Prefrontal Cortex-Driven Dopamine Signals in the Striatum Show Unique Spatial and Pharmacological Properties.

Dopamine (DA) signals in the striatum are critical for a variety of vital processes, including motivation, motor learning, and reinforcement learning. Striatal DA signals can be evoked by direct activation of inputs from midbrain DA neurons (DANs) as well as cortical and thalamic inputs to the striatum. In this study, we show that in vivo optogenetic stimulation of prelimbic (PrL) and infralimbic (IL) cortical afferents to the striatum triggers an increase in extracellular DA concentration, which coincides with elevation of striatal acetylcholine (ACh) levels. This increase is blocked by a nicotinic ACh receptor (nAChR) antagonist. Using single or dual optogenetic stimulation in brain slices from male and female mice, we compared the properties of these PrL/IL-evoked DA signals with those evoked by stimulation from midbrain DAN axonal projections. PrL/IL-evoked DA signals are undistinguishable from DAN evoked DA signals in their amplitudes and electrochemical properties. However, PrL/IL-evoked DA signals are spatially restricted and preferentially recorded in the dorsomedial striatum. PrL/IL-evoked DA signals also differ in their pharmacological properties, requiring activation of glutamate and nicotinic ACh receptors. Thus, both in vivo and in vitro results indicate that cortical evoked DA signals rely on recruitment of cholinergic interneurons, which renders DA signals less able to summate during trains of stimulation and more sensitive to both cholinergic drugs and temperature. In conclusion, cortical and midbrain inputs to the striatum evoke DA signals with unique spatial and pharmacological properties that likely shape their functional roles and behavioral relevance.SIGNIFICANCE STATEMENT Dopamine signals in the striatum play a critical role in basal ganglia function, such as reinforcement and motor learning. Different afferents to the striatum can trigger dopamine signals, but their release properties are not well understood. Further, these input-specific dopamine signals have only been studied in separate animals. Here we show that optogenetic stimulation of cortical glutamatergic afferents to the striatum triggers dopamine signals both in vivo and in vitro These afferents engage cholinergic interneurons, which drive dopamine release from dopamine neuron axons by activation of nicotinic acetylcholine receptors. We also show that cortically evoked dopamine signals have other unique properties, including spatial restriction and sensitivity to temperature changes than dopamine signals evoked by stimulation of midbrain dopamine neuron axons.

Striatal Cholinergic Interneurons Are a Novel Target of Corticotropin Releasing Factor.

Cholinergic interneurons (CINs) are critical regulators of striatal network activity and output. Changes in CIN activity are thought to encode salient changes in the environment and stimulus-response-outcome associations. Here we report that the stress-associated neuropeptide corticotropin releasing factor (CRF) produces a profound and reliable increase in the spontaneous firing of CINs in both dorsal striatum and nucleus accumbens (NAc) through activation of CRF type 1 receptors, production of cAMP and reduction in spike accommodation in male mice. The increase of CIN firing by CRF results in the activation muscarinic acetylcholine receptors type 5, which mediate potentiation of dopamine transmission in the striatum. This study provides critical mechanistic insight into how CRF modulates striatal activity and dopamine transmission in the NAc to likely account for CRF facilitation of appetitive behaviors.SIGNIFICANCE STATEMENT Although the presence of CRF receptors in the dorsal and ventral striatum has been acknowledged, the cellular identity and the functional consequences of receptor activation is unknown. Here we report that striatal cholinergic interneurons express CRF-R1 receptors and are acutely activated by the neuropeptide CRF that is released in response to salient environmental stimuli. Cholinergic interneurons make <1% of the cells in the striatum but are critical regulators of the striatal circuitry and its output. CRF's fast and potent activation of cholinergic interneurons could have far reaching behavioral implications across motivated behaviors controlled by the striatum.

Distinctive Modulation of Dopamine Release in the Nucleus Accumbens Shell Mediated by Dopamine and Acetylcholine Receptors.

