability of a fixed-dose challenge injection of cocaine (10 mg/kg, i.p.) to enhance MFB electrical stimulation-evoked dopamine release in AcbSh in adults. The magnitude of this effect was genotype-dependent., Conclusions: These results suggest a genotype-dependent mechanism by which nicotine exposure during adolescence causes persistent changes in the sensitivity to "hard" stimulants such as cocaine.

Although behavioral inflexibility and Purkinje cell loss are both well established in autism, it is unknown if these phenomena are causally related. Using a mouse model, we tested the hypothesis that developmental abnormalities of the cerebellum, including Purkinje cell loss, result in behavioral inflexibility. Specifically, we made aggregation chimeras (Lc/+<-->+/+) between lurcher (Lc/+) mutant embryos and wildtype (+/+) control embryos. Lurcher mice lose 100% of their Purkinje cells postnatally, while chimeric mice lose varying numbers of Purkinje cells. We tested these mice on the acquisition and serial reversals of an operant conditional visual discrimination, a test of behavioral flexibility in rodents. During reversals 1 and 2, all groups of mice committed similar numbers of "perseverative" errors (those committed while session performance was <= 40% correct). Lurchers, however, committed a significantly greater number of "learning" errors (those committed while session performance was between 41% and 85% correct) than both controls and chimeras, and most were unable to advance past reversal 3. During reversals 3 and 4, chimeras, as a group, committed more "perseverative", but not "learning" errors than controls, although a comparison of Purkinje cell number and performance in individual mice revealed that chimeras with fewer Purkinje cells made more "learning" errors and had shorter response latencies than chimeras with more Purkinje cells. These data suggest that developmental cerebellar Purkinje cell loss may affect higher level cognitive processes which have previously been shown to be mediated by the prefrontal cortex, and are commonly deficient in autism spectrum disorders., (Copyright 2010 Elsevier Inc. All rights reserved.)

Dopaminergic neurons in the substantia nigra pars compacta and ventral tegmental area of the midbrain form the nigrostriatal and mesocorticolimbic dopaminergic pathways that, respectively, project to dorsal and ventral striatum (including prefrontal cortex). These midbrain dopaminergic nuclei and their respective forebrain and cortical target areas are well established as serving a critical role in mediating voluntary motor control, as evidenced in Parkinson's disease, and incentive-motivated behaviors and cognitive functions, as exhibited in drug addiction and schizophrenia, respectively. Although it cannot be disputed that excitatory and inhibitory amino acid-based neurotransmitters, such as glutamate and GABA, play a vital role in modulating activity of midbrain dopaminergic neurons, recent evidence suggests that acetylcholine may be as important in regulating dopaminergic transmission. Midbrain dopaminergic cell tonic and phasic activity is closely dependent upon projections from hindbrain pedunculopontine and the laterodorsal tegmental nuclei, which comprises the only known cholinergic inputs to these neurons. In close coordination with glutamatergic and GABAergic activity, these excitatory cholinergic projections activate nicotinic and muscarinic acetylcholine receptors within the substantia nigra and ventral tegmental area to modulate dopamine transmission in the dorsal/ventral striatum and prefrontal cortex. Additionally, acetylcholine-containing interneurons in the striatum also constitute an important neural substrate to provide further cholinergic modulation of forebrain striatal dopaminergic transmission. In this review, we examine neurological and psychopathological conditions associated with dysfunctions in the interaction of acetylcholine and dopamine and conventional and new pharmacological approaches to treat these disorders.

Introduction: Muscarinic M(5) receptors are the only muscarinic receptor subtype expressed by dopamine-containing neurons of the ventral tegmental area. These cells play an important role for the reinforcing properties of psychostimulants and M(5) receptors modulate their activity. Previous studies showed that M(5) receptor knockout (M (5) (-/-) ) mice are less sensitive to the reinforcing properties of addictive drugs., Materials and Methods: Here, we investigate the role of M(5) receptors in the effects of amphetamine and cocaine on locomotor activity, locomotor sensitization, and dopamine release using M (5) (-/-) mice backcrossed to the C57BL/6NTac strain., Statistical Analyses: Sensitization of the locomotor response is considered a model for chronic adaptations to repeated substance exposure, which might be related to drug craving and relapse. The effects of amphetamine on locomotor activity and locomotor sensitization were enhanced in M (5) (-/-) mice, while the effects of cocaine were similar in M (5) (-/-) and wild-type mice., Results: Consistent with the behavioral results, amphetamine-, but not cocaine, -elicited dopamine release in nucleus accumbens was enhanced in M (5) (-/-) mice., Discussion: The different effects of amphetamine and cocaine in M (5) (-/-) mice may be due to the divergent pharmacological profile of the two drugs, where amphetamine, but not cocaine, is able to release intracellular stores of dopamine. In conclusion, we show here for the first time that amphetamine-induced hyperactivity and dopamine release as well as amphetamine sensitization are enhanced in mice lacking the M(5) receptor. These results support the concept that the M(5) receptor modulates effects of addictive drugs.

