Dopamine Release In Response Research Articles

Dopamine release plateau and outcome signals in dorsal striatum contrast with classic reinforcement learning formulations

We recorded dopamine release signals in centromedial and centrolateral sectors of the striatum as mice learned consecutive versions of visual cue-outcome conditioning tasks. Dopamine release responses differed for the centromedial and centrolateral sites. In neither sector could these be accounted for by classic reinforcement learning alone as classically applied to the activity of nigral dopamine-containing neurons. Medially, cue responses ranged from initial sharp peaks to modulated plateau responses; outcome (reward) responses during cue conditioning were minimal or, initially, negative. At centrolateral sites, by contrast, strong, transient dopamine release responses occurred at both cue and outcome. Prolonged, plateau release responses to cues emerged in both regions when discriminative behavioral responses became required. At most sites, we found no evidence for a transition from outcome signaling to cue signaling, a hallmark of temporal difference reinforcement learning as applied to midbrain dopaminergic neuronal activity. These findings delineate a reshaping of striatal dopamine release activity during learning and suggest that current views of reward prediction error encoding need review to accommodate distinct learning-related spatial and temporal patterns of striatal dopamine release in the dorsal striatum.

Nucleus accumbens sub-regions experience distinct dopamine release responses following acute and chronic morphine exposure.

The social and economic consequences of the opioid epidemic are tragic and far-reaching. Yet, opioids are indisputably necessary in clinical settings where they remain the most useful treatment for severe pain. To combat this crisis, we must improve our understanding of opioid function in the brain, particularly the neural mechanisms that underlie opioid dependence and addictive behaviors. This study uses fiber photometry to examine dopamine changes that occur in response to repeated morphine, and morphine withdrawal, at multiple stages of a longitudinal opioid-dependence paradigm. We reveal key differences in how dopamine levels respond to opioid administration in distinct sub-regions of the ventral striatum and lay a foundation for future opioid research that appreciates our contemporary understanding of the dopamine system.

Metabolic sensing in AgRP regulates sucrose preference and dopamine release in the nucleus accumbens.

Hunger increases the motivation for calorie consumption, often at the expense of low-taste appeal. However, the neural mechanisms integrating calorie-sensing with increased motivation for calorie consumption remain unknown. Agouti-related peptide (AgRP) neurons in the arcuate nucleus of the hypothalamus sense hunger, and the ingestion of caloric solutions promotes dopamine release in the absence of sweet taste perception. Therefore, we hypothesised that metabolic-sensing of hunger by AgRP neurons would be essential to promote dopamine release in the nucleus accumbens in response to caloric, but not non-caloric solutions. Moreover, we examined whether metabolic sensing in AgRP neurons affected taste preference for bitter solutions under conditions of energy need. Here we show that impaired metabolic sensing in AgRP neurons attenuated nucleus accumbens dopamine release in response to sucrose, but not saccharin, consumption. Furthermore, metabolic sensing in AgRP neurons was essential to distinguish nucleus accumbens dopamine response to sucrose consumption when compared with saccharin. Under conditions of hunger, metabolic sensing in AgRP neurons increased the preference for sucrose solutions laced with the bitter tastant, quinine, to ensure calorie consumption, whereas mice with impaired metabolic sensing in AgRP neurons maintained a strong aversion to sucrose/quinine solutions despite ongoing hunger. In conclusion, we demonstrate normal metabolic sensing in AgRP neurons drives the preference for calorie consumption, primarily when needed, by engaging dopamine release in the nucleus accumbens.

Angiotensin II involvement in the development and persistence of amphetamine-induced sensitization: Striatal dopamine reuptake implications.

