Phosphorylated Ser187-SNAP25-modulated hyperfunction of glutamatergic system in the vmPFC mediates depressive-like behaviors in male mice.

Dysfunctional glutamatergic neurotransmission contributes importantly to the pathophysiology of depression. However, the underlying neural mechanisms of glutamatergic dysfunction remain poorly understood. Here, we employed chronic unpredictable mild stress (CUMS) to induce depression-like behavior in male mice and to assess the alterations of glutamatergic system within the ventromedial prefrontal cortex (vmPFC). Male mice subjected to CUMS showed an increase in levels of glutamate content, synaptosomal GluN2B-NMDA receptors (GluN2B-NMDARs) and phosphorylated synaptosomal associated protein 25 KD of Ser187 (pSer187-SNAP25), which is involved in synaptic vesicular fusion processes in the vmPFC. Downregulation of pSer187-SNAP25 via the TAT-S187 fusion peptide efficiently alleviated CUMS-induced depressive-like behaviors in male mice by reversing the increase of glutamate content and synaptosomal GluN2B-NMDARs. These findings demonstrated a critical role for pSer187-SNAP25-mediated glutamatergic dysfunction in CUMS-induced depressive-like behaviors, suggesting the potential of pS187-SNAP25 inhibitors for further investigation on depression management.

MicroRNA-132 is involved in morphine dependence via modifying the structural plasticity of the dentate gyrus neurons in rats.

Repeated morphine exposure has been shown to induce neuronal plasticity in reward-related areas of the brain. miR-132, a CREB-induced and activation-dependent microRNA, has been suggested to be involved in the neuronal plasticity by increasing neuronal dendritic branches and spinogenesis. However, it is still unclear whether miR-132 is related to morphine dependence. Here, we investigate whether miR-132 is involved in morphine dependence and whether it is related to the structural plasticity of the dentate gyrus (DG) neurons. Sprague-Dawley rats are treated with increasing doses of morphine injection for six consecutive days to develop morphine dependence. Our results show that dendritic branching and spinogenesis of the DG neurons of morphine dependent rats are increased. Morphine treatment (24 h) promotes the differentiation of N2a cells stably expressing µ-opioid receptor by up-regulating miR-132 expression. Moreover, inhibiting miR-132 3p (but not 5p) of the DG neurons can reverse the structural plasticity and disrupt the formation of morphine dependence in rats. These findings indicate that miR-132 in the DG neurons is involved in morphine dependence via modifying the neuronal plasticity.

Cognitive impairments in adult mice with RIP140 overexpression in neural stem cells.

Receptor-interacting protein 140 (RIP140) is a transcription co-regulator of several transcription factors and a signal transduction regulator. RIP140 was recently implicated in the regulation of cognitive functions. The gene that encodes RIP140 is located on chromosome 21. An increase in RIP140 expression was observed in the fetal cerebral cortex and hippocampus in Down syndrome patients who exhibited strong cognitive disabilities. We hypothesized that RIP140 overexpression affects cognitive function in adult neural development. The present study used a Cre-dependent adeno-associated virus to selectively overexpress RIP140 in neural stem cells using nestin-Cre mice. RIP140 overexpression efficiency was evaluated at the subgranular zone (SGZ) of the dorsal dentate gyrus (dDG) and the subventricular zone (SVZ) of the lateral ventricles (LVs). Mice with RIP140 overexpression in the SGZ exhibited deficits in cognitive function and spatial learning and memory, measured in the Morris water maze, object-place recognition test, and novel object recognition test. However, overexpression of RIP140 in SVZ only impaired performance in the Morris water maze and novel object recognition test but not in the object-place recognition test. Altogether, these results indicated defects in cognitive functions that were associated with RIP140 overexpression in neural stem cells and revealed a behavioral phenotype that may be used as a framework for further investigating the neuropathogenesis of Down syndrome.

The role of the nucleus accumbens OXR1 in cocaine-induced locomotor sensitization.