Deep Brain Stimulation (DBS) provides therapeutic benefit for several neuropathologies including Parkinson's disease (PD), epilepsy, chronic pain, and depression. Despite well established clinical efficacy, the mechanism(s) of DBS remains poorly understood. In this review we begin by summarizing the current understanding of the DBS mechanism. Using this knowledge as a framework, we then explore a specific hypothesis regarding DBS of the subthalamic nucleus (STN) for the treatment of PD. This hypothesis states that therapeutic benefit is provided, at least in part, by activation of surviving nigrostriatal dopaminergic neurons, subsequent striatal dopamine release, and resumption of striatal target cell control by dopamine. While highly controversial, we present preliminary data that are consistent with specific predications testing this hypothesis. We additionally propose that developing new technologies, e.g., human electrometer and closed-loop smart devices, for monitoring dopaminergic neurotransmission during STN DBS will further advance this treatment approach.

A 16-channel chip for wireless in vivo recording of chemical and electrical neural activity is described. The 7.83-mm2 IC is fabricated using a 0.5-microm CMOS process and incorporates a 71-microW, 3rd-order, configurable, DeltaSigma modulator per channel, achieving an input-referred noise of 4.69 microVrms in 4-kHz BW and 94.1 pArms in 5-kHz BW for electrical and fastscan voltammetric chemical neurosensing, respectively. Brain extracellular levels of dopamine elicited by electrical stimulation of the medial forebrain bundle have been recorded wirelessly on multiple channels using 300-V/s fast-scan cyclic voltammetry in the anesthetized rat.

In this study, fixed potential amperometry was used to examine several pathways by which Deep Brain Stimulation (DBS) of the subthalamic nucleus (STN) or dopamine axons within the dorsal forebrain bundle (DFB) release striatal dopamine, thus potentially providing therapeutic benefits for Parkinson's Disease patients. In urethane anesthetized mice, electrical stimulations (20 monophasic pulses at 50 Hz every 30 sec) were applied to the STN or DFB while infusing the local anesthetic lidocaine (4%) into the substantia nigra compacta (SNc) or pedunculopontine tegmental nucleus (PPT). Findings suggest that DFB stimulation activates ascending SNc dopamine axons, while STN stimulation evokes striatal dopamine release directly via excitatory glutamatergic inputs to SNc dopamine cells and indirectly via excitatory cholinergic/glutamatergic STN-PPT-SNc pathways.

The receptors that couple to the G protein Gz in vivo are still relatively unknown. In this study, we investigated the effects of various dopamine receptor agonists in a mouse deficient in the alpha subunit of Gz. The dopamine D1-like receptor agonist SKF38393 stimulated comparable locomotor activity in both wildtype mice and mice lacking Galphaz. In contrast, the dopamine D2-like receptor agonist quinpirole suppressed locomotor activity in both groups of mice, but this suppression was significantly smaller in Galphaz knockout mice. Consistent with these behavioural observations, quinpirole inhibition of dopamine release in the forebrain nucleus accumbens evoked by electrical stimulation of dopamine axons was significantly attenuated in mice lacking Galphaz. In addition, hypothermia and adrenocorticotropic hormone release resulting from activation of dopamine D2-like receptors were also significantly reduced in Galphaz knockout mice. However, adrenocorticotropic hormone secretion induced by corticotrophin releasing hormone and the serotonin 1A receptor agonist 8-hydroxy-dipropylamino-tetralin were similar between wildtype and Galphaz knockout mice. Western blot analysis showed that the expression levels of Galphai, Galphao, Galphas, Galphaq and Gbeta were the same in the brains of mice of both genotypes. Overall, our data suggest that Gz proteins are functionally coupled to dopamine D2-like receptors in vivo.