Nucleus accumbens (NAc) shell shows unique dopamine (DA) signals in vivo and plays a unique role in DA-dependent behaviors such as reward-motivated learning and the response to drugs of abuse. A disynaptic mechanism for DA release was reported and shown to require synchronized firing of cholinergic interneurons (CINs) and activation of nicotinic acetylcholine (ACh) receptors (nAChRs) in DA neuron (DAN) axons. The properties of this disynaptic mechanism of DA transmission are not well understood in the NAc shell. In this study, in vitro fast-scan cyclic voltammetry was used to examine the modulation of DA transmission evoked by CINs firing in the shell of mice and compared with other striatal regions. We found that DA signals in the shell displayed significant degree of summation in response to train stimulation of CINs, contrary to core and dorsal striatum. The summation was amplified by a D2-like receptor antagonist and experiments with mice with targeted deletion of D2 receptors to DANs or CINs revealed that D2 receptors in CINs mediate a fast inhibition observed within 100 ms of the first pulse, whereas D2 autoreceptors in DAN terminals are engaged in a slower inhibition that peaks at ∼500 ms. ACh also contributes to the use-dependent inhibition of DA release through muscarinic receptors only in the shell, where higher activity of acetylcholinesterase minimizes nAChR desensitization and promotes summation. These findings show that DA signals are modulated differentially by endogenous DA and ACh in the shell, which may underlie the unique features of shell DA signals in vivoSIGNIFICANCE STATEMENT The present study reports that dopamine (DA) release evoked by activation of cholinergic interneurons displays a high degree of summation in the shell and shows unique modulation by endogenous DA and acetylcholine. Desensitization of nicotinic receptors, which is a prevailing mechanism for use-dependent inhibition in the nucleus accumbens core and dorsal striatum, is also minimal in the shell in part due to elevated acetylcholinesterase activity. This distinctive modulation of DA transmission in the shell may have functional implications in the acquisition of reward-motivated behaviors and reward seeking.

Murine CD8+ Invariant Natural Killer T Cells are Negatively Selected by CD1d Expressed on Thymic Epithelial Cells and Dendritic Cells.

BACKGROUND: CD1d-dependent invariant natural killer (iNKT) cells are found as either CD4 single positive (SP) or CD4/CD8 double negative (DN) cells in mice. The size of the CD8+ iNKT population is extremely small. It is known that CD1d expression on developing thymocytes is sufficient for iNKT development and co-receptor choice, which is driven by Th-POK expression. This study aimed to examine the factors involved in the CD4/CD8 co-receptor choice of iNKT cells in addition to Th-POK-driven silencing of CD8 expression. METHODS: In this study, we compared iNKT cells of wild-type (WT) mice with those of transgenic mice in which CD1d expression is restricted to developing thymocytes by the proximal Lck (pLCK) promoter. CD8 positive iNKT cell population were analyzed by flow cytometry. RESULTS: We found that there was a substantial population of CD8+ iNKT cells in the thymus and spleen of transgenic mice, and these cells are negatively selected in between Stage 2 and Stage 3 of their developmental program by the CD1d expressed on Thymic epithelial cell (TEC) and Dendritic cells in WT mice. CONCLUSION: We conclude that TEC expression of CD1d in the murine thymus contributed to co-receptor choice of iNKT cells, in addition to Th-POK-driven silencing of CD8. Therefore, mostly CD4 SP and DN iNKT cells are produced under normal physiological conditions in mice.

Muscarinic regulation of dopamine and glutamate transmission in the nucleus accumbens.

