Examination of neuroinflammatory cytokine interleukin-1 beta expression in the medial prefrontal cortex, amygdala, and hippocampus for the paradoxical effects of reward and aversion induced by morphine.

A growing body of evidence has shown that abused drugs could simultaneously induce the paradoxical effect-reward and aversion. Moreover, the medial prefrontal cortex (mPFC), amygdala, and hippocampus were involved in this paradoxical effect by abused drugs. However, no research examined whether neuroinflammatory changes in the mPFC [including cingulate cortex area 1 (Cg1); prelimbic cortex (PrL); infralimbic cortex (IL)], basolateral amygdala, and hippocampus [e.g., CA1, CA2, CA3, and dentate gyrus (DG)] after morphine-induced reward in conditioned place preference (CPP) and aversion in conditioned taste aversion (CTA). The results showed that after morphine administration, the consumption of a 0.1% saccharin solution decreased; the mean time spent in the morphine-paired side compartment of the CPP box increased, indicating that morphine simultaneously induced the paradoxical effects of reward and aversion. The PrL and IL of the mPFC, the BLA of the amygdala, the CA1, CA2, CA3, and DG of the hippocampus but not the Cg1 presented hyperactive IL-1ß expression in response to morphine's aversion and reward. The mPFC, amygdala, and hippocampus may appear neuroinflammation activity following morphine-induced paradoxical effect-reward in CPP and aversion in CTA. The present data may provide a better understanding of the relationship between neuroinflammation and morphine addiction.

Neuronal apoptosis induced by morphine withdrawal is mediated by the p75 neurotrophin receptor.

Morphine withdrawal evokes neuronal apoptosis through mechanisms that are still under investigation. We have previously shown that morphine withdrawal increases the levels of pro-brain-derived neurotrophic factor (BDNF), a proneurotrophin that promotes neuronal apoptosis through the binding and activation of the pan-neurotrophin receptor p75 (p75NTR). In this work, we sought to examine whether morphine withdrawal increases p75NTR-driven signaling events. We employed a repeated morphine treatment-withdrawal paradigm in order to investigate biochemical and histological indicators of p75NTR-mediated neuronal apoptosis in mice. We found that repeated cycles of spontaneous morphine withdrawal promote an accumulation of p75NTR in hippocampal synapses. At the same time, TrkB, the receptor that is crucial for BDNF-mediated synaptic plasticity in the hippocampus, was decreased, suggesting that withdrawal alters the neurotrophin receptor environment to favor synaptic remodeling and apoptosis. Indeed, we observed evidence of neuronal apoptosis in the hippocampus, including activation of c-Jun N-terminal kinase (JNK) and increased active caspase-3. These effects were not seen in saline or morphine-treated mice which had not undergone withdrawal. To determine whether p75NTR was necessary in promoting these outcomes, we repeated these experiments in p75NTR heterozygous mice. The lack of one p75NTR allele was sufficient to prevent the increases in phosphorylated JNK and active caspase-3. Our results suggest that p75NTR participates in the neurotoxic and proinflammatory state evoked by morphine withdrawal. Because p75NTR activation negatively influences synaptic repair and promotes cell death, preventing opioid withdrawal is crucial for reducing neurotoxic mechanisms accompanying opioid use disorders.

The role of HINT1 protein in morphine addiction: An animal model-based study.

Drug addiction is a recurrent, chronic brain disease. The existing treatment methods have limitations, such as poor adherence and inability to completely avoid relapse. Histidine triad nucleotide-binding protein 1 (HINT1) is involved in many neuropsychiatric diseases, such as schizophrenia, pain, and drug dependence. Studies have confirmed that there is a genetic link between HINT1 and addictions such as nicotine and cocaine. However, there is no research on the role of HINT1 protein in morphine addiction at home and abroad. Thus, we designed this project by constructing different types of morphine addiction animal models, including conditioned place preference and behavioral sensitization. We comprehensively examined the participation of HINT1 protein in key brain regions associated with addiction, including prefrontal cortex, nucleus accumbens, corpus striatum, and hippocampus, in different stages of different models. In addition, we used HINT1 knockout mice to establish the above models and physical dependence model to investigate the effect of HINT1 protein deletion on morphine addiction-related behaviors. We found that HINT1 has varying degrees of involvement in different stages of multiple addictive animal models. The absence of HINT1 can attenuate morphine-mediated addictive behavior to a certain extent and can alleviate the withdrawal symptoms of morphine.