Amphetamine (AMPH) exposure induces behavioural and neurochemical sensitization observed in rodents as hyperlocomotion and increased dopamine release in response to a subsequent dose. Brain Angiotensin II modulates dopaminergic neurotransmission through its AT1 receptors (AT1-R), positively regulating striatal dopamine synthesis and release. This work aims to evaluate the AT1-R role in the development and maintenance of AMPH-induced sensitization. Also, the AT1-R involvement in striatal dopamine reuptake was analysed. The sensitization protocol consisted of daily AMPH administration for 5days and tested 21 days after withdrawal. An AT1-R antagonist, candesartan, was administered before or after AMPH exposure to evaluate the participation of AT1-R in the development and maintenance of sensitization, respectively. Sensitization was evaluated by locomotor activity and c-Fos immunostaining. Changes in dopamine reuptake kinetics were evaluated 1day after AT1-R blockade withdrawal treatment, with or without the addition of AMPH in vitro. The social interaction test was performed as another behavioural output. Repeated AMPH exposure induced behavioural and neurochemical sensitization, which was prevented and reversed by candesartan. The AT1-R blockade increased the dopamine reuptake kinetics. Neither the AMPH administration nor the AT1-R blockade altered the performance of social interaction. Our results highlight the AT1-R's crucial role in AMPH sensitization. The enhancement of dopamine reuptake kinetics induced by the AT1-R blockade might attenuate the neuroadaptive changes that lead to AMPH sensitization and its self-perpetuation. Therefore, AT1-R is a prominent candidate as a target for pharmacological treatment of pathologies related to dopamine imbalance, including drug addiction and schizophrenia.

Aerobic Exercise and Endocannabinoids: A Narrative Review of Stress Regulation and Brain Reward Systems.

Aerobic exercise is a widely adopted practice, not solely for enhancing fitness and reducing the risk of various diseases but also for its ability to uplift mood and aid in addressing depression and anxiety disorders. Within the scope of this narrative review, we seek to consolidate current insights into the endocannabinoid-mediated regulation of stress and the brain's reward mechanism resulting from engaging in aerobic exercise. A comprehensive search was conducted across Medline, SPORTDiscus, Pubmed, and Scopus, encompassing data available until November 30, 2023. This review indicates that a bout of aerobic exercise, particularly of moderate intensity, markedly augments circulating levels of endocannabinoids-N-arachidonoyl-ethanolamine (AEA) and 2-acylglycerol (2-AG), that significantly contributes to mood elevation and reducing stress in healthy individuals. The current understanding of how aerobic exercise impacts mental health and mood improvement is still unclear. Moderate and high-intensity aerobic exercise modulatesstress through a negative feedback mechanism targeting both the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system, thereby facilitating stress regulation crucial role in endocannabinoid synthesis, ultimately culminating in the orchestration of negative feedback across multiple tiers of the HPA axis, coupled with its influence over cortical and subcortical brain structures. The endocannabinoid has been observed to govern the release of neurotransmitters from diverse neuronal populations, implying a universal mechanism that fine-tunes neuronal activity and consequently modulates both emotional and stress-related responses. Endocannabinoids further assume a pivotal function within brain reward mechanisms, primarily mediated by CB1 receptors distributed across diverse cerebral centers. Notably, these endocannabinoids partake in natural reward processes, as exemplified in aerobic exercise, by synergizing with the dopaminergic reward system. The genesis of this reward pathway can be traced to the ventral tegmental area, with dopamine neurons predominantly projecting to the nucleus accumbens, thereby inciting dopamine release in response to rewarding stimuli.

