Role of Serotonin via 5-HT2B Receptors in the Reinforcing Effects of MDMA in Mice

The amphetamine derivative 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) reverses dopamine and serotonin transporters to produce efflux of dopamine and serotonin, respectively, in regions of the brain that have been implicated in reward. However, the role of serotonin/dopamine interactions in the behavioral effects of MDMA remains unclear. We previously showed that MDMA-induced locomotion, serotonin and dopamine release are 5-HT_2B receptor-dependent. The aim of the present study was to determine the contribution of serotonin and 5-HT_2B receptors to the reinforcing properties of MDMA.We show here that 5-HT_2B ^−/− mice do not exhibit behavioral sensitization or conditioned place preference following MDMA (10 mg/kg) injections. In addition, MDMA-induced reinstatement of conditioned place preference after extinction and locomotor sensitization development are each abolished by a 5-HT_2B receptor antagonist (RS127445) in wild type mice. Accordingly, MDMA-induced dopamine D1 receptor-dependent phosphorylation of extracellular regulated kinase in nucleus accumbens is abolished in mice lacking functional 5-HT_2B receptors. Nevertheless, high doses (30 mg/kg) of MDMA induce dopamine-dependent but serotonin and 5-HT_2B receptor-independent behavioral effects.These results underpin the importance of 5-HT_2B receptors in the reinforcing properties of MDMA and illustrate the importance of dose-dependent effects of MDMA on serotonin/dopamine interactions.     

Ketanserin pretreatment attenuates MDMA-induced dopamine release in the striatum as measured by in vivo microdialysis

Systemic administration of the amphetamine analogue, 3,4-methylenedioxymethamphetamine (MDMA) produced a dose-dependent increase in the extracellular concentration of dopamine (DA) in the striatum as measured by in vivo microdialysis in awake, freely-moving rats. The extracellular concentration of the DA metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), was significantly decreased in dialysate samples following the administration of MDMA (10 and 20 mg/kg, i.p.). The serotonin-2 (5-HT2) antagonist ketanserin (3 mg/kg, i.p.) had no effect on the extracellular concentration of DA or DOPAC in the striatum of vehicle- treated rats. The administration of ketanserin (3 mg/kg) 1 hr prior to MDMA (20 mg/kg) significantly attenuated the MDMA- induced increase in the extracellular concentration of DA without affecting the decrease in DOPAC concentrations. These data are suggestive that MDMA administration increases DA release in the striatum of awake, freely-moving rats. In addition, MDMA-induced increase in the extracellular concentration of DA in the striatum is mediated, in part, via 5-HT2 receptor mechanisms.     

Evidence for D2 receptor mediation of amphetamine-induced normalization of locomotion and dopamine transporter function in hypoinsulinemic rats

Dopamine (DA) D2 receptors regulate DA transporter (DAT) activity, and mediate some behavioral effects of amphetamine. DA clearance and amphetamine-stimulated locomotion are reduced in hypoinsulinemic [streptozotocin (STZ)-treated] rats, and these deficits are normalized by repeated treatment with amphetamine. Here, a role for D2 receptors in mediating amphetamine-induced normalization of these parameters was investigated. One week after a saline or STZ injection (50 mg/kg), rats were treated with amphetamine (1.78 mg/kg), raclopride (0.056 mg/kg), saline, or combinations thereof, every-other-day for 8 days with locomotor activity measured following each treatment. Conditioned place preference (CPP) for amphetamine and in vivo chronoamperometry to measure DA clearance were carried out on days 17 and 18, respectively, after STZ or saline. Baseline locomotion and DA clearance were significantly reduced in STZ-treated rats compared with control rats. In STZ-treated rats, amphetamine treatment normalized DA clearance, and restored the locomotor-stimulating effects of amphetamine. Raclopride prevented normalization of these parameters. Amphetamine produced CPP in both STZ-treated and control rats; raclopride significantly attenuated amphetamine-induced CPP in control and not in STZ-treated rats. These results support a role for D2 receptors in regulating DA transporter activity, and further demonstrate that D2 receptors contribute to changes in sensitivity to amphetamine in hypoinsulinemic rats.     

