Opioid Receptor Gene Expression Research Articles

Opioid receptor and dopaminergic gene expression increase in the brains of dominant medaka Oryzias latipes males after repeated fights.

The central opioid system and dopaminergic activity in mammals play key roles in mediating social reward, impulsivity, cognition, decision making, and motivation for learning and social interactions. Repeated positive fighting experiences enhance the gene expression levels of μ-type opioid receptor (Mor), tyrosine hydroxylase (Th), an enzyme involved in dopamine synthesis, and dopamine receptor type 2 (D2r) in the reward-related brain regions of aggressive mice. However, it remains unclear whether the opioid system and dopaminergic activity are associated with repeated winning in fish. In this study, we investigated changes in the expression levels of Mor, Th1, and D2r in different regions of the brain of adult medaka Oryzias latipes males after intermittent and continuous fight for 3 days. When a pair of males was provided a fighting opportunity for 20 min per day, we noted that within the 3-day observation period, aggressive winning males showed significantly higher expression levels of Mor in telencephalon and diencephalon, Th1 in diencephalon, and D2r in telencephalon than subordinate losing males. However, no such differences in gene expression level were observed between winning and losing males in the 3-day continuous fight. Further, no differences were detected in the total number of aggressive actions among the winners from each fighting test. However, the total number of "chase" actions, with a stronger aggressiveness index, was higher for the repeated winning male in the three-time intermittent fight than for the winner in the 3-day continuous fight. These findings suggest that repeated intermittent winning experiences with strong aggressiveness could be perceived as a reward by O. latipes males.

Morphine Analgesia, Cannabinoid Receptor 2, and Opioid Growth Factor Receptor Cancer Tissue Expression Improve Survival after Pancreatic Cancer Surgery.

Pancreatic cancer (PDAC) has a poor prognosis despite surgical removal and adjuvant therapy. Additionally, the effects of postoperative analgesia with morphine and piritramide on survival among PDAC patients are unknown, as are their interactions with opioid/cannabinoid receptor gene expressions in PDAC tissue. Cancer-specific survival data for 71 PDAC patients who underwent radical surgery followed by postoperative analgesia with morphine (n = 48) or piritramide (n = 23) were therefore analyzed in conjunction with opioid/cannabinoid receptor gene expressions in the patients' tumors. Receptor gene expressions were determined using the quantitative real-time polymerase chain reaction. Patients receiving morphine had significantly longer cancer-specific survival (CSS) than those receiving piritramide postoperative analgesia (median 22.4 vs. 15 months; p = 0.038). This finding was supported by multivariate modelling (p < 0.001). The morphine and piritramide groups had similar morphine equipotent doses, receptor expression, and baseline characteristics. The opioid/cannabinoid receptor gene expression was analyzed in a group of 130 pancreatic cancer patients. Of the studied receptors, high cannabinoid receptor 2 (CB2) and opioid growth factor receptor (OGFR) gene expressions have a positive influence on the length of overall survival (OS; p = 0.029, resp. p = 0.01). Conversely, high delta opioid receptor gene expression shortened OS (p = 0.043). Multivariate modelling indicated that high CB2 and OGFR expression improved OS (HR = 0.538, p = 0.011, resp. HR = 0.435, p = 0.001), while high OPRD receptor expression shortened OS (HR = 2.264, p = 0.002). Morphine analgesia, CB2, and OGFR cancer tissue gene expression thus improved CSS resp. OS after radical PDAC surgery, whereas delta opioid receptor expression shortened OS.

Abstract 2201: Effect of opioid and cannabinoid receptors gene expression on survival of patients with colorectal cancer