Re-exposure to drug or drug-associated cues after withdrawal can induce behavioral sensitization expression in animals or increase in the expected effect to drug in humans, which mean an enhanced drug seeking/taking motivation to trigger relapse after abstinence. The Nucleus accumbens (NAc) is known to play a key role in mediating this motivation. Recently, it has been shown that systemic administration of orexin receptor 1 (OXR1) antagonist attenuates animals' motivation behavior to take drug by self-administration paradigm, which is more effectively than orexin receptor 2 (OXR2) antagonist. However, the effect of OXR1 in the NAc on drug-induced locomotor sensitization remains elusive. The present study was designed to investigate the effect of OXR1 in the NAc on chronic cocaine-induced locomotor sensitization. Rats were given 10 mg/kg cocaine intraperitoneal injection (i.p.) for five consecutive days, followed by 10 mg/kg cocaine re-exposure (challenge) on the 14th day of withdrawal. Results showed that re-exposure to cocaine after withdrawal could induce locomotor sensitization expression in cocaine-sensitized rats. Simultaneously, the number of OXR1 positive neurons and OXR1 membrane protein level in the NAc core but not the shell were significantly increased following the cocaine re-exposure. Further, micro-infusion of SB-334867, an OXR1 selective antagonist, into the NAc core but not the shell before cocaine re-exposure, significantly attenuated the expression of locomotor sensitization in rats. The findings demonstrate that OXR1 in the NAc core partially mediates the expression of chronic cocaine-induced locomotor sensitization.

Top-down control of the medial orbitofrontal cortex to nucleus accumbens core pathway in decisional impulsivity.

Decisional impulsivity is one of the risk factors for occurrence and development of many mental disorders, and that the dysfunctions of orbitofrontal cortex (OFC) and nucleus accumbens core (NAcC) are at least involved. Although previous studies have shown that the role of OFC as a whole in regulating decision-making impulse behavior is inconsistent, it's still unclear that the roles of the subregions of OFC including their projections to the NAcC in decisional impulsivity. The present study was designed to investigate the roles of OFC subregions, medial OFC (mOFC) and lateral OFC (lOFC) and their projections to the NAcC in decisional impulsivity in free-moving rats. We found that rats with low level of decisional impulsivity (LI) showed higher neuronal activity in both the mOFC and lOFC, and more neurons in mOFC but not lOFC projecting to the NAcC were activated, compared with high level of decisional impulsivity (HI) rats. The mOFC-NAcC projections of LI rats showed stronger information communication in beta and low gamma oscillations in the expected reward choice and delay time windows. Further, specific activation (in HI rats) or inhibition (in LI rats) of the mOFC-NAcC pathway could partly reverse their decisional impulsive behaviors. The findings first demonstrated that the mOFC-NAcC pathway was more important than the lOFC-NAcC pathway to the top-down control in decisional impulsivity, which could be a new neural physiological mechanism for psychiatric disorders associated with decisional impulsivity.

AMPA Receptor in Ventromedial Prefrontal Cortex Plays Different Roles in the Recent and Remote Retrieval of Morphine-Associated Memory.

Previous studies demonstrate that drug addiction can share the neural circuits in the brain with normal learning and memory. Re-exposure to drug-associated contexts, one way to retrieve the drug-associated memory, can trigger strong psychic craving and even relapse in addicts after prolonged abstinence. The ventromedial prefrontal cortex (vmPFC) has been shown to be involved in time-dependent reinstatement of drug self-administration. This work is designed to investigate the role of AMPA receptor (AMPAR) in the vmPFC in the recent and remote retrieval of morphine-associated memory. Rats were re-exposed to the morphine-paired context 1 day (recent) and 3 weeks (remote) after morphine conditioned place preference (CPP) training. Results showed that membrane expression of GluA1 and GluA2 in the vmPFC was decreased following the recent retrieval, while the membrane expression of GluA1 and GluA2 in the vmPFC was increased following the remote retrieval of morphine-associated memory. Furthermore, the microinfusion of Tat-GluA2-3Y, a GluA2 endocytosis inhibitor, into the vmPFC impaired the recent retrieval of morphine-associated memory. The microinfusion of AMPAR antagonist NBQX into the vmPFC prevented the remote retrieval of morphine-associated memory. Taking together, the present study proved that AMPAR in the vmPFC played different roles in the recent and remote retrieval of morphine-associated memory.

