Dopamine D2 Receptor Expression Research Articles

Garcinia cambogia extract alters anxiety, sociability, and dopamine turnover in male Swiss albino mice

Obesity is a global concern, closely allied with somatic and psychosomatic disorders. Herbal drugs are available in modern medicine to treat obesity. Garcinia camobogia being used by so many people trying to lose weight produces various systemic side effects. The study was conducted to assess its effect on anxiety, sociability, and dopamine turnover in male mice. Twenty-one male Swiss albino mice of either were divided into three groups with seven mice in each group. Control group was given distilled water (0.5 ml p.o.) and the other two groups received Garcinia cambogia extract at two different doses, a low and a higher dose (100 mg/kg and 500 mg/kg. p.o.) Each animal received a single oral dose daily, which was administered using an oral gavage for fourteen consecutive days. Effect of test drugs on anxiety was evaluated using open field test. Sociability and social novelty were evaluated using three chambers test. Results (mean ± SD) were analyzed using one-way ANOVA test followed by Tukey’s test. Garcinia cambogia extract significantly increased the time spent in the corners in the open field test, significantly reduced sociability and social novelty in the three-chamber test, significantly reduced dopamine turnover in the brain with a significant decrease in dopamine metabolite homovanillic acid (HVA) and increased D2 receptor expression in ventral tegmental area. Garcinia cambogia extract have significant anxiogenic effect along with reduced sociability and social novelty in male mice. Moreover, these effects could be related to the altered dopamine turnover and D2 receptor expression in mice brain.Article HighlightsChronic used of alcoholic extract of Garcinia campbogia lead to a significant increase in anxiety that was manifested by the reduced time in the center zone and increased immobility in the open field test.Garcinia camobogia chronic administration has a profound impact on sociability and social novelty with a significant decrease in both behavioral patterns compared to the control group.These effects could be attributed to the noticed change in the dopamine turnover in the brain with a significant decrease in dopamine metabolite (HVA) and an upward expression of D2 receptors in return.

The Antagonism of Corticotropin-Releasing Factor Receptor-1 in Brain Suppress Stress-Induced Propofol Self-Administration in Rats.

Propofol addiction has been detected in humans and rats, which may be facilitated by stress. Corticotropin-releasing factor acts through the corticotropin-releasing factor (CRF) receptor-1 (CRF1R) and CRF2 receptor-2 (CRF2R) and is a crucial candidate target for the interaction between stress and drug abuse, but its role on propofol addiction remains unknown. Tail clip stressful stimulation was performed in rats to test the stress on the establishment of the propofol self-administration behavioral model. Thereafter, the rats were pretreated before the testing session at the bilateral lateral ventricle with one of the doses of antalarmin (CRF1R antagonist, 100–500 ng/site), antisauvagine 30 (CRF2R antagonist, 100–500 ng/site), and RU486 (glucocorticoid receptor antagonist, 100–500 ng/site) or vehicle. The dopamine D1 receptor (D1R) in the nucleus accumbens (NAc) was detected to explore the underlying molecular mechanism. The sucrose self-administration establishment and maintenance, and locomotor activities were also examined to determine the specificity. We found that the establishment of propofol self-administration was promoted in the tail clip treated group (the stress group), which was inhibited by antalarmin at the dose of 100–500 ng/site but was not by antisauvagine 30 or RU486. Accordingly, the expression of D1R in the NAc was attenuated by antalarmin, dose-dependently. Moreover, pretreatments fail to change sucrose self-administration behavior or locomotor activities. This study supports the role of CRF1R in the brain in mediating the central reward processing through D1R in the NAc and provided a possibility that CRF1R antagonist may be a new therapeutic approach for the treatment of propofol addiction.

Effects of Chronic Social Defeat Stress on Behavior and Dopamine Receptors in Adolescent Mice With 6-Hydroxydopamine Lesions of the Medial Prefrontal Cortex.

Background: Social stress factors in schizophrenia have long-term effects, but will only induce symptoms in a portion of individuals, even if exposed to identical stress.Methods: In the current experiment, we examined mice with 6-hydroxydopamine (6-OHDA)-induced medial prefrontal cortical (mPFC) injury to select for members of a “stress-susceptible group,” and observed the changes in their behavior and the expression of D1 and D2 dopamine receptors in the amygdala and hippocampus.Results: We observed that after chronic social defeat stress, 72.6% of the 6-OHDA lesioned mice exhibited stress response to aggressors, compared to 52.3% of the blank control group. Both the 6-OHDA lesion + social defeat and social defeat groups exhibited anxiety and depression-like behavior. However, social cognitive impairment in the mice from the 6-OHDA lesion + social defeat group was more significant and the D1 expression levels in the amygdala were significantly decreased.Conclusion: These results suggest that the reason that adolescent mice with cortical injury were highly sensitive to defeat stress and had more prominent social cognitive impairment may be the decreased selectivity of D1 in the amygdala.