Effect of Essential Oil of Zhumeria majdae on Morphine Tolerance and Dependence in Mice.

OBJECTIVE: To evaluate the effects of Zhumeria majdae essential oil (ZMEO) on morphine dependence and tolerance in mice. METHODS: ZMEO (10, 20, and 40 mg/kg) and clonidine (0.1 mg/kg) as the positive control were injected intraperitoneally (i.p.). The effect of ZMEO and clonidine on the dependence were evaluated by counting the number of jumps induced by naloxone (5 mg/kg) while the tolerance was evaluated by the tail-flick test. RESULTS: ZMEO at the dose of 10 mg/kg during the development period led to a significant inhibition of morphine tolerance (P<0.01), while it led to reduced morphine dependence with the doses of 20 and 40 mg/kg. ZMEO at two dose levels of 20 and 40 mg/kg indicated significant antinociceptive activity (P>0.01), and significantly reduced the withdrawal signs (number of jumps) of mice (P>0.01). CONCLUSIONS: ZMEO had significant effects on morphine tolerance and dependence. The linalool rich essential oil of Z. majdae plays a major role in the reduction of tolerance and dependence induced by morphine.

Long non-coding RNA MEG3 attends to morphine-mediated autophagy of HT22 cells through modulating ERK pathway.

Context: Morphine is an alkaloid isolated from the poppy plants. The addiction of morphine is a very serious social issue. Some long non-coding RNAs (lncRNAs) have been proposed to engage in drug addiction. Objective: Whether lncRNA maternally expressed gene 3 (MEG3) attended to morphine-mediated autophagy of mouse hippocampal neuronal HT22 cells was probed. Materials and methods: HT22 cells were subjected to 10 µM morphine for 24 h. Cell autophagy was assessed by measuring LC3-II/LC3-I and Beclin-1 expression. qRT-PCR was carried out to measure MEG3 expression. SiRNA oligoribonucleotides targeting MEG3 (si-MEG3) was transfected to silence MEG3. The orexin1 receptor (OX1R), c-fos, p/t-ERK and p/t-PKC expressions were tested by western blotting. SCH772984 was used as an inhibitor of ERK pathway. Results: Morphine elevated OX1R (2.92 times), c-fos (2.06 times), p/t-ERK (2.04 times) and p/t-PKC (2.4 times), Beclin-1 (3.2 times) and LC3-II/LC3-I (3.96 times) expression in HT22 cells. Moreover, followed by morphine exposure, the MEG3 expression was also elevated in HT22 cells (3.03 times). The silence of MEG3 lowered the Beclin-1 (1.85 times), LC3-II/LC3-I (2.12 times), c-fos (1.39 times) and p/t-ERK (1.44 times) expressions in morphine-treated HT22 cells. Inhibitor of ERK pathway SCH772984 further promoted the influence of MEG3 silence on morphine-caused Beclin-1 (1.97 times) and LC3-II/LC3-I (1.92 times) expressions decreases. Conclusions: Up-regulation of MEG3 attended to the morphine-caused autophagy of HT22 cells might be through elevating c-fos expression and promoting ERK pathway activation. More experiments are also needed in the future to analyse the influence of other lncRNAs in drug addiction.

Dysregulation of Dopaminergic Regulatory Factors TH, Nurr1, and Pitx3 in the Ventral Tegmental Area Associated with Neuronal Injury Induced by Chronic Morphine Dependence.

