Involvement of the sigma 1 receptor in the motivational effects of ethanol in mice

In the present study, we examined the involvement of the sigma(1) (sigma(1)) receptor in several behavioral manifestations of ethanol addiction. Administration of ethanol (0.5, 1, and 2 g/kg) in Swiss mice dose-dependently induced locomotor stimulation, conditioned place preference, and conditioned taste aversion, which are considered as behavioral index of drug-induced reward. Pretreatment with the selective sigma(1) receptor antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD1047, 3-30 mg/kg) dose-dependently blocked ethanol (1 g/kg)-induced hyperlocomotion and taste aversion and ethanol (2 g/kg)-induced place preference. Pretreatment with the selective sigma(1) receptor agonist 2-(4-morpholino)ethyl 1-phenylcyclohexane-1-carboxylate (PRE-084, 1-10 mg/kg) before ethanol (0.5 g/kg) failed to affect the resulting locomotor stimulation, but dose-dependently enhanced the conditioned place preference. Each sigma(1) receptor ligand was devoid of behavioral effect by itself. These observations show that activation of the sigma(1) receptor is a necessary component of ethanol-induced motivational effects and suggest a new pharmacological target for alleviating ethanol addiction.     

Acquisition, expression, and reinstatement of ethanol-induced conditioned place preference in mice: effects of exposure to stress and modulation by mecamylamine

Nicotinic acetylcholine receptors mediate some of the rewarding and motivational effects of ethanol, including relapses. Relapses are common in drug addicts during abstinence when exposure to any stressor ensues. However, the role of nicotinic acetylcholine receptors in the ethanol- and stress-induced reinstatement of ethanol-induced conditioned place preference has not yet been explored. Therefore, the present study investigated the influence of mecamylamine, a nicotinic acetylcholine receptors antagonist on acquisition, expression, and reinstatement of ethanol-induced conditioned place preference in adult male Swiss mice. The results revealed that mecamylamine (0.1-10 μg/mouse, intracerebroventricularly) dose dependently prevented the development, expression, and reinstatement of ethanol-induced conditioned place preference. Further, acute treatment with mecamylamine blocked the restraint stress and forced swim stress-induced reinstatement of ethanol-induced conditioned place preference. All of these treatments had no influence on the locomotor activity. Therefore, it is concluded that mecamylamine blocks the acquisition, expression and reinstatement of conditioned reinforcing effects of ethanol without per se reinforcing or aversive influence. This ability of mecamylamine might be a potential advantage in the treatment of alcoholism.     

Pharmacological interaction with the sigma1 (σ1)-receptor in the acute behavioral effects of antidepressants

Selective agonists of the sigma-1 (σ(1)) ligand-operated chaperone protein, like igmesine or PRE-084, are antidepressants in preclinical depression models. σ(1)-Protein activation may contribute to the antidepressant efficacy of drugs known to act as selective serotonin-reuptake inhibitors (SSRI) or noradrenaline reuptake inhibitors through direct or indirect involvement of the σ(1)-receptor in the drug effect. We here compared antidepressant effects in two behavioral procedures, the forced swimming test (FST) and conditioned fear stress (CFS). The involvement of the σ(1)-receptor was examined using a co-treatment with the σ(1)-antagonist BD1047 or using σ(1)-knockout (KO) mice. Igmesine but not PRE-084 decreased FST immobility. The SSRI fluoxetine and sertraline, but not fluvoxamine, and the tricyclic antidepressants imipramine, desipramine, and amitriptyline were also effective. Only the effect of igmesine was blocked by BD1047 or in σ(1)-KO mice. Igmesine, PRE-084, fluvoxamine, and sertraline decreased the CFS immobility in a BD1047- and σ(1)-KO-sensitive manner. Among tricyclics, only amitriptyline was effective and its effect was unaffected by BD1047 or in σ(1)-KO mice. The behavioral effects induced by mixed σ(1)-receptor/SSRI antidepressants, like fluvoxamine or sertraline, may therefore involve a non-selective action at both targets. Moreover, the CFS appears to more reliably uncover a σ(1) pharmacological component in antidepressant screening.     

