VTA Of Rats Research Articles

Dopaminergic responses to identity prediction errors depend differently on the orbitofrontal cortex and hippocampus.

Adaptive behavior depends on the ability to predict specific events, particularly those related to rewards. Armed with such associative information, we can infer the current value of predicted rewards based on changing circumstances and desires. To support this ability, neural systems must represent both the value and identity of predicted rewards, and these representations must be updated when they change. Here we tested whether prediction error signaling of dopamine neurons depends on two areas known to represent the specifics of rewarding events, the HC and OFC. We monitored the spiking activity of dopamine neurons in rat VTA during changes in the number or flavor of expected rewards designed to induce errors in the prediction of reward value or reward identity, respectively. In control animals, dopamine neurons registered both error types, transiently increasing firing to additional drops of reward or changes in reward flavor. These canonical firing signatures of value and identity prediction errors were significantly disrupted in rats with ipsilateral neurotoxic lesions of either HC or OFC. Specifically, HC lesions caused a failure to register either type of prediction error, whereas OFC lesions caused persistent signaling of identity prediction errors and much more subtle effects on signaling of value errors. These results demonstrate that HC and OFC contribute distinct types of information to the computation of prediction errors signaled by dopaminergic neurons.

The mGluR2/3 agonist pomaglumetad methionil normalizes aberrant dopamine neuron activity via action in the ventral hippocampus.

The group 2 metabotropic glutamate receptor (mGluR2/3) agonist, pomaglumetad methionil (POM), showed promise as a novel antipsychotic in preclinical research but failed to show efficacy in clinical trials, though it has been suggested that it may be effective in certain patient populations. Although previous studies have shown that mGluR2/3 agonists have no effect on dopamine (DA) in wild type rats, we used the methylzoxymethanol acetate (MAM) model to determine whether POM may indirectly normalize DA neuron activity in a model representative of the hyperdopaminergic state thought to underlie psychosis, compared to SAL rats, using in vivo, anesthetized, electrophysiological recordings. POM dose-dependently reduced the number of spontaneously active DA neurons in the VTA of MAM rats to control levels without affecting DA firing in SAL rats, which persisted following 14d repeated treatment with POM. In female MAM rats, POM significantly reduced DA neuron population activity only during proestrous and estrous stages. MAM rats also demonstrated dose-dependent improvement in novel object recognition following acute POM, which was not observed in SAL rats. Similar to the MAM rats, DA neuron population activity was increased in a hippocampal-dependent manner following acute restraint stress. Administration of POM prior to 2 h restraint stress prevented the restraint-induced increase in DA neuron population activity, and this effect was blocked by pretreatment with an mGluR2/3 antagonist. Thus, the ability of POM to reduce the hyperdopaminergic activity in both MAM rats and in wild type rats following restraint stress suggests that it can indirectly regulate DA neuron activity, which may underlie its potential therapeutic effects.

RGS2 Modulates Cocaine Self‐administration by Controlling Dopamine D2 Autoreceptor Activity

