Extinction Of Morphine Conditioned Place Preference Research Articles

Uncoupling nNOS-PSD-95 in mPFC inhibits morphine priming-induced reinstatement after extinction training

Extremely high relapse rate is the dramatic challenge of drug abuse at present. Environmental cues play an important role in relapse of drug abuse. However, the specific mechanism underlying relapse remains unclear. Using morphine conditioned place preference (CPP) model, we show that association of neuronal nitric oxide synthase (nNOS) with postsynaptic density-95 (PSD-95) plays a significant role in morphine priming-induced reinstatement. The nNOS-PSD-95 coupling and c-Fos expression in the medial prefrontal cortex (mPFC) was significantly increased after extinction of morphine CPP. Dissociation of nNOS-PSD-95 in the mPFC by ZL006 inhibited the reinstatement of morphine CPP induced by a priming dose of morphine. Significantly reduced phosphorylation of cAMP-response element binding protein (CREB) in the mPFC was observed in the mice exposed to morphine after the extinction training. Uncoupling nNOS-PSD-95 reversed the morphine-induced CREB dysfunction. Moreover, effects of ZL006 on the reinstatement of morphine CPP and CREB activation depended on nNOS-PSD-95 target. Together, our findings suggest that nNOS-PSD-95 in the mPFC contributes to reinstatement of morphine CPP, possibly through CREB dysfunction, offering a potential target to prevent relapse of drug abuse.

Role of D1-like and D2-like dopamine receptors within the ventral tegmental area in stress-induced and drug priming-induced reinstatement of morphine seeking in rats.

The ventral tegmental area (VTA) as a major source of dopamine neurons projecting to cortical and limbic regions has a crucial role in reward as well as stress processes. Dopamine is a predominant neurotransmitter in the reward system, which plays an important role in both drug priming-induced and cue-induced reinstatement of cocaine and heroin seeking. It has been shown that this neurotransmitter has a role in stress-induced relapse to drug seeking. Therefore, the present study aims to evaluate the effects of intra-VTA administration of SCH-23390, as a dopamine D1-like receptor antagonist, and sulpiride, as a dopamine D2-like receptor antagonist, on drug priming-induced and food deprivation (FD)-induced reinstatement. The rats were bilaterally implanted by two separate cannulae into the VTA. After the acquisition and extinction of morphine-conditioned place preference, the animals received different doses of SCH-23390 or sulpiride (0.15, 0.4, 1.5 and 4 mg/0.3 µl vehicle per side) into the VTA on the reinstatement day and tested for drug priming-induced reinstatement of morphine (1 mg/kg) or FD-induced reinstatement facilitated by an ineffective dose of morphine (0.5 mg/kg) in separate groups. Our findings indicated that the D1/D2-like receptor antagonists attenuated the drug priming-induced and FD-induced reinstatement. However, these decrements were more significant in groups of animals that received a 24-h FD as a stressor. The data may suggest a role for the VTA dopaminergic system in relapse to drugs of abuse, which may be induced either by re-exposure to morphine or exposure to a stressor.

Effect of Dopamine D1 Receptor Activation on Extinction of Morphine CPP

The dopamine D1 receptor (D1R) mediates drug reward and morphology of accumbal neurons. We used a morphine conditioned place preference (CPP) mouse model to study the role of D1R in context‐reward associative learning and related dendritic morphology changes. To acquire CPP, a morphine group received saline or morphine 10 mg/kg s.c. on alternate days, while CPP controls received saline on all days, immediately before 8 daily place conditioning sessions. Post‐conditioning, morphine CPP mice expressed significantly higher place preference than saline mice. To induce extinction, mice were repeatedly exposed to the place conditioning environment in a drug‐free state. Morphine CPP mice received s.c. saline, 0.5 mg/kg SKF81297 (D1R agonist), or 0.8 mg/kg SKF81297 immediately after each extinction session, while controls received saline. After every two days of extinction training mice were tested for place preference. D1R agonist treatment inhibited extinction of place preference in a dose dependent manner. Mean place preference score of mice treated with the highest dose of agonist was double that of mice treated with saline. One day after the final place preference test brains were isolated and processed using Golgi‐Cox staining followed by digital tracing of accumbal neuron morphology. We previously showed that extinction of morphine CPP is associated with decreased dendritic complexity of neurons in the nucleus accumbens core. Since D1R agonist inhibits CPP extinction, we hypothesize that neurons from mice treated with 0.8 mg/kg SKF81297 will be prevented from undergoing extinction‐related changes, and will have higher dendritic complexity than controls.

