Cai-Lian Cui

The role of NR2B containing NMDA receptor in place preference conditioned with morphine and natural reinforcers in rats

It has been reported that N-methyl-D-aspartate (NMDA) receptor is implicated in drug addiction and antagonists of the NMDA receptor complex can inhibit the development and expression of conditioned place preference (CPP) induced by several addictive drugs, implying that this class of compounds might be considered as candidate for the treatment of substance abuse. To explore this possibility, it is important to evaluate whether the inhibitory effect of NMDA receptor antagonists would be confined to behaviors produced by drugs of abuse only, but not by natural reinforcers. According to the quantitative changes of NMDA receptor subunits, including NR1, NR2A, and NR2B, induced by diverse types of reinforcers, we chose NR2B subunit as the target of research. Experimental results showed that (1) an augmented expression of NR2B subunit was revealed by Western blotting in the nucleus accumbens (NAc) and the hippocampus in rats with CPP induced by morphine, but not by natural rewards such as food, novel environment and social interaction. (2) Ifenprodil, an antagonist highly selective for NR2B subunit of the NMDA receptor, produced a dose-dependent reduction in CPP induced by morphine and novel environment, but not that by food consumption and social interaction. Taking together, these findings suggested that NR2B containing NMDA receptor may be more involved with morphine reward rather than natural rewards, and that antagonism of NR2B may have a potential for the treatment of morphine abuse.

NR2B-containing NMDA receptor is required for morphine-but not stress-induced reinstatement

Glutamate receptors are known to be densely distributed in the forebrain rewarding circuits, and glutamatergic transmission is actively involved in the regulation of rewarding and reinstating effects of drugs of abuse. Here we investigated the possible involvement of the N-methyl-D-aspartate (NMDA) receptors in the reinstatement of extinguished morphine conditioned place preference (CPP) in rats. We found that previously extinguished morphine (3 mg/kg, i.p.) CPP was markedly reinstated by a priming injection of morphine (2 mg/kg, i.p.) or an acute environmental stressor (forced swim for 10 min), but not by the stress induced by a 24-h food deprivation. Parallel with this, protein levels of the NMDA receptor 2B subunit (NR2B) were elevated in the nucleus accumbens (NAc) and the hippocampus, but not the prefrontal cortex, of reinstated rats. Systemic administration of an NR2B selective antagonist ifenprodil (1, 3, 10 mg/kg, i.p.) attenuated the reinstatement induced by a priming morphine injection, although not by the forced swim. Ifenprodil (2.0 microg/rat) directly injected into the NAc shell or the CA1 region of the dorsal hippocampus produced a similar effect. These results indicate that the NR2B-containing NMDA receptors in the NAc and the dorsal hippocampus play a significant role in mediating the reinstatement of rewarding responses to morphine.

Suppression of morphine withdrawal by electroacupuncture in rats: dynorphin and κ-opioid receptor implicated

Our previous work has demonstrated that 100-Hz electroacupuncture (EA) or 100-Hz transcutaneous electrical nerve stimulation (TENS) was very effective in ameliorating the morphine withdrawal syndrome in rats and humans. The mechanism was obscure. (1) Rats were made dependent on morphine by repeated morphine injections (5-140 mg/kg, s.c., twice a day) for eight days. They were then given 100-Hz EA for 30 min 24 h after the last injection of morphine. A marked increase in tail flick latency (TFL) was observed. This effect of 100-Hz EA could be blocked by naloxone (NX) at 20 mg/kg, but not at 1 mg/kg, suggesting that 100-Hz EA-induced analgesia observed in morphine-dependent rats is mediated by kappa-opioid receptors. (2) A significant decrease of the concentration of dynorphin A (1-17) immunoreactivity (-ir) was observed in the spinal perfusate in morphine-dependent rats, that could be brought back to normal level by 100-Hz EA. (3) 100-Hz EA was very effective in suppressing NX-precipitated morphine withdrawal syndrome. This effect of EA could be prevented by intrathecal administration of nor-BNI (2.5 micrograms/20 microliters), a kappa-opioid receptor antagonist, or dynorphin A (1-13) antibodies (25 micrograms/20 microliters) administered 10 min prior to EA. In conclusion, while the steady-state spinal dynorphin release is low in morphine-dependent rats, it can be activated by 100-Hz EA stimulation, which may be responsible for eliciting an analgesic effect and ameliorating morphine withdrawal syndrome, most probably via interacting with kappa-opioid receptor at spinal level.