Cholinergic transmission in the striatum functions as a key modulator of dopamine (DA) transmission and synaptic plasticity, both of which are required for reward and motor learning. Acetylcholine (ACh) can elicit striatal DA release through activation of nicotinic ACh receptors (nAChRs) on DA axonal projections. However, it remains controversial how muscarinic ACh receptors (mAChRs) modulate striatal DA release, with studies reporting both potentiation and depression of striatal DA transmission by mAChR agonists. This study investigates the mAChR-mediated regulation of release from three types of midbrain neurons that project to striatum: DA, DA/glutamate, and glutamate neurons. We found that M5 mAChRs potentiate DA and glutamate release only from DA and DA/glutamate projections from the midbrain. We also show that M2/M4 mAChRs depress the nAChR-dependent mechanism of DA release in the striatum. These results suggest that M5 receptors on DA neuron terminals enhance DA release, whereas M2/M4 autoreceptors on cholinergic terminals inhibit ACh release and subsequent nAChR-dependent DA release. Our findings clarify the mechanisms of mAChR-dependent modulation of DA and glutamate transmission in the striatum.

Glutamate and dopamine transmission from midbrain dopamine neurons share similar release properties but are differentially affected by cocaine.

Synaptic transmission between ventral tegmental area and nucleus accumbens (NAc) is critically involved in reward-motivated behaviors and thought to be altered in addiction. In addition to dopamine (DA), glutamate is packaged and released by a subset of mesolimbic DA neurons, eliciting EPSCs onto medium spiny neurons in NAc. Little is known about the properties and modulation of glutamate release from DA midbrain terminals and the effect of cocaine. Using an optogenetic approach to selectively activate midbrain DA fibers, we compared the properties and modulation of DA transients and EPSCs measured using fast-scan cyclic voltammetry and whole-cell recordings in mouse brain slices. DA transients and EPSCs were inhibited by DA receptor D2R agonist and showed a marked paired-pulse depression that required 2 min for full recovery. Cocaine depressed EPSCs amplitude by 50% but enhanced the overall DA transmission from midbrain DA neurons. AMPA and NMDA receptor-mediated EPSCs were equally inhibited by cocaine, suggesting a presynaptic mechanism of action. Pharmacological blockage and genetic deletion of D2R in DA neurons prevented the cocaine-induced inhibition of EPSCs and caused a larger increase in DA transient peak, confirming the involvement of presynaptic D2R. These findings demonstrate that acute cocaine inhibits DA and glutamate release from midbrain DA neurons via presynaptic D2R but has differential overall effects on their transmissions in the NAc. We postulate that cocaine, by blocking DA reuptake, prolongs DA transients and facilitates the feedback inhibition of DA and glutamate release from these terminals.

Screening of non-steroidal anti-inflammatory drugs for inhibitory effects on the activities of six UDP-glucuronosyltransferases (UGT1A1, 1A3, 1A4, 1A6, 1A9 and 2B7) using LC-MS/MS.

Non-steroidal anti-inflammatory drugs (NSAIDs) are used widely to relieve pain and to decrease inflammation. Several clinical studies have reported that NSAIDs inhibit uridine 5'-diphospho-glucuronosyltransferase (UGT) enzymes. Therefore, the study evaluated the inhibitory potential of 15 NSAIDs on the activities of six UGT isoforms (i.e. UGT1A1, 1A3, 1A4, 1A6, 1A9 and 2B7) in human liver microsomes (HLMs). Among the 15 NSAIDs tested here, mefenamic acid and diclofenac inhibited all UGTs tested in this study. Piroxicam and niflumic acid inhibited UGT1A9 activity (IC50 = 73.8 µm and 0.38 µm, respectively) and naproxen selectively inhibited UGT2B7 activity (IC50 = 53.1 µm), whereas it did not inhibit the other UGTs tested (IC50 > 200 µm). Diflunisal inhibited the UGT1A1 (IC50 = 33.0 µm) and UGT1A9 (IC50 = 19.4 µm). Acetaminophen, fenoprofen, ibuprofen, ketoprofen, meloxicam, phenylbutazone, salicylic acid and sulindac showed negligible inhibitory effects on the six UGTs (IC50 > 100 µm). These results suggest that some NSAIDs have the potential to inhibit UGTs in vitro.