The impact of a high-fat diet on physical activity and dopamine neurochemistry in the striatum is sex and strain dependent in C57BL/6J and DBA/2J mice

ABSTRACT Background Obesity has been linked to behavioral and biochemical changes, such as reduced physical activity, dysregulated dopamine metabolism, and gene expression alterations in the brain. The impact of a continuous high-fat diet and resulting state of obesity may vary depending on sex and genetics. Objective The aim of this study was to investigate the impact of a high-fat diet on physical activity, gene expression in the striatum, and dopamine neurochemistry using male and female mice from different strains as a model to examine sex and strain influences on dopamine-mediated behavior and neurobiology. Methods Male and female mice from the C57BL/6J (B6J) and DBA/2J (D2J) strains were randomly assigned a control low-fat diet with 10% kcal fat or a high-fat diet with 60% kcal fat for 16 weeks. We assessed ambulation and habituation using the open field test; dopamine release and reuptake using ex-vivo fast scan cyclic voltammetry; and striatal mRNA expression of dopamine receptor D2, alpha synuclein, and tyrosine hydroxylase. Results Mice fed a high-fat diet exhibited reduced motor activity, but only obese B6J male mice displayed reduced habituation. Dopamine clearance in the dorsal striatum was reduced only in obese D2J mice, while dopamine clearance in the nucleus accumbens core was reduced only in male obese D2J mice. Striatal dopamine receptor D2 gene expression was upregulated exclusively in obese male B6J mice. Conclusion Our study provides evidence for important sex and strain influences on the impact of a high-fat diet and obesity-induced behavior alterations and neurobiology dysregulation in the striatum.

Reduced expression of dopamine D2 receptors on astrocytes in R6/1 HD mice and HD post-mortem tissue

Dysfunction of the central dopaminergic system is thought to contribute to some of the clinical features of Huntington’s disease (HD), and dopamine (DA) receptor antagonists are commonly used to good effect in its treatment. It is well established that there is an early significant reduction in neuronal D2 receptors in HD, considered to be a compensatory response to increased dopaminergic activity. However, no studies have examined the expression of D2 receptors on astrocytes which is important given that these cells have been shown to play a role in the pathogenesis of HD, as well as express dopamine receptors and modulate DA homeostasis in the normal brain. We therefore sought to investigate the expression of D2 receptors on astrocytes in HD, and found them to be reduced in both the R6/1 HD mouse model, and in human post-mortem brain in comparison to controls, suggesting that astrocytes may be important in DA-dependent aspects of HD. Further studies are needed to determine the functional significance of this finding.

Binge-like Alcohol Exposure in Adolescence: Behavioural, Neuroendocrine and Molecular Evidence of Abnormal Neuroplasticity… and Return.

Binge alcohol consumption among adolescents affects the developing neural networks underpinning reward and stress processing in the nucleus accumbens (NAc). This study explores in rats the long-lasting effects of early intermittent exposure to intoxicating alcohol levels at adolescence, on: (1) the response to natural positive stimuli and inescapable stress; (2) stress-axis functionality; and (3) dopaminergic and glutamatergic neuroadaptation in the NAc. We also assess the potential effects of the non-intoxicating phytocannabinoid cannabidiol, to counteract (or reverse) the development of detrimental consequences of binge-like alcohol exposure. Our results show that adolescent binge-like alcohol exposure alters the sensitivity to positive stimuli, exerts social and novelty-triggered anxiety-like behaviour, and passive stress-coping during early and prolonged withdrawal. In addition, serum corticosterone and hypothalamic and NAc corticotropin-releasing hormone levels progressively increase during withdrawal. Besides, NAc tyrosine hydroxylase levels increase at late withdrawal, while the expression of dopamine transporter, D1 and D2 receptors is dynamically altered during binge and withdrawal. Furthermore, the expression of markers of excitatory postsynaptic signaling—PSD95; Homer-1 and -2 and the activity-regulated spine-morphing proteins Arc, LIM Kinase 1 and FOXP1—increase at late withdrawal. Notably, subchronic cannabidiol, during withdrawal, attenuates social- and novelty-induced aversion and passive stress-coping and rectifies the hyper-responsive stress axis and NAc dopamine and glutamate-related neuroplasticity. Overall, the exposure to binge-like alcohol levels in adolescent rats makes the NAc, during withdrawal, a locus minoris resistentiae as a result of perturbations in neuroplasticity and in stress-axis homeostasis. Cannabidiol holds a promising potential for increasing behavioural, neuroendocrine and molecular resilience against binge-like alcohol harmful effects.