Role of serine racemase in behavioral sensitization in mice after repeated administration of methamphetamine

Background

The N-methyl-D-aspartate (NMDA) receptors play a role in behavioral abnormalities observed after administration of the psychostimulant, methamphetamine (METH). Serine racemase (SRR) is an enzyme which synthesizes D-serine, an endogenous co-agonist of NMDA receptors. Using Srr knock-out (KO) mice, we investigated the role of SRR on METH-induced behavioral abnormalities in mice.

Methodology/Principal Findings

Evaluations of behavior in acute hyperlocomotion, behavioral sensitization, and conditioned place preference (CPP) were performed. The role of SRR on the release of dopamine (DA) in the nucleus accumbens after administration of METH was examined using in vivo microdialysis technique. Additionally, phosphorylation levels of ERK1/2 proteins in the striatum, frontal cortex and hippocampus were examined using Western blot analysis. Acute hyperlocomotion after a single administration of METH (3 mg/kg) was comparable between wild-type (WT) and Srr-KO mice. However, repeated administration of METH (3 mg/kg/day, once daily for 5 days) resulted in behavioral sensitization in WT, but not Srr-KO mice. Pretreatment with D-serine (900 mg/kg, 30 min prior to each METH treatment) did not affect the development of behavioral sensitization after repeated METH administration. In the CPP paradigm, METH-induced rewarding effects were demonstrable in both WT and Srr-KO mice. In vivo microdialysis study showed that METH (1 mg/kg)-induced DA release in the nucleus accumbens of Srr-KO mice previously treated with METH was significantly lower than that of the WT mice previously treated with METH. Interestingly, a single administration of METH (3 mg/kg) significantly increased the phosphorylation status of ERK1/2 in the striatum of WT, but not Srr-KO mice.

Conclusions/Significance

These findings suggest first, that SRR plays a role in the development of behavioral sensitization in mice after repeated administration of METH, and second that phosphorylation of ERK1/2 by METH may contribute to the development of this sensitization as seen in WT but not Srr-KO mice.     

Ketamine pretreatment exacerbated 3,4-methylenedioxymethamphetamine-induced central dopamine toxicity

Currently, joint use of ketamine and 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) represents a specific combination of polydrug abuse. Long-lasting and even aggravated central neuronal toxicity associated with mixing ketamine and MDMA use is of special concern. This study was undertaken to examine the modulating effects of ketamine treatment on later MDMA-induced dopamine and serotonin neurotoxicity. We found that repeated administration of ketamine (50 mg/kg x 7) at 1.5-h intervals did not render observable dopamine or serotonin depletion in catecholaminergic target regions examined. In contrast, three consecutive doses of MDMA (20 mg/kg each) at 2-h intervals produced long-lasting dopamine and serotonin depletions in striatum, nucleus accumbens and prefrontal cortex. More importantly, pretreatment with binge doses of ketamine (50 mg/kg x 7 at 1.5-h intervals) 12 h prior to the MDMA dosing regimen (20 mg/kg x 3 at 2-h intervals) aggravated the MDMA-induced dopaminergic toxicity. Nonetheless, such binge doses of ketamine treatment did not affect MDMA-induced serotonergic toxicity. These results, taken together, indicate that binge use of ketamine specifically enhances the MDMA-induced central dopaminergic neurotoxicity in adult mouse brain.     

Differential effects of accumbens core vs. shell lesions in a rat concurrent conditioned place preference paradigm for cocaine vs. social interaction

Background

A main challenge in the therapy of drug dependent individuals is to help them reactivate interest in non-drug-associated activities. Among these activities, social interaction is doubly important because treatment adherence itself depends on it. We previously developed a rat experimental model based on the conditioned place preference (CPP) paradigm in which only four 15-min episodes of social interaction with a gender- and weight-matched male conspecific (i) reversed CPP from cocaine to social interaction despite continuing cocaine training and (ii) prevented the reinstatement of cocaine CPP. In the present study, we investigated if the two subregions of the nucleus accumbens (Acb), i.e., the core (AcbC) and the shell (AcbSh), would differentially affect CPP for cocaine vs social interaction.

