DA Signaling Research Articles

Role of dopamine in reward expectation and predictability during execution of action sequences.

Reward-associated cues serve different functions depending on whether they precede or terminate action sequences. Cues that precede action sequences and signal opportunity for reward could serve as GO signals to initiate the sequence, whereas sequence termination cues could serve as response feedback by signaling reward delivery. Reward expectation during sequence execution depends on these cues and might condition whether behavior is habitual or goal-directed. However, it remains unknown how sequence initiation and termination cues differentially affect reward expectation and contribute to habit learning. Further, while mesolimbic dopamine plays a key role in cue-induced reward expectation and sequence learning, how dynamic changes in dopamine signals differ depending on the response strategy is unclear. Here, we determined how mesolimbic DA signals change over training during cue-mediated sequence learning, depending on the type of cue and the nature of behavioral control. We found sequence initiation and termination cues differentially affect reward expectation during action sequences, with the termination cue contributing to habit and automaticity. Distinct response strategies induced by sequence initiation and termination cues induced differential changes in mesolimbic DA signals that captured variations in reward expectation along sequence execution. Notably, habit-like behavior induced by the sequence termination cue was associated with a rapid shift in DA signals from reward retrieval to the cue. This habit-like behavior was reflected in behavioral inflexibility and attenuated DA reward prediction error signals. Finally, using optogenetics, we provide evidence that phasic DA activity elicited by the sequence termination cue is critical for the development of habit-like behavior.

Electrophysiological and Behavioral Markers of Hyperdopaminergia in DAT-KO Rats.

Background/Objectives: Dopamine dysfunction (DA) is a hallmark of many neurological disorders. In this case, the mechanism of changes in dopamine transmission on behavior remains unclear. This study is a look into the intricate link between disrupted DA signaling, neuronal activity patterns, and behavioral abnormalities in a hyperdopaminergic animal model. Methods: To study the relationship between altered DA levels, neuronal activity, and behavioral deficits, local field potentials (LFPs) were recorded during four different behaviors in dopamine transporter knockout rats (DAT-KO). At the same time, local field potentials were recorded in the striatum and prefrontal cortex. Correlates of LFP and accompanying behavioral patterns in genetically modified (DAT-KO) and control animals were studied. Results: DAT-KO rats exhibited desynchronization between LFPs of the striatum and prefrontal cortex, particularly during exploratory behavior. A suppressive effect of high dopamine levels on the striatum was also observed. Wild-type rats showed greater variability in LFP patterns across certain behaviors, while DAT-KO rats showed more uniform patterns. Conclusions: The decisive role of the synchrony of STR and PFC neurons in the organization of motor acts has been revealed. The greater variability of control animals in certain forms of behavior probably suggests greater adaptability. More uniform patterns in DAT-KO rats, indicating a loss of striatal flexibility when adapting to specific motor tasks. It is likely that hyperdopaminergy in the DAT-KO rat reduces the efficiency of information processing due to less synchronized activity during active behavior.

Parkinson’s disease gene, Synaptojanin1, dysregulates the surface maintenance of the dopamine transporter

Missense mutations of PARK20/SYNJ1 (synaptojanin1/Synj1) were found in complex forms of familial Parkinsonism. However, the Synj1-regulated molecular and cellular changes associated with dopaminergic dysfunction remain unknown. We now report a fast depletion of evoked dopamine and impaired maintenance of the axonal dopamine transporter (DAT) in the Synj1 haploinsufficient (Synj1+/−) neurons. While Synj1 has been traditionally known to facilitate the endocytosis of synaptic vesicles, we provide in vitro and in vivo evidence demonstrating that Synj1 haploinsufficiency results in an increase of total DAT but a reduction of the surface DAT. Synj1+/− neurons exhibit maladaptive DAT trafficking, which could contribute to the altered DA release. We showed that the loss of surface DAT is associated with the impaired 5’-phosphatase activity and the hyperactive PI(4,5)P2–PKCβ pathway downstream of Synj1 deficiency. Thus, our findings provided important mechanistic insight for Synj1-regulated DAT trafficking integral to dysfunctional DA signaling, which might be relevant to early Parkinsonism.

Haploinsufficiency of the Parkinson's disease gene synaptojanin1 is associated with abnormal responses to psychomotor stimulants and mesolimbic dopamine signaling.