Activation of the spinal sigma-1 receptor enhances NMDA-induced pain via PKC- and PKA-dependent phosphorylation of the NR1 subunit in mice

BACKGROUND AND PURPOSE: Previously we demonstrated that the spinal sigma-1 receptor (Sig-1 R) plays an important role in pain transmission, although the exact mechanism is still unclear. It has been suggested that Sig-1 R agonists increase glutamate-induced calcium influx through N-methyl-D-aspartate (NMDA) receptors. Despite data suggesting a link between Sig-1 Rs and NMDA receptors, there are no studies addressing whether Sig-1 R activation directly affects NMDA receptor sensitivity. EXPERIMENTAL APPROACH: We studied the effect of intrathecal (i.t.) administration of Sig-1 R agonists on protein kinase C (PKC) and protein kinase A (PKA) dependent phosphorylation of the NMDA receptor subunit NR1 (pNR1) as a marker of NMDA receptor sensitization. In addition, we examined whether this Sig-1 R mediated phosphorylation of NR1 plays an important role in sensory function using a model of NMDA-induced pain. KEY RESULTS: Both Western blot assays and image analysis of pNR1 immunohistochemical staining in the spinal cord indicated that i.t. injection of the Sig-1 R agonists, PRE-084 or carbetapentane dose dependently enhanced pNR1 expression in the murine dorsal horn. This increased pNR1 expression was significantly reduced by pretreatment with the specific Sig-1 R antagonist, BD-1047. In another set of experiments Sig-1 R agonists further potentiated NMDA-induced pain behaviour and pNR1 immunoreactivity and this was also reversed with BD-1047. CONCLUSIONS AND IMPLICATIONS: The results of this study suggest that the activation of spinal Sig-1 R enhances NMDA-induced pain via PKC- and PKA-dependent phosphorylation of the NMDA receptor NR 1 subunit.     

Sigma-1 receptors do not regulate calcium influx through voltage-dependent calcium channels in mouse brain synaptosomes

Several lines of evidence suggest that σ(1) receptors regulate intracellular calcium concentration [Ca(2+)](i). However, no previous studies have demonstrated a consistent role for these receptors in the modulation of extracellular calcium entry through plasmalemmal voltage-dependent calcium channels (VDCCs). To search for evidence of such a role we compared [Ca(2+)](i) under basal conditions and after depolarization with KCl in fura-2-loaded synaptosomes from wild-type and σ(1) receptor knockout (σ(1)R-KO) mice. We also tested the effects of the selective σ(1) receptor agonists PRE-084 and (+)-pentazocine and antagonists BD-1047 and NE-100 on the increase in [Ca(2+)](i) induced by depolarization with 60mM KCl. Mibefradil, a nonselective blocker of VDCCs, was used as a positive control. Basal [Ca(2+)](i) and the increase in [Ca(2+)](i) caused by KCl-induced depolarization were similar in brain synaptosomes from both wild-type and σ(1)R-KO mice. Mibefradil (1-30 μM) and all σ(1) receptor ligands studied (3-100 μM) inhibited the KCl-induced increase in [Ca(2+)](i) in a concentration-dependent way. The order of maximum inhibition for the ligands compared here was NE-100>BD-1047=PRE 084>(+)-pentazocine. There were no appreciable differences in their effects between wild-type and σ(1)R-KO mice. These findings indicate that σ(1) receptors are not involved in calcium influx through VDCCs or in the inhibitory effects of these σ(1) ligands on Ca(2+) channels.     

Selective blockade of the orexin-2 receptor attenuates ethanol self-administration, place preference, and reinstatement

Rationale

Orexin-1 receptor antagonists have been shown to block the reinforcing effects of drugs of abuse and food. However, whether blockade of orexin-2 receptor has similar effects has not been determined. We have recently described the in vitro and in vivo effects of JNJ-10397049, a selective and brain penetrant orexin-2 receptor antagonist.

Objective

The goal of these studies was to evaluate whether systemic administration of JNJ-10397049 blocks the rewarding effects of ethanol and reverses ethanol withdrawal in rodents. As a comparison, SB-408124, a selective orexin-1 receptor antagonist, was also evaluated.