The ventral tegmental area (VTA), a critical portion of the mesencephalic dopamine system, is thought to be involved in the development and maintenance of addiction. It has been proposed that the dopaminergic regulatory factors TH, Nurr1, and Pitx3 are crucial for determining the survival and maintenance of dopaminergic neurons. Thus, the present study investigated whether abnormalities in these dopaminergic regulatory factors in the VTA were associated with neuronal injury induced by chronic morphine dependence. Rat models with different durations of morphine dependence were established. Thionine staining was used to observe morphological changes in the VTA neurons. Immunohistochemistry and western blot were used to observe changes in the expression of the dopaminergic regulatory proteins TH, Nurr1, and Pitx3. Thionine staining revealed that prolonged morphine dependence resulted in dopaminergic neurons with edema, a lack of Nissl bodies, and pyknosis. Immunohistochemistry showed that the number of TH⁺, Nurr1⁺, and Pitx3⁺ cells, and the number of TH⁺ cells expressing Nurr1 or Pitx3, significantly decreased in the VTA after a long period of morphine dependence. Western blot results were consistent with the immunohistochemistry findings. Chronic morphine exposure resulted in abnormalities in dopaminergic regulatory factors and pathological changes in dopaminergic neurons in the VTA. These results suggest that dysregulation of dopaminergic regulatory factors in the VTA are associated with neuronal injury induced by chronic morphine dependence.

Loss of Sfrp2 contributes to the neurological disorders related with morphine withdrawal via Wnt/ß-catenin signaling.

Morphine administration is a medical problem characterized by compulsive opioid use that causes terrible negative consequences. The exact mechanisms of morphine-induced dependence and morphine withdrawal symptoms remain unclear. Recent studies have revealed that the upregulation of Wnt/ß-catenin signaling plays important roles in morphine exposure and morphine withdrawal. Secreted frizzled-related protein 2 (Sfrp2) can prevent the activation of Wnt/ß-catenin signaling by competing with the Frizzled receptor for Wnt ligands. We conducted this study aimed to evaluate the effect of iatrogenic trauma induced by stereotactic surgery and the protective effect of stereotaxic Sfrp2 injection on morphine withdrawal symptoms in Male Sprague Dawley (SD) rats. Many techniques including western blot analysis and immunoprecipitation were used. Anxiety-related behaviors, morphine withdrawal syndrome, and dendritic spines were also examined in male SD rats after morphine treatment and stereotaxic injection of Sfrp2. Western blot results suggested that Wnt signaling was activated in the nucleus accumbens of SD rats suffering from morphine withdrawal and that Sfrp2 attenuated the overexpression of Wnt signaling. Similarly, the withdrawal-like symptoms of morphine dependent rats were abrogated by intracerebral Sfrp2 injection. The iatrogenic trauma induced by stereotactic surgery showed no influence on the Wnt signaling and withdrawal-like symptoms. Moreover, the results of Golgi-cox staining and DiI staining indicated that the damage on proximal spine density caused by morphine treatment was restored by intracerebral Sfrp2 injection. Together, the data presented here indicated that Sfrp2 abrogated the neurological disorders and loss of proximal spine related with morphine withdrawal via Wnt/ß-catenin signaling.

Sinomenine Protects Against Morphine Dependence through the NMDAR1/CAMKII/CREB Pathway: A Possible Role of Astrocyte-Derived Exosomes.

Sinomenine is a nonaddictive alkaloid used to prevent morphine dependence, even thoughits mechanism isnot fully understood. Astrocytes aggravate the pathological process in their neighboring cellsthrough exosomes in central nervous system diseases. However, the effect of sinomenine on astrocyte-derived exosomes for the amelioration of morphine dependence has not been reported yet. In this study, we found that sinomenine prevented the morphine-induced conditionedplace preference in mice. Sinomenine reduced the levels of cAMP and intracellular Ca2+ in morphine-treated SH-SY5Y cells. Moreover, sinomenine inhibited the expressions of p-NMDAR1/NMDAR1, p-CAMKII/CAMKII, and p-CREB/CREB in the hippocampusof morphine-dependent mice and SH-SY5Y cells. Furthermore, we found that sinomenine inhibitedthe morphine-induced activation of astrocytesin vivo and in vitro. Afterwards, exosomes were isolated from cultured primary astrocytes treated with phosphate buffer saline (PBS, ctl-exo), morphine (mor-exo), or morphine and sinomenine (Sino-exo). Subsequently, morphine-treated SH-SY5Y cells were treated with ctl-exo, mor-exo, and Sino-exo. Results showed that Sino-exo reduced the level of cAMP, intracellular Ca2+, and the expression of p-CAMKII/CAMKII and p-CREB/CREB in morphine-treated SH-SY5Y cells. In conclusion, we demonstrated that sinomenine exhibited protective effects against morphine dependencein vivo and in vitro through theNMDAR1/CAMKII/CREB pathway. Sinomenine-induced alterationof the function of astrocyte-derived exosomes may contribute to the antidependence effects of sinomenine in morphine dependence.