0039 Investigating the role of striatal dopamine in sleep and narcolepsy-cataplexy

Abstract Introduction Dopamine release in the striatum is known to govern reward, motor, and sleep behaviors. There also exists a link between pharmacological manipulation of dopamine receptors and cataplexy occurrence, yet the precise spatial and temporal dynamics of dopamine release in relation to cataplexy onset are not understood. In the present study, we evaluate dopamine release dynamics in orexin knockout (OX KO) mice during cataplexy and physiological behaviors. Methods OX KO mice were implanted with EEG/EMG electrodes, and dLight1.1 was expressed in the nucleus accumbens core (NAcc), shell (NAcSh), and dorsolateral striatum (DLS) to perform in vivo fiber photometry of dopamine release in freely-moving animals. In NAcc and NAcSh mice, ChrimsonR was retrogradely expressed in the ventral tegmental area (VTA), to allow for precise optogenetic control of midbrain dopamine projections to different regions of the striatum. We also expressed dLight1.1 in the NAcc of wildtype (WT) mice as a control. Three different stimulation parameters were used in independent recordings: phasic 20 Hz stimulation, phasic 10-40 Hz variable stimulation, and tonic 2 Hz stimulation. Results First, we show that while dopamine release in response to rewarding behaviors is muted in OX KO animals, there is no difference in dopamine release across sleep state transitions between OX KO and WT animals. Second, we demonstrate that there is a striking increase in dopamine release in both the NAcc and NAcSh, but not in the DLS, at the onset of cataplexy. This increase occurs independently of the behaviors that the animals were engaged in immediately prior to cataplexy, suggesting that the increase is characteristic of all cataplexy episodes. Finally, we find that while high frequency phasic stimulation did not affect cataplexy frequency, low frequency, tonic stimulation reduced both cataplexy and REM occurrence. Conclusion We show that there are differences in dopamine release in response to rewarding events, but not changes in sleep states, in OX KO and WT animals. We also identify dopamine release in the ventral striatum as a key node in cataplexy regulation, which helps to further our understanding of the limbic circuitry that underlies narcolepsy symptoms. Support (if any) University of Michigan Gilmore Award and Rackham Graduate Research Award.

Mechanical Stimulation Alters Chronic Ethanol-Induced Changes to VTA GABA Neurons, NAc DA Release and Measures of Withdrawal.

Therapeutic activation of mechanoreceptors (MStim) in osteopathy, chiropractic and acupuncture has been in use for hundreds of years with a myriad of positive outcomes. It has been previously shown to modulate the firing rate of neurons in the ventral tegmental area (VTA) and dopamine (DA) release in the nucleus accumbens (NAc), an area of interest in alcohol-use disorder (AUD). In this study, we examined the effects of MStim on VTA GABA neuron firing rate, DA release in the NAc, and behavior during withdrawal from chronic EtOH exposure in a rat model. We demonstrate that concurrent administration of MStim and EtOH significantly reduced adaptations in VTA GABA neurons and DA release in response to a reinstatement dose of EtOH (2.5 g/kg). Behavioral indices of EtOH withdrawal (rearing, open-field crosses, tail stiffness, gait, and anxiety) were substantively ameliorated with concurrent application of MStim. Additionally, MStim significantly increased the overall frequency of ultrasonic vocalizations, suggesting an increased positive affective state.

A unidirectional but not uniform striatal landscape of dopamine signaling for motivational stimuli

Dopamine signals in the striatum are critical for motivated behavior. However, their regional specificity and precise information content are actively debated. Dopaminergic projections to the striatum are topographically organized. Thus, we quantified dopamine release in response to motivational stimuli and associated predictive cues in six principal striatal regions of unrestrained, behaving rats. Absolute signal size and its modulation by stimulus value and by subjective state of the animal were interregionally heterogeneous on a medial to lateral gradient. In contrast, dopamine-concentration direction of change was homogeneous across all regions: appetitive stimuli increased and aversive stimuli decreased dopamine concentration. Although cues predictive of such motivational stimuli acquired the same influence over dopamine homogeneously across all regions, dopamine-mediated prediction-error signals were restricted to the ventromedial, limbic striatum. Together, our findings demonstrate a nuanced striatal landscape of unidirectional but not uniform dopamine signals, topographically encoding distinct aspects of motivational stimuli and their prediction.

The enduring behavioral and neurobiological effects of a flavor cue paired with alcohol drinking during adolescence on the incentive properties of the flavor cue in adulthood in female alcohol-preferring (P) rats