Methods

Rats were trained to orally self-administer ethanol (8% v/v) or saccharin (0.1% v/v) under a fixed-ratio 3 schedule of reinforcement. A separate group of rats received a liquid diet of ethanol (8% v/v) and withdrawal signs were evaluated 4?h after ethanol discontinuation. In addition, ethanol-induced increases in extracellular dopamine levels in the nucleus accumbens were tested. In separate experiments, the acquisition, expression, and reinstatement of conditioned place preference (CPP) were evaluated in mice.

Results

Our results indicate that JNJ-10397049 (1, 3, and 10?mg/kg, sc) dose-dependently reduced ethanol self-administration without changing saccharin self-administration, dopamine levels, or withdrawal signs in rats. Treatment with JNJ-10397049 (10?mg/kg, sc) attenuated the acquisition, expression, and reinstatement of ethanol CPP and ethanol-induced hyperactivity in mice. Surprisingly, SB-408124 (3, 10 and 30?mg/kg, sc) did not have any effect in these procedures.

Conclusions

Collectively, these results indicate, for the first time, that blockade of orexin-2 receptors is effective in reducing the reinforcing effects of ethanol.     

Involvement of the sigma(1) receptor in cocaine-induced conditioned place preference: possible dependence on dopamine uptake blockade.

The involvement of the sigma(1) receptor on the rewarding effects of cocaine was examined using the conditioned place preference (CPP) procedure in C57BL/6 mice. Acquisition or expression of cocaine (20 mg/kg i.p.)-induced CPP was significantly decreased by pre-treatment with the selective sigma(1) receptor antagonists N,N-dipropyl-2-(4-methoxy-3-(2-phenylethoxy)phenyl)ethylamine (NE-100) or N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD1047), 1-10 mg/kg, i.p. The sigma(1) receptor agonists igmesine or 2-(4-morpholinoethyl-1-phenylcyclohexane-1-carboxylate hydrochloride (PRE-084) failed to induce CPP when injected alone. Moreover, the CPP induced by N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP), a selective dopamine reuptake inhibitor, was blocked by treatments with the sigma(1) receptor antagonists as was similarly observed with cocaine. In addition, the repetitive treatment with cocaine during conditioning increased sigma(1) receptor mRNA expression in the nucleus accumbens, but not in the caudate putamen, prefrontal cortex or cerebellum. These data show that the sigma(1) receptor is not only necessary for acquisition of the cocaine-induced CPP, but that it is also implicated in its expression, confirming that activation of the sigma(1) receptor is induced during cocaine's early effects. The sigma(1) receptor is activated consequently to dopamine reuptake blockade and is not sufficient to induce CPP by itself. The mechanism of the sigma(1) receptor involvement in CPP and the selectivity toward the CPP-inducing drug remains however to be determined. These results show that strategies targeting the sigma(1) receptor with selective antagonists may allow effective attenuation of cocaine's rewarding properties and, in turn, offer new treatment strategies against drug addiction.     

The σ1 receptor agonist 4-PPBP elicits ERK1/2 phosphorylation in primary neurons: A possible mechanism of neuroprotective action