The effect of amitriptyline administration on pain-related behaviors in morphine-dependent rats: Hypoalgesia or hyperalgesia?

Pain control in opioid-dependent individuals is a clinical complication. The present study investigated the effects of different doses of amitriptyline in the three stages of the formalin test in morphine-dependent rats (MDRs). Morphine dependency was induced using the oral method, and then, amitriptyline-induced antinociceptive effects were measured at 4 doses (2.5, 5, 10, and 20 mg/kg) and compared with the control group in a formalin-based model of pain. There was no observed antinociceptive effect in the MDRs and morphine-naïve rats (MNRs) in phase I. In the interphase, amitriptyline induced pain suppression at doses of 5 and 20 mg/kg. In phase II, at doses of 5, 10, and 20 mg/kg, the hypoalgesic effect on pain-related behaviors was seen in the MNRs. In MDRs, amitriptyline at doses of 2.5 and 5 mg/kg caused the hyperalgesic effect, whereas at 10 and 20 mg/kg doses, it induced a hypoalgesic effect. A significant attenuation was observed in the latency to fall from the accelerating rotarod at doses of 10 and 20 mg/kg in the MDRs, and at a dose of 20 mg/kg in the MNRs. Data showed that amitriptyline dose-dependently induced paradoxical hypo- and hyper-algesic effects in MDRs.

Socialization Alleviates Burden of Oxidative-Stress in Hippocampus and Prefrontal Cortex in Morphine Addiction Period in Male Rats.

INTRODUCTION: Addiction is a compulsive drug-seeking and drug-taking behavior. Reduction of high-risk behaviors can reduce the burden of addiction in society and can improve the overall prognosis of drug addiction. The aim of this study is to show that reduction of oxidative stress with socialization will reduce occurrence of high-risk behavior during addiction period. METHOD: Fifty-four male Sprague-Dawley rats were randomly divided into four groups: socialized, isolated, addicted socialized and addicted isolated. For inducing morphine dependence, rats received morphine (5 mg/rat/kg/day) for 14 days. Socialization was induced by putting two rats in a large cage for 14 days. On the other hand, isolation was induced by putting rats in separate small cages covered with black plastic for the same period. At the end of the study, rats were experimented with shuttle box for assessing avoidance memory and also tested with social interaction test to measure noveltyseeking behavior and anxiety level. Then, animals were sacrificed for neurochemical analysis. Brain was isolated to assess oxidative-stress (OS) indices such as malondialdehyde (MDA), glutathione and nitrite/nitrate in prefrontal cortex and hippocampus. RESULTS: After 14 days of morphine injection, rats in socialized group had improved avoidance memory, increased anxiety levels and reduced novelty-seeking behavior. Furthermore, isolated rats had reduced glutathione and nitrite/nitrate, and higher MDA levels in prefrontal cortex and hippocampus as compared to socialized rats. CONCLUSION: Pair state had positive effect on OS indices in prefrontal cortex and hippocampus and results in the reduction of relapse and poor prognosis. Thus, OS plays an important role in alleviation of severity of addiction period.

Agmatine inhibits chronic morphine exposure-induced impairment of hippocampal neural progenitor proliferation in adult rats.

Our previous studies have shown that agmatine inhibited opioid dependence, yet the neural mechanism remains unclear. Growing evidence showed that opioids decrease neurogenesis in the adult hippocampal subgranular zone by inhibiting neural progenitor proliferation. However, whether agmatine affects chronic opioid exposure-induced impairment to hippocampal neural progenitor cell proliferation remains unknown. In the present study, we investigated the role of agmatine in hippocampal neural progenitors in morphine dependence rats. We found that chronic administration of morphine for 12 days induced morphine dependence in rats. This treatment not only decreased the proliferation of hippocampal neural progenitors in the granule cell layer, but also decreased the levels of hippocampal cAMP, pCREB and BDNF. However, these alterations can be restored to normal levels by co-treatment of agmatine (10mg/kg, s.c.). In vitro treatment with agmatine (10µM) for two days significantly increased proliferation of the cultured hippocampal neural progenitors. Concurrent treatment of agmatine (10µM) with morphine (10 or 50µM) reversed the supression of morphine-induced neural progenitor proliferation. In conclusion, we found that agmatine abolished chronic morphine-induced decrease in proliferation of hippocampal progenitors in vivo and in vitro, which may be due to the increase in cAMP-CREB-BDNF signaling. The enhancement of agmatine to proliferation of hippocampal progenitors may be one of the important mechanisms involved in the inhibition of morphine dependence by agmatine.