Abstract Introduction: Colorectal cancer (CRC) is one of the leading causes of cancer death in the world. CRC patients are often treated with opioid (e.g., morphine, or synthetic opioid piritramide) analgesia for pain, nausea, and side effects of chemotherapy. These analgesics act through opioid and cannabinoid receptors, which pathways are involved in tumor progression and metastases and thus can negatively affect the survival of patients. In our previous studies, we analyzed the presence of circulating tumor cells (CTCs) in two groups of CRC patients. One group received morphine analgesia (MA) and second piritramide analgesia (PA). We found that MA associated with increased CTCs levels and significantly shorter cancer-specific survival (CSS). These findings lead to further analysis of the opioid and cannabinoid receptors tumor gene expressions. We expected that the different expression of specific receptors in tumor tissue makes a difference between the effects of MA and PA on patients´ survival. Methods: Gene expression of opioid receptors µ (OPRM), κ (OPRK), δ (OPRD), nociceptin (OPRL) and cannabinoid receptors 1 and 2 (CB1, CB2) was analyzed in RNA purified from tumor tissues in 131 patients with CRC. Expression of markers was detected using real-time RT-PCR on LightCycler 1536 from Roche. Β-actin gene expression was used for gene expression normalization. Specific cut-off values were calculated for each marker using maxstat R software, ver. 3.3.1. Relationship between expression of receptors in tumor tissue and patients’ survival was analyzed using COX regression, Kruskal-Wallis/ANOVA test, and Kaplan-Meier method. Results: In total, 118 patients (45 females and 73 males, average age 68 years), of clinical stage-III were analyzed. It was found that MA in CRC patients was associated with significantly shorter cancer-specific survival (CSS; p=0,027). The univariate survival analysis revealed that CRC patients with high OPRM tumor tissue gene expression had significantly longer overall survival (OS; p=0.017) and patients with CB2 gene expression had significantly longer disease-free survival (DFS; p=0,029). All other tested opioid receptors expressions had no statistically significant effect on patients’ survival. Conclusion: The diverse opioid receptors’ expressions on tumor and immune cells can affect the survival of cancer patients treated with opioid analgesia. Morphine perioperative analgesia seems to shorten the CCS in CRC patients in our study. However, further research is required to elucidate the effect of opioids on different cell populations. Acknowledgement: This study was supported by Ministry of Health of the Czech Republic [NV18-03-00470]; Palacky University Olomouc [LF 2022_012]; European Regional Development Fund [ENOCHCZ.02.1.01/0.0/0.0/16_019/0000868) and European Union - Next Generation EU (EXCELES LX22NPO5102). Citation Format: Monika Vidlarova, Josef Srovnal, Emil Berta, Sona Gurska, Alona Rehulkova, Pavla Kourilova, Marian Hajduch. Effect of opioid and cannabinoid receptors gene expression on survival of patients with colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2201.

Epigenetic Modulation of Opioid Receptors by Drugs of Abuse.

Chronic exposure to drugs of abuse produces profound changes in gene expression and neural activity associated with drug-seeking and taking behavior. Dysregulation of opioid receptor gene expression is commonly observed across a variety of abused substances including opioids, cocaine, and alcohol. Early studies in cultured cells showed that the spatial and temporal gene expression of opioid receptors are regulated by epigenetic mechanisms including DNA and histone modifications and non-coding RNAs. Accumulating evidence indicate that drugs of abuse can modulate opioid receptor gene expression by targeting various epigenetic regulatory networks. Based on current cellular and animal models of substance use disorder and clinical evidence, this review summarizes how chronic drug exposure alters the gene expression of mu, delta, kappa, and nociceptin receptors via DNA and histone modifications. The influence of drugs of abuse on epigenetic modulators, such as non-coding RNAs and transcription factors, is also presented. Finally, the therapeutic potential of manipulating epigenetic processes as an avenue to treat substance use disorder is discussed.

Solid Tumor Opioid Receptor Expression and Oncologic Outcomes: Analysis of the Cancer Genome Atlas and Genotype Tissue Expression Project.