Although sigma 1 (σ₁) receptors and mitogen-activated protein kinases (MAPKs) are known modulators of neuroprotection, a role for MAPK signaling pathways in σ receptor-mediated neuroprotection has not been investigated in detail.The present study aims to investigate the possible link between σ₁ receptors and MAPKs in neuroprotection. Primary mixed cortical and hippocampal neurons were treated with σ₁ receptor agonists PRE-084 or 4-PPBP in a time- and concentration-dependent manner; and in another set of experiments, cells were pre-incubated with σ₁ receptor antagonist BD1047 or MEK inhibitor PD98059 in a concentration-dependent manner prior to PRE-084 or 4-PPBP treatment. Levels of phosphorylated and total ERK1/2, JNK and p38-MAPK were determined with western blotting and ERK1/2 phosphorylation was confirmed with immunofluorescence. To investigate neuroprotection by σ₁ receptors, cells were pre-treated with PRE-084 or 4-PPBP and glucose-starved for various times: in the presence or absence of pre-incubated BD1047 or PD98059. Cell viability was then measured with MTT assay. Both PRE-084 and 4-PPBP caused phosphorylation of ERK1/2, but not p38-MAPK and JNK. ERK1/2 phosphorylation was inhibited by BD1047 and PD98059 in a concentration-dependent manner. Immunofluorescence confirmed the phosphorylation of ERK1/2 by PRE-084 and 4-PPBP and its inhibition by BD1047 and PD98059. Pre-treating glucose-deprived neurons with 4-PPBP, but not PRE-084; caused neuroprotection which was inhibited by BD1047 and PD98059. 4-PPBP, but not PRE-084; causes ERK1/2 phosphorylation-mediated neuroprotection. This presents a novel mechanism by σ₁ receptors in modulating neuroprotection.     

The anti-amnesic and neuroprotective effects of donepezil against amyloid beta25-35 peptide-induced toxicity in mice involve an interaction with the sigma1 receptor

BACKGROUND AND PURPOSE: The acetylcholinesterase inhibitor, donepezil, is also a high affinity sigma(1) receptor agonist. We examined the involvement of sigma(1) receptors in its anti-amnesic and neuroprotective properties against amyloid beta(25-35) peptide-induced toxicity in mice. EXPERIMENTAL APPROACH: Mice were given an intracerebroventricular (i.c.v.) injection of Abeta(25-35) peptide (9 nmol) 7-9 days before being tested for spontaneous alternation and passive avoidance. Hippocampal lipid peroxidation was measured 7 days after Abeta(25-35) injection to evaluate oxidative stress. Donepezil, the sigma(1) agonist PRE-084 or the cholinesterase (ChE) inhibitors tacrine, rivastigmine and galantamine were administered either 20 min before behavioural sessions to check their anti-amnesic effects, or 20 min before Abeta(25-35) injection, or 24 h after Abeta(25-35) injection and then once daily before behavioural sessions, to check their pre- and post-i.c.v. neuroprotective activity, respectively. KEY RESULTS: All the drugs tested were anti-amnesic, but only the effects of PRE-084 and donepezil were prevented by the sigma(1) antagonist BD1047. Only PRE-084 and donepezil showed neuroprotection when administered pre i.c.v.; they blocked lipid peroxidation and learning deficits, effects inhibited by BD1047. Post i.c.v., PRE-084 and donepezil showed complete neuroprotection whereas the other ChE inhibitors showed partial effects. BD1047 blocked these effects of PRE-084, attenuated those of donepezil, but did not affect the partial effects of the other ChE inhibitors. CONCLUSIONS AND IMPLICATIONS: The potent anti-amnesic and neuroprotective effects of donepezil against Abeta(25-35)-induced toxicity involve both its cholinergic and sigma(1) agonistic properties. This dual action may explain its sustained activity compared to other ChE inhibitors.     

The selective metabotropic glutamate receptor 7 allosteric agonist AMN082 prevents reinstatement of extinguished ethanol-induced conditioned place preference in mice

Alcohol dependence is considered a major public health problem in modern societies. The role for glutamatergic neurotransmission in the reinforcing effects of ethanol is becoming increasingly evident. Our previous findings have shown that in rats, the mGluR7 positive allosteric agonist AMN082, but not its allosteric antagonist MMPIP, prevented ethanol consumption and preference in the two-bottle choice paradigm. This study was conducted to determine the effects of AMN082 and MMPIP on the extinction and reinstatement of ethanol-elicited place preference (CPP) in C57BL/6 mice. AMN082 and MMPIP were administered during extinction of ethanol CPP to determine whether mGluR7 signaling is required. Furthermore, the effects of AMN082 and MMPIP on reinstatement of CPP were also evaluated. Finally, spontaneous locomotor activity and ethanol pharmacokinetics were assessed following systemic administration of AMN082 and MMPIP. Our results indicate that mGluR7 pharmacological modulation had no effect on ethanol-elicited CPP extinction. In contrast, mGluR7 activation using AMN082 reduced ethanol-induced CPP reinstatement, an effect reversed by co-administration of MMPIP. Collectively, these results indicate, for the first time, that activation of the mGluR7 receptor is effective in reducing the reinstatement of conditioned rewarding effects of ethanol. Taken together, the efficacy of AMN082 on the various phases of alcohol-CPP could represent an interesting pharmacological approach and could open a new line of research for the development of therapies to reduce ethanol intake in patients.     