The synaptojanin-1 (SYNJ1) gene is known to be important for dopamine-related disorders. Recent evidence has demonstrated that Synj1 deficient mice (Synj1 +/-) have impairments in dopaminergic synaptic vesicular recycling. However, less is known about how Synj1 deficits affect the mesolimbic system, reward processing, and motivated behavior. To examine the role of the Synj1 gene in motivated behavior, we subjected male and female Synj1 +/- and Synj1 +/+ mice to a battery of behavioral tests evaluating hedonic responses, effortful responding, and responses to psychomotor stimulants. We observed that Synj1 +/- mice exhibit few differences in reward processing and motivated behavior, with normal hedonic responses and motivated responding for sucrose. However, male but not female Synj1 +/- demonstrated an attenuated conditioned place preference for cocaine that could not be attributed to deficits in spatial memory. To further understand the dopamine signaling underlying the attenuated response to cocaine in these mutant mice, we recorded nucleus accumbens dopamine in response to cocaine and observed that Synj1 +/- male and female mice took longer to reach peak dopamine release following experimenter-administered cocaine. However, female mice also showed slower decay in accumbens dopamine that appear to be linked to differences in cocaine-induced DAT responses. These findings demonstrate that SYNJ1 deficiencies result in abnormal mesolimbic DA signaling which has not previously been demonstrated. Our work also highlights the need to develop targeted therapeutics capable of restoring deficits in DAT function, which may be effective for reversing the pathologies associated with Synj1 mutations.

The human VGLUT3-pT8I mutation elicits uneven striatal DA signaling, food or drug maladaptive consumption in male mice

Cholinergic striatal interneurons (ChIs) express the vesicular glutamate transporter 3 (VGLUT3) which allows them to regulate the striatal network with glutamate and acetylcholine (ACh). In addition, VGLUT3-dependent glutamate increases ACh vesicular stores through vesicular synergy. A missense polymorphism, VGLUT3-p.T8I, was identified in patients with substance use disorders (SUDs) and eating disorders (EDs). A mouse line was generated to understand the neurochemical and behavioral impact of the p.T8I variant. In VGLUT3T8I/T8I male mice, glutamate signaling was unchanged but vesicular synergy and ACh release were blunted. Mutant male mice exhibited a reduced DA release in the dorsomedial striatum but not in the dorsolateral striatum, facilitating habit formation and exacerbating maladaptive use of drug or food. Increasing ACh tone with donepezil reversed the self-starvation phenotype observed in VGLUT3T8I/T8I male mice. Our study suggests that unbalanced dopaminergic transmission in the dorsal striatum could be a common mechanism between SUDs and EDs.

Neighborhood socioeconomic deprivation and individual-level socioeconomic status are associated with dopamine-mediated changes to monocyte subset CCR2 expression via a cAMP-dependent pathway

Social determinants of health (SDoH) include socioeconomic, environmental, and psychological factors that impact health. Neighborhood socioeconomic deprivation (NSD) and low individual-level socioeconomic status (SES) are SDoH that associate with incident heart failure, stroke, and cardiovascular mortality, but the underlying biological mechanisms are not well understood. Previous research has demonstrated an association between NSD, in particular, and key components of the neural-hematopoietic-axis including amygdala activity as a marker of chronic stress, bone marrow activity, and arterial inflammation. Our study further characterizes the role of NSD and SES as potential sources of chronic stress related to downstream immunological factors in this stress-associated biologic pathway. We investigated how NSD, SES, and catecholamine levels (as proxy for sympathetic nervous system activation) may influence monocytes which are known to play a significant role in atherogenesis. First, in an ex vivo approach, we treated healthy donor monocytes with biobanked serum from a community cohort of African Americans at risk for CVD. Subsequently, the treated monocytes were subjected to flow cytometry for characterization of monocyte subsets and receptor expression. We determined that NSD and serum catecholamines (namely dopamine [DA] and norepinephrine [NE]) associated with monocyte C–C chemokine receptor type 2 (CCR2) expression (p < 0.05), a receptor known to facilitate recruitment of monocytes towards arterial plaques. Additionally, NSD associated with catecholamine levels, especially DA in individuals of low SES. To further explore the potential role of NSD and the effects of catecholamines on monocytes, monocytes were treated in vitro with epinephrine [EPI], NE, or DA. Only DA increased CCR2 expression in a dose-dependent manner (p < 0.01), especially on non-classical monocytes (NCM). Furthermore, linear regression analysis between D2-like receptor surface expression and surface CCR2 expression suggested D2-like receptor signaling in NCM. Indicative of D2-signaling, cAMP levels were found to be lower in DA-treated monocytes compared to untreated controls (control 29.78 pmol/ml vs DA 22.97 pmol/ml; p = 0.038) and the impact of DA on NCM CCR2 expression was abrogated by co-treatment with 8-CPT, a cAMP analog. Furthermore, Filamin A (FLNA), a prominent actin-crosslinking protein, that is known to regulate CCR2 recycling, significantly decreased in DA-treated NCM (p < 0.05), indicating a reduction of CCR2 recycling. Overall, we provide a novel immunological mechanism, driven by DA signaling and CCR2, for how NSD may contribute to atherogenesis. Future studies should investigate the importance of DA in CVD development and progression in populations disproportionately experiencing chronic stress due to SDoH.