Methodology/Principal Findings

Animals were concurrently trained for CPP pairing cocaine with one compartment and social interaction with the other (i.e., mutually exclusive stimulus presentation during training). Excitotoxic lesioning of the AcbC or the BLA shifted CPP toward social interaction, whereas AcbSh inactivation shifted CPP toward cocaine.

Conclusions

Overall, our findings suggest that inactivation of the AcbC or the BLA is sufficient to shift CPP away from a drug of abuse toward social interaction. Lesioning the AcbSh produced the opposite effect.     

Studies,using in vivo microdialysis,on the effect of the dopamine uptake inhibitor GBR 12909 on 3,4-methylenedioxymethamphetamine ('ecstasy')-induced dopamine release and free radical formation in the mouse striatum

The present study examined the mechanisms by which 3,4-methylenedioxymethamphetamine (MDMA) produces long-term neurotoxicity of striatal dopamine neurones in mice and the protective action of the dopamine uptake inhibitor GBR 12909. MDMA (30 mg/kg, i.p.), given three times at 3-h intervals, produced a rapid increase in striatal dopamine release measured by in vivo microdialysis (maximum increase to 380 +/- 64% of baseline). This increase was enhanced to 576 +/- 109% of baseline by GBR 12909 (10 mg/kg, i.p.) administered 30 min before each dose of MDMA, supporting the contention that MDMA enters the terminal by diffusion and not via the dopamine uptake site. This, in addition to the fact that perfusion of the probe with a low Ca(2+) medium inhibited the MDMA-induced increase in extracellular dopamine, indicates that the neurotransmitter may be released by a Ca(2+) -dependent mechanism not related to the dopamine transporter. MDMA (30 mg/kg x 3) increased the formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) from salicylic acid perfused through a probe implanted in the striatum, indicating that MDMA increased free radical formation. GBR 12909 pre-treatment attenuated the MDMA-induced increase in 2,3-DHBA formation by approximately 50%, but had no significant intrinsic radical trapping activity. MDMA administration increased lipid peroxidation in striatal synaptosomes, an effect reduced by approximately 60% by GBR 12909 pre-treatment. GBR 12909 did not modify the MDMA-induced changes in body temperature. These data suggest that MDMA-induced toxicity of dopamine neurones in mice results from free radical formation which in turn induces an oxidative stress process. The data also indicate that the free radical formation is probably not associated with the MDMA-induced dopamine release and that MDMA does not induce dopamine release via an action at the dopamine transporter.     

THC Prevents MDMA Neurotoxicity in Mice

The majority of MDMA (ecstasy) recreational users also consume cannabis. Despite the rewarding effects that both drugs have, they induce several opposite pharmacological responses. MDMA causes hyperthermia, oxidative stress and neuronal damage, especially at warm ambient temperature. However, THC, the main psychoactive compound of cannabis, produces hypothermic, anti-inflammatory and antioxidant effects. Therefore, THC may have a neuroprotective effect against MDMA-induced neurotoxicity. Mice receiving a neurotoxic regimen of MDMA (20 mg/kg ×4) were pretreated with THC (3 mg/kg ×4) at room (21°C) and at warm (26°C) temperature, and body temperature, striatal glial activation and DA terminal loss were assessed. To find out the mechanisms by which THC may prevent MDMA hyperthermia and neurotoxicity, the same procedure was carried out in animals pretreated with the CB₁ receptor antagonist AM251 and the CB₂ receptor antagonist AM630, as well as in CB₁, CB₂ and CB₁/CB₂ deficient mice. THC prevented MDMA-induced-hyperthermia and glial activation in animals housed at both room and warm temperature. Surprisingly, MDMA-induced DA terminal loss was only observed in animals housed at warm but not at room temperature, and this neurotoxic effect was reversed by THC administration. However, THC did not prevent MDMA-induced hyperthermia, glial activation, and DA terminal loss in animals treated with the CB₁ receptor antagonist AM251, neither in CB₁ and CB₁/CB₂ knockout mice. On the other hand, THC prevented MDMA-induced hyperthermia and DA terminal loss, but only partially suppressed glial activation in animals treated with the CB₂ cannabinoid antagonist and in CB₂ knockout animals. Our results indicate that THC protects against MDMA neurotoxicity, and suggest that these neuroprotective actions are primarily mediated by the reduction of hyperthermia through the activation of CB₁ receptor, although CB₂ receptors may also contribute to attenuate neuroinflammation in this process.     