Abstract MP61: Sex Difference In The Response Of Human Renal Proximal Tubule Cells To A Nephrotoxic Agent.

Our previous work indicated that the renal dopamine D2 receptor (D2R) has a significant role in regulating renal inflammation and injury, as well as in blood pressure control. In mice, D2R has protective effects in the kidney by limiting the inflammatory and fibrotic reaction; impaired D2R function results in renal inflammation and damage. Some common single nucleotide polymorphisms (SNPs; rs 6276 and 6277) in the human DRD2 gene are associated with decreased D 2 R expression and function and high blood pressure. To determine the effects of the presence of SNPs in the response to the nephrotoxic aristolochic acid (AA, 5μg/ml, 24 h), we studied immortalized human renal proximal tubule cells isolated from normal tissue of nephrectomies and genotyped for DRD2 SNPs and DRD2 wild-type (WT). We also determined whether this response is sex dependent. D2R protein was higher in male than in female WT (135±5 vs 100±4%; n=3/group; P<0.04) and lower in males with SNPs (43±2%, P<0.05) and females with SNPs (23±2%,P<0.05), compared with their respective WT counterparts. In both male groups (WT and SNPs), AA increased D2R protein by 80-100% but had no effect in WT females and increased ~50% in females with SNPs. The TNFα mRNA was higher in males with WT and SNPs which was increased by AA 9-10-fold in WT males and females but only 2-3-fold in those with SNPs. The TGFβ mRNA was similar in WT males and females and increased to the same extent in both groups with SNPs and was not affected by AA in all groups. Col1a1 mRNA was higher (30%) in WT males and females than those with SNPs; AA decreased Col1a1 mRNA in all groups. FN1 mRNA was higher (30-40%) in males and females with SNPs than WT; AA increased FN1 mRNA only in males and females with SNPs. The mRNA expression of the cell proliferation marker Ki-67 was higher in WT females than WT males (1.5-2-fold) and higher with SNPs than WT in both groups; AA increased Ki-67 mRNA in both groups and to a greater extent in males than in females. Taken together our data indicate that the presence of DRD2 SNPs affects the baseline expression of inflammatory and fibrotic factors and the response to AA is dependent on both sex and the presence of DRD2 SNPs. These data may have potential clinical translation since rs6276/6277 is commonly expressed (42%/23%) in the human population.

Nardosinone Alleviates Parkinson's Disease Symptoms in Mice by Regulating Dopamine D2 Receptor.

Nardostachyos Radix et Rhizoma (nardostachys) is the root and rhizome of Nardostachys jatamansi DC. Recent studies have shown that nardostachys may exert an anti-PD effect. In this study, the UHPLC-LTQ-Orbitrap-MS method was used to analyze the brain components of nardostachys in rats. Based on the results of UHPLC-LTQ-Orbitrap-MS analysis, nardosinone was identified to be the most effective anti-PD compound in nardostachys. To further verify this inference, a mouse PD model was established and the effect of nardosinone on PD mice was determined using classic behavioral tests. The results showed that nardosinone was indeed effective for relieving PD symptoms in mice. Moreover, network pharmacology analysis was used to elucidate the mechanism underlying the anti-PD effect of nardosinone. Dopamine receptor D2 (DRD2) was identified as the key target of nardosinone-PD interaction network, which was further verified by molecular docking and Western blotting. The results demonstrated that nardosinone and DRD2 could interact with each other. Furthermore, the expression level of DRD2 was decreased in the brain tissue of PD mice, and nardosinone could restore its expression to a certain extent. In conclusion, our findings suggest that nardosinone may reduce the motor and cognitive symptoms in the animal PD model by regulating DRD2 expression.