Dentate gyrus µ-opioid receptor-mediated neurogenic processes are associated with alterations in morphine self-administration.

Adult hippocampal dentate gyrus (DG) neural stem cells (NSCs) continuously undergo proliferation and differentiation, producing new functional neurons that remodel existing synaptic circuits. Although proliferation of these adult DG NSCs has been implicated in opiate dependence, whether NSC neuronal differentiation and subsequent dendritogenesis are also involved in such addictive behavior remains unknown. Here, we ask whether opiate exposure alters differentiation and dendritogenesis of DG NSCs and investigate the possibility that these alterations contribute to opiate addiction. We show that rat morphine self-administration (MSA), a paradigm that effectively mimics human opiate addiction, increases NSC neuronal differentiation and promotes neuronal dendrite growth in the adult DG. Further, we demonstrate that the µ-opioid receptor (MOR) is expressed on DG NSCs and that MSA leads to a two-fold elevation of endogenous MOR levels in doublecortin expressing (DCX+) NSC progenies in the rat DG. MOR expression is also detected in the cultured rat NSCs and morphine treatment in vitro increases NSC neuronal differentiation and dendritogenesis, suggesting that MOR mediates the effect of morphine on NSC neuronal differentiation and maturation. Finally, we show that conditional overexpression of MOR in DG NSCs under a doxycycline inducible system leads to facilitation of the acquisition of MSA in rats, without affecting the extinction process. We advocate that targeting MOR selectively in the DG NSC population might offer a novel therapeutic intervention for morphine addiction.

MicroRNA-132 in the Adult Dentate Gyrus is Involved in Opioid Addiction Via Modifying the Differentiation of Neural Stem Cells.

MicroRNA-132 (miR-132), a small RNA that regulates gene expression, is known to promote neurogenesis in the embryonic nervous system and adult brain. Although exposure to psychoactive substances can increase miR-132 expression in cultured neural stem cells (NSCs) and the adult brain of rodents, little is known about its role in opioid addiction. So, we set out to determine the effect of miR-132 on differentiation of the NSCs and whether this effect is involved in opioid addiction using the rat morphine self-administration (MSA) model. We found that miR-132 overexpression enhanced the differentiation of NSCs in vivo and in vitro. Similarly, specific overexpression of miR-132 in NSCs of the adult hippocampal dentate gyrus (DG) during the acquisition stage of MSA potentiated morphine-seeking behavior. These findings indicate that miR-132 is involved in opioid addiction, probably by promoting the differentiation of NSCs in the adult DG.

Wnt7a in Mouse Insular Cortex Contributes to Anxiety-like Behavior During Protracted Abstinence from Morphine.

Anxiety is considered an important protracted abstinence symptom that can aggravate craving and relapse risk in opioid addicts. Although the insular cortex (IC) has been reported to be a key brain region in mediating emotional and motivational alterations induced by drug consumption and withdrawal, the role of IC in anxiety related to protracted abstinence remains elusive. In this study, we found that: (1) anxiety-like behavior in morphine-dependent mice became significant after 28 days of withdrawal, while their physical symptoms became undetectable. (2) Activated glutamatergic neurons in the medial IC, but not the anterior or posterior IC were significantly increased after 28 days of withdrawal. Bilateral lesion of the medial IC, but not the anterior or posterior IC with ibotenic acid (IBO) alleviated the anxiety-like behavior. (3) Expression of Wnt7a in the medial IC was significantly increased after 28 days of withdrawal, and specific down-regulation of Wnt7a with AAV-shWnt7a also alleviated the anxiety-like behavior. The findings reveal the medial IC is involved in mediating anxiety-like behavior related to morphine protracted abstinence, in which Wnt7a plays a critical role.

Combining gray matter volume in the cuneus and the cuneus-prefrontal connectivity may predict early relapse in abstinent alcohol-dependent patients.