BackgroundAlcohol use disorders (AUDs) affect 15 million people nationwide, 4% of which are adolescents (ages 12–17) and adolescents who binge drink significantly increase their likelihood of suffering from an AUD in adulthood. Research shows that cues (i.e. flavors) paired with alcohol (EtOH) produce significant cue-induced alcohol craving and contribute to relapse in adolescent and adult populations. However, there is a lack of research focused on how cues that accompany EtOH drinking during adolescence, affect EtOH craving later in life. The current study sought to examine the sex- and developmental-dependent effects of adolescent exposure to flavor cues associated with EtOH on operant-lick behavior and cue-induced dopamine (DA) levels within the nucleus accumbens shell (AcbSh; reward structure) in adulthood. MethodsAdolescent alcohol-preferring (P) rats were randomly assigned to one of 4 groups and received 24 hr. access to three bottles on their home cage: Paired: 0.1% blueberry flavor extract (BB) + 15% v/v EtOH and 2 water bottles; Unpaired: 0.1% BB, 15% v/v EtOH, and water; 15% EtOH alone, and 2 water bottles; BB alone and 2 water bottles. Home cage fluid consumption was measured for 2-weeks. On the third week bottles were removed and all animals underwent 9 days of operant training using an operant sipper paradigm. This consisted of two sipper spouts connected to the computer by a lickometer, which registered tongue contacts with the sipper tube (Paired: BB+EtOH or water; Unpaired BB or EtOH; EtOH alone: EtOH or water; BB alone: BB or water). When the fixed ratio (FR) requirement for number of licks/tongue contacts was met, a liquid delivery solenoid dispensed 0.05 ml of fluid into the sipper tube. Following the final operant session all rats remained in their home-cage for approximately 40 days until adulthood at which point they were returned to the operant chambers and tested for appetitive and consummatory behavior in response to the flavor cue (all rats: BB or water; NO EtOH). Two weeks after the final operant session all rats underwent microdialysis testing to examine cue-induced DA levels in the AcbSh. Results: Data indicated that animals in the paired group exhibited a significantly greater level of licking at the BB sipper and a significantly greater level of DA release in response to the flavor cue compared to the other groups. ConclusionsOverall, the data suggest that cues paired with EtOH during adolescence may produce persistent changes to the behavioral and neurobiological mechanisms that contribute to an increased risk of developing an AUD later in life.

Specificity of Varenicline in Blocking Mesolimbic Circuit Activation to Natural and Drug Rewards

The mesolimbic dopamine (DA) system reinforces behaviors that are critical for survival. However, drug dependence can occur when drugs of abuse, such as nicotine, highjack this reinforcement system. Pharmacologically targeting the DA system to selectively block drug reinforcement requires a detailed understanding of the neural circuits and molecular pathways that lead to the reward-based activation of mesolimbic circuits. Varenicline is an approved smoking cessation drug that has been shown to block nicotine-evoked DA increases in the nucleus accumbens (NAc) through action on nicotinic acetylcholine receptors. Because these receptors have been implicated in the reinforcement of other addictive substances, we explored the possibility that varenicline could broadly affect reward processing. We used in vivo fiber photometry to monitor midbrain DA neuron activity and striatal DA levels following either natural or drug rewards in mice treated with varenicline. We demonstrate that varenicline pretreatment enhances the suppression of nicotine-evoked DA release by attenuating DA neuron activity in the VTA. Varenicline’s ability to attenuate DA release is highly specific to nicotine, and varenicline slightly elevates DA release when co-administered with morphine or ethanol. Furthermore, varenicline has no effect on DA release in response to naturally rewarding behavior such as food intake or exercise. These results demonstrate the exquisite specificity with which varenicline blocks nicotine reward and highlight the complexity with which different rewards activate the mesolimbic DA system.

The Associations between COMT and MAO-B Genetic Variants with Negative Symptoms in Patients with Schizophrenia.

Negative symptoms of schizophrenia, including anhedonia, represent a heavy burden on patients and their relatives. These symptoms are associated with cortical hypodopamynergia and impaired striatal dopamine release in response to reward stimuli. Catechol-O-methyltransferase (COMT) and monoamine oxidase type B (MAO-B) degrade dopamine and affect its neurotransmission. The study determined the association between COMT rs4680 and rs4818, MAO-B rs1799836 and rs6651806 polymorphisms, the severity of negative symptoms, and physical and social anhedonia in schizophrenia. Sex-dependent associations were detected in a research sample of 302 patients with schizophrenia. In female patients with schizophrenia, the presence of the G allele or GG genotype of COMT rs4680 and rs4818, as well as GG haplotype rs4818-rs4680, which were all related to higher COMT activity, was associated with an increase in several dimensions of negative symptoms and anhedonia. In male patients with schizophrenia, carriers of the MAO-B rs1799836 A allele, presumably associated with higher MAO-B activity, had a higher severity of alogia, while carriers of the A allele of the MAO-B rs6651806 had a higher severity of negative symptoms. These findings suggest that higher dopamine degradation, associated with COMT and MAO-B genetic variants, is associated with a sex-specific increase in the severity of negative symptoms in schizophrenia patients.