Morphine Withdrawal Increases Brain-Derived Neurotrophic Factor Precursor.

Morphine has been shown to increase the expression of brain-derived neurotrophic factor (BDNF) in the brain. However, little is known about the effect of morphine withdrawal on BDNF and its precursor protein, or proBDNF, which induces neuronal apoptosis. In this work, we examined whether BDNF and proBDNF levels change in rats chronically injected with escalating doses of morphine and those who undergo spontaneous withdrawal for 60 h. We observed, in the frontal cortex and striatum, that the ratio of BDNF to proBDNF changed depending upon the experimental paradigm. Morphine treatment and morphine withdrawal increased both BDNF and proBDNF levels. However, the increase in proBDNF immunoreactivity in withdrawal rats was more robust than that observed in morphine-treated rats. proBDNF is processed either intracellularly by furin or extracellularly by the tissue plasminogen activator (tPA)/plasminogen system or matrix metalloproteases (MMPs). To examine the mechanisms whereby chronic morphine treatment and morphine withdrawal differentially affects BDNF/proBDNF, the levels MMP-3 and MMP-7, furin, and tPA were analyzed. We found that morphine increases tPA levels, whereas withdrawal causes a decrease. To confirm the involvement of tPA in the morphine-mediated effect on BDNF/proBDNF, we exposed cortical neurons to morphine in the presence of the tPA inhibitor plasminogen activator inhibitor-1 (PAI-1). This inhibitor reversed the morphine-mediated decrease in proBDNF, supporting the hypothesis that morphine increases the availability of BDNF by promoting the extracellular processing of proBDNF by tPA. Because proBDNF could negatively influence synaptic repair, preventing withdrawal is crucial for reducing neurotoxic mechanisms associated with opioid abuse.

Alterations in brain activation in response to prolonged morphine withdrawal-induced behavioral inflexibility in rats.

RATIONALE: The inability to stop a repetitive maladaptive behavior is a main problem in addictive disorders. Neuroadaptations that are associated with behavioral inflexibility may be involved in compulsive drug use. OBJECTIVES: The aim of the present study was to investigate the pattern of behavioral inflexibility during morphine withdrawal and map brain activation that is linked to alterations in flexibility. METHODS: We first analyzed the effects of chronic morphine exposure on reversal learning after 2-week (short-term) and 6-week (prolonged) morphine withdrawal. We then compared the level of neuronal activation using cFos immunohistochemistry in 15 brain areas between rats that underwent morphine withdrawal and saline-control rats after a test of reversal learning. RESULTS: Only prolonged morphine withdrawal impaired reversal learning. Rats that exhibited impairments in reversal learning presented a significant decrease in cFos expression in the orbitofrontal cortex (OFC), including the medial, lateral, and ventral OFC. cFos expression significantly increased in the dorsomedial striatum and major subregions of the medial prefrontal cortex (mPFC) in the morphine group. Rats that underwent prolonged morphine withdrawal exhibited no significant changes in cFos expression in the dorsolateral striatum, nucleus accumbens, amygdala, paraventricular thalamic nucleus, or motor cortex. The rats that underwent short-term withdrawal did not present any changes in cFos expression in any of these brain regions. CONCLUSION: Altogether, these data suggest that alterations in the function of the frontal cortex and its striatal connections during the late morphine withdrawal phase may underlie the disruption of inhibitory control in opioid dependence.

Morphine Withdrawal Modifies Prion Protein Expression in Rat Hippocampus.