IntroductionRepeated exposure to drugs of abuse reduces midbrain dopamine (DA) D2 autoreceptor (D2AR) levels, which is associated with enhanced motivation for drug and escalation of drug intake. Notably, drug self‐administration disrupts the ability of D2ARs to inhibit DA release in the nucleus accumbens (NAc) and abolishes midbrain D2AR‐mediated G protein signaling. However, what regulates midbrain D2AR function remains unclear. The family of regulator of G protein signaling (RGS) proteins negatively modulates GPCR signaling by accelerating GTP hydrolysis and terminating G protein signaling. Among all the subtypes of RGS proteins, we previously showed that RGS2 is expressed in midbrain dopaminergic neurons where D2ARs are located. Importantly, we demonstrated that RGS2 is a negative modulator of D2R‐mediated G protein signaling in neuroblastoma 2a cells. We hypothesize that RGS2 in DA neurons may regulate D2AR activity and drug self‐administration. Thus, this project will determine whether RGS2 regulates cocaine self‐administration by modulating D2AR function in midbrain dopaminergic neurons.MethodsViral microinjectionsMale and female TH‐Cre Long Evans rats (~10 weeks old) were injected into bilateral VTA with an AAV expressing a RGS2 mutant with N‐terminus‐deletion (RGS2ΔN) or empty control vector. Three weeks post‐virus infusion, infection was verified using immunocytochemistry and Western blotting.Behavioral AssaysThree weeks post‐viral infusion, baseline locomotor activity was measured. Intravenous catheters were implanted and rats were trained to self‐administer cocaine. Multiple facets of cocaine self‐administration behaviors were measured including behavioral economic assessment of motivation to take cocaine (threshold protocol), extinction training and cue/cocaine‐primed reinstatement of cocaine seeking. In a separate cohort of rats, cocaine‐induced locomotor activity was measured.Functional CharacterizationIn vivo microdialysis experiments were performed in the NAc to measure extracellular DA levels elicited by cocaine or amphetamine challenge. Further, fast‐scan cyclic voltammetry was used to measure D2AR‐mediated inhibition of DA release and potassium Kv1.2 regulation of DA release in NAc slices of rats virally infused with the RGS2ΔN or empty control virus.ResultsWe found that inhibiting RGS2 activity by overexpressing RGS2ΔN in the VTA of rats significantly reduced motivation for cocaine and cocaine‐primed reinstatement of cocaine seeking. Cocaine‐induced locomotor activity was also reduced by overexpression of RGS2ΔN and was paralleled by blunted extracellular DA levels in the NAc after psychostimulant exposure. Further, RGS2ΔN overexpression significantly increased D2AR‐mediated inhibition of DA release and reduced electrically‐evoked DA release via upregulation of Kv1.2 channels in the NAc. Additionally, RGS2ΔN overexpression reduced D2AR‐mediated inhibition of locomotor activity; however, baseline and D1R‐stimulated locomotor activity were not altered. The present study provides first time evidence that RGS2 plays a critical role in cocaine self‐administration by regulating midbrain D2AR function.Support or Funding InformationThis work is supported by NIH R01DA042862, P50DA006634, F31AA025532

RGS2 Regulates Cocaine Self‐Administration through Midbrain Dopamine D2 Autoreceptors

IntroductionRepeated exposure to drugs of abuse alters the transmission of the dopaminergic system including dopamine D2 autoreceptors (D2ARs). Reduced midbrain D2ARs is associated with enhanced motivation for drugs and increased drug intake. Additionally, drug self‐administration disrupts the ability of D2ARs to inhibit dopamine release in the nucleus accumbens (NAcc) and abolishes midbrain D2AR‐mediated G protein signaling. However, what regulates midbrain D2AR function remains unclear. The family of regulator of G protein signaling (RGS) proteins negatively modulates many GPCR signaling by accelerating GTP hydrolysis and terminating G protein signaling. Among all the subtypes of RGS proteins, we previously have shown that RGS2 is expressed in midbrain dopaminergic neurons where D2ARs are located. Importantly, we have demonstrated that RGS2 is a negative modulator of dopamine D2 receptor‐mediated G protein signaling in neuroblastoma 2a cells. We hypothesize that RGS2 in dopamine neurons may regulate D2AR activity and thus drug self‐administration. Thus, this project will determine whether RGS2 regulates cocaine self‐administration by modulating D2AR function in midbrain dopaminergic neurons.MethodsMale TH‐Cre Long Evans rats (~10 weeks old) were injected bilaterally into the VTA with an AAV expressing a loss‐of‐function RGS2 mutant with N‐terminus‐deletion (RGS2x1– 79) or empty control vector. Three weeks post‐virus infusion, infection was verified using immunocytochemistry and Western blotting. Immunohistochemistry assays were used to visualize the co‐localization of mCherry‐tagged RGS2x1‐79 virus and tyrosine hydroxylase in the VTA of rats. Western blotting was performed on VTA tissue lysates to measure levels of HA‐tagged RGS2x1‐79 and RGS2.Three weeks post‐viral infusion, baseline locomotor activity was measured. Intravenous catheters were then implanted and rats were trained to self‐administer cocaine. Multiple facets of cocaine self‐administration behaviors were measured including behavioral economic assessment of motivation to take cocaine (threshold protocol), extinction training and cue/cocaine‐primed reinstatement of cocaine seeking. In a separate cohort of rats, cocaine‐induced locomotor activity was measured three weeks post‐viral infusion.To understand the role of RGS2 in regulating midbrain D2AR‐mediated G protein signaling, fast‐scan cyclic voltammetry was used to measure D2AR‐mediated inhibition of dopamine release in the NAcc of rats virally infused with the RGS2x1–79 mutant or empty control virus. Brain slices containing the NAcc were stimulated with increasing doses of D2/D3 agonist quinpirole and dopamine release was measured.ResultsWe found that inhibiting RGS2 activity by overexpressing a loss‐of‐function RGS2x1–79 mutant in the VTA of rats significantly reduced motivation for cocaine and decreased cocaine‐primed reinstatement of cocaine seeking. Further, overexpression of the RGS2x1–79 mutant significantly reduced cocaine‐induced locomotor activity. The present study provides first time evidence that RGS2 plays a critical role in cocaine self‐administration by regulating midbrain D2AR function.Support or Funding InformationNIH DA042862, DA006634, AA025532This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Constitutive activation of kappa opioid receptors at ventral tegmental area inhibitory synapses following acute stress.