Differential effects of sigma1 receptor blockade on self-administration and conditioned reinstatement motivated by cocaine vs natural reward.

Growing evidence suggests a role for sigma(1) (sigma(1)) receptors in cognitive function, anxiety, depression, regulation of stress responses, and, recently, the appetitive effects of cocaine as measured by conditioned place preference. This study was designed to extend understanding of the role of sigma(1) receptors in addiction-relevant conditioned effects of cocaine by testing the effects of a potent and selective sigma(1) receptor antagonist, BD1047, on conditioned reinstatement of cocaine-seeking. To determine whether modification of conditioned reinstatement by BD1047 is selective for drug-directed behavior or reflects general suppressant effects on motivated behavior, BD1047 was tested also on reinstatement induced by stimuli conditioned to a natural reward, sweetened condensed milk (SCM). Additionally, because sigma(1) receptors have been implicated also in processes linked to the acute reinforcing actions of cocaine, tests of the effects of BD1047 on cocaine self-administration-including a comparison with the sigma(1) antagonist effects on SCM self-administration-were conducted as well. Cocaine self-administering male Wistar rats were trained to associate a discriminative stimulus (S(D)) with the availability of cocaine or SCM, and then subjected to reinstatement tests following extinction of cocaine or SCM-reinforced behavior. BD1047 (1-30 mg/kg) reversed response reinstatement induced by the cocaine S(D) at 20 and 30 mg/kg but did not modify SCM S(D)-induced responding at all but the highest 30 mg dose, at which responding was reversed to extinction levels. BD1047 did not modify responding reinforced directly by SCM or cocaine. The findings support a role for sigma(1) receptors in regulating conditioned responses to cocaine-related contextual stimuli and identify this receptor as a potential treatment target for the prevention of craving and relapse.     

The role of group I mGlu receptors in the expression of ethanol-induced conditioned place preference and ethanol withdrawal seizures in rats

In animal models, N-methyl-d-aspartate (NMDA) receptors antagonists inhibit physical dependence and the reinforcing effects of ethanol. The group I metabotropic glutamate (mGlu) receptors antagonists (mGlu1 and mGlu5) attenuate excitatory effect of glutamate by functional modulation of the glutamate/NMDA receptors. The objective of the present study was to evaluate the effects of a selective mGlu5 receptors antagonist—MTEP, and mGlu1 receptors antagonist—EMQMCM, on two processes relevant to alcohol addiction: the expression of ethanol-induced conditioned place preference (CPP) paradigm, and ethanol withdrawal audiogenic seizures in rats. Our experiments indicated that EMQMCM at the doses of 5 and 10 mg/kg, and MTEP at the doses of 2.5 and 5 mg/kg, significantly attenuated the expression of ethanol CPP. Furthermore, both group I mGlu receptor antagonists, i.e. EMQMCM at the dose of 10 mg/kg and MTEP at the dose of 5 mg/kg, attenuated audiogenic seizures induced by the sound stimulus 12 h after withdrawal of ethanol in dependent rats. Our study shows the importance of mGlu5 and mGlu1 receptors for the expression of ethanol-induced CPP and withdrawal seizures, although mGlu5 receptors antagonist (MTEP) was more potent than the antagonist of mGlu1 receptors (EMQMCM).     