Mutation of a positively charged cytoplasmic motif within CD1d results in multiple defects in antigen presentation to NKT cells.

CD1d is an MHC class I-like molecule that presents glycolipid Ags to types I and II NKT cells. The YxxI motif in the cytoplasmic tail of CD1d contributes to its intracellular localization to the endolysosomal compartment and is important for Ag presentation to type I NKT cells. In this study, we identified the (327-329)RRR motif in CD1d and showed that it is critical for the control of CD1d intracellular trafficking and Ag presentation. The replacement of the arginines in this motif with alanines resulted in the extensive accumulation of CD1d in lysosomes but did not affect the cell surface expression. The defect in its cellular localization was accompanied by defects in Ag presentation to both type I and type II NKT cells. These results demonstrated that the (327-329)RRR motif of CD1d is required for proper cellular distribution of CD1d and optimal Ag presentation to both type I and type II NKT cells.

A lipidomic platform establishment for structural identification of skin ceramides with non-hydroxyacyl chains.

The stratum corneum (SC) is the outermost layer of skin that functions as a barrier and protects against environmental influences and transepidermal water loss. Its unique morphology consists of keratin-enriched corneocytes embedded in a distinctive mixture of lipids containing mainly ceramides, free fatty acids, and cholesterol. Ceramides are sphingolipids consisting of sphingoid bases, which are linked to fatty acids by an amide bond. Typical sphingoid bases in the skin are composed of dihydrosphingosine (dS), sphingosine (S), phytosphingosine (P), and 6-hydroxysphingosine (H), and the fatty acid acyl chains are composed of non-hydroxy fatty acid (N), α-hydroxy fatty acid (A), ω-hydroxy fatty acid (O), and esterified ω-hydroxy fatty acid (E). The 16 ceramide classes include several combinations of sphingoid bases and fatty acid acyl chains. Among them, N-type ceramides are the most abundant in the SC. Mass spectrometry (MS)/MS analysis of N-type ceramides using chip-based direct infusion nanoelectrospray-ion trap mass spectrometry generated the characteristic fragmentation pattern of both acyl and sphingoid units, which could be applied to structural identification of ceramides. Based on the MS/MS fragmentation patterns of N-type ceramides, comprehensive fragmentation schemes were proposed. In addition, mass fragmentation patterns, which are specific to the sphingoid backbone of N-type ceramides, were found in higher m/z regions of tandem mass spectra. These characteristic and general fragmentation patterns were used to identify N-type ceramides in human SC. Based on established MS/MS fragmentation patterns of N-type ceramides, 52 ceramides (including different classes of NS, NdS, NP, and NH) were identified in human SC. The MS/MS fragmentation patterns of N-type ceramides were characterized by interpreting their product ion scan mass spectra. This information may be used to identify N-type ceramides in the SC of human, rat, and mouse skin.

Leucine-rich repeat kinase 2 limits dopamine D1 receptor signaling in striatum and biases against heavy persistent alcohol drinking.

The transition from hedonic alcohol drinking to problematic drinking is a hallmark of alcohol use disorder that occurs only in a subset of drinkers. This transition requires long-lasting changes in the synaptic drive and the activity of striatal neurons expressing dopamine D1 receptor (D1R). The molecular mechanisms that generate vulnerability in some individuals to undergo the transition are less understood. Here, we report that the Parkinson's-related protein leucine-rich repeat kinase 2 (LRRK2) modulates striatal D1R function to affect the behavioral response to alcohol and the likelihood that mice transition to heavy, persistent alcohol drinking. Constitutive deletion of the Lrrk2 gene specifically from D1R-expressing neurons potentiated D1R signaling at the cellular and synaptic level and enhanced alcohol-related behaviors and drinking. Mice with cell-specific deletion of Lrrk2 were more prone to heavy alcohol drinking, and consumption was insensitive to punishment. These findings identify a potential novel role for LRRK2 function in the striatum in promoting resilience against heavy and persistent alcohol drinking.