Stressful experiences potently activate kappa opioid receptors (κORs). κORs in the ventral tegmental area regulate multiple aspects of dopaminergic and non-dopaminergic cell function. Here we show that at GABAergic synapses on rat VTA dopamine neurons, a single exposure to a brief cold-water swim stress induces prolonged activation of κORs. This is mediated by activation of the receptor during the stressor followed by a persistent, ligand-independent constitutive activation of the κOR itself. This lasting change in function is not seen at κORs at neighboring excitatory synapses, suggesting distinct time courses and mechanisms of regulation of different subsets of κORs. We also provide evidence that constitutive activity of κORs governs the prolonged reinstatement to cocaine-seeking observed after cold water swim stress. Together, our studies indicate that stress-induced constitutive activation is a novel mechanism of κOR regulation that plays a critical role in reinstatement of drug seeking.

Temporal Specificity of Reward Prediction Errors Signaled by Putative Dopamine Neurons in Rat VTA Depends on Ventral Striatum

Dopamine neurons signal reward prediction errors. This requires accurate reward predictions. It has been suggested that the ventral striatum provides these predictions. Here we tested this hypothesis by recording from putative dopamine neurons in the VTA of rats performing a task in which prediction errors were induced by shifting reward timing or number. In controls, the neurons exhibited error signals in response to both manipulations. However, dopamine neurons in rats with ipsilateral ventral striatal lesions exhibited errors only to changes in number and failed to respond to changes in timing of reward. These results, supported by computational modeling, indicate that predictions about the temporal specificity and the number of expected reward are dissociable and that dopaminergic prediction-error signals rely on the ventral striatum for the former but not the latter.

Changed state – changed brain: shift of the dominant frequency of theta oscillations in the rat VTA during stereotypic locomotion

Changed state – changed brain: shift of the dominant frequency of theta oscillations in the rat VTA during stereotypic locomotion

PPARα regulates cholinergic-driven activity of midbrain dopamine neurons via a novel mechanism involving α7 nicotinic acetylcholine receptors.

Ventral tegmental area dopamine neurons control reward-driven learning, and their dysregulation can lead to psychiatric disorders. Tonic and phasic activity of these dopaminergic neurons depends on cholinergic tone and activation of nicotinic acetylcholine receptors (nAChRs), particularly those containing the β2 subunit (β2*-nAChRs). Nuclear peroxisome proliferator-activated receptors type-α (PPARα) tonically regulate β2*-nAChRs and thereby control dopamine neuron firing activity. However, it is unknown how and when PPARα endogenous ligands are synthesized by dopamine cells. Using ex vivo and in vivo electrophysiological techniques combined with biochemical and behavioral analysis, we show that activation of α7-nAChRs increases in the rat VTA both the tyrosine phosphorylation of the β2 subunit of nAChRs and the levels of two PPARα endogenous ligands in a Ca(2+)-dependent manner. Accordingly, in vivo production of endogenous PPARα ligands, triggered by α7-nAChR activation, blocks in rats nicotine-induced increased firing activity of dopamine neurons and displays antidepressant-like properties. These data demonstrate that endogenous PPARα ligands are effectors of α7-nAChRs and that their neuromodulatory properties depend on phosphorylation of β2*-nAChRs on VTA dopamine cells. This reveals an autoinhibitory mechanism aimed at reducing dopamine cell overexcitation engaged during hypercholinergic drive. Our results unveil important physiological functions of nAChR/PPARα signaling in dopamine neurons and how behavioral output can change after modifications of this signaling pathway. Overall, the present study suggests PPARα as new therapeutic targets for disorders associated with unbalanced dopamine-acetylcholine systems.