The hippocampus is a vulnerable brain structure susceptible to damage during aging and chronic stress. Repeated exposure to opioids may alter the brain so that it functions normally when the drugs are present, thus, a prolonged withdrawal might lead to homeostatic changes headed for the restoration of the physiological state. Abuse of morphine may lead to Reacting Oxygen Species-induced neurodegeneration and apoptosis. It has been proposed that during morphine withdrawal, stress responses might be responsible, at least in part, for long-term changes of hippocampal plasticity. Since prion protein is involved in both, Reacting Oxygen Species mediated stress responses and synaptic plasticity, in this work we investigate the effect of opiate withdrawal in rats after morphine treatment. We hypothesize that stressful stimuli induced by opiate withdrawal, and the subsequent long-term homeostatic changes in hippocampal plasticity, might modulate the Prion protein expression. Our results indicate that abstinence from the opiate induced a time-dependent and region-specific modification in Prion protein content, indeed during morphine withdrawal a selective unbalance of hippocampal Prion Protein is observable. Moreover, Prion protein overexpression in hippocampal tissue seems to generate a dimeric structure of Prion protein and α-cleavage at the hydrophobic domain. Stress factors or toxic insults can induce cytosolic dimerization of Prion Protein through the hydrophobic domain, which in turn, it stimulates the α-cleavage and the production of neuroprotective Prion protein fragments. We speculate that this might be the mechanism by which stressful stimuli induced by opiate withdrawal and the subsequent long-term homeostatic changes in hippocampal plasticity, modulate the expression and the dynamics of Prion protein.

Dendrosomal nanocurcumin prevents morphine self-administration behavior in rats despite CA1 damage.

Dendrosomal nanocurcumin (DNC) is fabricated from esterification of oleic acid and polyethylene glycol residues with curcumin. DNC has shown antioxidant, neuroprotective, and neurogenesis-enhancing effects. In addition, it can attenuate morphine tolerance. Morphine self-administration is associated with neurodegenerative changes of CA1 neurons in the adult hippocampus. The present study evaluated the effect of DNC pretreatment on morphine self-administration and hippocampal damage. Rats were pretreated with DNC (5 and 10 mg/kg, intraperitoneally) 30 min before a morphine self-administration paradigm performed in 2-h/sessions for 12 days under a FR-1 schedule. Pretreatment with both doses of DNC markedly suppressed morphine intake. Morphine self-administration resulted in a 71% reduction in the number of hippocampal CA1 neurons. DNC (5 mg/kg) pretreatment only marginally improved (by 22%) neuronal loss in this area. The data suggest that the effect of DNC on morphine self-administration is largely independent of the CA1 area. A functional restoration and regulation of reward circuit activity by DNC may reduce the motivation for morphine despite CA1 damage.

Prohormone convertase 2 (PC2) null mice have increased mu opioid receptor levels accompanied by altered morphine-induced antinociception, tolerance and dependence.

Chronic morphine treatment increases the levels of prohormone convertase 2 (PC2) in brain regions involved in nociception, tolerance and dependence. Thus, we tested if PC2 null mice exhibit altered morphine-induced antinociception, tolerance and dependence. PC2 null mice and their wild-type controls were tested for baseline hot plate latency, injected with morphine (1.25-10mg/kg) and tested for antinociception 30min later. For tolerance studies, mice were tested in the hot plate test before and 30min following morphine (5mg/kg) on day 1. Mice then received an additional dose so that the final dose of morphine was 10mg/kg on this day. On days 2-4, mice received additional doses of morphine (20, 40 and 80mg/kg on days 1, 2, 3, and 4, respectively). On day 5, mice were tested in the hot plate test before and 30min following morphine (5mg/kg). For withdrawal studies, mice were treated with the escalating doses of morphine (10, 20, 40 and 80mg/kg) for 4days, implanted with a morphine pellet on day 5 and 3 days later injected with naloxone (1mg/kg) and signs of withdrawal were recorded. Morphine dose-dependently induced antinociception and the magnitude of this response was greater in PC2 null mice. Tolerance to morphine was observed in wild-type mice and this phenomenon was blunted in PC2 null mice. Withdrawal signs were also reduced in PC2 null mice. Immunohistochemical studies showed up-regulation of the mu opioid receptor (MOP) protein expression in the periaqueductal gray area, ventral tegmental area, lateral hypothalamus, medial hypothalamus, nucleus accumbens, and somatosensory cortex in PC2 null mice. Likewise, naloxone specific binding was increased in the brains of these mice compared to their wild-type controls. The results suggest that the PC2-derived peptides may play a functional role in morphine-induced antinociception, tolerance and dependence. Alternatively, lack of opioid peptides led to up-regulation of the MOP and altered morphine-induced antinociception, tolerance and dependence.