Viral Tracing Confirms Paranigral Ventral Tegmental Area Dopaminergic Inputs to the Interpeduncular Nucleus Where Dopamine Release Encodes Motivated Exploration.

Midbrain dopaminergic (DAergic) neurons of the ventral tegmental area (VTA) are engaged by rewarding stimuli and encode reward prediction error to update goal-directed learning. However, recent data indicate that VTA DAergic neurons are functionally heterogeneous with emerging roles in aversive signaling, salience, and novelty, based in part on anatomic location and projection, highlighting a need to functionally characterize the repertoire of VTA DAergic efferents in motivated behavior. Previous work identifying a mesointerpeduncular circuit consisting of VTA DAergic neurons projecting to the interpeduncular nucleus (IPN), a midbrain area implicated in aversion, anxiety-like behavior, and familiarity, has recently come into question. To verify the existence of this circuit, we combined presynaptic targeted and retrograde viral tracing in the dopamine transporter-Cre mouse line. Consistent with previous reports, synaptic tracing revealed that axon terminals from the VTA innervate the caudal IPN; whereas, retrograde tracing revealed DAergic VTA neurons, predominantly in the paranigral region, project to the nucleus accumbens shell, as well as the IPN. To test whether functional DAergic neurotransmission exists in the IPN, we expressed the genetically encoded DA sensor, dLight 1.2, in the IPN of C57BL/6J mice and measured IPN DA signals in vivo during social and anxiety-like behavior using fiber photometry. We observed an increase in IPN DA signal during social investigation of a novel but not familiar conspecific and during exploration of the anxiogenic open arms of the elevated plus maze. Together, these data confirm VTA DAergic neuron projections to the IPN and implicate this circuit in encoding motivated exploration.

Understanding the role of dopamine in cancer: past, present and future.

Dopamine (DA, 3-hydroxytyramine) is a member of the catecholamine family and is classically characterized according to its role in the central nervous system as a neurotransmitter. In recent decades, many novel and intriguing discoveries have been made about the peripheral expression of DA receptors (DRs) and the role of DA signaling in both normal and pathological processes. Drawing from decades of evidence suggesting a link between DA and cancer, the DA pathway has recently emerged as a potential target in antitumor therapies. Due to the onerous, expensive and frequently unsuccessful nature of drug development, the repurposing of dopaminergic drugs for cancer therapy has the potential to greatly benefit patients and drug developers alike. However, the lack of clear mechanistic data supporting the direct involvement of DRs and their downstream signaling components in cancer represents an ongoing challenge that has limited the translation of these drugs to the clinic. Despite this, the breadth of evidence linking DA to cancer and non-tumor cells in the tumor microenvironment justifies further inquiry into the potential applications of this treatment modality in cancer. Herein, we review the literature characterizing the interplay between the DA signaling axis and cancer, highlighting key findings, and then propose rational lines of investigation to follow.

Dopamine D2‐Like Receptor Signaling and Downregulation of Filamin‐A May Drive the Association Between Neighborhood Socioeconomic Status and CCR2 Expression on Monocytes