Induction of conditioned place preference and dopamine release by salsolinol in posterior VTA of rats: Involvement of μ-opioid receptors

Salsolinol (Sal), locally administered into the posterior VTA (pVTA) of rats, produces psychomotor responses and reinforcing effects, probably, through the activation of μ-opioid receptors (MORs). The neurochemical correlates of these phenomena are, however, practically unknown. In this paper, we explore the neurochemical events and the mechanisms involved in these behaviors. To do that, we test the ability of Sal, directly microinjected into the pVTA, to induce conditioned place preference (CPP) and to increase dopamine levels in the nucleus accumbens shell. Bilateral injections of 30 pmol of Sal induced a strong CPP (rats spent around 70% of the total test time), a result that could be explained by the fact that Sal microinjected into the pVTA increased DA levels in the ipsilateral accumbens up to 141% of baseline. The local pretreatment with β-FNA, an antagonist of MORs, prevented this increase, supporting our hypothesis on the involvement of MORs in the Sal-derived effects.

GABA and Glutamate Overflow in the VTA and Ventral Pallidum of Alcohol-Preferring AA and Alcohol-Avoiding ANA Rats after Ethanol

Earlier findings suggest that dopaminergic neurons are probably not critically involved in ethanol self-administration behavior and in the differential intake of ethanol by the alcohol-preferring AA (Alko Alcohol) and non-preferring ANA (Alko Non-Alcohol) rat lines selected for differential ethanol intake. The purpose of the present study was, therefore, to clarify the role of GABAergic and glutamatergic afferents and efferents with the mesolimbic dopamine system in the control of ethanol intake as well as in differential intake of ethanol by AA and ANA rats. The effects of an acute dose of ethanol (1 or 2 g/kg i.p.) on the levels of GABA and glutamate in the ventral pallidum and the ventral tegmental area of AA and ANA rats were monitored with in vivo microdialysis. The concentrations of GABA and glutamate in the dialysates were determined with a high performance liquid chromatography system using fluorescent detection. Ethanol significantly decreased the extracellular levels of GABA in the ventral pallidum but not in the ventral tegmental area. The ANA rats were more sensitive than the AA rats to the suppressive effect of ethanol on pallidal GABA levels. Ethanol did not have any effect on the concentrations of glutamate in either rat line. The suppressive effect of ethanol on the extracellular levels of GABA in the ventral pallidum suggests a role for pallidal GABAergic transmission in the control of ethanol consumption.

DHEA Lessens Depressive-Like Behavior via GABA-ergic Modulation of the Mesolimbic System

Alterations in the levels of dehydroepiandrosterone (DHEA) in the brain can allosterically modulate gamma-aminobutyric-acid-type-A (GABA(A)R), N-methyl-D-aspartate (NMDAR), and Sigma-1 (sigma 1R) receptors. In humans, DHEA has antidepressive effects; however, the mechanism is unknown. We examined whether alterations in DHEA also occur in an animal model of depression, the Flinders-sensitive-line (FSL) rats, with the intention of determining the brain site of DHEA action and its antidepressant mechanism. We discovered that DHEA levels were lower in some brain regions involved with depression of FSL rats compared to Sprague-Dawley (SD) controls. Moreover, DHEA (1 mg/kg IP for 14 days)-treated FSL rats were more mobile in the forced swim test than FSL controls. In the NAc and VTA, significant changes were observed in the levels of the delta-subunit of GABA(A), but not of sigma 1R mRNA, in FSL rats compared to SD rats. The delta-subunit controls the sensitivity of the GABA(A)R to the neurosteroid. Indeed, treatment (14 days) of FSL rats with the GABA(A) agonist muscimol (0.5 mg/kg), together with DHEA (a negative modulator of GABA(A)), reversed the effect of DHEA on immobility in the swim test. Perfusion of DHEA sulfate (DHEAS) (3 nM and 30 nM for 14 days) into the VTA and NAc of FSL rats improved their performance in the swim test for at least 3 weeks post-treatment. Our results imply that alterations in DHEA are involved in the pathophysiology of depression and that the antidepressant action of DHEA is mediated via GABA(A)Rs in the NAc and VTA.