Rationale: Aminoadamantanes represent a class of NMDA glutamate receptor antagonists that reduce alcohol consumption and may prevent alcohol-induced neuronal adaptations and side effects., Objective: Behavioral specificity of memantine and amantadine on alcohol drinking in a schedule-induced polydipsia (SIP) task was investigated in mice., Methods: Male C57BL/6J mice were food-deprived and divided into four groups: 5% alcohol SIP, water SIP, 1 h limited access regulatory water drinking, and a control group to determine if either drug altered ethanol drinking. Behavioral specificity of memantine (5, 10, and 25 mg/kg, ip) and amantadine (20, 40, and 60 mg/kg, ip) was determined by comparing alterations in alcohol or water consumption in SIP and regulatory water drinking. Drug effects on SIP drinking-specific measures (grams per kilogram consumption) were also compared to nondrinking measures (locomotion, head-entries for food, and lick efficiency)., Results: Compared to saline, memantine reduced alcohol SIP drinking (10 and 25 mg/kg). Memantine increased locomotion during alcohol SIP (25 mg/kg) and during water SIP (5 and 25 mg/kg). In contrast, amantadine reduced both alcohol SIP (40 mg/kg) and water SIP (40 and 60 mg/kg). Both drugs reduced regulatory water consumption over the entire dose range tested. Blood alcohol concentrations indicated consumption of physiologically meaningful amounts of alcohol during SIP, and that changes in alcohol metabolism did not account for drug-induced reductions in alcohol drinking., Conclusions: In addition to reducing alcohol drinking, both drugs had other behavioral effects that included reductions in regulatory drinking. These results suggest that the therapeutic utility of these drugs for ameliorating human alcohol addiction remains questionable.

The precise mechanism whereby continuous high-frequency electrical stimulation of the subthalamic nucleus ameliorates motor symptoms of Parkinson's disease is unknown. We examined the effects of high-frequency stimulation of regions dorsal to and within the subthalamic nucleus on dopamine efflux in the striatum of urethane-anaesthetized rats using constant potential amperometry. Complementary extracellular electrophysiological studies determined the activity of subthalamic nucleus neurons in response to similar electrical stimulation of the subthalamic nucleus. High-frequency stimulation of the subthalamic nucleus increased action potential firing in the subthalamic nucleus only during the initial stimulation period and was followed by a cessation of firing over the remainder of stimulation. Electrical stimulation of the subthalamic nucleus with 15 pulses elicited stimulus-time-locked increases in striatal dopamine efflux with maximal peak effects occurring at 50 Hz frequency and 300 microA intensity. Extended subthalamic nucleus stimulation (1000 pulses at 50 Hz; 300 microA) elicited a similar peak increase in striatal dopamine efflux that was followed by a relatively lower steady-state elevation in extracellular dopamine over the course of stimulation. In contrast, extended stimulation immediately adjacent and dorsal to the subthalamic nucleus resulted in an 11-fold greater increase in dopamine efflux that remained elevated over the course of the stimulation. Immunohistochemical staining for tyrosine hydroxylase revealed catecholaminergic fibers running immediately dorsal to and through the subthalamic nucleus. Taken together, these results suggest that enhanced dopamine release within the basal ganglia may be an important mechanism whereby high-frequency stimulation of the subthalamic nucleus improves motor symptoms of Parkinson's disease.

Laterodorsal (LDT) and pedunculopontine (PPT) tegmental nuclei in the mesopontine project cholinergic inputs to the midbrain ventral tegmental area (VTA) and substantia nigra pars compacta (SNc), respectively, to directly and indirectly influence the activity of dopamine neuronal cells via actions on muscarinic and nicotinic receptors. The present study investigated the role of midbrain muscarinic receptors in the functional modulation of VTA and SNc dopamine cell activity as reflected by alterations in, respectively, nucleus accumbens (NAc) and striataldopamine efflux. In vivo chronoamperometry was used to measure changes in basal dopamine efflux via stearate-graphite paste electrodes implanted unilaterally in the NAc or striatum of urethane-anaesthetized rats, following blockade or activation of, respectively, VTA or SNc muscarinic receptors. Intra-VTA or -SNc infusion of the muscarinic antagonist scopolamine (200 microg/microL) reduced, respectively, NAc and striatal dopamine efflux while infusion of the muscarinic and nicotinic agonist carbachol (0.5 microg/microL) or the prototypical muscarinic agonist muscarine (0.5 microg/microL) increased NAc and striatal dopamine efflux. Transient decreases in dopamine efflux preceded these increases selectively in the striatum, suggesting a reduction in excitatory or increase in inhibitory drive to the SNc by preferential activation of M3 muscarinic receptors on GABA interneurons and glutamatergic inputs. This was confirmed by showing that selective blockade of M3 receptors with p-F-HHSiD (0.5 microg/microL) increased striatal, but not NAc, dopamine efflux. Together, these findings suggest that midbrain muscarinic receptors, probably M5 subtypes on VTA and SNc dopamine neurons, contribute to the tonic excitatory regulation of forebrain basal dopamine transmission whereas presynaptic M3 receptors serve to counter excessive excitation of nigral dopamine cell activity.