Sex differences in cholinergic regulation of dopamine release mechanisms underlying reward learning

Substance use disorder (SUD) is a chronic, recurring brain disease characterized by significant dysfunction in reward-seeking behavior. SUD research focused on understanding the neural mechanisms in the brain's reward circuitry has overwhelmingly utilized male subjects, even though epidemiological evidence shows that women are the most susceptible population. The neural control of reward is dependent on tonic/phasic dopamine release in the NAc that are subject to heavy modulation by cholinergic interneurons (ChATs) signaling through nicotinic acetylcholine receptors (nAChRs) located directly on dopamine terminals; a process that is essential to encoding information about environmental reward predictive cues. Importantly, dopamine release in the NAc can be elicited completely independent of action potential firing from the soma – through activation of α4β2*-containing nAChRs located on dopamine terminals - highlighting the critical role that this local microcircuit plays in controlling dopamine neurotransmission. Previous work suggests that ChAT control of reward learning and regulation of dopamine release through nAChRs is fundamentally different between males and females, yet the reward information encoding processes and mechanisms that underlie sex differences in reward learning are largely unknown. To understand how the neural circuits that underlie reward learning are differentially modulated between males and females, we took a multifaceted approach to outlining sex differences in ChAT regulation of tonic/phasic dopamine release mechanisms through nAChR modulation in the NAc. Using fast-scan cyclic voltammetry paired with pharmacology we measured the potentiating effect of 17β-estradiol with and without application of the selective α4β2-nAChR antagonist, Dhβe, on sub-second tonic/phasic dopamine release in NAc slices from male and naturally cycling female mice. First, we found that 17β-estradiol enhanced tonic dopamine release in both sexes with greater biological effects in males. Additionally, 17β-estradiol potentiated dopamine release in response to phasic stimulation patterns in males with no significant effect in females. To investigate how ovarian activity affects the ability of 17β-estradiol to potentiate tonic/phasic dopamine release, ovariectomized females were utilized, showing a similar potentiating effect of 17β-estradiol on tonic/phasic dopamine release as seen in the males. Finally, blocking α4β2*-nAChRs with Dhβe reduced the potentiating effects of 17β-estradiol on dopamine release in males and ovariectomized females, but had no effect in female mice with intact ovaries. This data suggests that circulating ovarian hormones alter the effect of α4β2*-nAChRs on dopamine terminals to regulate dopamine release in the NAc. Moving forward, it will be critical to directly link these sex differences to reward learning for the development of sex-specific pharmacotherapies to treat SUD.

Selenoprotein P Modulates Methamphetamine Enhancement of Vesicular Dopamine Release in Mouse Nucleus Accumbens Via Dopamine D2 Receptors.

Dopamine (DA) transmission plays a critical role in processing rewarding and pleasurable stimuli. Increased synaptic DA release in the nucleus accumbens (NAc) is a central component of the physiological effects of drugs of abuse. The essential trace element selenium mitigates methamphetamine-induced neurotoxicity. Selenium can also alter DA production and turnover. However, studies have not directly addressed the role of selenium in DA neurotransmission. Selenoprotein P (SELENOP1) requires selenium for synthesis and transports selenium to the brain, in addition to performing other functions. We investigated whether SELENOP1 directly impacts (1) DA signaling and (2) the dopaminergic response to methamphetamine. We used fast-scan cyclic voltammetry to investigate DA transmission and the response to methamphetamine in NAc slices from C57/BL6J SELENOP1 KO mice. Recordings from SELENOP1 KO mouse slices revealed reduced levels of evoked DA release and slower DA uptake rates. Methamphetamine caused a dramatic increase in vesicular DA release in SELENOP1 KO mice not observed in wild-type controls. This elevated response was attenuated by SELENOP1 application through a selenium-independent mechanism involving SELENOP1-apolipoprotein E receptor 2 (ApoER2) interaction to promote dopamine D2 receptor (D2R) function. In wild-type mice, increased vesicular DA release in response to methamphetamine was revealed by blocking D2R activation, indicating that the receptor suppresses the methamphetamine-induced vesicular increase. Our data provide evidence of a direct physiological role for SELENOP1 in the dopaminergic response to methamphetamine and suggest a signaling role for the protein in DA transmission.