Spinal neuronal NOS activation mediates sigma-1 receptor-induced mechanical and thermal hypersensitivity in mice: involvement of PKC-dependent GluN1 phosphorylation

BACKGROUND AND PURPOSE We recently demonstrated that activation of the spinal sigma-1 receptor induces mechanical and thermal hypersensitivity via calcium-dependent second messenger cascades and phosphorylation of the spinal NMDA receptor GluN1 subunit (pGluN1). Here we examined the role of NO in this process, as it plays a critical role in PKC-mediated calcium signalling and the potentiation of NMDA receptor function. EXPERIMENTAL APPROACH The effects of intrathecal (i.t.) pretreatment with nNOS inhibitors on PRE084 (sigma-1 receptor agonist)-induced pain were assessed in mice by use of mechanical allodynia and thermal hyperalgesia tests. Western blot analysis, immunoprecipitation and immunohistochemical techniques were used to determine effects of these treatments on spinal pGluN1-immunoreactive (ir) cells, whether PRE084 induces a time-dependent modification of nNOS activity in the dorsal horn, and if any changes in nNOS activity can be blocked by sigma-1 receptor, calcineurin or soluble guanylyl cyclase (sGC) inhibitors. KEY RESULTS PRE084, injected i.t., induced mechanical and thermal hypersensitivity, and increased the number of PKC- and PKA-dependent pGluN1-ir cells in spinal cord. This PRE084-induced hypersensitivity and increase in PKC-dependent pGluN1 expression were blocked by pretreatment with N(G) -nitro-L-arginine methyl ester (L-NAME) or 7-nitroindazole (7-NI). PRE084 also time-dependently decreased the ratio of phosphorylated nNOS (pnNOS) to nNOS expression and the number of spinal pnNOS-ir cells. This decrease in pnNOS was prevented by BD1047, a sigma-1 receptor antagonist and cyclosporin A, a calcineurin inhibitor, but not by a sGC inhibitor. CONCLUSIONS AND IMPLICATIONS Spinal sigma-1 receptor-induced sensitization is mediated by an increase in nNOS activity, which is associated with an NO-induced increase in PKC-dependent pGluN1 expression.     

Role of test activity in ethanol-induced disruption of place preference expression in mice

Rationale Reduced expression of a drug-induced conditioned place preference (CPP) may reflect a decrease in the drug’s conditioned rewarding effects. However, CPP is also open to disruption by processes unrelated to the underlying motivation. In unpublished studies, we previously observed that ethanol pretreatment before testing disrupted expression of ethanol-induced CPP in DBA/2J mice. We hypothesized that this interference effect was due to large ethanol-induced increases in activity. Objective The present studies were designed to examine the relationship between test activity and expression of ethanol-induced CPP both in the presence and absence of ethanol. To assess the generality of this relationship, we examined these effects both in DBA/2J (which are highly activated by ethanol) and in NZB/B1NJ mice (which show similar CPP, but less ethanol-induced activation). Materials and methods In separate experiments, inbred mice from each strain underwent ethanol (2 g/kg) place conditioning. Saline or ethanol was then administered immediately before the test. Results Ethanol, given immediately before the test, blocked the expression of ethanol CPP in DBA/2J, but not in NZB/B1NJ mice. Moreover, ethanol significantly increased test activity levels in DBA/2J and to a much lesser degree in NZB/B1NJ mice. Correlation analyses showed an inverse phenotypic relationship between preference and test activity, reflecting stronger preferences in less active mice. Conclusions Disruption of ethanol-CPP observed in DBA/2J mice may be a consequence of high ethanol-induced activity levels. More generally, these studies suggest that competing behaviors can affect expression of a drug-induced CPP independent of affecting the conditioned rewarding effects of the drug.     

Intrathecal injection of the neurosteroid, DHEAS, produces mechanical allodynia in mice: involvement of spinal sigma-1 and GABAA receptors

Background and purpose:

The neurosteroid, dehydroepiandrosterone sulphate (DHEAS) and its non-sulphated form, DHEA, are considered as crucial endogenous modulators of a number of important physiological events. Evidence suggests that DHEAS and DHEA modulate central nervous system-related functions by activating sigma-1 receptors and/or allosterically inhibiting γ-aminobutyric acic receptor type A (GABA_A) receptors. As both the sigma-1 receptor and the GABA_A receptor play important roles in spinal pain transmission, the present study was designed to examine whether intrathecally injected DHEAS or DHEA affect nociceptive signalling at the spinal cord level.