BACKGROUND: Developing more effective strategies to prevent relapse remains one of the major challenges of treating substance dependence. Previous studies have identified brain abnormalities in abstinent alcoholics. However, whether these persistent brain deficits in abstinence could predict early relapse to alcohol use has not been well established. This study aimed to identify biomarkers of relapse vulnerability by investigating persistent brain abnormalities in abstinent alcohol-dependent patients. METHODS: Brain imaging and impulsive behavior data were collected from 56 abstinent alcohol-dependent male inpatients and 33 age-matched male healthy controls. Voxel-based morphometry was used to investigate the differences of grey matter volume between the groups. The resting-state functional connectivity was examined using brain areas with gray matter deficits as seed regions. A preliminary prospective study design was used to classify patients into abstainers and relapsers after a 62-day average abstinence period. RESULTS: Compared with healthy controls, both relapsers and abstainers exhibited significantly reduced gray matter volume in the cuneus. Functional connectivity analysis revealed that relapsers relative to abstainers demonstrated increased cuneus-centered negative functional connectivity within a network of brain regions which are involved in executive control and salience. Abnormal gray matter volume in the left cuneus and the functional connectivity between the right cuneus and bilateral dorsolateral prefrontal cortex could successfully predict relapse during the 3-month follow-up period. CONCLUSIONS: Findings suggest that the abnormal gray matter volume in the cuneus and resting-state cuneus-prefrontal functional connectivity may play an important role in poor treatment outcomes in alcoholics and serve as useful neural markers of relapse vulnerability.

Phosphorylated SNAP25 in the CA1 regulates morphine-associated contextual memory retrieval via increasing GluN2B-NMDAR surface localization.

Although our previous studies have demonstrated both protein kinase C (PKC) and GluN2B-containing N-methyl-d-aspartate receptor (GluN2B-NMDAR) play crucial roles in morphine-associated learning and memory, the relationship between them remains unexplored. In this study, we validated the enhanced PKC and membrane GluN2B protein expression in the hippocampal CA1 after morphine conditioned place preference (CPP) expression in rats. Interestingly, we also found that phosphorylation of SNAP25 at Ser187 (pSer187-SNAP25), a PKC-activated target, was significantly increased following morphine CPP expression. Blocking the pSer187-SNAP25 by intra-CA1 injection of an interfering peptide impaired morphine CPP expression and accompanied by the reduced ratio of GluN2B membrane/total in the CA1. In addition, intra-CA1 blockade of pSer187-SNAP25 did not affect natural learning and memory process as evidenced by intact sucrose-induced CPP expression and normal locomotor activity in rats. Therefore, our results reveal that enhanced pSer187-SNAP25 by PKC recruits GluN2B-NMDAR to the membrane surface in the hippocampal CA1 and mediates context-induced addiction memory retrieval. Our findings in this study fill in the missing link and provide better understanding of the molecular mechanisms involved in morphine-associated contextual memory retrieval.

Role of Glutamatergic Projections from the Ventral CA1 to Infralimbic Cortex in Context-Induced Reinstatement of Heroin Seeking.

The prelimbic cortex (PL) and infralimbic cortex (IL) play a role in context-induced reinstatement of heroin seeking in an animal model of drug relapse. Both the PL and IL receive direct glutamatergic projections from the ventral CA1 (vCA1), which is also involved in context-induced reinstatement of cocaine and heroin seeking. Here we studied the role of vCA1-PL and vCA1-IL projections in context-induced reinstatement of heroin seeking by using electrophysiological, neuropharmacological, chemogenetic, and molecular methods. We showed that context-induced reinstatement of heroin seeking caused selective activation of the vCA1-IL but not vCA1-PL glutamatergic projections, decreased synaptosomal GluA2 expression in the IL, impaired basal synaptic transmission, and facilitation of long-term depression (LTD) in the vCA1-IL pathway. Additionally, chemogenetic inactivation of the vCA1-IL but not vCA1-PL pathway decreased context-induced reinstatement of heroin seeking. Inactivation of the vCA1-IL pathway also reversed synaptosomal GluA2 downregulation and basal transmission reduction, and blocked LTD induction. Taken together, our results demonstrate a critical role of the vCA1-IL glutamatergic projection in context-induced reinstatement of heroin seeking in a rat model of drug relapse.