Acupuncture for the Treatment of Drug Addiction

Over the last three decades there has been an increasing interest in acupuncture treatment of substance abuse around the world. Three important steps can be identified in this field. Dr. Wen of Hong Kong was the first (1972) to report that acupuncture at 4 body points and 2 ear points combined with electrical stimulation can relieve opioid withdrawal signs in the addicts. The second major step was made by Dr. M. Smith in New York, the head of the National Acupuncture Detoxification Association (NADA) of the USA, who finalized a protocol (1985), using only ear points without electrical stimulation for the treatment of drug abuse. The recent advance in this field was made by Dr. Han of the Peking University, Beijing, who characterized a protocol (2005), using electrical stimulation of identified frequencies on body points to ameliorate heroin withdrawal signs and prevent relapse of heroin use. In this review, the efficacy of acupuncture and related techniques for the treatment of drug dependence in experimental settings and clinical practice will be reviewed, and the possible mechanisms underlying this effect be discussed.

Peripheral electrical stimulation reversed the cell size reduction and increased BDNF level in the ventral tegmental area in chronic morphine-treated rats

Chronic morphine administration induces functional and morphological alterations in the mesolimbic dopamine system (MLDS), which is believed to be the neurobiological substrate of opiate addiction. Our previous studies have demonstrated that peripheral electrical stimulation (PES) can suppress morphine withdrawal syndrome and morphine-induced conditioned place preference (CPP) in rats. The present study was designed to investigate if PES could reverse the cell size reduction induced by chronic morphine treatment in the ventral tegmental area (VTA), which is an important area of the MLDS. Immunohistochemical observations showed that the cell size of dopaminergic neurons in the VTA reduced significantly in the chronic morphine-treated rats with a concomitant decrease in the number of BDNF-positive cells compared to the saline-treated rats. A much milder morphological change, accompanying with an increased number of BDNF-positive cells, was observed in dopaminergic neurons in the rats that received repeated 100 Hz PES after morphine withdrawal. In another experiment, enzyme-linked immunosorbent assay (ELISA) reconfirmed a significant up-regulation of BDNF protein level in the VTA in the rats received 100 Hz PES after morphine abstinence. These results indicate that PES could facilitate the morphological recovery of the VTA dopaminergic cells damaged by chronic morphine treatment and up-regulate the BDNF protein level in the VTA. Activation of endogenous BDNF by PES may play a role in the recovery of the injured dopaminergic neurons in the morphine addictive rats.

Repeated 2 Hz peripheral electrical stimulations suppress morphine-induced CPP and improve spatial memory ability in rats

Our previous studies have shown that 2 Hz peripheral electrical stimulation (PES) can suppress morphine-induced conditioned place preference (CPP) in the rat, although the mechanisms remain unclear. Since CPP involves the mechanism of learning and memory, it is rational to ask whether the suppressive effect of repeated 2 Hz PES on morphine-induced CPP is due to an impairment of the function of spatial learning and memory. Rats were trained with 4 mg/kg morphine, i.p. for 4 days to establish the CPP. Twenty-four hours after the CPP testing, they were given PES at 2 Hz once a day for 1, 3 or 5 days, followed by another CPP testing. The results showed that (1) the morphine-induced CPP was significantly inhibited by 3 or 5 consecutive sessions, but not by single session of 2 Hz PES. (2) A test of spatial leaning and memory ability using the Morris water maze task revealed that 2 Hz PES per se exhibited a promoting, rather than a deteriorating effect on the ability of spatial memory. (3) 2 Hz PES by itself produced a moderate yet significant CPP. The results imply that (a) a low frequency PES can produce a rewarding effect as revealed by the CPP testing, which may account, at least in part, for its suppressive effect on morphine induced CPP, (b) the suppressive effect of PES on morphine induced CPP is not due to a deteriorating effect on the ability of spatial memory.

The role of striatal NMDA receptors in drug addiction.

The past decade has witnessed an impressive accumulation of evidence indicating that the excitatory amino acid glutamate and its receptors, in particular the N-methyl-D-aspartate (NMDA) receptor subtype, play an important role in drug addiction. Various lines of research using animal models of drug addiction have demonstrated that drug-induced craving is accompanied by significant upregulation of NR2B subunit expression. Furthermore, selective blockade of NR2B-containing NMDA receptors in the striatum, especially in the nucleus accumbens (NAc) can inhibit drug craving and reinstatement. The purpose of this review is to examine the role of striatal NMDA receptors in drug addiction. After a brief description of glutamatergic innervation and NMDA receptor subunit distribution in the striatum, we discuss potential mechanisms to explain the role of striatal NMDA receptors in drug addiction by elucidating signaling cascades involved in the regulation of subunit expression and redistribution, phosphorylation of receptor subunits, as well as activation of intracellular signals triggered by drug experience. Understanding the mechanisms regulating striatal NMDA receptor changes in drug addiction will provide more specific and rational targets to counteract the deleterious effects of drug addiction.