Discovery of tetrahydropalmatine and protopine regulate the expression of dopamine receptor D2 to alleviate migraine from Yuanhu Zhitong formula

BackgroundMigraine is the third most common disease worldwide, leading to severely decreased quality of life for the patients. In spite of great efforts endeavored in pharmacological and nonpharmacological therapeutic strategies for treating migraine, the outcome is rather disappointing in terms of efficacy. Compelling evidence shows that the expression level of dopamine receptor D2 (DRD2) plays an essential role in progression of migraine. PurposeTo explore potential therapeutical possibilities, the attention was paid to Yuanhu Zhitong formula (YHZTF), which is a classical traditional Chinese medicine prescription frequently applied to relieve pain. The aim of this study was to identify the promising compounds derived from YHZTF with anti-migraine effects and investigate the underlying molecular mechanism. MethodsThe high-resolution mass spectrometry and molecular networking were performed for comprehensive chemical profiling of YHZTF. Network pharmacology was used to generate herbal-component-target-pathway network. Based on the pathway enrichment analysis, the active substances of anti-migraine and the potential molecular mechanism were further determined by performing animal experiments combined with molecular docking strategy. ResultsIn total, 31 substances were identified in YHZTF, including alkaloids such as tetrahydropalmatine and protopine. The analysis of herbal-component-target-pathway network suggests that the alkaloid substances (e.g. tetrahydropalmatine and protopine) from YHZTF target dopamine receptors, thus can be linked to neuroactive ligand-receptor interaction pathways. In a nitroglycerin-induced migraine animal model, pretreatment with tetrahydropalmatine or protopine substantially lessened the aberrant migraine-like symptoms. The results of molecular docking analysis showed that tetrahydropalmatine and protopine had strong affinities to dopamine receptor D2 (DRD2). Using RT-qPCR, the investigators found that DRD2 was significantly down-regulated at the mRNA level in brain tissues of tetrahydropalmatine and protopine-treated group compared to the control group. ConclusionCollectively, the results provide reliable evidence showing that the active substances tetrahydropalmatine and protopine from YHZTF lessens migraine symptoms in an in vivo mouse model suggestively via regulating expression of DRD2. These findings shed light on novel therapeutic strategies and targets to treat migraine using natural products.

Repeated cocaine administration upregulates CB2 receptor expression in striatal medium-spiny neurons that express dopamine D1 receptors in mice.

Cannabinoid CB2 receptors (CB2R) are importantly involved in drug reward and addiction. However, the cellular mechanisms underlying CB2R action remain unclear. We have previously reported that cocaine self-administration upregulates CB2R expression in midbrain dopamine (DA) neurons. In the present study, we investigated whether cocaine or heroin also alters CB2R expression in striatal medium-spiny neuronsthat express dopamineD1 or D2 receptors (D1-MSNs, D2-MSNs) and microglia. Due to the concern of CB2R antibody specificity, we developed three mouse CB2-specific probes to detect CB2R mRNA using quantitative RT-PCR and RNAscope in situ hybridization (ISH) assays. We found that a single injection of cocaine failed to alter, while repeated cocaine injections or self-administration dose-dependently upregulated CB2R gene expression in both brain (cortex and striatum) and periphery (spleen). In contrast, repeated administration ofheroin produced a dose-dependent reduction in striatal CB2 mRNA expression. RNAscope ISH assays detected CB2R mRNA in striatal D1- and D2-MSNs, not in microglia. We then used transgenic CX3CR1eGFP/+ microglia reporter mice and D1- or D2-Cre-RiboTag mice to purify striatal microglia or ribosome-associated mRNAs from CX3CR1eGFP/+,D1-MSNs, or D2-MSNs, respectively. We found that CB2R upregulation occurred mainly in D1-MSNs, not in D2-MSNs or microglia, in the nucleus accumbens rather than the dorsal striatum. These findings indicate that repeated cocaine exposure may upregulate CB2R expression in both brain and spleen, with regional and cell type-specific profiles. In the striatum, CB2R upregulation occurs mainly in D1-MSNs in the nucleus accumbens. Given the important role of D1-MSNs in brain reward function, the present findings provide new insight into mechanisms by which brain CB2Rs modulate cocaine action.