Social determinants of health (SDoH) include socioeconomic, environmental, and psychological factors that impact health. Low neighborhood socioeconomic status (nSES) is a SDoH that associates with cardiovascular mortality in longitudinal studies. While nSES as a chronic stress contributes to adverse health outcomes, the molecular mechanisms and pathogenesis are poorly understood. Previously, we found that residing in lower nSES areas may alter monocyte expression of C‐C chemokine receptor type 2 (CCR2), a regulator of monocyte recruitment during atherogenesis. To explore the effects of nSES as a chronic stress on monocyte CCR2 expression, we treated monocytes in vitro for 4 hours with catecholamines (epinephrine [Epi], norepinephrine [NE], or dopamine [DA]) used as stress biomarkers. Only DA increased CCR2 expression in a dose‐dependent manner (p&lt;0.01), especially on non‐classical monocytes (NCM). In our current study, we investigated DA receptor signaling to learn which pathways may contribute to increases in CCR2 expression. Dopamine acts on five known receptors, the D1‐like receptors (D1 and D5) and D2‐like receptors (D2, D3, and D4). First, we performed flow cytometry on untreated monocytes and found D2 receptors were most abundant on the surface of all monocyte subsets (ie., classical monocytes [CM], intermediate monocytes [IM], and NCM as determined by CD14/CD16 expression). Furthermore, spearman correlation between D2‐like receptor surface expression and surface CCR2 expression in NCM suggested D2‐like receptor signaling (R2=0.79, p=0.04). Because the D2‐like receptor response is known to decrease cAMP levels compared to a D1‐like receptor response, a cAMP assay was performed on monocytes with DA treatment. Indicative of D2‐signaling, cAMP levels were found to be lower in DA‐treated monocytes compared to untreated controls (ctr 29.78pmol/ml vs DA 22.97 pmol/ml; p=0.038). We then investigated downstream mechanisms following DA signaling that could result in increased CCR2 expression. Filamin A (FlnA), a prominent actin‐cross‐linking protein, is known to regulate CCR2 recycling. We examined the expression of FlnA by flow cytometry and RT‐qPCR on flow sorted monocytes with and without DA treatment. There was a significant decrease in FlnA expression in NCM (p &lt; 0.05), indicating a slowing of CCR2 recycling. Expression of an associated scaffold protein mRNA, b‐arrestin 1, was decreased by 66% in NCM (p= 0.008). Overall, we provide a novel immunological mechanism, driven by DA signaling and CCR2, for how nSES may contribute to atherogenesis. Future studies should investigate the importance of DA in CVD development and progression in populations disproportionately experiencing chronic stress due to SDoH.

Human activity recognition for static and dynamic activity using convolutional neural network

Evaluated activity as a detail of the human physical movement has become a leading subject for researchers. Activity recognition application is utilized in several areas, such as living, health, game, medical, rehabilitation, and other smart home system applications. An accelerometer was popular sensors to recognize the activity, as well as a gyroscope, which can be embedded in a smartphone. Signal was generated from the accelerometer as a time-series data is an actual approach like a human actifvity pattern. Motion data have acquired in 30 volunteers. Dynamic actives (walking, walking upstairs, walking downstairs) as DA and static actives (laying, standing, sitting) as SA were collected from volunteers. SA and DA it's a challenging problem with the different signal patterns, SA signals coincide between activities but with a clear threshold, otherwise the DA signal is clearly distributed but with an adjacent upper threshold. The proposed network structure achieves a significant performance with the best overall accuracy of 97% . The result indicated the ability of the model for human activity recognition purposes.

Zinc antagonizes iron-regulation of tyrosine hydroxylase activity and dopamine production in Drosophila melanogaster

BackgroundDopamine (DA) is a neurotransmitter that plays roles in movement, cognition, attention, and reward responses, and deficient DA signaling is associated with the progression of a number of neurological diseases, such as Parkinson’s disease. Due to its critical functions, DA expression levels in the brain are tightly controlled, with one important and rate-limiting step in its biosynthetic pathway being catalyzed by tyrosine hydroxylase (TH), an enzyme that uses iron ion (Fe2+) as a cofactor. A role for metal ions has additionally been associated with the etiology of Parkinson’s disease. However, the way dopamine synthesis is regulated in vivo or whether regulation of metal ion levels is a component of DA synthesis is not fully understood. Here, we analyze the role of Catsup, the Drosophila ortholog of the mammalian zinc transporter SLC39A7 (ZIP7), in regulating dopamine levels.ResultsWe found that Catsup is a functional zinc transporter that regulates intracellular zinc distribution between the ER/Golgi and the cytosol. Loss-of-function of Catsup leads to increased DA levels, and we showed that the increased dopamine production is due to a reduction in zinc levels in the cytosol. Zinc ion (Zn2+) negatively regulates dopamine synthesis through direct inhibition of TH activity, by antagonizing Fe2+ binding to TH, thus rendering the enzyme ineffective or non-functional.ConclusionsOur findings uncovered a previously unknown mechanism underlying the control of cellular dopamine expression, with normal levels of dopamine synthesis being maintained through a balance between Fe2+ and Zn2+ ions. The findings also provide support for metal modulation as a possible therapeutic strategy in the treatment of Parkinson’s disease and other dopamine-related diseases.