Impact of chronic morphine on delta opioid receptor-expressing neurons in the mouse hippocampus.

Delta opioid (DOP) receptors participate to the control of chronic pain and emotional responses. Recent data also identified their implication in spatial memory and drug-context associations pointing to a critical role of hippocampal delta receptors. To better appreciate the impact of repeated drug exposure on their modulatory activity, we used fluorescent knock-in mice that express a functional delta receptor fused at its carboxy-terminus with the green fluorescent protein in place of the native receptor. We then tested the impact of chronic morphine treatment on the density and distribution of delta receptor-expressing cells in the hippocampus. A decrease in delta receptor-positive cell density was observed in the CA1, CA3 and dentate gyrus without alteration of the distribution across the different GABAergic populations that mainly express delta receptors. This effect partly persisted after four weeks of morphine abstinence. In addition, we observed increased DOP receptor expression at the cell surface compared to saline-treated animals. In the hippocampus, chronic morphine administration thus induces DOP receptor cellular redistribution and durably decreases delta receptor-expressing cell density. Such modifications are likely to alter hippocampal physiology, and to contribute to long-term cognitive deficits.

Targeted exosome-mediated delivery of opioid receptor Mu siRNA for the treatment of morphine relapse.

Cell-derived exosomes have been demonstrated to be efficient carriers of small RNAs to neighbouring or distant cells, highlighting the preponderance of exosomes as carriers for gene therapy over other artificial delivery tools. In the present study, we employed modified exosomes expressing the neuron-specific rabies viral glycoprotein (RVG) peptide on the membrane surface to deliver opioid receptor mu (MOR) siRNA into the brain to treat morphine addiction. We found that MOR siRNA could be efficiently packaged into RVG exosomes and was associated with argonaute 2 (AGO2) in exosomes. These exosomes efficiently and specifically delivered MOR siRNA into Neuro2A cells and the mouse brain. Functionally, siRNA-loaded RVG exosomes significantly reduced MOR mRNA and protein levels. Surprisingly, MOR siRNA delivered by the RVG exosomes strongly inhibited morphine relapse via the down-regulation of MOR expression levels. In conclusion, our results demonstrate that targeted RVG exosomes can efficiently transfer siRNA to the central nervous system and mediate the treatment of morphine relapse by down-regulating MOR expression levels. Our study provides a brand new strategy to treat drug relapse and diseases of the central nervous system.

The effect of various morphine weaning regimens on the sequelae of opioid tolerance involving physical dependency, anxiety and hippocampus cell neurodegeneration in rats.

Chronic consumption of morphine induces physical dependency, anxiety, and neurodegeneration. In this study, morphine on its own has been used for the management of morphine-induced dependency, oxidative stress, and apoptosis. Forty-eight male rats were randomly divided into six groups. Rats in groups 1-5 were made morphine dependent by an increasing manner of morphine for 7 days (15-45 mg/kg). For the next 14 days, morphine was administered using the following regimen: (i) once daily 45 mg/kg (positive controls), (ii) the same dose at additional intervals (6 h longer than the previous intervals each time), (iii) 45 mg/kg of morphine at irregular intervals like of 12, 24, 36 h, (iv) decreasing dose once daily (every time 2.5 mg/kg less than the former dosage). Group 5 received 45 mg/kg of morphine and 10 mg/kg of SOD mimetic agent (M40401) injection per day. Group 6 (negative control) received saline solution only. On day 22, all animals received naloxone (3 mg/kg) and their Total Withdrawal Index (TWI) and blood cortisol levels were measured. After drug treatment, hippocampus cells were isolated, and oxidative, antioxidative, and apoptotic factors were evaluated. Various regimens of morphine reduced TWI, cortisol levels, Bax activity, caspase-3, caspase-9, TNF-α, and IL-1ß and lipid peroxidation. In all treatment groups, GSH level, superoxide dismutase, glutathione peroxidase, and Bcl-2 activity were significantly increased. Furthermore, SOD mimetic agent c diminished morphine effect on SOD activity. Thus, varying the dosage regimen of morphine can reduce the severity of morphine-induced dependency and neurodegeneration.