An enhancer-AAV toolbox to target and manipulate distinct interneuron subtypes.

In recent years, we and others have identified a number of enhancers that, when incorporated into rAAV vectors, can restrict the transgene expression to particular neuronal populations. Yet, viral tools to access and manipulate fine neuronal subtypes are still limited. Here, we performed systematic analysis of single cell genomic data to identify enhancer candidates for each of the cortical interneuron subtypes. We established a set of enhancer-AAV tools that are highly specific for distinct cortical interneuron populations and striatal cholinergic neurons. These enhancers, when used in the context of different effectors, can target (fluorescent proteins), observe activity (GCaMP) and manipulate (opto- or chemo-genetics) specific neuronal subtypes. We also validated our enhancer-AAV tools across species. Thus, we provide the field with a powerful set of tools to study neural circuits and functions and to develop precise and targeted therapy.

Characterizing the conductance underlying depolarization-induced slow current in cerebellar Purkinje cells.

Brief strong depolarization of cerebellar Purkinje cells produces a slow inward cation current [depolarization-induced slow current (DISC)]. Previous work has shown that DISC is triggered by voltage-sensitive Ca influx in the Purkinje cell and is attenuated by blockers of vesicular loading and fusion. Here, we have sought to characterize the ion channel(s) underlying the DISC conductance. While the brief depolarizing steps that triggered DISC were associated with a large Ca transient, the onset of DISC current corresponded only with the Ca transient decay phase. Furthermore, substitution of external Na with the impermeant cation N-methyl-d-glucamine produced a complete and reversible block of DISC, suggesting that the DISC conductance was not Ca permeant. Transient receptor potential cation channel, subfamily M, members 4 (TRPM4) and 5 (TRPM5) are nonselective cation channels that are opened by Ca transients but do not flux Ca. They are expressed in Purkinje cells of the posterior cerebellum, where DISC is large, and, in these cells, DISC is strongly attenuated by nonselective blockers of TRPM4/5. However, measurement of DISC currents in Purkinje cells derived from TRPM4 null, TRPM5 null, and double null mice as well as wild-type mice with TRPM4 short hairpin RNA knockdown showed a partial attenuation with 35-46% of current remaining. Thus, while the DISC conductance is Ca triggered, Na permeant, and Ca impermeant, suggesting a role for TRPM4 and TRPM5, these ion channels are not absolutely required for DISC.

CYP2J2 and CYP2C19 are the major enzymes responsible for metabolism of albendazole and fenbendazole in human liver microsomes and recombinant P450 assay systems.

Albendazole and fenbendazole are broad-spectrum anthelmintics that undergo extensive metabolism to form hydroxyl and sulfoxide metabolites. Although CYP3A and flavin-containing monooxygenase have been implicated in sulfoxide metabolite formation, the enzymes responsible for hydroxyl metabolite formation have not been identified. In this study, we used human liver microsomes and recombinant cytochrome P450s (P450s) to characterize the enzymes involved in the formation of hydroxyalbendazole and hydroxyfenbendazole from albendazole and fenbendazole, respectively. Of the 10 recombinant P450s, CYP2J2 and/or CYP2C19 was the predominant enzyme catalyzing the hydroxylation of albendazole and fenbendazole. Albendazole hydroxylation to hydroxyalbendazole is primarily mediated by CYP2J2 (0.34 µl/min/pmol P450, which is a rate 3.9- and 8.1-fold higher than the rates for CYP2C19 and CYP2E1, respectively), whereas CYP2C19 and CYP2J2 contributed to the formation of hydroxyfenbendazole from fenbendazole (2.68 and 1.94 µl/min/pmol P450 for CYP2C19 and CYP2J2, respectively, which are rates 11.7- and 8.4-fold higher than the rate for CYP2D6). Correlation analysis between the known P450 enzyme activities and the rate of hydroxyalbendazole and hydroxyfenbendazole formation in samples from 14 human liver microsomes showed that albendazole hydroxylation correlates with CYP2J2 activity and fenbendazole hydroxylation correlates with CYP2C19 and CYP2J2 activities. These findings were supported by a P450 isoform-selective inhibition study in human liver microsomes. In conclusion, our data for the first time suggest that albendazole hydroxylation is primarily catalyzed by CYP2J2, whereas fenbendazole hydroxylation is preferentially catalyzed by CYP2C19 and CYP2J2. The present data will be useful in understanding the pharmacokinetics and drug interactions of albendazole and fenbendazole in vivo.