Loss of mGluR1-LTD following cocaine exposure accumulates Ca2+-permeable AMPA receptors and facilitates synaptic potentiation in the prefrontal cortex

Addiction results from drug-elicited alterations of synaptic plasticity mechanisms in dopaminergic reward circuits. Impaired metabotropic glutamate receptor (mGluR)-dependent long-term depression (LTD) and accumulation of synaptic Ca2+-permeable AMPA receptors (CP-AMPARs) following drug exposure have emerged as important mechanisms underlying drug craving and relapse. Here we show that repeated cocaine exposure in vivo causes transient but complete loss of mGluR1- and mTOR (mammalian target of rapamycin)-dependent LTD in layer 5 pyramidal neurons of mouse prefrontal cortex (PFC), a major dopaminergic target in the reward circuitry. This mGluR1-LTD impairment was prevented by in vivo administration of an mGluR1 positive allosteric modulator (PAM) and rescued by inhibition of dopamine D1 receptors, suggesting that impaired mGluR1 tone and excessive D1 signaling underlie this LTD deficit. Concurrently, CP-AMPARs were generated, indicated by increased sensitivity to the CP-AMPAR inhibitor Naspm and rectification of synaptic AMPAR currents, which were reversed by PAM in cocaine-exposed mice. Finally, these CP-AMPARs mediate an abnormal spike-timing-dependent long-term potentiation enabled by cocaine exposure. Our findings reveal a mechanism by which cocaine impairs LTD and remodels synaptic AMPARs to influence Hebbian plasticity in the PFC. Failure to undergo LTD may prevent the reversal of drug-potentiated brain circuits to their baseline states, perpetuating addictive behaviors. HIGHLIGHTS A mGluR1- and mTOR-dependent LTD is present in the mouse medial prefrontal cortex. Repeated cocaine exposure in vivo temporally but completely abolishes prefrontal mGluR1-LTD. Impaired mGluR1 function and excessive D1 DA signaling likely underlie cocaine impairment of mGluR1-LTD. Ca2+-permeable AMPA receptors are generated by cocaine exposure, likely resulting from mGluR1-LTD impairment, and contribute to a cocaine-induced extended spike timing LTP.

Abstract 327: Asphyxial Cardiac Arrest Induces Dynamic Changes in Dopamine Neurotransmission and Linked Behavioral Deficits

Introduction: Cardiac arrest survival has improved with advances in resuscitation care, but survivors face impairments from the resulting hypoxic-ischemic brain injury (HIBI). Given the popular clinical use of DA modulators, despite limited understanding of disturbances in DA neurotransmission after HIBI, we characterized striatal DA signaling and behavioral deficits in a rat model of asphyxial cardiac arrest (ACA). Hypothesis: ACA-induced HIBI alters DA neurotransmission linked to behavioral deficits. Methods: Adult male Sprague-Dawley rats (n=41) underwent either Sham procedures (n=10) or 5-min no-flow ACA (n=28) insult. Fast-scan cyclic voltammetry (FSCV) and maximal medial forebrain bundle stimulations (60Hz, 10s) were used to characterize presynaptic DA signaling in dorsal striatum (D-Str). FSCV findings were compared with sensorimotor processing [acoustic startle responses (ASR)], open field exploration (total distance &amp; exploratory zone entries), myoclonus, and anhedonia (sucrose preference testing). Results: ACA increased maximum evoked overflow (fig 1) and several DA release-based kinetic metrics. ACA hindered sensorimotor processing via increased ASR %change, elicited myoclonic responses to auditory stimuli, reduced mobility &amp; exploration, and increased anhedonia. Many behavioral measures correlated with D-Str neurotransmission ( fig 2 ). Conclusions: ACA causes early hypodopaminergia that evolves to a hyperdopaminergic state by 2 weeks that is associated with behavioral dysfunction. Future work should further characterize striatal pathology post-ACA and identify treatments to resolve altered DA signaling and behavioral deficits.