BackgroundOpioid receptors are expressed not only by neural cells in the central nervous system, but also by many solid tumor cancer cells. Whether perioperative opioids given for analgesia after tumor resection surgery might inadvertently activate tumor cells, promoting recurrence or metastasis, remains controversial. We analysed large public gene repositories of solid tumors to investigate differences in opioid receptor expression between normal and tumor tissues and their association with long–term oncologic outcomes.MethodsWe investigated the normalized gene expression of µ, κ, δ opioid receptors (MOR, KOR, DOR), Opioid Growth Factor (OGFR), and Toll-Like 4 (TLR4) receptors in normal and tumor samples from twelve solid tumor types. We carried out mixed multivariable logistic and Cox regression analysis on whether there was an association between these receptors’ gene expression and the tissue where found, i.e., tumor or normal tissue. We also evaluated the association between tumor opioid receptor gene expression and patient disease–free interval (DFI) and overall survival (OS).ResultsWe retrieved 8,780 tissue samples, 5,852 from tumor and 2,928 from normal tissue, of which 2,252 were from the Genotype Tissue Expression Project (GTEx) and 672 from the Cancer Genome Atlas (TCGA) repository. The Odds Ratio (OR) [95%CI] for gene expression of the specific opioid receptors in the examined tumors varied: MOR: 0.74 [0.63–0.87], KOR: 1.27 [1.17–1.37], DOR: 1.66 [1.48–1.87], TLR4: 0.29 [0.26–0.32], OGFR: 2.39 [2.05–2.78]. After controlling all confounding variables, including age and cancer stage, there was no association between tumor opioid receptor expression and long–term oncologic outcomes.ConclusionOpioid receptor gene expression varies between different solid tumor types. There was no association between tumor opioid receptor expression and recurrence. Understanding the significance of opioid receptor expression on tumor cells remains elusive.

Hippocampal mu opioid receptors are modulated following cocaine self-administration in rat.

Cocaine addiction is a complex pathology induced by long-term brain changes. Understanding the neurochemical changes underlying the reinforcing effects of this drug of abuse is critical for reducing the societal burden of drug addiction. The mu opioid receptor plays a major role in drug reward. This receptor is modulated by chronic cocaine treatment in specific brain structures, but few studies investigated neurochemical adaptations induced by voluntary cocaine intake. In this study, we investigated whether intravenous cocaine-self administration (0.33mg/kg/injection, fixed-ratio 1 [FR1], 10days) in rats induces transcriptional and functional changes of the mu opioid receptor in reward-related brain regions. Epigenetic processes with histone modifications were examined for two activating marks, H3K4Me3, and H3K27Ac. We found an increase of mu opioid receptor gene expression along with a potentiation of its functionality in hippocampus of cocaine self-administering animals compared to saline controls. Chromatin immunoprecipitation followed by qPCR revealed no modifications of the histone mark H3K4Me3 and H3K27Ac levels at mu opioid receptor promoter. Our study highlights the hippocampus as an important target to further investigate neuroadaptive processes leading to cocaine addiction.

Preclinical and Clinical Evidence for a Distinct Regulation of Mu Opioid and Type 1 Cannabinoid Receptor Genes Expression in Obesity.

Among endogenous signaling networks involved in both rewarding and homeostatic mechanisms of obesity, a relevant role is played by the endocannabinoid (ECS) and the opioid (EOS) systems. We here studied the transcriptional regulation of ECS and EOS genes in the hypothalamus of Diet-induced obesity rats, a preclinical model of obesity, as well as in humans with obesity and healthy controls. A significant and selective increase in type 1 cannabinoid receptor gene (Cnr1) expression was observed at the beginning of obesity development (5 weeks on high fat diet) as well as after 21 weeks of high diet exposure. After 5 weeks on high fat diet, selective up-regulation of mu opioid receptor gene (Oprm1) expression was also observed. Consistently, epigenetic studies showed a selective and significant decrease in DNA methylation at specific CpG sites at both gene promoters in overweight rats, but only after 5 weeks on high fat diet. Moreover, significantly lower levels of DNA methylation were observed at selected CpG sites of both receptor gene promoters, analyzed in peripheral blood mononuclear cells from younger (<30 years old) humans with obesity, as well as in those with shorter time length from disease onset. Taken together, we here provide evidence of selective, synergistic and time-dependent transcriptional regulation of CNR1 and OPRM1 genes in overweight rats, as well as in human subjects. These alterations in genes regulation could contribute to the development of the obese phenotype, and we thus suggest CNR1 and OPRM1 epigenetic modulation as possible biomarkers of obesity development. Due to the reversible nature of the epigenetic hallmark, our data might also open new avenue to early environmental strategies of intervention.