In vitro metabolism of obovatol and its effect on cytochrome P450 enzyme activities in human liver microsomes.

Obovatol, a major constituent of the leaves of Magnolia obovata Thunb, is known to inhibit nuclear factor-κB activity and arachidonic acid-induced platelet aggregation. This study was performed to identify the metabolites of obovatol in human liver microsomes. Human liver microsomes incubated with obovatol in the presence of NADPH and/or UDPGA resulted in the formation of six metabolites, M1-M6. M1 and M2 were identified as hydroxyobovatol, on the basis of liquid chromatography/tandem mass spectrometric (LC-MS/MS) analysis. M1, M2 and obovatol were further metabolized to their glucuronide conjugates, obovatol-glucuronide (M3), obovatol-diglucuronide (M4) and hydroxyobovatol-glucuronide (M5 and M6). The inhibitory potency of obovatol on eight major human P450s was also investigated in human liver microsomes. In these experiments, obovatol strongly inhibited CYP2C19-mediated S-mephenytoin hydroxylase activity with an IC(50) value of 0.8 µM, which could have implications for drug-drug interactions.

Hepatocellular Metabolic Abnormalities Induced by Long-Term Exposure to Novel Brominated Flame Retardant, Hexabromobenzene.

Novel brominated flame retardants (NBFRs) are widely used to avoid environmental accumulation concerns and because of the regulations imposed on classical BFRs. However, recent studies have not revealed the negative effects of NBFR accumulation and exposure on humans. We conducted a metabolomics study on hexabromobenzene (HBB), one of the NBFRs, to investigate its effect on hepatocytes. Gas chromatography-mass spectrometry-based metabolite profiling was performed to observe metabolic perturbations by treating human livertissue-derived HepG2 cell lines with HBB for maximum 21 days. Metabolic pathway enrichment using 17 metabolite biomarkers determined via univariate and multivariate statistical analysis verified that long-term accumulation of HBB resulted in distinct diminution of eight amino acids and five other metabolites. Molecular docking of the biomarker-related enzymes revealed the potential molecular mechanism of hepatocellular response to HBB exposure, which disrupts the energy metabolism of hepatic cells. Collectively, this study may provide insights into the hidden toxicity of bioaccumulating HBB and unveil the risks associated with non-regulated NBFRs.

Lipidomic Analysis of Cervicovaginal Fluid for Elucidating Prognostic Biomarkers and Relevant Phospholipid and Sphingolipid Pathways in Preterm Birth.

Cervicovaginal fluid (CVF) is an excellent specimen for monitoring preterm birth (PTB) as it characterizes cervical metabolites, the vaginal environment, and specific host immune responses. However, extensive lipid analysis of CVF to explain PTB has not been studied. In this study, we performed a systematic analysis combining high-throughput lipid analysis and omics to discover the unique metabolic properties of the cervix. Liquid chromatography-high resolution mass spectrometry successfully detected a total of 190 lipids in the CVF of 30 PTB and 30 term birth (TB) pregnant women. The whole lipidomics dataset analyzed by combining multivariate and univariate statistical analysis revealed 35 lipid biomarkers, including phospholipids and sphingolipids. Remarkably, sphingomyelin, which plays a physiologically essential role in sphingolipids, was significantly downregulated in PTB. Metabolic pathway study provides a close relationship between vaginal microbial organization and cell membrane formation, further supporting the robustness of our findings. Sphingolipids and phospholipids, which were determined to be important lipids for predicting PTB in our study, showed a high value of receiver operating characteristic (ROC) curve >0.7, indicating that a lipid diagnostic test and understanding the mechanism of lipids is highly related to the vaginal microbiome. Therefore, our result has high potential as a predictor of PTB.