Distinct Roles of Dopamine Receptors in the Lateral Thalamus in a Rat Model of Decisional Impulsivity.

The thalamus and central dopamine signaling have been shown to play important roles in high-level cognitive processes including impulsivity. However, little is known about the role of dopamine receptors in the thalamus in decisional impulsivity. In the present study, rats were tested using a delay discounting task and divided into three groups: high impulsivity (HI), medium impulsivity (MI), and low impulsivity (LI). Subsequent in vivo voxel-based magnetic resonance imaging revealed that the HI rats displayed a markedly reduced density of gray matter in the lateral thalamus compared with the LI rats. In the MI rats, the dopamine D1 receptor antagonist SCH23390 or the D2 receptor antagonist eticlopride was microinjected into the lateral thalamus. SCH23390 significantly decreased their choice of a large, delayed reward and increased their omission of lever presses. In contrast, eticlopride increased the choice of a large, delayed reward but had no effect on the omissions. Together, our results indicate that the lateral thalamus is involved in decisional impulsivity, and dopamine D1 and D2 receptors in the lateral thalamus have distinct effects on decisional impulsive behaviors in rats. These results provide a new insight into the dopamine signaling in the lateral thalamus in decisional impulsivity.

CRFR1 in the ventromedial caudate putamen modulates acute stress-enhanced expression of cocaine locomotor sensitization.

Repeated exposure to psychostimulants induces a long-lasting enhancement of locomotor activity called behavioral sensitization, which is often reinforced by stress after drug withdrawal. The mechanisms underlying these phenomena remain elusive. Here we explored the effects of acute stress 3 or 14 days after the cessation of chronic cocaine treatment on the expression of locomotor sensitization induced by a cocaine challenge in rats and the key brain region and molecular mechanism underlying the phenomenon. A single session of forced swimming, as an acute stress (administered 2 days after the cessation of cocaine), significantly enhanced the expression of cocaine locomotor sensitization 14 days after the final cocaine injection (challenge at 12 days after acute stress) but not 3 days after the cessation of cocaine (challenge at 1 day after acute stress). The result indicated that acute stress enhanced the expression of cocaine locomotor sensitization after incubation for 12 days rather than 1 day after the last cocaine injection. Moreover, the enhancement in locomotor sensitization was paralleled by a selective increase in the number of the c-Fos+ cells, the level of CRFR1 mRNA in the ventromedial caudate putamen (vmCPu). Furthermore, the enhancement was significantly attenuated by CRFR1 antagonist NBI-27914 into the vmCPu, implying that the up-regulation of CRFR1 in the vmCPu seems to be critical in the acute stress-enhanced expression of cocaine locomotor sensitization. The findings demonstrate that the long-term effect of acute stress on the expression of cocaine locomotor sensitization is partially mediated by CRFR1 in the vmCPu.

Glutamatergic Projections from the Entorhinal Cortex to Dorsal Dentate Gyrus Mediate Context-Induced Reinstatement of Heroin Seeking.

Reexposure to the context associated with heroin intake provokes relapse to drug taking after abstinence. The dorsal dentate gyrus (dDG) and entorhinal cortex (EC) have been implicated in contextual memory processing, but the underlying circuit mechanisms in context-induced relapse remain poorly understood. In this study, using a self-administration rat model, we found that activation and synaptic transmission of glutamatergic projections from the EC to the upper blade of dentate gyrus (dDGub) were significantly enhanced during context-induced reinstatement of heroin seeking. This effect was associated with increased of phosphorylation of GluN2B-containing NMDA receptors (GluN2B) at Y1472, ratio of GluN2B membrane/total protein levels, and expression of downstream extracellular signal-regulated kinase-1/2 (ERK1/2) in the dDG region. Furthermore, DREADD-mediated specific inactivation of the EC-dDG pathway or disconnection of the pathway with local postsynaptic GluN2B-ERK1/2 signaling both decreased context-induced reinstatement of heroin seeking. These experimental manipulations had no effect on saccharin-reinforced responding and general locomotor activity in rats. Our results indicate that the EC-dDG pathway mediates context-induced reinstatement of heroin seeking, via the activation of postsynaptic GluN2B-ERK1/2 signaling in the dDG.