Early life stress alters opioid receptor mRNA levels within the nucleus accumbens in a sex-dependent manner

Early life stress (ELS) strongly impacts mental health, but little is known about its interaction with biological sex and postnatal development to influence risk and resilience to psychopathologies. A number of psychiatric disorders, such as social anhedonia and drug addiction, involve dysfunctional opioid signaling; moreover, there is evidence for differential central opioid function in males vs. females. The present study examined opioid receptor gene expression in the nucleus accumbens (NAc) and amygdala of male and female rats subjected to a neonatal predator odor exposure (POE) paradigm to model ELS. Brain tissue was collected at two developmental time points: neonatal and juvenile. Results showed that, following the neonatal POE experience, opioid receptor mRNA levels in the NAc were differentially regulated at the neonatal and juvenile time points. POE downregulated neonatal mu- and kappa-opioid receptor mRNA levels in neonatal females, but upregulated mu- and delta-opioid receptor mRNA levels in juvenile females. Intriguingly, POE had no significant effect on NAc opioid receptor mRNA levels in males at either time point, indicating that the impact of POE on opioid system development is sex-dependent. Finally, POE failed to alter amygdalar opioid receptor gene expression in either sex at either time-point. The spatiotemporally- and sex-specific impact of ELS within the developing brain may confer differential risk or resilience for males and females to develop atypical opioid-regulated behaviors associated with conditions such as depression and addiction.

Механизмы контроля потребления алкоголя: экспрессия генов ноцицептин/каппа-опиоидной системы в мозге крыс

Каппа-опиоидная и ноцицептиновая системы играют важную роль в модуляции функций дофаминергической системы «награды», однако их роль в механизмах формирования аддиктивного поведения до конца не ясна. Цель исследования: сравнить уровни мРНК каппа-опиоидного (OPRK1) и ноцицептинового (OPRL1) рецепторов, а также их эндогенных лигандов - препродинорфина (PDYN) и препроноцицептина (PDYN) в мозге животных с различным уровнем предпочтения алкоголя. Методы: потребление алкоголя у половозрелых крыс-самцов Wistar регистрировали с 60-го по 85-й дни жизни в модели «свободный выбор» между водой и 10% раствором этанола. Относительный уровень мРНК в структурах мозга определяли на 86-й день жизни методом ПЦР в реальном времени. Результаты: Экспрессия мРНК PDYN и PNOC в стриатуме, и OPRK1 и OPRL1 в миндалине была достоверно выше у «отвергающих», т.е. контролирующих потребление алкоголя на постоянно низком уровне животных, по сравнению с «предпочитающими», увеличившими потребление алкоголя в течение эксперимента. Заключение: более высокий уровень экспрессии генов эндогенных опиоидов PDYN и PNOC и их рецепторов в исследованных областях мозга может обусловливать меньшую гедоническую привлекательность алкоголя, играя превентивную роль и снижая риск злоупотребления алкоголем Kappa-opioidergic and nociceptinergic systems both inhibit the mesolimbic reward circuitry but their role in mechanisms of addictive behavior still is not well understood. Objective of the study was to compare expression of kappa opioid and nociceptin receptor genes (OPRK1 and OPRL1, respectively) and their endogenous ligands, preprodynorphin (PDYN) and prepronociceptin (PNOC), in the mesolimbic areas of rats with high and low voluntary alcohol consumption. Methods. Individually housed male Wistar rats were given a 25-day-long two-bottle (10% ethanol/water) free choice trial. mRNA levels were measured using the real-time polymerase chain reaction (qPCR). Results. Alcohol preferring rats progressively increased their ethanol consumption over the course of experiment while non-preferring, low-drinking animals controlled their alcohol intake near the baseline level. Alcohol non-preferring rats were identified to have significantly higher levels of PDYN and PNOC mRNA in the striatum and OPRK1 and OPRL1 mRNA in the amygdala compared to ethanol preferring animals. Conclusion. We suggested that higher levels of the “anti-reward opioid system” gene expression in mesolimbic structures may blunt the hedonic response to alcohol and thus preclude the increase in alcohol preference and uncontrolled excessive alcohol intake.