Cortical neurochemical signaling of gustatory stimuli and their visceral consequences during the acquisition and consolidation of taste aversion memory

The insular cortex (IC) has a crucial role in taste recognition memory, including conditioned taste aversion (CTA). CTA is a learning paradigm in which a novel taste stimulus (CS) is associated with gastric malaise (US), inducing aversion to the CS in future encounters. The role of the IC in CTA memory formation has been extensively studied. However, the functional significance of neurotransmitter release during the presentation of taste stimuli and gastric malaise-inducing agents remains unclear. Using microdialysis in free-moving animals, we evaluated simultaneous changes in glutamate, norepinephrine and dopamine release in response to the presentation of an innate appetitive or aversive gustatory novel stimulus, as well as after i.p. administration of isotonic or hypertonic gastric malaise-inducing solutions. Our results demonstrate that the presentation of novel stimuli, regardless of their innate valence, induces an elevation of norepinephrine and dopamine. Administration of a gastric malaise inducing agent (LiCl) promotes an elevation of glutamate regardless of its concentration. In comparison, norepinephrine release is related to the LiCl concentration and its equimolar NaCl control. Additionally, we evaluated their functional role on short and long-term taste aversion memory. Results indicate that the blockade of noradrenergic β1,2 receptors in the IC spares CTA acquisition and memory consolidation. In contrast, blockade of dopamine D1/D5 receptors impaired CTA consolidation, whereas the NMDA receptor blockade impedes both acquisition and consolidation of CTA. These results suggest that dopaminergic and noradrenergic release are related to the salience of conditioned taste stimuli. However, only cortical D1/D5 dopaminergic activity, but not the noradrenergic β1,2 activity, is involved in the acquisition and consolidation of taste memory formation. Additionally, glutamatergic activity signals visceral distress caused by LiCl administration and activates NMDA receptors necessary for the acquisition and consolidation of long-lasting taste aversion memory.

Coordinated Postnatal Maturation of Striatal Cholinergic Interneurons and Dopamine Release Dynamics in Mice.

Dynamic changes in motor abilities and motivated behaviors occur during the juvenile and adolescent periods. The striatum is a subcortical nucleus critical to action selection, motor learning, and reward processing. Its tonically active cholinergic interneuron (ChI) is an integral regulator of the synaptic activity of other striatal neurons, as well as afferent axonal projections of midbrain dopamine (DA) neurons; however, little is known about its development. Here, we report that ChI spontaneous activity increases during postnatal development of male and female mice, concomitant with a decreased afterhyperpolarization (AHP). We characterized the postnatal development of four currents that contribute to the spontaneous firing rate of ChIs, including ISK, IA, Ih, and INaP We demonstrated that the developmental increase in INaP drives increased ChI firing rates during the postnatal period and can be reversed by the INaP inhibitor, ranolazine. We next addressed whether immature cholinergic signaling may lead to functional differences in DA release during the juvenile period. In the adult striatum, nicotinic acetylcholine receptors (nAChRs) prevent linear summation of DA release in response to trains of high-frequency stimuli. We show that, in contrast, during the second postnatal week, DA release linearly sums with trains of high-frequency stimuli. Consistently, nAChR antagonists exert little effect on dopamine release at postnatal day (P)10, but enhance the summation of evoked DA release in mice older than postnatal day P28. Together, these results reveal that postnatal maturation of ChI activity is due primarily to enhanced INaP and identify an interaction between developing cholinergic signaling and DA neurotransmission in the juvenile striatum.SIGNIFICANCE STATEMENT Motor skills and motivated behavior develop rapidly in juvenile rodents. Recent work has highlighted processes that contribute to the postnatal maturation of striatal principal neurons during development. The functional development of the striatal cholinergic interneuron (ChI), however, has been unexplored. In this study, we tracked the ontogeny of ChI activity and cellular morphology, as well as the developmental trajectory of specific conductances that contribute to the activity of these cells. We further report a link between cholinergic signaling and dopamine (DA) release, revealing a change in the frequency-dependence of DA release during the early postnatal period that is mediated by cholinergic signaling. This study provides evidence that striatal microcircuits are dynamic during the postnatal period and that they undergo coordinated maturation.