Midbrain Dopamine Controls Anxiety-like Behavior by Engaging Unique Interpeduncular Nucleus Microcircuitry

BackgroundDopamine (DA) is hypothesized to modulate anxiety-like behavior, although the precise role of DA in anxiety behaviors and the complete anxiety network in the brain have yet to be elucidated. Recent data indicate that dopaminergic projections from the ventral tegmental area (VTA) innervate the interpeduncular nucleus (IPN), but how the IPN responds to DA and what role this circuit plays in anxiety-like behavior are unknown. MethodsWe expressed a genetically encoded G protein–coupled receptor activation–based DA sensor in mouse midbrain to detect DA in IPN slices using fluorescence imaging combined with pharmacology. Next, we selectively inhibited or activated VTA→IPN DAergic inputs via optogenetics during anxiety-like behavior. We used a biophysical approach to characterize DA effects on neural IPN circuits. Site-directed pharmacology was used to test if DA receptors in the IPN can regulate anxiety-like behavior. ResultsDA was detected in mouse IPN slices. Silencing/activating VTA→IPN DAergic inputs oppositely modulated anxiety-like behavior. Two neuronal populations in the ventral IPN (vIPN) responded to DA via D1 receptors (D1Rs). vIPN neurons were controlled by a small population of D1R neurons in the caudal IPN that directly respond to VTA DAergic terminal stimulation and innervate the vIPN. IPN infusion of a D1R agonist and antagonist bidirectionally controlled anxiety-like behavior. ConclusionsVTA DA engages D1R-expressing neurons in the caudal IPN that innervate vIPN, thereby amplifying the VTA DA signal to modulate anxiety-like behavior. These data identify a DAergic circuit that mediates anxiety-like behavior through unique IPN microcircuitry.

Characterization of AN6001, a positive allosteric modulator of α6β2-containing nicotinic acetylcholine receptors

α6β2-Containing nicotinic acetylcholine receptors (α6β2* nAChRs) are predominantly expressed in midbrain dopaminergic neurons, including substantia nigra pars compacta (SNc) neurons and their projections to striatal regions, where they regulate dopamine release and nigrostriatal activity. It is well established that nAChR agonists exert protection against dopaminergic neurotoxicity in cellular assays and parkinsonian animal models. Historically, drug development in the nAChR field has been mostly focused on development of selective agonists and positive allosteric modulators (PAMs) for the predominant neuronal nAChRs, α7 and α4β2. Here, we report the discovery and characterization of AN6001, a novel selective α6β2* nAChR PAM. AN6001 mediated increases in both nicotine potency and efficacy at the human α6/α3β2β3V9’S nAChR in HEK293 cells, and it positively modulated ACh-evoked currents through both α6/α3β2β3V9’S and a concatenated β3-α6-β2-α6-β2 receptor in Xenopus oocytes, displaying EC50 values of 0.58 µM and 0.40 µM, respectively. In contrast, the compound did not display significant modulatory activity at α4β2, α3β4, α7 and muscle nAChRs. AN6001 also increased agonist-induced dopamine release from striatal synaptosomes and augmented agonist-induced global cellular responses and inward currents in dopaminergic neurons in SNc slices (measured by Ca2+ imaging and patch clamp recordings, respectively). Finally, AN6001 potentiated the neuroprotective effect of nicotine at MPP+-treated primary dopaminergic neurons. Overall, our studies demonstrate the existence of allosteric sites on α6β2* nAChRs and that positive modulation of native α6β2* receptors strengthens DA signaling. Hence, AN6001 represents an important tool for studies of α6β2* nAChRs and furthermore underlines the therapeutic potential in these receptors in Parkinson’s disease.

Accumbal Dopamine Release Tracks the Expectation of Dopamine Neuron-Mediated Reinforcement

SUMMARYDopamine (DA) transmission in the nucleus accumbens (NAc) facilitates cue-reward associations and appetitive action. Reward-related accumbal DA release dynamics are traditionally ascribed to ventral tegmental area (VTA) DA neurons. Activation of VTA to NAc DA signaling is thought to reinforce action and transfer reward-related information to predictive cues’ allowing cues to guide behavior and elicit dopaminergic activity. Here, we use optogenetics to control DA neuron activity and voltammetry to simultaneously record accumbal DA release in order to quantify how reinforcer-evoked dopaminergic activity shapes conditioned mesolimbic DA transmission. We find that cues predicting access to DA neuron self-stimulation elicit conditioned responding and NAc DA release. However, cue-evoked DA release does not reflect the cost or magnitude of DA neuron activation. Accordingly, conditioned accumbal DA release selectively tracks the expected availability of DA-neuron-mediated reinforcement. This work provides insight into how mesolimbic DA transmission drives and encodes appetitive action.