Involvement of opioid system in behavioral despair induced by social isolation stress in mice

Social isolation stress (SIS) as a type of chronic stress could induce depressive- and anxiety-like behaviors. Our study evaluates the role of opioid system on negative behavioral impacts of SIS in male NMRI mice. We investigated effects of morphine, a nonselective opioid receptor (OR) agonist, naltrexone (NLX), an OR antagonist, naltrindole (NLT), a delta opioid receptor (DOR) antagonist, SNC80, a DOR agonist, U-69593, a kappa opioid receptor (KOR) agonist, nor-Binaltorphimine, a selective KOR antagonist and cyprodime hydrochloride a selective mu opioid receptor (MOR) antagonist on depressive- and anxiety-like behaviors. Using RT-PCR we evaluated ORs gene expression in mice brain. Our findings showed that SIS induced anxiety- and depressive-like behavior in the forced swimming test, open field test, splash test and hole-board test. Moreover, administration of SNC-80 significantly mitigated anxiety- and depressive-like behaviors. NLT decreased grooming-activity in the splash test. Excitingly, administration of agents affecting KOR failed to alter the negative effects of SIS. RT-PCR demonstrated that MOR and KOR gene expression decreased in socially isolated mice; however, SIS did not affect DORs expression. Our findings suggest that SIS at least in part, probably via altering endogenous opioids particularly MORs and KORs but not DORs mediated negative impacts on behavior; also, it could be concluded that DORs might be considered as a novel target for studying depression and anxiety.

The standardized Withania somnifera Dunal root extract alters basal and morphine-induced opioid receptor gene expression changes in neuroblastoma cells

BackgroundBehavioral studies demonstrated that the administration of Withania somnifera Dunal roots extract (WSE), prolongs morphine-elicited analgesia and reduces the development of tolerance to the morphine’s analgesic effect; however, little is known about the underpinning molecular mechanism(s). In order to shed light on this issue in the present paper we explored whether WSE promotes alterations of μ (MOP) and nociceptin (NOP) opioid receptors gene expression in neuroblastoma SH-SY5Y cells.MethodsA range of WSE concentrations was preliminarily tested to evaluate their effects on cell viability. Subsequently, the effects of 5 h exposure to WSE (0.25, 0.50 and 1.00 mg/ml), applied alone and in combination with morphine or naloxone, on MOP and NOP mRNA levels were investigated.ResultsData analysis revealed that morphine decreased MOP and NOP receptor gene expression, whereas naloxone elicited their up-regulation. In addition, pre-treatment with naloxone prevented the morphine-elicited gene expression alterations. Interestingly, WSE was able to: a) alter MOP but not NOP gene expression; b) counteract, at its highest concentration, morphine-induced MOP down-regulation, and c) hamper naloxone-induced MOP and NOP up-regulation.ConclusionPresent in-vitro data disclose novel evidence about the ability of WSE to influence MOP and NOP opioid receptors gene expression in SH-SY5Y cells. Moreover, our findings suggest that the in-vivo modulation of morphine-mediated analgesia by WSE could be related to the hindering of morphine-elicited opioid receptors down-regulation here observed following WSE pre-treatment at its highest concentration.

Arcuate nucleus homeostatic systems reflect blood leptin concentration but not feeding behaviour during scheduled feeding on a high-fat diet in mice.

Hypothalamic homeostatic and forebrain reward‐related genes were examined in the context of scheduled meal feeding without caloric restriction in C57BL/6 mice. Mice fed ad libitum but allowed access to a palatable high‐fat (HF) diet for 2 hours a day rapidly adapted their feeding behaviour and consumed approximately 80% of their daily caloric intake during this 2‐hour scheduled feed. Gene expression levels were examined during either the first or second hour of scheduled feeding vs 24 hours ad libitum feeding on the same HF diet. Gene expression of neuropeptide Y, agouti‐related peptide, cocaine‐ and amphetamine‐regulated transcript, pro‐opiomelanocortin, long‐form leptin receptor and suppressor of cytokine signalling‐3 in the hypothalamic arcuate nucleus (ARC), as well as enkephalin, dynorphin, dopamine‐2‐receptor and dopamine‐3‐receptor in the nucleus accumbens (NAcc) in the forebrain, were measured by in situ hybridisation. Mice fed ad libitum on a HF diet had the highest total caloric intake, body weight gain, fat mass and serum leptin, whereas schedule‐fed mice had a mild obese phenotype with intermediate total caloric intake, body weight gain, fat mass and serum leptin. The effects of feeding regime on ARC gene expression were emphasised by significant positive or negative correlations with body weight gain, fat mass and blood leptin, although they did not appear to be related to feeding behaviour in the schedule‐fed groups (ie, the large, binge‐type meals) and did not reveal any potential candidates for the regulation of these meals. Mechanisms underlying large meal/binge‐type eating may be regulated by nonhomeostatic hedonic processes. However, assessment of opioid and dopamine receptor gene expression in the NAcc did not reveal evidence of involvement of these genes in regulating large meals. This complements our previous characterisation of ARC and NAcc genes in schedule‐fed mice and rats, although it still leaves open the fundamental question about the underlying mechanisms of meal feeding.