Age-dependent effects of protein restriction on dopamine release

Despite the essential role of protein intake for health and development, very little is known about the impact of protein restriction on neurobiological functions, especially at different stages of the lifespan. The dopamine system is a central actor in the integration of food-related processes and is influenced by physiological state and food-related signals. Moreover, it is highly sensitive to dietary effects during early life periods such as adolescence due to its late maturation. In the present study, we investigated the impact of protein restriction either during adolescence or adulthood on the function of the mesolimbic (nucleus accumbens) and nigrostriatal (dorsal striatum) dopamine pathways using fast-scan cyclic voltammetry in rat brain slices. In the nucleus accumbens, protein restriction in adults increased dopamine release in response to low and high frequency trains of stimulation (1–20 Hz). By contrast, protein restriction during adolescence decreased nucleus accumbens dopamine release. In the dorsal striatum, protein restriction at adulthood has no impact on dopamine release but the same diet during adolescence induced a frequency-dependent increase in stimulated dopamine release. Taken together, our results highlight the sensitivity of the different dopamine pathways to the effect of protein restriction, as well as their vulnerability to deleterious diet effects at different life stages.

5'UTR polymorphism in the serotonergic receptor HTR3A gene is differently associated with striatal Dopamine D2/D3 receptor availability in the right putamen in Fibromyalgia patients and healthy controls-Preliminary evidence.

Extensive literature has investigated the role of serotonin (5-HT) in the control of the central dopamine (DA) systems, and their dysfunction in the pathological conditions. 5-HT stimulates the local DA release in striatal regions via activation of various receptors including serotonin receptor-3 (5-HT3). Several studies have related polymorphisms (SNPs) in the serotonin receptor-3 (HTR3) genes to be associated with the pain modulation and endogenous pain suppression. A few studies suggested a functional role of 5'UTR SNP in the serotonergic receptor HTR3A gene (rs1062613) in the development of the chronic pain and Fibromyalgia syndrome (FMS) in particular. Here, we investigated the effect of a 5'UTR SNP in the serotonergic receptor HTR3A gene (rs1062613) on striatal dopamine D2/D3 receptor (DRD2) availability and reward-associated DA release in response to unpredictable monetary rewards in 23 women with FMS and 17 age-matched healthy female controls. Furthermore, we aimed to examine if SNP rs1062613 is associated with thermal pain and pain tolerance thresholds. We used PET and [11 C]raclopride to assess the DRD2 availability. In the same participants we used the [11 C]raclopride PET bolus-plus-infusion method to measure the [11 C]raclopride receptor binding potential (ΔBP) between an unpredictable reward condition and a sensorimotor control condition. DRD2 availability and ΔBP were assessed in MRI-based striatal regions of interest. Thermal pain and pain tolerance thresholds were assessed outside the scanner. The frequency of SNP rs1062613 genotype differed significantly between groups, indicating that CC homozygotes were more frequent in FMS patients (82.6%) than in healthy controls (41.3%). Our results showed a significant main effect of SNP rs1062613 on [11 C]raclopride binding potential in the right caudate nucleus indicating a higher DRD2 receptor availability for CC-genotype of this SNP. Furthermore, we found a significant group × SNP interaction on [11 C]raclopride binding potential in the right putamen, indicating a higher DRD2 availability in T-carriers compared to CC genotype of SNP rs1062613 in FMS patients, whereas this effect was not present in healthy controls. However, we did not find an influence of SNP rs1062613 on reward-related DA release. In addition, there was no association between SNP rs1062613 and pain threshold or pain tolerance threshold in our data. These preliminary results indicate that SNP rs1062613 in the serotonergic receptor HTR3A gene possibly modulates the DRD2 receptor availability.