Motivational learning biases are differentially modulated by genetic determinants of striatal and prefrontal dopamine function

Dopaminergic neurotransmission plays a pivotal role in appetitively motivated behavior in mammals, including humans. Notably, action and valence are not independent in motivated tasks, and it is particularly difficult for humans to learn the inhibition of an action to obtain a reward. We have previously observed that the carriers of the DRD2/ANKK1 TaqIA A1 allele, that has been associated with reduced striatal dopamine D2 receptor expression, showed a diminished learning performance when required to learn response inhibition to obtain rewards, a finding that was replicated in two independent cohorts. With our present study, we followed two aims: first, we aimed to replicate our finding on the DRD2/ANKK1 TaqIA polymorphism in a third independent cohort (N = 99) and to investigate the nature of the genetic effects more closely using trial-by-trial behavioral analysis and computational modeling in the combined dataset (N = 281). Second, we aimed to assess a potentially modulatory role of prefrontal dopamine availability, using the widely studied COMT Val108/158Met polymorphism as a proxy. We first report a replication of the above mentioned finding. Interestingly, after combining all three cohorts, exploratory analyses regarding the COMT Val108/158Met polymorphism suggest that homozygotes for the Met allele, which has been linked to higher prefrontal dopaminergic tone, show a lower learning bias. Our results corroborate the importance of genetic variability of the dopaminergic system in individual learning differences of action–valence interaction and, furthermore, suggest that motivational learning biases are differentially modulated by genetic determinants of striatal and prefrontal dopamine function.

Bacteroides uniformis CECT 7771 Modulates the Brain Reward Response to Reduce Binge Eating and Anxiety-Like Behavior in Rat

Food addiction (FA) is characterized by behavioral and neurochemical changes linked to loss of food intake control. Gut microbiota may influence appetite and food intake via endocrine and neural routes. The gut microbiota is known to impact homeostatic energy mechanisms, but its role in regulating the reward system is less certain. We show that the administration of Bacteroides uniformis CECT 7771 (B. uniformis) in a rat FA model impacts on the brain reward response, ameliorating binge eating and decreasing anxiety-like behavior. These effects are mediated, at least in part, by changes in the levels of dopamine, serotonin, and noradrenaline in the nucleus accumbens and in the expression of dopamine D1 and D2 receptors in the prefrontal cortex and intestine. B. uniformis reverses the fasting-induced microbiota changes and increases the abundance of species linked to healthy metabolotypes. Our data indicate that microbiota-based interventions might help to control compulsive overeating by modulating the reward response.

Overexpression of dopamine receptor D2 promotes colorectal cancer progression by activating the β-catenin/ZEB1 axis.

Colorectal cancer (CRC) is a recurring cancer that is often resistant to conventional therapies and therefore requires the development of molecular‐based therapeutic approaches. Dopamine receptor D2 (DRD2) is associated with the growth of many types of tumors, but its oncogenic role in CRC is unclear. Here, we observed that elevated DRD2 expression was associated with a poor survival rate among patients with CRC. Depletion of DRD2 suppressed CRC cell growth and motility by downregulating β‐catenin/ZEB signaling in vitro and in vivo, whereas overexpression of DRD2 promoted CRC cell progression. Inhibition of DRD2 by the antagonist pimozide inhibited tumor growth and lymph node metastasis in vivo and enhanced the cytotoxic effects of conventional agents in vitro. Taken together, our findings indicate that targeting the DRD2/β‐catenin/ZEB1 signaling axis is a potentially promising therapeutic strategy for patients with CRC.

171-OR: Dopaminergic Signaling in the Ventral Tegmental Area of the Brain Mediates the Impaired Sympathoadrenal Response to Hypoglycemia

The mechanism by which recurrent hypoglycemia (RH) impairs the sympathoadrenal response to hypoglycemia remains unknown. To explore altered brain dopaminergic signaling as a mechanism, 10 weeks old rats were randomized to 3 days: 1) recurrent saline (RS), 2) insulin (2-1.2 U/kg, sc) induced RH (25-50 mg/dl), or 3) RH + antecedent dopamine receptor antagonist metoclopramide (MET, 3 mg/kg, ip). qPCR of brain biopsies demonstrated RH downregulated dopaminergic signaling, noted by decreased expression of dopamine D2 receptor (Drd2, 52%*) and increased dopamine transporter (DAT, ~1.9-fold*) in the ventral tegmental area (VTA); an effect prevented by MET (Figure 1A). To test whether recurrent dopamine activation in the VTA is sufficient to impair the sympathoadrenal response to hypoglycemia, a second rat cohort was randomized to 3-day recurrent VTA infusion of: 1) aCSF (control), or 2) Drd2 agonist bromocriptine (Bromo; 5 µg/d). During hyperinsulinemic (20 mU/kg/min) hypoglycemic (∼45 mg/dl) clamps, recurrent Bromo resulted in an increased glucose infusion rate (1.7-fold*) and blunted epinephrine response (~50%*, Figure 1B). These results demonstrate that blunted dopaminergic signaling in the VTA induced by RH contributes to the impaired sympathoadrenal response, which may be associated with recurrent brain dopaminergic activation. *p<0.05.View largeDownload slideView largeDownload slide DisclosureR. Agrawal: None. S. Sharma: None. S. Fisher: None. FundingNational Institutes of Health (R01NS070235-01A1, R01DK118082)