The expression of opioid genes in non-classical reward areas depends on early life conditions and ethanol intake

The young brain is highly sensitive to environmental influences that can cause long-term changes in neuronal function, possibly through altered gene expression. The endogenous opioid system continues to mature after birth and because of its involvement in reward, an inadequate maturation of this system could lead to enhanced susceptibility for alcohol use disorder. Recent studies show that the classical reward areas nucleus accumbens and ventral tegmental area are less affected by early life stress whereas endogenous opioids in non-classical areas, e.g. dorsal striatum and amygdala, are highly responsive. The aim was to investigate the interaction between early life conditions and adult voluntary ethanol intake on opioid gene expression. Male Wistar rats were exposed to conventional rearing, 15, or 360min of daily maternal separation (MS) postnatal day 1–21, and randomly assigned to ethanol or water drinking postnatal week 10–16. Rats exposed to early life stress (MS360) had increased opioid receptor gene (Oprm1, Oprd1 and Oprk1) expression in the dorsal striatum. Ethanol drinking was associated with lower striatal Oprd1 and Oprk1 expression solely in rats exposed to early life stress. Furthermore, rats exposed to early life stress had high inherent Pomc expression in the amygdala but low expression after ethanol intake. Thus, adverse events early in life induced changes in opioid gene expression and also influenced the central molecular response to ethanol intake. These long-term consequences of early life stress can contribute to the enhanced risk for excessive ethanol intake and alcohol use disorder seen after exposure to childhood adversity.

Effects of bingeing on fat during adolescence on the reinforcing effects of cocaine in adult male mice

Binge eating is a specific form of overeating characterized by intermittent excessive eating. In addition to altering the neurobiological reward system, several studies have highlighted that consumption of palatable food increases vulnerability to drug use. The aim of the present study was to evaluate the effects of a high-fat diet consumed in a binge pattern during adolescence on the reinforcing effects of cocaine.After 40 days of binge-eating for 2 h, three days a week (PND 29–69), the reinforcing effects of cocaine on conditioning place preference and intravenous self-administration paradigm were evaluated in adolescent male mice. Circulating leptin and ghrelin levels and the effects of bingeing on fat on CB1 mu opioid receptor (MOr) and ghrelin receptor (GHSR) gene expression in the Nucleus Accumbens (NAcc) and Ventral Tegmental Area (VTA) were also assessed.Our results showed a significant escalation in the consumption of a high-fat diet between the first and last week. High-fat binge (HFB) animals were more sensitive to the reinforcing effects of a subthreshold dose of cocaine in the paradigms assayed, and animals under fat withdrawal were more vulnerable to the reinstatement of conditioned place preference. HFB mice also showed enhanced cocaine self-administration. After fat withdrawal, exposure to a new fat binge reinstated cocaine seeking. Although HFB did not modify leptin levels, a decrease in plasmatic ghrelin was observed. Moreover, this pattern of fatty diet resulted in a reduction of MOr and CB1 gene expression in the NAcc and an increase in GHSR expression in the VTA.We propose that bingeing on fat during adolescence induces long-lasting changes in the brain through the sensitization of brain reward circuits, which predisposes individuals to seek cocaine during adulthood.

Proteasome subunit and opioid receptor gene expression down-regulation induced by paraquat and maneb in human neuroblastoma SH-SY5Y cells.

Paraquat (PQ) and maneb (MB) are able to induce neurotoxic effects by promoting α-synuclein (α-syn) aggregates and altering tyrosine hydroxylase (TH), thus increasing the risk of Parkinson's disease (PD). These pesticides promote neurotoxic effects also by affecting proteasome function that normally regulate protein turnover. We investigated the effects of the two pesticides exposure on multiple targets involved in PD, using SH-SY5Y cells. First, we evaluated TH and α-syn protein levels following PQ and MB cell exposure and a significant increase of these protein levels was observed. Subsequently, since a relationship between ubiquitin/proteasome and opioid receptors has been proposed, the effects of pesticides on their gene expression have been investigated. A decrease of β1 and Rpt3 proteasome subunit mRNA levels, together with the μ and δ opioid receptor down-regulation, was detected. The reported alterations, here simultaneously observed, help to clarify the involvement of multiple biological markers implicated in PD, often separately evaluated.