Re-exposure to morphine-associated context facilitated long-term potentiation in the vSUB-NAc glutamatergic pathway via GluN2B-containing receptor activation.

The glutamatergic projection from the ventral subiculum of the hippocampus (vSUB) to the nucleus accumbens (NAc) shell has been reported to play a key role in drug-related behavior. The GluN2B subunit of N-methyl-D-aspartate receptors (NMDARs) in the NAc can be selectively elevated after the retrieval of drug-conditioned memory. However, whether the increased GluN2B-containing NMDARs (GluN2B-NMDARs) are able to alter the synaptic plasticity of the vSUB-NAc glutamatergic pathway remains unclear. Here, we found that the long-term potentiation (LTP) in the vSUB-NAc pathway was facilitated and the GluN2B subunit protein level was elevated in synaptoneurosomes of the NAc shell, but not in the core, following morphine-induced conditioned place preference (CPP) expression in rats. The facilitated LTP was prevented by the GluN2B-NMDAR antagonist RO25-6981. Also, a neurochemical disconnection following microinjection of RO25-6981 into the NAc shell, plus microinfusion of GABA agonist baclofen and muscimol into the contralateral vSUB prevented the expression of morphine-induced CPP. These findings suggest that the retrieval of drug-associated memory potentiated synaptic plasticity in the vSUB-NAc pathway, which was dependent on GluN2B-NMDAR activation in the NAc shell. These findings provide a new explanation for the mechanisms that underlie the morphine-associated-context memory. The GluN2B-NMDARs may be regarded as a potential target for erasing morphine-related memory.

Alterations in Brain Structure and Functional Connectivity in Alcohol Dependent Patients and Possible Association with Impulsivity.

BACKGROUND: Previous studies have documented that heightened impulsivity likely contributes to the development and maintenance of alcohol use disorders. However, there is still a lack of studies that comprehensively detected the brain changes associated with abnormal impulsivity in alcohol addicts. This study was designed to investigate the alterations in brain structure and functional connectivity associated with abnormal impulsivity in alcohol dependent patients. METHODS: Brain structural and functional magnetic resonance imaging data as well as impulsive behavior data were collected from 20 alcohol dependent patients and 20 age- and sex-matched healthy controls respectively. Voxel-based morphometry was used to investigate the differences of grey matter volume, and tract-based spatial statistics was used to detect abnormal white matter regions between alcohol dependent patients and healthy controls. The alterations in resting-state functional connectivity in alcohol dependent patients were examined using selected brain areas with gray matter deficits as seed regions. RESULTS: Compared with healthy controls, alcohol dependent patients had significantly reduced gray matter volume in the mesocorticolimbic system including the dorsal posterior cingulate cortex, the dorsal anterior cingulate cortex, the medial prefrontal cortex, the orbitofrontal cortex and the putamen, decreased fractional anisotropy in the regions connecting the damaged grey matter areas driven by higher radial diffusivity value in the same areas and decreased resting-state functional connectivity within the reward network. Moreover, the gray matter volume of the left medial prefrontal cortex exhibited negative correlations with various impulse indices. CONCLUSIONS: These findings suggest that chronic alcohol dependence could cause a complex neural changes linked to abnormal impulsivity.

Over-expression of the GluN2B subunit in the forebrain facilitates the acquisition of morphine-related positive and aversive memory in rats.