Functional MHCI deficiency induces ADHD-like symptoms with increased dopamine D1 receptor expression

Inappropriate synaptic development has been proposed as a potential mechanism of neurodevelopmental disorders, including attention-deficit hyperactivity disorder (ADHD). Major histocompatibility complex class I (MHCI), an immunity-associated molecule expressed by neurons in the brain, regulates synaptic development; however, the involvement of MHCI in these disorders remains elusive. We evaluated whether functional MHCI deficiency induced by β2m−/−Tap1−/− double-knockout in mice leads to abnormalities akin to those seen in neurodevelopmental disorders. We found that functional MHCI deficiency induced locomotor hyperactivity, motor impulsivity, and attention deficits, three major symptoms of ADHD. In contrast, these mice showed normal spatial learning, behavioral flexibility, social behavior, and sensorimotor integration. In the analysis of the dopamine system, upregulation of dopamine D1 receptor (D1R) expression in the nucleus accumbens and a greater locomotor response to D1R agonist SKF 81297 were found in the functional MHCI-deficient mice. Low-dose methylphenidate, used for the treatment of ADHD patients, alleviated the three behavioral symptoms and suppressed c-Fos expression in the D1R-expressing medium spiny neurons of the mice. These findings reveal an unexpected role of MHCI in three major symptoms of ADHD and may provide a novel landmark in the pathogenesis of ADHD

The Effects of Dopamine D2 Receptor Specific Deletion in the Renal Proximal Tubule of Mice are Sex Dependent

We have reported that the dopamine D2 receptor (D2R) has a major effect in preventing inflammation and injury in the mouse kidney and in human renal proximal tubule cells (hRPTCs). Lack of or decreased expression of D2R in the mouse kidney or in hRPTCs carrying genetic variants of the receptor that decrease its expression results in an increase in inflammatory factors and injury markers. Because dopamine is synthesized in the RPT and regulated by D2R, we developed a model to determine the effects of D2R in the RPT by generating Drd2fl/fl, PSGLT2::Cre+ mice (D2RPT-/-) that lack D2R only in the RPT and Drd2 fl/fl, PSGLT2::Cre- (D2RPT+/+) mice that do not have the deletion. We hypothesized that the D2R plays a role in the protection of females from renal injury, relative to males. We studied male and female mice on normal salt (NS; 0.4% NaCl) and high salt (HS; 4% NaCl) diets. On NS diet, male D2RPT-/- had higher D2R protein expression in the renal cortex than male D2RPT+/+ (0.85 ± 0.06 vs 0.49 ± 0.11, D2R/GAPDH; n=5; P<0.05) and female D2RPT-/- had higher D2R expression than female D2RPT+/+ (2.95 ± 0.69 vs 1.72 ± 0.35, D2R/GAPDH; n=5; P<0.05). HS increased D2R expression in both male groups (D2RPT+/+ 0.49 ± 0.11 vs 1.04 ± 0.08; n=3-5; P<0.05; D2RPT-/- 0.85 ± 0.06 vs 1.28 ± 0.19, D2R/GAPDH; n=3-5, P<0.05) but decreased its expression in both female groups (D2RPT+/+ 1.72 ± 0.35 vs 0.91 ± 0.05; n=4-5; P<0.05; n=5; D2RPT-/- 2.95 ± 0.69 vs 0.95 ± 0.04, D2R/GAPDH; n=4-5, P<0.05). The transcription factor Nurr1 is involved in the regulation of D2R expression. Nurr1 expression on NS was higher in females of both groups (D2RPT+/+ 1.57± 0.29; D2RPT-/-1.96 ± 0.20, Nurr1/GAPDH; n=4-5; P<0.05) than in males (D2RPT+/+ 0.24 ± 0.05; D2RPT-/-0.38 ± 0.17, Nurr1/GAPDH). HS increased Nurr1 expression in males (D2RPT+/+0.24± 0.05 vs 1.36 ± 0.22; D2RPT-/-0.38± 0.17 vs 0.89 ± 0.19, Nurr1/GAPDH; n=4-5; P<0.05), tended to decrease it in female D2RPT+/+ (1.57± 0.29 vs 1.26 ± 0.19, Nurr1/GAPDH) but decreased significantly in D2RPT-/- (1.96 ± 0.20 vs 0.76± 0.11 ratio Nurr1/GAPDH; n=4-5; P<0.05). The mRNA expression of the injury marker Kim-1 on NS was lower in female than in male mice and was increased in both males and females with D2RPT-/- (1.69 ± 0.09 and 0.36 ± 0.02 fold-change) compared with D2R PT+/+ (1.02 ± 0.03 and 0.15 ± 0.01 fold-change). On HS, there was a decrease in females with D2RPT-/- (0.36 ± 0.02 vs 0.13 ± 0.01 fold-change; n=4-5; p<0.05) and an increase in males with D2RPT-/- (1.69 ± 0.09 vs 3.34 ± 0.56 fold-change; n=4-5; p<0.05). These results show that renal D2R expression is higher in female mice then males and HS diet resulting in increased inflammation and injury elicits an increase in the expression of the receptor in males but a decrease in females. Nurr1 expression is related to D2R expression on NS but has a different response to HS in males and females. The expression of Kim-1 was lower in females than in males regardless of diet and genotype suggesting that increased basal levels of the D2R results in a protective effect. Our findings indicate that the D2R is part of the protective response to renal injury in females.