Estrogen Dependent Response to Nicotine in Substantia Nigra and Ventral Tegmental Area of OVX female rats

The incidence of Parkinson's disease is higher in men than women and nicotine (Nic) reduces the risk. To study the interaction between Nic and estrogen (E), OVX rats were treated for 16 days with estradiol benzoate (EB) or vehicle and received Nic injections on days 13–16 (twice daily). Tyrosine hydroxylase (TH) and GTP cyclohydrolase (GTPCH) mRNA levels were determined by qRT‐PCR in VTA and SN. The VTA of OVX rats was especially susceptible to the lowest dose of Nic. In contrast, with EB treatment, only the highest dose of Nic was effective. In SN, both doses of Nic did not change TH mRNA levels in OVX rats with or without EB injections, but EB treatment increased sensitivity of GTPCH gene to Nic. To determine whether E can modulate Nic triggered transcriptional regulation of TH and GTPCH genes, dopaminergic MN9D cells were co‐transfected with pGTPCH/Luc and expression vector for ERa or ERβ. The results revealed that Nic and E elevated GTPCH promoter activity with both ERa and ERβ. The response was reduced with Nic and E combined. The findings provide insight for specificity of Nic regulation of catecholamine and tetrahydrobiopterin biosynthesis in DA neurons in gender specific fashion.

The effects of ANJUNNING on tyrosine hydroxylase (TH) and glial fibrillary acidic protein (GFAP) in VTA of morphine dependent SD rats

目的 观察安君宁对吗啡依赖大鼠腹侧被盖区(VTA)内酪胺酸羟化酶(TH)和胶质原纤维酸性蛋白(GFAP)表达的影响.方法选择体质量在180～220g雄性SD大鼠30只为研究对象,动物随机分为5组(每组动物6只),即单用生理盐水正常对照组(Normal组)、其余四组大鼠则先制成吗啡成瘾模型:以5mg/kg/次开始,每天增加5mg,一直增加到第10天50mg·kg-1·次-1,每天腹腔注射吗啡2次.第11天开始自然戒断,四组成瘾大鼠随机分成吗啡成瘾后戒断并安君宁治疗12d组(P12E)、吗啡成瘾后戒断并淀粉治疗12d组(P12EC),吗啡成瘾后戒断并安君宁治疗30d组(P30E)、吗啡成瘾后戒断并淀粉治疗30d组(P30EC).安君宁和淀粉均为每天灌胃2次,安君宁剂量为3 g·kg-1·次-1,对照组喂等量淀粉.用ABC法测VTA的TH与GFAP的免疫组织化学反应;测定阳性神经元的平均光密度(OD)值.结果5组大鼠(Normal、P12EC、P12E、P30EC、P30E组)VTA中TH免疫反应的强度分别为(0.1888±0.045)、(0.4471±0.063)、(0.1834±0.039)、(0.3224±0.044)、(0.1788±0.042),VTA中GFAP免疫反应的强度分别为(0.1538±0.045)、(0.2768±0.056)、(0.1808±0.036)、(0.2512±0.051)、(0.1427±0.034).吗啡成瘾大鼠VTA中TH和GFAP免疫反应的强度持续高于淀粉组(P＜0.05),安君宁治疗12d或30d能显著性降低VTA中TH、GFAP免疫反应强度(P＜0.05),逐渐接近淀粉对照组.结论吗啡成瘾能导致大鼠VTA内的一些可塑性的损伤,而安君宁能促进这些损伤的修复,提示其可用于阿片类成瘾的治疗。

Increased mRNA levels of tyrosine hydroxylase and dopamine transporter in the VTA of male rats after chronic food restriction