GluN2B-containing N-methyl-d-aspartate (NMDA) receptors in the brain are known to have an important role in drug-associated learning and memory. Selective blockage of GluN2B-containing NMDA receptors (GluN2B-NMDARs) has been shown to impair morphine-induced conditioned place preference (CPP) without affecting natural reward-induced CPP. In the present study, GluN2B transgenic rats with over-expressed GluN2B-subunits in the forebrain were used to assess the susceptibility to CPP induced by morphine and natural rewards as well as to naloxone-induced conditioned place aversion (CPA). The results showed that GluN2B transgenic rats exhibited a relatively higher susceptibility to morphine-induced CPP and naloxone-induced CPA than their wild-type littermates did, while they retained the similar sensitivity as wild-type rats to CPP induced by natural reinforcers (food and sucrose). These findings suggest that increased level of GluN2B-NMDARs in forebrain facilitates formation of drug-related memory, but not that associated with natural rewards. GluN2B-NMDARs might be a potential target for the treatment of drug abuse.

Electroacupuncture Ameliorates Propofol-Induced Cognitive Impairment via an Opioid Receptor-Independent Mechanism.

While general anesthesia is known to induce cognitive deficits in elderly and pediatric patients, its influence on adults is less well-characterized. The present study was designed to evaluate the influence of propofol on the learning and memory of young adult rats, as well as the potential neuroprotective role of electroacupuncture (EA) in propofol-induced cognitive impairment. Intravenous anesthesia with propofol was administered to young adult male Sprague-Dawley (SD) rats for 6 h, and EA was administered three times before and after anesthesia. The Morris Water Maze (MWM) test was conducted to determine the rat's cognitive performance following the anesthesia treatment. Our results showed that propofol induced obvious cognitive impairment in young adult rats, which could be ameliorated by multiple EA treatments. Moreover, the decreased level of phosphorylated glycogen synthase kinase 3 ß (pGSK-3ß) in the CA1 region of the hippocampus accompanying the cognitive impairment was also reversed by EA treatment. Further experiments demonstrated that neither 2 nor 10 mg/kg (I.P.) naloxone blocked the effect of EA, indicating that the neuroprotective effect of EA on propofol-induced cognitive impairment was not mediated via the opioid receptors. The present study suggests that EA could ameliorate the cognitive impairment induced by prolonged anesthesia with propofol in young adult rats, which is likely associated with pGSK-3ß levels in the CA1 independently of opioid receptors. These findings imply that EA may be used as a potential neuroprotective therapy for post-operative cognitive dysfunction (POCD).

Essential role of the NO signaling pathway in the hippocampal CA1 in morphine-associated memory depends on glutaminergic receptors.

The nitric oxide (NO)/soluble guanylyl cyclase (sGC)/cGMP-dependent protein kinase (PKG) signaling pathway has been reported to play a key role in memory processing. However, little is known about its role in drug-associated reward memory. Here, we report the following. 1) The NO pathway in the CA1 is critical for the retrieval of morphine-associated reward memory. Specifically, the nNOS, sGC and PKG protein levels in the CA1 were increased after the expression of morphine conditioned place preference (CPP). Intra-CA1 injection of an NOS, sGC or PKG inhibitor prevented morphine CPP expression. 2) The involvement of the NO pathway in morphine CPP requires NR2B-containing NMDA receptors (NR2B-NMDARs). NR2B-NMDAR expression was elevated in the CA1 following morphine CPP expression, and intra-CA1 injection of the NR2B-NMDAR antagonist Ro25-6981 not only blocked morphine CPP expression but also inhibited the up-regulation of nNOS, sGC and PKG. Moreover, the Ro25-6981-induced blockade of morphine CPP was abolished by intra-CA1 injection of a NOS substrate or an sGC activator. 3) The NR2B-NMDAR stimulated the NO pathway by up-regulating the phosphorylation of Akt(Ser473). Morphine CPP expression enhanced the pAkt(Ser473) level, which has been corroborated to regulate nNOS activity, and this effect was reversed by intra-CA1 injection of Ro25-6981. 4) GluR1 acted downstream of the NO pathway. The membrane level of GluR1 in the CA1 was increased after morphine CPP expression, and this effect was prevented by pre-injection of a PKG inhibitor into the CA1. Additionally, co-immunoprecipitation revealed an interaction between PKG and GluR1; this result further indicated a role of PKG in regulating GluR1 trafficking. Collectively, the results of our study demonstrated that the activation of the NR2B-NMDAR/NO/sGC/PKG signaling pathway is necessary for the retrieval of morphine-associated reward memory.