Experimental approach:

We first determined whether intrathecal (i.t.) DHEA or DHEAS injection was able to affect nociceptive thresholds to peripheral mechanical stimulation and subsequently examined whether this effect was mediated by sigma-1 or the GABA_A receptors.

Key results:

The i.t. DHEAS injection dose-dependently decreased the nociceptive threshold to mechanical stimulation, thus producing mechanical allodynia. Moreover, this DHEAS-induced mechanical allodynia was significantly reduced by administration of the sigma-1 receptor antagonist, BD-1047 or the GABA_A receptor agonist, muscimol. Conversely, i.t. DHEA had no effect on mechanical sensitivity. However, when i.t. DHEA was combined with the GABA_A receptor antagonist bicuculline, DHEA dose-dependently produced mechanical allodynia similar to that of DHEAS. This effect was blocked by BD-1047 and by muscimol.

Conclusions and implications:

These findings indicate that i.t. injection of DHEAS produces mechanical allodynia and that the development of this mechanical allodynia is mediated by sigma-1 and GABA_A receptors. The findings of this study raise several interesting questions for further investigations into the mechanisms underlying neurosteroid modulation of spinal pain transmission.British Journal of Pharmacology (2009) 157, 666–673; doi:10.1111/j.1476-5381.2009.00197.x; published online 30 April 2009     

Sigma1 receptor antagonist BD1047 enhances reversal of conditioned place preference from cocaine to social interaction

We have previously shown that only four 15-min social interaction episodes with a male adult conspecific reversed cocaine conditioned place preference (CPP) even despite continuing CPP training with cocaine. In the present study, we investigated if BD1047, a sigma1 receptor antagonist that has been shown to inhibit the expression of cocaine CPP, is able to enhance this effect. BD1047, given as a 10-min pretreatment, dose-dependently (ED50 of 0.0036 mg/kg i.p.) decreased the time spent in the previously cocaine-associated compartment in favour of the time spent in the compartment in which a single social interaction had taken place. Our findings indicate that sigma1 blockade may be used therapeutically to enhance treatment adherence in social interaction-based rehabilitation programs.     

An increase in spinal dehydroepiandrosterone sulfate (DHEAS) enhances NMDA-induced pain via phosphorylation of the NR1 subunit in mice: Involvement of the sigma-1 receptor

Our laboratory has recently demonstrated that an increase in the spinal neurosteroid, dehydroepiandrosterone sulfate (DHEAS) facilitates nociception via the activation of sigma-1 receptors and/or the allosteric inhibition GABA_A receptors. Several lines of evidence have suggested that DHEAS positively modulates N-methyl-d-aspartate (NMDA) receptor activity within the central nervous system. Moreover, we have demonstrated that the activation of sigma-1 receptors increases NMDA receptor activity. Since NMDA receptors play a key role in the enhancement of pain perception, the present study was designed to determine whether spinally administered DHEAS modulates NMDA receptor-mediated nociceptive activity and whether this effect is mediated by sigma-1 or GABA_A receptors. Intrathecal (i.t.) DHEAS was found to significantly potentiate i.t. NMDA-induced spontaneous pain behaviors. Subsequent immunohistochemical analysis demonstrated that i.t. DHEAS also increased protein kinase C (PKC)- and protein kinase A (PKA)-dependent phosphorylation of the NMDA receptor subunit NR1 (pNR1), which was used as a marker of NMDA receptor sensitization. The sigma-1 receptor antagonist, BD-1047, but not the GABA_A receptor agonist, muscimol, dose-dependently suppressed DHEAS’s facilitatory effect on NMDA-induced nociception and pNR1 expression. In addition, pretreatment with either a PKC or PKA blocker significantly reduced the facilitatory effect of DHEAS on NMDA-induced nociception. Conversely the GABA_A receptor antagonist, bicuculline did not affect NMDA-induced pain behavior or pNR1 expression. The results of this study suggest that the DHEAS-induced enhancement of NMDA-mediated nociception is dependent on an increase in PKC- and PKA-dependent pNR1. Moreover, this effect of DHEAS on NMDA receptor activity is mediated by the activation of spinal sigma-1 receptors and not through the inhibition of GABA_A receptors.     