Histone deacetylase inhibitors relieve morphine resistance in neuropathic pain after peripheral nerve injury

Neuropathic pain is often insensitive to morphine. Our previous study has demonstrated that neuron-restrictive silencer factor represses mu opioid receptor (MOP) gene expression in the dorsal root ganglion (DRG) via histone hypoacetylation-mediated mechanisms after peripheral nerve injury, thereby causing loss of peripheral morphine analgesia. Here, we showed that histone deacetylase (HDAC) inhibitors, such as trichostatin A and valproic acid, restored peripheral and systemic morphine analgesia in neuropathic pain. Also, these agents blocked nerve injury-induced MOP down-regulation in the DRG. These results suggest that HDAC inhibitors could serve as adjuvant analgesics to morphine for the management of neuropathic pain.

A new potent analgesic agent with reduced liability to produce morphine tolerance

The therapeutic use of opioids is limited by the development of tolerance to the analgesic effect and the cellular and molecular mechanisms underlying this phenomenon are still not completely understood. For this reason the search for new analgesic derivatives, endowed with lower tolerance, is always an active field. The newly synthesized 14-O-Methylmorphine-6-sulfate (14-O-MeM6SU) shows high efficacy in in vitro assays and a strong analgesic action in the rat tail flick test. The aim of present work was to investigate: the analgesic effect of 14-O-MeM6SU in mouse tail-flick test; the tolerance to analgesic effect of 14-O-MeM6SU compared to morphine in mice, the effects of test compounds on glutamatergic neurotransmission by measuring spontaneous excitatory postsynaptic currents (sEPSCs) of layer V pyramidal cells from rat prefrontal cortices; and the effect of acute and chronic 14-O-MeM6SU treatments on opioid receptor gene expression in SH-SY5Y neuroblastoma cells expressing μ-opioid (MOP) and nociceptin/opioid receptor-like 1 (NOP) receptors. 14-O-MeM6SU was 17 times more potent than morphine in analgesia and had long duration of action in analgesic dose equipotent to morphine. Mice were treated subcutaneously (s.c.) either with 200 μmol/kg morphine or with 14-O-MeM6SU (12 μmol/kg) twice daily for three days. The magnitude of tolerance or cross-tolerance indicated by the shift in antinociceptive ED50 measured was greater for morphine compared to 14-O-MeM6SU. Subsequent to behavioral testing, patch-clamp experiments in layer V pyramidal neurons of rat prefrontal cortical slices in the presence of bicuculline were performed. Both 14-O-MeM6SU (0.1 μM) and morphine (1 μM) decreased the frequency of sEPSCs, indicating reduction of glutamate release. The effect of the novel compound was reversed by the opioid receptor antagonist naloxone, indicating an opioid mediated action. In contrast, the amplitude was not affected. Finally, gene expression data showed a dose dependent down-regulation of MOP receptor after 24h and 48 h exposure to 14-O-MeM6SU. Interestingly, no changes were detected for NOP receptor gene expression. The specific lack of this effect could be related to the lower tolerance development to analgesic effect of 14-O-MeM6SU. Furthermore, 14-O-MeM6SU displayed high intrinsic efficacy possibly an important factor in the observed effects. Further, the observed inhibition of glutamatergic signaling might be attributed also to the reduction of opioid tolerance. Based on our results the development of a new clinically important, safe analgesic agent might be possible.

Role of steroid hormones and morphine treatment in the modulation of opioid receptor gene expression in brain structures in the female rat.