Hippocampal Long-Term Potentiation Is Disrupted during Expression and Extinction But Is Restored after Reinstatement of Morphine Place Preference

Learned associations between environmental cues and morphine use play an important role in the maintenance and/or relapse of opioid addiction. Although previous studies suggest that context-dependent morphine treatment alters glutamatergic transmission and synaptic plasticity in the hippocampus, their role in morphine conditioned place preference (CPP) and reinstatement remains unknown. We investigated changes in synaptic plasticity and NMDAR expression in the hippocampus after the expression, extinction, and reinstatement of morphine CPP. Here we report that morphine CPP is associated with increased basal synaptic transmission, impaired hippocampal long-term potentiation (LTP), and increased synaptic expression of the NR1 and NR2b NMDAR subunits. Changes in synaptic plasticity, synaptic NR1 and NR2b expression, and morphine CPP were absent when morphine was not paired with a specific context. Furthermore, hippocampal LTP was impaired and synaptic NR2b expression was increased after extinction of morphine CPP, indicating that these alterations in plasticity may be involved in the mechanisms underlying the learning of drug-environment associations. After extinction of morphine CPP, a priming dose of morphine was sufficient to reinstate morphine CPP and was associated with LTP that was indistinguishable from saline control groups. In contrast, morphine CPP extinguished mice that received a saline priming dose did not show CPP and had disrupted hippocampal LTP. Finally, we found that reinstatement of morphine CPP was prevented by the selective blockade of the NR2b subunit in the hippocampus. Together, these data suggest that alterations in synaptic plasticity and glutamatergic transmission play an important role in the reinstatement of morphine CPP.

Galnon facilitates extinction of morphine-conditioned place preference but also potentiates the consolidation process.

Learning and memory systems are intimately involved in drug addiction. Previous studies suggest that galanin, a neuropeptide that binds G-protein coupled receptors, plays essential roles in the encoding of memory. In the present study, we tested the function of galnon, a galanin receptor 1 and 2 agonist, in reward-associated memory, using conditioned place preference (CPP), a widely used paradigm in drug-associated memory. Either before or following CPP-inducing morphine administration, galnon was injected at four different time points to test the effects of galanin activation on different reward-associated memory processes: 15 min before CPP training (acquisition), immediately after CPP training (consolidation), 15 min before the post-conditioning test (retrieval), and multiple injection after post-tests (reconsolidation and extinction). Galnon enhanced consolidation and extinction processes of morphine-induced CPP memory, but the compound had no effect on acquisition, retrieval, or reconsolidation processes. Our findings demonstrate that a galanin receptor 1 and 2 agonist, galnon, may be used as a viable compound to treat drug addiction by facilitating memory extinction process.

Neuronal activity-regulated pentraxin expressed in medial prefrontal cortex neurons is not necessary for extinction of heroin self-administration

The medial prefrontal cortex (mPFC) plays a key role in extinction learning. Previously, we found that expression of a neuronal activity-regulated pentraxin (Narp) dominant-negative construct in the mPFC of mice blocked extinction of morphine-conditioned place preference. To further investigate the role of mPFC Narp in the extinction of drug seeking, we tested whether mPFC Narp is necessary for the extinction of heroin self-administration in rats. Specifically, we injected an adeno-associated viral vector expressing a dominant-negative form of Narp (NarpN) into the infralimbic region of the mPFC of rats and compared lever presses during extinction to those of rats injected with a control virus. In contrast to our previous study, we found that injection of NarpN did not affect extinction of heroin self-administration. Our findings suggest that mPFC Narp is necessary for extinction of opiate seeking in the Pavlovian-conditioned place preference paradigm but not in the operant paradigm of drug self-administration.

Blockade of cue- and drug-induced reinstatement of morphine-induced conditioned place preference with intermittent sucrose intake

Sucrose intake has been suggested to alter the expression of morphine-induced conditioned place preference (CPP). To date, the potential effects of sucrose intake on the extinction and drug-induced reinstatement of CPP have not been determined. In the present study, sucrose solution (15%) was given prior to, during, and following the acquisition of morphine-induced CPP. Place preference was subsequently assessed during expression, extinction, and morphine-induced reinstatement. The results showed that the sucrose solution given prior to place conditioning training transiently suppressed the expression of morphine CPP. Sucrose solution given during place conditioning training had no effects on the expression, extinction, and reinstatement of CPP. When the sucrose solution was given following the acquisition of morphine CPP, the extinction of morphine CPP was accelerated, and morphine-induced reinstatement was profoundly inhibited. The above results demonstrated that sucrose intake could differentially affect the expression, extinction, and reinstatement of morphine-induced CPP, depending on the interference schedules. Our findings suggest that offering non-drug rewards could be a valuable approach to maintain abstinence and preventing relapse in drug addicts.