Acquisition and expression of ethanol-induced conditioned place preference in mice is inhibited by naloxone

The effects of opioid antagonists on conditioned reward produced by ethanol provide variable and sometimes conflicting results, especially in mice. In the present set of experiments, male C57BL/6 mice received 4 vehicle and 4 ethanol conditionings, and the rewarding effects of ethanol were assessed in an unbiased version of the conditioned place preference (CPP) apparatus and an unbiased stimulus assignment procedure. Intraperitoneal (ip) administration of ethanol (2 g/kg, but not 1 g/kg) resulted in the conditioned reward when conditionings lasted for 6 min but not when conditioning lasted for 20 min. Administration of the non-selective opioid receptor antagonist naloxone (1 and 5 mg/kg) before the conditionings attenuated the acquisition of ethanol-induced place preference. Naloxone (1 mg/kg) also inhibited expression of the CPP response, but it did not alter the preference of vehicle-conditioned mice, suggesting the lack of its own motivational effects in this experimental setting. Taken together, the present results suggest that an unbiased version of ethanol-induced CPP in C57BL/6 mice could be a valid model for the study of the motivational effects of ethanol, confirming and expanding previous findings that have demonstrated inhibitory effects of opioid receptor antagonist on alcohol conditioned reward.     

CB1 receptor knockout mice display reduced ethanol-induced conditioned place preference and increased striatal dopamine D2 receptors.

Cannabinoids and ethanol activate the same reward pathways, and recent advances in the understanding of the neurobiological basis of alcoholism suggest that the CB1 receptor system may play a key role in the reinforcing effects of ethanol and in modulating ethanol intake. In the present study, male CB1 receptors knockout mice generated on a CD1 background displayed decreased ethanol-induced conditioned place preference (CPP) compared to wild-type (CB1(+/+)) mice. Ethanol (0.5, 1.0, 1.5, and 2.0 g/kg) induced significant CPP in CB1(+/+) mice at all doses tested, whereas it induced significant CPP only at the highest dose of ethanol (2.0 g/kg) in CB1(-/-) mice. However, there was no genotypic difference in cocaine (20 mg/kg)-induced CPP. There was also no genotypic difference, neither in cocaine (10-50 mg/kg) nor in D-amphetamine (1.2-5 mg/kg)-induced locomotor effects. In addition, mutant and wild-type mice did not differ in sensitivity to the anxiolytic effects of ethanol (1.5 g/kg) when tested using the elevated plus maze. Interestingly, this decrease in ethanol efficacy to induce CPP in CB1(-/-) mice was correlated with an increase in D2/D3 receptors, as determined by [3H]raclopride binding, whereas there was no difference in D1-like receptors, as determined by [3H]SCH23390 binding, measured in the striatum from drug-naive mice. This increase in D2/D3 binding sites observed in CB1 knockout mice was associated with an altered locomotor response to the D2/D3 agonist quinpirole (low doses 0.02-0.1 mg/kg) but not to an alteration of quinpirole (0.1-1.0 mg/kg)-induced CPP compared to wild-type mice. Altogether, the present results indicate that lifelong deletion of CB1 receptors reduced ethanol-induced CPP and that these reduced rewarding effects of ethanol are correlated to an overexpression of striatal dopamine D2 receptors.     

100Hz电针对大鼠可卡因CPP重建的影响

目的:探讨100Hz电针对大鼠可卡因条件位置偏爱(Conditioned Place Preference,CPP)重建的影响.方法:采用可卡因诱导大鼠CPP重建模型,观察100 Hz电针对大鼠可卡因CPP重建的作用及选择性κ阿片受体拮抗剂nor-BNI对电针作用的影响.结果:100 Hz电针5次刺激抑制了可卡因(5 mg/kg)引燃CPP重建,nor-BNI(10μg/5μl)翻转了电针对可卡因CPP重建的抑制作用.结论:多次电针可通过κ阿片受体抑制可卡因引燃CPP的重建.