This study determined the effects of acute treatment with morphine on the expression of the Oprm1, Oprk1, and Oprd1 genes (which encode μ, κ, and δ receptors, respectively) in the striatum, hypothalamus, and periaqueductal gray (PAG) in ovariectomized female rats treated with estrogen. Ovariectomized female rats were divided into five equal groups. Two groups received estrogen (50 µg/kg, 54 h before testing) and saline (ES group) or 3.5 mg/kg morphine (EM group) 2 h before euthanasia. The SS group received saline solution 54 and 2 h before the experiments. The SM group received saline 54 h and 3.5 mg/kg morphine 2 h before the experiments. The W group remained undisturbed. The genes expression were evaluated. Oprm1 and Oprk1 expression were activated, respectively, in the hypothalamus and PAG and in the striatum and PAG by morphine only in estrogen-treated animals. Oprd1 expression in the hypothalamus and PAG was activated by morphine in both estrogen-treated and -nontreated animals. The Oprm1 and Oprk1 gene response to morphine might depend on estrogen, whereas the Oprd1 gene response to morphine might not depend on estrogen, supporting the hypothesis of a functional role for ovarian hormones in opioid receptor-mediated functional adaptations in the female brain.

Beneficial effects of co-treatment with dextromethorphan on prenatally methadone-exposed offspring.

BackgroundHeroin use among young women of reproductive age has drawn much attention around the world. Although methadone is widely used in maintenance therapy for heroin/morphine addiction, the long-term effects of prenatal exposure to methadone and preventative therapy remain unclear. For revealing this question, female pregnant Sprague–Dawley rats were sub-grouped to receive (1) vehicle, (2) methadone 5 mg/kg at embryonic day 3 (E3) and then 7 mg/kg from E4 to E20, (3) dextromethorphan (DM) 3 mg/kg, and (4) methadone + DM (the rats received methadone followed by DM treatment), subcutaneously, twice a day from E3 to E20. The body weight, natural withdrawal, pain sensitivity, ED50, conditioned place preference and water maze were conducted at different postnatal stages (P1 to P79) of offspring. The quantitative real-time RT-PCR and electrophysiology were also used to measure the gene expression of opioid receptors in the spinal cord and changes of LTP/LTD in the hippocampus, separately.ResultsPrenatal exposure to methadone or DM did not affect survival rate, body weight, water maze and LTP or LTD of offspring. However, prenatal methadone significantly increased the withdrawal symptoms, pain sensitivity, addiction liability and decreased the mRNA expression of pain related opioid receptors. Co-administration of DM with methadone in the maternal rats effectively prevented these abnormalities of offspring induced by methadone.ConclusionsOur study clearly showed that co-administration of dextromethorphan with methadone in the maternal rats prevented the adverse effects induced by prenatal methadone exposure. It implies that dextromethorphan may have a potential to be used in combination with methadone for maintenance treatment in pregnant heroin-addicted women to prevent the adverse effects induced by methadone on offspring.Electronic supplementary materialThe online version of this article (doi:10.1186/s12929-015-0126-2) contains supplementary material, which is available to authorized users.

Whole-genome expression profile in zebrafish embryos after chronic exposure to morphine: identification of new genes associated with neuronal function and mu opioid receptor expression.

BackgroundA great number of studies have investigated changes induced by morphine exposure in gene expression using several experimental models. In this study, we examined gene expression changes during chronic exposure to morphine during maturation and differentiation of zebrafish CNS.ResultsMicroarray analysis showed 254 genes whose expression was identified as different by at least 1.3 fold change following chronic morphine exposure as compared to controls. Of these, several novel genes (grb2, copb2, otpb, magi1b, grik-l, bnip4 and sox19b) have been detected for the first time in an experimental animal model treated with morphine. We have also identified a subset of genes (dao.1, wls, bnip4 and camk1γb) differentially expressed by chronic morphine exposure whose expression is related to mu opioid receptor gene expression. Altered expression of copb2, bnip4, sox19b, otpb, dao.1, grik-l and wls is indicative of modified neuronal development, CNS patterning processes, differentiation and dopaminergic neurotransmission, serotonergic signaling pathway, and glutamatergic neurotransmission. The deregulation of camk1γb signaling genes suggests an activation of axonogenesis and dendritogenesis.ConclusionsOur study identified different functional classes of genes and individual candidates involved in the mechanisms underlying susceptibility to morphine actions related to CNS development. These results open new lines to study the treatment of pain and the molecular mechanisms involved in addiction. We also found a set of zebrafish-specific morphine-induced genes, which may be putative targets in human models for addiction and pain processes.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-874) contains supplementary material, which is available to authorized users.