Dopamine, Opioids, and Positron Emission Tomography Imaging of the Human Brain: Contrasting Findings in Opioid Use Disorder and Healthy Volunteers

SEE CORRESPONDING ARTICLE ON PAGE 356 Striatal Dopamine Release in Response to Morphine: A [11C]Raclopride Positron Emission Tomography Study in Healthy MenBiological PsychiatryVol. 86Issue 5PreviewPreclinical and human positron emission tomography studies have produced inconsistent results regarding the effects of opioids on mesolimbic dopamine (DA). Here, we quantify striatal DA release (measured by [11C]raclopride displacement) in response to an intravenous infusion of morphine, and its relationship with morphine-induced subjective effects, in healthy, nondependent opioid–experienced participants. Full-Text PDF

Prefrontal cortical dopamine release in clinical high risk for psychosis during a cognitive task: a [11C]FLB457 positron emission tomography study

Research suggests decreased cortical dopamine is a neural correlate of cognitive deficits in schizophrenia. Evidence of impaired cognitive task-induced cortical dopamine release was demonstrated in patients with psychosis. However, whether cortical dopamine release in response to a cognitive task in clinical high risk for psychosis (CHR) is also impaired, is currently unknown. We aimed to test dopamine release in the dorsolateral prefrontal cortex (DLPFC) and the anterior cingulate cortex (ACC) in antipsychotic-free CHR participants and healthy controls (HC) performing the Wisconsin Card Sorting Task (WCST). Two [11C]FLB457 PET scans were conducted for 13 CHR and 15 HC while performing the WCST and the sensorimotor control task (SMCT), respectively. A magnetic resonance image was acquired for anatomical delineation. Percentage change in binding potential (ΔBPND) in ACC and DLPFC in WCST were compared with the SMCT between CHR and HC. Mixed model analysis revealed no statistically significant differences in the cognitive task induced ΔBPND in any ROIs. There were no main effect of group (F(1, 26) = 0.348; p = 0.560) or ROI (F(1, 26) = 1.080; p = 0.308) and no significant Group x ROI interaction (F(1, 26) = 0.049; p = 0.826). Our findings suggest no statistically significant difference between CHR and HC in cognitive task-induced cortical dopamine release. This is the first in vivo study to illustrate that the cortical hypodopaminergic state observed in schizophrenia may not be present in its putative high-risk state.

Reward Prediction Error Modulates Saccade Vigor.

Movement vigor, defined as the reciprocal of the latency from availability of reward to its acquisition, changes with reward magnitude: movements exhibit shorter reaction time and increased velocity when they are directed toward more rewarding stimuli. This invigoration may be due to release of dopamine before movement onset, which has been shown to be modulated by events that signal reward prediction error (RPE). Here, we generated an RPE event in the milliseconds before movement onset and tested whether there was a relationship between RPE and vigor. Human subjects (both sexes) made saccades toward an image. During execution of the primary saccade, we probabilistically changed the position and content of that image, encouraging a secondary saccade. On some trials, the content of the secondary image was more valuable than the first image, resulting in a positive RPE (+RPE) event that preceded the secondary saccade. On other trials, this content was less valuable (-RPE event). We found that reaction time of the secondary saccade was affected in an orderly fashion by the magnitude and direction of the preceding RPE event: the most vigorous saccades followed the largest +RPE, whereas the least vigorous saccades followed the largest -RPE. Presence of the secondary saccade indicated that the primary saccade had experienced a movement error, inducing trial-to-trial adaptation. However, this learning from movement error was not modulated by the RPE event. The data suggest that RPE events, which are thought to transiently alter the release of dopamine, modulate the vigor of the ensuing movement.SIGNIFICANCE STATEMENT Does dopamine release in response to a stimulus serve to invigorate the ensuing movement? To test this hypothesis, we relied on the fact that reward prediction error (RPE) is a strong modulator of dopamine. Our innovation was a task in which an RPE event occurred precisely before onset of a stimulus-driven movement. We probabilistically produced a combination of large or small, negative or positive RPE events and observed that saccade vigor carried a robust signature of the preceding RPE event: high vigor saccades followed +RPE events, whereas low vigor saccades followed -RPE events. This suggests that in humans, vigor is partly controlled through release of dopamine in the moments before onset of a movement.