Unexpected, biologically salient stimuli elicit a short-latency, phasic response in midbrain dopaminergic (DA) neurons. Although this signal is important for reinforcement learning, the information it conveys to forebrain target structures remains uncertain. One way to decode the phasic DA signal would be to determine the perceptual properties of sensory inputs to DA neurons. After local disinhibition of the superior colliculus in anesthetized rats, DA neurons became visually responsive, whereas disinhibition of the visual cortex was ineffective. As the primary source of visual afferents, the limited processing capacities of the colliculus may constrain the visual information content of phasic DA responses.

The pedunculopontine tegmental nucleus appears to influence striatal dopamine activity via cholinergic and glutamatergic afferents to dopaminergic cells of the substantia nigra pars compacta. We measured changes in striatal dopamine oxidation current (dopamine efflux) in response to electrical stimulation of the pedunculopontine tegmental nucleus using in vivo electrochemistry in urethane-anaesthetized rats. Pedunculopontine tegmental nucleus stimulation evoked a three-component change in striatal dopamine efflux, consisting of: (i) an initial rapid increase of 2 min duration; followed by (ii) a decrease below prestimulation levels of 9 min duration; then by (iii) a prolonged increase lasting 35 min. Intra-nigral infusions of the ionotropic glutamate receptor antagonist kynurenate (10 microg/ microL) or the nicotinic cholinergic receptor antagonist mecamylamine (5 microg/0.5 microL) selectively attenuated the rapid first component, while systemic injections of the muscarinic cholinergic antagonist scopolamine (5 mg/kg, i.p.) diminished the second and third components. In addition, intra-pedunculopontine tegmental nucleus infusions of the M2 muscarinic antagonist methoctramine (50 microg/ microL) selectively abolished the inhibitory second component, while intranigral infusions of scopolamine (200 microg/ microL) selectively abolished the prolonged third component. Intra-nigral infusions of the metabotropic glutamate receptor antagonist (+)-alpha-methyl-4-carboxyphenylglycine (2 microg/ microL) had no effect on pedunculopontine tegmental nucleus-elicited striatal dopamine efflux. These results suggest that the pedunculopontine tegmental nucleus utilizes nicotinic and ionotropic glutamate receptors in the substantia nigra to mediate rapid activation, M2-like muscarinic autoreceptors in the pedunculopontine tegmental nucleus to mediate decreased activation, and muscarinic receptors in the substantia nigra (probably of the M5 subtype) to mediate prolonged activation, of the nigrostriatal dopaminergic system.

Abstinence following 'binge' use of psychostimulants is hypothesized to be related to a depletion of synaptic dopamine (DA) in the nucleus accumbens. The present study, therefore, tested the pharmacological responsiveness of the mesolimbic DA system to d-amphetamine injections, measured by in vivo chronoamperometry with stearate-modified graphite paste electrodes, during voluntary abstinence when rats were given prolonged free availability to d-amphetamine. Rats self-administered i.v. d-amphetamine (FR-1 time out 30 s; 0.25 mg/kg per inf) in three sessions, each separated by approximately 24 h, (1) to a criterion of 12 infusions; (2) for 24 h and (3) for 48 h. During the third session, when self-administration had ceased for at least 1.5 h (abstinence), and DA levels were near, or below, pre-drug baseline values, rats received passive i.v. injections of d-amphetamine or vehicle in a pattern that mimicked self-administration patterns during the first hour of the 48 h session. In contrast to the significant increases in DA efflux observed during the first hour of self-administration, d-amphetamine injections during abstinence did not increase DA oxidation currents. Furthermore, the length of the abstinence period was correlated with the time required for DA to return to pre-abstinence values. Together, these results suggest that the mesolimbic DA system is pharmacologically unresponsive to the actions of d-amphetamine during abstinence, and that resumption of drug use is associated with 'recovery of function' in the mesolimbic DA system.