3293 Region Specific Dysregulation of Dopaminergic Signaling in Mice Displaying Excessive Over-Grooming

OBJECTIVES/SPECIFIC AIMS: The objective of this study was to determine if dopamine signaling is altered in a mouse model displaying excessive self-grooming and further elucidate the potential utility of compounds targeting the striatal DA system in modulating repetitive behaviors. METHODS/STUDY POPULATION: Here, we report studies using fast-scan cyclic voltammetry (FSCV) in mice lacking the postsynaptic protein SAP90/PSD95-associated protein (SAPAP3 KO mice) as well as control littermates. Rodent self-grooming provides a behavioral output with which one can monitor repetitive, self-directed, patterned behavior that has great translational value to OCD-like disorders. Total time spent grooming was monitored in SAPAP3KO mice and control littermates. To further examine the role of DA in regulating repetitive grooming behaviors the magnitude and kinetics of DA transients were assessed using FSCV in ex vivo slice preparations as well as in anesthetized mice in vivo. DA transients were elicited in the dorsolateral striatum (DLS), dorsomedial striatum (DMS); and nucelus accumbens core (NAcc). In some experiments mice were crossed with DAT-Cre animals and channelrhodopsin 2 (ChR2) was virally expressed in DA neurons to allow optical stimulation of DA transients. RESULTS/ANTICIPATED RESULTS: As previously reported, SAPAP3 KO mice showed excessive grooming compared to control littermates at the age assessed (4-5 months). DA transients evoked by a single electrical pulse in slices from SAPAP3 KO mice were not significantly different from those observed in slices from control littermates in any of the regions tested including the DLS, DMS and NAcc. However, when four electrical pulses were applied at a frequency of 10Hz to mimic DA neuron bursting, the magnitude of DA transients observed in the DMS and NAcc of SAPAP3 mice were greater than those evoked in control littermates.Interestingly, phasic stimulation produced similar DA transients in the DLS of both genotypes suggesting that phasic DA signaling was not globally altered. To confirm this finding we crossed SAPAP3 KO mice with DAT-Cre mice and injected ChR2 containing virus into the midbrain to selectively express ChR2 in DA neurons. Transients were then optically evoked resulting in selective activation of DA neurons. Optical stimulation produced a pronounced enhancement of DA release in SAPAP3 KO mice specifically in the DMS and only following phasic-like stimulation. DISCUSSION/SIGNIFICANCE OF IMPACT: These exciting findings suggest that DA signaling in SAPAP3KO mice is dysregulated in a very precise manner that is sub-region specific as well as dependent on the pattern of stimulation. These results suggest that targeted therapies that can modulate these specific modes of dopaminergic signaling in these distinct striatal subregions could provide improved efficacy in OCD patients that are resistant to SSRI treatment.

The lateral preoptic area and ventral pallidum embolden behavior

While recently completing a study of the effects of stimulating the lateral preoptic area (LPO) and ventral pallidum (VP) on locomotion and other movements, we also noticed LPO and VP effects on motivational drive and threat tolerance. Here, we have investigated these latter effects by testing conditioned place preference (CPP), behavior on the elevated plus maze (EPM) and the willingness of sated rats to occupy a harshly lit open field center to acquire sweet pellets, a measure of threat tolerance, following infusions of vehicle or bicuculline (bic) into the LPO and VP. LPO-bic infusions robustly increased total locomotion, and, in direct proportion, occupancy of both the harshly lit field center and open arms of the EPM. LPO bic also generated CPP, but did not increase sweet pellet ingestion. These effects were attenuated by dopamine D1 and D2 receptor antagonists, whether given individually or as a cocktail and systemically or infused bilaterally into the nucleus accumbens. VP-bic infusions did not increase total locomotion, but preferentially increased field center occupancy. VP-bic-infused rats compulsively ingested sweet pellets and did so even under the spotlight, whereas harsh illumination suppressed pellet ingestion in the control groups. VP bic produced CPP and increased open arm occupancy on the EPM. These effects were attenuated by pretreatment with dopamine receptor antagonists given systemically or as bilateral infusions into the VP, except for % distance in the field center (by D1 or D2 antagonists) and pellet ingestion (by D1 antagonist). Thus, boldness generated in association with LPO activation is tightly tied to locomotor activation and, as is locomotion itself, strongly DA dependent, whereas that accompanying stimulation of the VP is independent of locomotor activation and, at least in part, DA signaling. Furthermore, respective emboldened behaviors elicited from neither LPO nor VP could clearly be attributed to goal pursuit. Rather, emboldening of behavior seems more to be a fixed action response not fundamentally different than previously for reported locomotion, pivoting, backing, gnawing, and eating elicited by basal forebrain stimulation.