Morphine-induced conditioned place preference in rats is inhibited by electroacupuncture at 2 Hz: Role of enkephalin in the nucleus accumbens

Our previous studies have demonstrated that morphine-induced conditioned place preference (CPP) can be inhibited by 2 Hz electroacupuncture (EA). This inhibition can be blocked by either the opioid receptor antagonist naloxone (i.p.) or lesion in the nucleus accumbens (NAc), providing evidence that endogenous opioid system in the NAc mediates the effects of EA. Here we report that 1) A single session of 2 Hz EA produced a significant increase of the content of enkephalin in the NAc of morphine-induced CPP rats, and this effect was stronger in three consecutive sessions of EA; 2) Intracerebroventricular injection of the mu-opioid receptor antagonist CTAP or delta-opioid receptor antagonist NTI, but not kappa-opioid receptor antagonist nor-BNI, dose-dependently reversed the inhibitory effects of 2 Hz EA on the expression of morphine-induced CPP; 3) Three consecutive sessions of 2 Hz EA up-regulated the mRNA level of preproenkephalin in the NAc of morphine-induced CPP rats. The results suggest that the inhibitory effects of 2 Hz EA on the expression of the morphine CPP is mediated by mu- and delta-, but not kappa-opioid receptor, possibly via accelerating both the release and synthesis of enkephalin in the NAc. These findings support the possibility of using 2 Hz EA for the treatment of opiate addiction.

Manipulation of and Sustained Effects on the Human Brain Induced by Different Modalities of Acupuncture: An fMRI Study

The javascript:void(0)manipulation and sustained effects of acupuncture have been investigated in multiple studies, but several findings are inconsistent with one another. One possible explanation for these discrepancies is that different modalities of acupuncture were utilized in these studies. In the present study, we investigated both the manipulation and sustained effects of acupuncture in different modalities, including manual acupuncture (MA), electroacupuncture (EA) and transcutaneous electrical acupoint stimulation (TEAS). MA, EA, TEAS and sensory control stimulation were applied to 18 healthy subjects, and combined block-designed and resting-state fMRI scans were performed. In analyzing these data, the block-designed datasets were used to assess the manipulation effect by employing a modified general linear model. The data from the resting states, before and after stimulation, were used to explore the brain networks involved in the sustained effect. The results showed that the two 1-min stimulation periods produced similar activation patterns in the sensory control with positive activation in the sensorimotor areas and negative activation in the default mode areas. Although similar patterns could be detected in the first stimulation period in MA, EA and TEAS, no positive activation result was observed in the second stimulation period, and EA showed a more extensive deactivation compared to MA and TEAS. Additionally, all three of the modalities of acupuncture stimulation could increase the instinct brain network in rest. A more secure and spatially extended connectivity of the default mode network was observed following MA and EA, and TEAS specifically increased the functional connectivity in the sensorimotor network. The present study suggested that different brain mechanisms might be recruited in different acupuncture modalities. In addition, the findings from our work could provide methodological information for further research into the mechanism of acupuncture.

NAc Shell Arc/Arg3.1 Protein Mediates Reconsolidation of Morphine CPP by Increased GluR1 Cell Surface Expression: Activation of ERK-Coupled CREB is Required

Background: Relapse into drug abuse evoked by reexposure to the drug-associated context has been a primary problem in the treatment of drug addiction. Disrupting the reconsolidation of drug-related context memory would therefore limit the relapse susceptibility. Methods: Morphine conditioned place preference (CPP) was used to assess activity-regulated cytoskeleton-associated protein (Arc/Arg3.1) and correlative molecule expression in the Nucleus accumbens (NAc) shell during the reconsolidation of morphine CPP. U0126 and Arc/Arg3.1 antisense oligodeoxynucleotide were adapted to evaluate the role and the underlying mechanism of Arc/Arg3.1 during the reconsolidation. Results: The retrieval of morphine CPP in rats specifically increased the Arc/Arg3.1 protein level in the NAc shell, accompanied simultaneously by increases in the phosphorylation of extracellular signal-regulated kinase1/2 (pERK1/2), the phosphorylation of Cyclic Adenosine monophosphate (cAMP) response element-binding (pCREB), and the up-regulation of the membrane α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors GluR1 subunit level. Intra-NAc shell infusion U0126, an inhibitor of the Mitogen-activated protein kinase kinase (MEK), prevented the retrieval-induced up-regulation of pERK1/2, pCREB, Arc/Arg3.1, and membrane GluR1 immediately after retrieval of morphine CPP. The effect of disrupting the reconsolidation of morphine CPP by U0126 could last for at least 14 days, and could not be evoked by a priming injection of morphine. Furthermore, the specific knockdown of Arc/Arg3.1 in the NAc shell decreased the membrane GluR1 level, and impaired both the reconsolidation and the reinstatement of morphine CPP. Conclusions: Arc/Arg3.1 in the NAc shell mediates the reconsolidation of morphine-associated context memory via up-regulating the level of membrane of GluR1, for which the local activation of the ERK-CREB signal pathway, as an upstream mechanism of Arc/Arg3.1, is required.