Noradrenaline in the bed nucleus of the stria terminalis is critical for stress-induced reactivation of morphine-conditioned place preference in rats

The effect of noradrenaline in the bed nucleus of the stria terminalis and locus coeruleus on maintenance and reactivation of morphine-conditioned place preference induced by footshock stress was investigated in rats. After receiving alternate injection of morphine (10 mg/kg) and saline for 6 consecutive days, the rats spent more time in the drug-paired compartment (morphine-conditioned place preference) on day 7. These animals did not show morphine-conditioned place preference on day 37 following sham-footshock once every 3 days from days 8 to 36 (28 days drug-free). However, 15 min of intermittent footshock once every 3 days could induce the maintenance of morphine-conditioned place preference on day 37 with significantly more time spent in the drug-paired compartment than on day 0. Microinjection of the α 2-adrenoceptor agonist, clonidine (0.1 or 1 μg), into the locus coeruleus 30 min before footshock did not affect stress-induced maintenance of conditioned place preference. However, infusions of clonidine (1 μg) into the bed nucleus of the stria terminalis significantly attenuated the maintenance of conditioned place preference induced by footshock stress. In another experiment, after a 21-day extinction of morphine-conditioned place preference, a single footshock could reactivate the morphine place preference that was significantly blocked by pretreatment with infusion of clonidine (0.1 or 1 μg) into the bed nucleus of the stria terminalis but not the locus coeruleus. Reactivation of morphine-conditioned place preference elicited by footshock stress was significantly inhibited by 6-hydroxydopamine-induced lesions in the ventral noradrenergic bundle, most of the norepinephrine input to the bed nucleus of the stria terminalis arising from caudal brain stem noradrenergic cell groups. In contrast, chemical lesions of the dorsal noradrenergic bundle that arises from the locus coeruleus had no such effects. These findings suggest that noradrenergic neurons in locus coeruleus are not involved in stress-induced reinstatement of drug-seeking and further clearly demonstrate that noradrenaline in the bed nucleus of the stria terminalis plays a critical role in mediating this effect. Comprehension of the neurochemical events underlying the stress-induced and the bed nucleus of the stria terminalis-mediated reinstatement of drug-seeking may, therefore, throw more light on the biological bases of drug dependence and addictive behavior

Differential roles of corticotropin‐releasing factor receptor subtypes 1 and 2 in opiate withdrawal and in relapse to opiate dependence

The possible effects on the morphine withdrawal signs of the nonspecific corticotropin-releasing factor (CRF) receptor antagonist alpha-helical CRF, the selective CRF receptor subtype 1 antagonist CP-154,526 and the selective CRF receptor subtype 2 antagonist antisauvagine-30 (AS-30) were investigated in rats. The most withdrawal signs, including jumping, teeth chatter, writhing, shakes, lacrimation, piloerection, irritability and diarrhoea, were attenuated by pretreatment with alpha-helical CRF (10 microg i.c.v.) and CP-154,526 (30 mg/kg i.p.). However, no morphine withdrawal signs except for diarrhea were significantly affected by pretreatment with AS-30 (10 microg, i.c.v.). To investigate the possible role of different CRFR antagonists (alpha-helical CRF, CP-154,526 and AS-30) in relapse to opiate dependence, the 28-day extinction of morphine-conditioned place preference (CPP) was used. The morphine-CPP disappeared following a 28-day extinction and then was reactivated by a single injection of 10 mg/kg morphine. Pretreatment with alpha-helical CRF (10 microg, i.c.v.) and CP-154, 526 (30 mg/kg, i.p.) could significantly block this reactivation of morphine-CPP. In contrast, pretreatment with AS-30 (1 or 10 microg i. c.v.) did not affect this reactivation of morphine-CPP. The present study demonstrated that activation of the CRF receptor is involved in morphine withdrawal signs and relapse to morphine dependence, and that the role of CRF receptor subtypes 1 and 2 in withdrawal and reactivation of morphine dependence is not identical. CRF receptor subtype 1, but not subtype 2, is largely responsible for the action of the CRF system on opiate dependence. These results suggest that the CRF receptor antagonists, particularly the CRF receptor subtype 1 antagonist, might be of some value in the treatment and prevention of drug dependence.

Cholecystokinin-B receptor antagonists attenuate morphine dependence and withdrawal in rats.

The possible effect of a cholecystokinin-8 agonist (caerulein) and antagonists (MK-329 and L365,260) on the development of morphine dependence and withdrawal were investigated in rats. Caerulein treatment (0.01 and 0.1 mg/kg) increased the incidence of naloxone-induced withdrawal syndromes and delayed the extinction of morphine-conditioned place preference in morphine-dependent animals. The signs of the morphine withdrawal syndromes and the formation of morphine-conditioned place preference were suppressed by pretreatment with L365,260 (0.1 and 1 mg/kg) and not affected by pretreatment with MK-329 (0.1 and 1 mg/kg). The present study demonstrated CCK, acting on CCK-B receptors, participates in the development of the opiate dependence. These findings suggest that CCK-B receptor antagonists might be of some value in the treatment and prevention the relapse of opiate addicts.