Bi‐directional cAMP signaling crosstalk between dopamine D2 receptors and the constitutively active orphan receptor GPR52

G protein-coupled receptors (GPCRs) are valuable drug targets with ~35% of FDA approved medicines targeting these receptors. However, nearly 120 GPCRs remain orphan receptors, whose endogenous ligands, G protein signaling, and therapeutic potential are unknown. Dopamine D2 receptor (D2R) antagonists are effective antipsychotics while D2R agonists correct motor dysfunction in Parkinson's disease. The novel human orphan receptor GPR52 was recently identified and determined to activate cAMP signaling cascades. Notably, GPR52 is primarily co-expressed in the striatum of the brain with dopamine D2 receptors. Here we elucidate G protein signaling mechanisms responsible for both constitutive and agonist-induced GPR52 cAMP signaling and examine signaling crosstalk between GPR52 and the D2R. Expression of human GPR52 in wildtype HEK293 cells profoundly elevated basal cAMP levels by over 100 fold (Glosensor assay), indicating high constitutive receptor activity. CRISPR/Cas9 stable knockout of Gs/olf G proteins in HEK293 cells eliminated the GPR52 constitutive activity. Subsequent addback of Gs to Gs/olf knockout cells rescued GPR52 constitutive activity to near wildtype levels of basal cAMP, while addback of Golf did not significantly elevate the constitutive activity. However, when treated with novel GPR52 agonist PW0787, both Gs and Golf showed strong agonist-induced responses with unchanged potency. These findings indicate high constitutive activity of GPR52 is mediated via Gs signaling, while agonist-induced GPR52 signaling occurs via either Gs or Golf. We hypothesized the high GPR52 constitutive signaling may set the basal tone of cAMP in cells to afford more robust effects from adenylyl cyclase inhibition by Gi/o-coupled receptors, such as the D2R. Expression of D2R alone in HEK293 cells produced low basal cAMP levels (~4000 light counts/sec, Glosensor assay), and treatments with agonist quinpirole and antagonist haloperidol both yielded minimal changes to cAMP levels (~1000-2000 light counts/sec). Notably, co-expression of GPR52 and D2R substantially increased basal cAMP levels (~500,000 light counts/sec). This elevated basal cAMP also allowed for larger windows of agonism and inverse agonism by D2R ligands quinpirole (decrease of ~500,000 light counts/sec) and haloperidol (increase of ~150,000 light counts/sec). When the cells were treated concurrently with the GPR52 agonist PW0787 to further elevate basal cAMP, the efficacies of quinpirole (decrease of ~1,500,000 light counts/sec) and haloperidol (increase of ~500,000 light counts/sec) grew even more significantly. These studies indicate that striatal orphan receptor GPR52 may set the tone of basal cAMP levels through constitutive activity to allow more dynamic changes in cAMP signaling by the D2R. These findings also suggest potential for GPR52 as a drug target by modulating D2R cAMP signaling in the striatum, with therapeutic possibilities for psychosis, Parkinson's disease, and substance use disorders.