PO-138 Mechanism of Cortical Information Output after Exercise Fatigue Induced by D2DR

Objective In this experiment, the Local field potential (LFPs) was observed in the substantia nigra compact and electrical activity change in corticostriatal pathway after D2DR intervention in exercise-induced fatigue rats. We analyzed the changes of DA neuron discharge and D2DR mediated corticostriatal pathway information transmission. To explore the mechanism of D2D2 mediated DA system in the information output of cortical M1 region.&#x0D; Methods Wistar rats were used to establish the model of exercise-induced fatigue. The rats were divided into control group (CG), 7 days fatigue group (7FG) and 24 hour recovery group (24RG). We used in vivo multichannel recording technology to record electrical activity in the M1, striatum and substantia nigra compact of rats and observed the electrophysiological changes after D2DR intervention. We also detected the expression of TH proteins in the dorsolateral striatum before and after exercise-induced fatigue by immunohistochemistry.&#x0D; Results 1) Compared with group CG, the expression of TH protein in the dorsolateral area of striatum was significantly decreased in group 7FG (P&lt;0.05). 2) Compared with the CG group, the power spectral density of the θ, α and β band of the SNc was increased after seven days of exhaustion exercise(P &lt; 0.05); After 24 hours of recovery, the PSD value decreased significantly compared with the 7FG group(P&lt;0.05). 3)Compared with the CG group the power spectral density of alpha (7-13Hz) and beta (15-30Hz) bands in the M1 region and striatum was increased in 7FG after injection D2DR agonist(P &lt; 0.05) .&#x0D; Conclusions After exercise-induced fatigue, the activity of substantia nigra was increased, and the activity of M1 and striatum was lower than that of the blank control group after the D2DR agonist injection. As a key receptor for the DA signal system, D2DR regulates the electrical activity of the nigrostriatal DA pathway and affects the comprehensive information output of the cortex, which can be regarded as a target for exercise-induced fatigue (NSFC: 31401018, SKXJX: 2014014, Corresponding houlj@bnu.edu.cn).

An Interaction between Serotonin Receptor Signaling and Dopamine Enhances Goal-Directed Vigor and Persistence in Mice.

The functionally selective 5-HT2C receptor ligand SB242084 can increase motivation and have rapid onset anti-depressant-like effects. We sought to identify the specific behavioral effects of SB242084 treatment and elucidate the mechanism in female and male mice. Using a quantitative behavioral approach, we determined that SB242084 increases the vigor and persistence of goal-directed activity across different types of physical work, particularly when work requirements are demanding. We found this influence of SB242084 on effort, rather than reward to be reflected in striatal DA measured during behavior. Using in vivo fast scan cyclic voltammetry, we found that SB242084 has no effect on reward-related phasic DA release in the NAc. Using in vivo microdialysis to measure tonic changes in extracellular DA, we also found no changes in the NAc. In contrast, SB242084 treatment increases extracellular DA in the dorsomedial striatum, an area that plays a key role in response vigor. These findings have several implications. At the behavioral level, this work shows that the capacity to work in demanding situations can be increased, without a generalized increase in motor activity or reward value. At the circuit level, we identified a pathway restricted potentiation of DA release and showed that this was the reason for the increased response vigor. At the cellular level, we show that a specific serotonin receptor cross talks to the DA system. Together, this information provides promise for the development of treatments for apathy, a serious clinical condition that can afflict patients with psychiatric and neurological disorders.SIGNIFICANCE STATEMENT Motivated behaviors are modulated by reward value, effort demands, and cost-benefit computations. This information drives the decision to act, which action to select, and the intensity with which the selected action is performed. Because these behavioral processes are all regulated by DA signaling, it is very difficult to influence selected aspects of motivated behavior without affecting others. Here we identify a pharmacological treatment that increases the vigor and persistence of responding in mice, without increasing generalized activity or changing reactions to rewards. We show that the 5-HT2C-selective ligand boosts motivation by potentiating activity-dependent DA release in the dorsomedial striatum. These results reveal a novel strategy for treating patients with motivational deficits, avolition, or apathy.