NKT cell-dependent regulation of secondary antigen-specific, conventional CD4+ T cell immune responses.

NKT cells are considered to be innate-like regulatory cells. However, their regulatory functions in adaptive immune responses have not been studied in detail. In this study, we investigated the immunoregulatory functions of NKT cells during the secondary phase of an Ag-specific CD4(+) T cell response. When compared with OVA-specific effector CD4(+) T cells adoptively transferred into NKT cell-deficient naive CD1d(-/-) mice, the same T cells transferred into naive CD1d(+/-) mice exhibited substantially stronger immune responses on OVA challenge. The enhanced immune response of the transferred CD4(+) T cells in the presence of NKT cells correlated with an increase in their proliferation in vivo. In addition, T cells transferred into CD1d(+/-) recipients showed enhanced cytokine productions relative to T cells in CD1d(-/-) recipients. To elucidate the physiological relevance of the regulatory role of NKT cells in a disease setting, OVA-specific asthma was induced in recipient mice after adoptive transfer of OVA-specific CD4(+) T cells. CD1d(+/-) recipients showed stronger asthmatic phenotypes in all indications when compared with CD1d(-/-) recipients. Taken together, these results suggest that NKT cells are critical for the regulation of Ag-specific, conventional CD4(+) T cells during the secondary phase of an adaptive immune response.

Dendritic glutamate release produces autocrine activation of mGluR1 in cerebellar Purkinje cells.

In recent years, it has become clear that, in addition to conventional anterograde transmission, signaling in neural circuits can occur in a retrograde manner. This suggests the additional possibility that postsynaptic release of neurotransmitter might be able to act in an autocrine fashion. Here, we show that brief depolarization of a cerebellar Purkinje cell triggers a slow inward current. This depolarization-induced slow current (DISC) is attenuated by antagonists of mGluR1 or TRP channels. DISC is eliminated by a mixture of voltage-sensitive Ca2+ channel blockers and is mimicked by a brief climbing fiber burst. DISC is attenuated by an inhibitor of vesicular glutamate transporters or of vesicular fusion. These data suggest that Ca2+-dependent postsynaptic fusion of glutamate-loaded vesicles evokes a slow inward current produced by activation of postsynaptic mGluR1, thereby constituting a useful form of feedback regulation.

Pain induces adaptations in ventral tegmental area dopamine neurons to drive anhedonia-like behavior.

The persistence of negative affect in pain leads to co-morbid symptoms such as anhedonia and depression-major health issues in the United States. The neuronal circuitry and contribution of specific cellular populations underlying these behavioral adaptations remains unknown. A common characteristic of negative affect is a decrease in motivation to initiate and complete goal-directed behavior, known as anhedonia. We report that in rodents, inflammatory pain decreased the activity of ventral tegmental area (VTA) dopamine (DA) neurons, which are critical mediators of motivational states. Pain increased rostromedial tegmental nucleus inhibitory tone onto VTA DA neurons, making them less excitable. Furthermore, the decreased activity of DA neurons was associated with reduced motivation for natural rewards, consistent with anhedonia-like behavior. Selective activation of VTA DA neurons was sufficient to restore baseline motivation and hedonic responses to natural rewards. These findings reveal pain-induced adaptations within VTA DA neurons that underlie anhedonia-like behavior.