Adult rats from undernourished dams show sex-dependent impaired expression in taste papillae and hypothalamus of genes responsible for sweet and fat detection and signalling

ABSTRACT Aim Individuals undernourished in utero or during early life are at high risk of developing obesity and metabolic disorders and show an increased preference for consuming sugary and fatty food. This study aimed at determining whether impaired taste detection and signalling in the lingual epithelium and the brain might contribute to this altered pattern of food intake. Methods The preference for feeding fat and sweet food and the expression in circumvallate papillae and hypothalamus of genes coding for sweet and fat receptors and transducing pathways were evaluated in adult rats born to control or calorie-restricted dams. Expression in the hypothalamus and the brain's reward system of genes involved in the homeostatic and hedonic control of food intake was also determined. Results Male and female undernourished animals exhibited increased expression in taste papillae and hypothalamus of T1R1, T1R2, CD36, gustducin, TRMP5 and PLC-β2 genes, all of which modulate sweet and fat detection and intracellular signalling. However, the severity of the effect was greater in females than in males. Moreover, male, but not female, undernourished rats consumed more standard and sweetened food than their control counterparts and presented increased hypothalamic AgRP and NPY mRNAs levels together with enhanced dopamine transporter and dopamine receptor D2 expression in the ventral tegmental area. Conclusions Maternal undernutrition induces sex-specific changes in food preferences and gene expression in taste papillae, hypothalamus and brain reward regions. The gene expression alterations in the male offspring are in line with their preference for consuming sugary and fatty food.

Neonatal programming with sex hormones: Effect on expression of dopamine D1 receptor and neurotransmitters release in nucleus accumbens in adult male and female rats

Steroid sex hormones produce physiological effects in reproductive and non-reproductive tissues, such as the brain. In the brain, sex hormones receptors are expressed in cortical, limbic and midbrain areas modulating memory, arousal, fear and motivation between other behaviors. One neurotransmitters system regulated by sex hormones is dopamine (DA), where during adulthood, sex hormones promote neurophysiological and behavioral effects on DA systems such as tuberoinfundibular (prolactin secretion), nigrostriatal (motor circuit regulation) and mesocorticolimbic (driving of motivated behavior). However, the long-term effects induced by neonatal exposure to sex hormones on DA release induced by D1 receptor activation and its expression in nucleus accumbens (NAcc) have not been fully studied. To answer this question, neurochemical, cellular and molecular techniques were used. The data show sex differences in NAcc DA extracellular levels induced by D1 receptor activation and protein content of this receptor in male and female control rats. In addition, neonatal programming with a single dose of TP increases the NAcc protein content of D1 receptors of adult male and female rats. Our results show new evidence related with sex differences that could explain the dependence to drug of abuse in males and females, which may be associated with increased reinforcing effects of drugs of abuse.

Nucleus accumbens neurons expressing dopamine D1 receptors modulate states of consciousness in sevoflurane anesthesia

Although general anesthesia (GA) enables patients to undergo surgery without consciousness, the precise neural mechanisms underlying this phenomenon have yet to be identified. In addition to many studies over the past two decades implicating the thalamus, cortex, brainstem, and conventional sleep-wake circuits in GA-induced loss of consciousness (LOC), some recent studies have begun to highlight the importance of other brain areas as well. Here, we found that population activities of neurons expressing dopamine D1 receptor (D1R) in the nucleus accumbens (NAc), a critical interface between the basal ganglia and limbic system, began to decrease before sevoflurane-induced LOC and gradually returned after recovery of consciousness (ROC). Chemogenetic activation of NAcD1R neurons delayed induction of and accelerated emergence from sevoflurane GA, whereas chemogenetic inhibition of NAcD1R neurons exerted opposite effects. Moreover, transient activation of NAcD1R neurons induced significant cortical activation and behavioral emergence during continuous steady-state GA with sevoflurane or deep anesthesia state with constant and stable burst-suppression oscillations. Taken together, our findings uncover that NAcD1R neurons modulated states of consciousness associated with sevoflurane GA and may represent an area for targeting GA-induced changes in consciousness and ameliorating related adverse effects.