Administration of the Glial Condition Medium in the Nucleus Accumbens Prolong Maintenance and Intensify Reinstatement of Morphine-Seeking Behavior

Accumulating evidence suggested that glial cells are involved in synaptic plasticity and behavioral changes induced by drugs abuse. The role of these cells in maintenance and reinstatement of morphine (MRP) conditioned place preference (CPP) remains poorly characterized. The aim of present study was to investigate the direct role of glial cells in nucleus accumbens (NAc) in the maintenance and reinstatement of MRP-seeking behavior. CPP induced with injection of MRP (5 mg/kg, s.c. for 3 days), lasted for 7 days after cessation of MRP treatment and priming dose of MRP (1 mg/kg, s.c.) reinstated the extinguished MRP-induced CPP. The astrocyte-conditioned medium (ACM) and neuroglia conditioned medium (NCM) exposed to MRP (10 and 100 µM) have been microinjected into the NAc. Intra-NAc administration of ACM during extinction period failed to change the maintenance of MRP-CPP, but MRP 100-treated ACM could slightly increase the magnitude of reinstatement. In contrast to ACM, intra-NAc administration of MRP 100-treated NCM caused slower extinction by 3 days and significantly increased the magnitude of reinstatement. Our findings suggest the involvement of glial cells activation in the maintenance and reinstatement of MRP-seeking behaviors, and provides new evidence that these cells might be a potential target for the treatment of MRP addiction.

     

Changes in microRNA expression profile in hippocampus during the acquisition and extinction of cocaine-induced conditioned place preference in rats

Background

MicroRNA (miRNA) emerges as important player in drug abuse. Yet, their expression profile in neurological disorder of cocaine abuse has not been well characterized. Here, we explored the changes of miRNA expression in rat hippocampus following repeated cocaine exposure and subsequent abstinence from cocaine treatment.

Results

Conditioned place preference (CPP) procedure was used to assess the acquisition and extinction of cocaine-seeking behavior in rats. MiRNA microarray was performed to examine miRNAs levels in rat hippocampus. Quantitative RT-PCR was conducted to further confirm results in microarray study. Finally, bioinformatic predictions were made to suggest potential target genes of cocaine-responsive miRNA in this study. MiRNA array found that 34 miRNA levels were changed in rat hippocampus while acquiring cocaine CPP and 42 miRNAs levels were altered after the cocaine-induced CPP were extinguished, as compared to normal controls. The findings from qRT-PCR study support results from microarray analysis.

Conclusions

The current study demonstrated dynamic changes in miRNA expression in rat hippocampus during the acquisition and extinction of cocaine-induced CPP. Some miRNAs which have been previously reported to be involved in brain disorders and drug abuse, including miR-133b, miR-134, miR-181c, miR-191, miR-22, miR-26b, miR-382, miR-409-3p and miR-504, were found to be changed in their expression following repeated cocaine exposure and subsequent abstinence from cocaine treatment. These findings may extend our understanding of the regulatory network underlying cocaine abuse and may provide new targets for the future treatment of drug abuse.     