Dieting as a strategy to reduce body weight often fails as it causes food cravings leading to bingeing and weight regain. Evidence from several lines of research suggests the presence of shared elements for neural regulation of food and drug craving. We quantified the expression of eight genes involved in dopamine signalling in brain regions related to the mesolimbic and nigrostriatal dopamine system in male rats subjected to chronic food restriction using quantitative real-time polymerase chain reaction. Food restriction strongly increased mRNA levels of tyrosine hydroxylase and the dopamine transporter in the ventral tegmental area. Quantitative autoradiography indicated that the dopamine transporter was also upregulated at the protein level in the shell of the nucleus accumbens. However, these effects were not observed after acute food deprivation. We suggest that the results reflect a sensitization of the mesolimbic dopamine pathway characterized by increased clearance of extracellular dopamine in the nucleus accumbens shell. Such sensitization of the mesolimbic dopamine system may be one of the underlying causes for the food cravings that interfere with dietary compliance.

Morphine withdrawal-induced abnormalities in the VTA: confocal laser scanning microscopy.

Morphine withdrawal is characterized by functional alterations at the level of the ventrotegmental area. We investigated the effects of chronic morphine administration and withdrawal on the morphological properties of immuno-labelled tyrosine hydroxylase-positive neurons of the rat ventrotegmental area with a confocal laser scanning microscope. Morphological evaluation revealed a reduction in the area and perimeter of tyrosine hydroxylase-positive somata in morphine-withdrawn rats. Conversely, the number of cells per field was found to have increased in the naloxone group. Collectively, the present results indicate that withdrawal from a chronic morphine treatment, and not chronic morphine per se, modifies cellular morphology of tyrosine hydroxylase-positive, presumably dopamine-containing, neurons of the rat VTA. This is consistent with the idea that withdrawal from morphine alters functioning of the mesolimbic dopamine system and provides a direct morphological correlate for the functional abnormalities typical of morphine withdrawal.

Δ9-Tetrahydrocannabinol excites rat VTA dopamine neurons through activation of cannabinoid CB1 but not opioid receptors

Behavioral, biochemical and recent electrophysiological data have increasingly implicated the involvement of dopamine in the central actions of cannabinoid compounds. However, the site and mechanism by which cannabinoids stimulate dopamine systems has been somewhat controversial. Central opioid systems have also been suggested to play a role in some cannabinoid-induced behaviors as evidenced by their attenuation in the presence of the opioid antagonist naloxone. However, recent studies using the cannabinoid receptor-selective antagonist SR141716A suggest that the central actions of psychoactive cannabinoids are mediated principally through activation of CB1 receptors. Using single cell electrophysiological recordings in the rat we assessed the effects of both SR141716A and naloxone on delta9-tetrahydrocannabinol (THC)-induced activation of ventral tegmental dopamine neurons. While dopamine cell firing was dose-dependently increased following cumulative dosing with delta9-THC it was partially or completely inhibited following pretreatment with 0.5 and 2 mg/kg SR141716A, respectively. However, 1 and 10 mg/kg naloxone failed to alter the response to delta9-THC. These data provide the first evidence that delta9-THC-induced changes in mesolimbic dopamine neuronal activity are mediated by the CB1 cannabinoid receptor, but a causal link for the involvement of opioid systems could not be established.

Investigation of behavioral and electrophysiological responses induced by selective stimulation of CCKB receptors by using a new highly potent CCK analog, BC 264

The new CCKB analog, Boc-Tyr (SO3H)-gNle-mGly-Trp-(NMe)-Nle-Asp-PheNH2 (BC 264) exhibited a high affinity (KI = 0.39 +/- 0.15 nM) and selectivity for central (B) versus peripheral (A) receptors (KI CCKA/KI CCKB = 910) in the rat. In agreement with these binding studies, BC 264 was at least 50 times more potent than CCK8 in stimulating the firing of rat CA hippocampal neurones. Furthermore stereotaxic injection of BC 264 or CCK8 in the VTA of rats resulted in potentiation of the dopamine-induced hypolocomotion. These two types of CCK8 responses have been previously shown in involve CCKB receptors. In contrast, after administration into the postero-median nucleus accumbens, the hypoexploration, the increase of emotionality of rats, or the potentiation of dopamine-induced hyperlocomotion were obtained after injection of CCK8 but not of BC 264, supporting the involvement of peripheral CCKA receptors in these CCK8 responses. Owing to its resistance to peptidases, BC 264 appears to be of great interest in the investigation of the still uncertain functional roles of CCK in the central nervous system.