Evidence for a role of Hsp70 in the neuroprotection induced by heat shock pre-treatment against 3,4-methylenedioxymethamphetamine toxicity in rat brain

3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') produces acute hyperthermia which increases the severity of the selective serotoninergic neurotoxicity produced by the drug in rats. Heat shock protein 70 (Hsp70) is a major inducible cellular protein expressed in stress conditions and which is thought to exert protective functions. MDMA (12.5 mg/kg, i.p.), given to rats housed at 22 degrees C, produced an immediate hyperthermia and increased Hsp70 in frontal cortex between 3 h and 7 days after administration. MDMA, given to rats housed at low ambient temperature (4 degrees C) produced transient hypothermia followed by mild hyperthermia but no increase in Hsp70 expression, while rats treated at elevated room temperature (30 degrees C) showed enhanced hyperthermia and similar expression of Hsp70 to that seen in rats housed at 22 degrees C. Fluoxetine-induced inhibition of 5-HT release and hydroxyl radical formation did not modify MDMA-induced Hsp70 expression 3 h later. Four- or 8-day heat shock (elevation of basal rectal temperature by 1.5 degrees C for 1 h) or geldanamycin pre-treatment induced Hsp70 expression and protected against MDMA-induced serotoninergic neurotoxicity without affecting drug-induced hyperthermia. Thus, MDMA-induced Hsp70 expression depends on the drug-induced hyperthermic response and not on 5-HT release or hydroxyl radical formation and pre-induction of Hsp70 protects against the long-term serotoninergic damage produced by MDMA.     

Serotonin-GABA interactions modulate MDMA-induced mesolimbic dopamine release

3,4,-Methylenedioxymethamphetamine (MDMA; 'ecstasy') acts at monoamine nerve terminals to alter the release and re-uptake of dopamine and 5-HT. The present study used microdialysis in awake rats to measure MDMA-induced changes in extracellular GABA in the ventral tegmental area (VTA), simultaneous with measures of extracellular dopamine (DA) in the nucleus accumbens (NAC) shell. (+)-MDMA (0, 2.5, 5 and 10 mg/kg, i.p.) increased GABA efflux in the VTA with a bell-shaped dose-response. This increase was blocked by application of TTX through the VTA probe. MDMA (5 mg/kg) increased 5-HT efflux in VTA by 1037% (p < 0.05). The local perfusion of the 5-HT(2B/2C) antagonist SB 206553 into the VTA reduced VTA GABA efflux after MDMA from a maximum of 229% to a maximum of 126% of basal values (p < 0.05), while having no effect on basal extracellular GABA concentrations. DA concentrations measured simultaneously in the NAC shell were increased from a maximum of 486% to 1320% (p < 0.05). The selective DA releaser d-amphetamine (AMPH) (4 mg/kg) also increased VTA GABA efflux (180%), did not alter 5-HT and increased NAC DA (875%) (p < 0.05), but the perfusion of SB 206553 into the VTA failed to alter these effects. These results suggest that MDMA-mediated increases in DA within the NAC shell are dampened by increases in VTA GABA subsequent to activation of 5-HT(2B/2C) receptors in the VTA.     

Effect of 3,4-Methylenedioxymethamphetamine on 3,4-Dihydroxyphenylalanine Accumulation in the Striatum and Nucleus Accumbens

The effect of the racemic mixture of 3,4-methylenedioxymethamphetamine (MDMA) on the synthesis of dopamine in the terminals of nigrostriatal and mesolimbic neurons was estimated by measuring the accumulation of 3,4-dihydroxyphenylalanine (DOPA) in the striatum and nucleus accumbens 30 min following the administration of the L-aromatic amino acid decarboxylase inhibitor, 3-hydroxybenzylhydrazine. MDMA produced an increase in DOPA accumulation in the striatum which was greater in magnitude and longer in duration than that in the nucleus accumbens. Although the concentrations of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in both the striatum and nucleus accumbens were reduced 3 h following an injection of MDMA (20 mg/kg), 5-HT and 5-HIAA concentrations were significantly reduced only in the striatum 7 days after the administration of MDMA. Pretreatment with a 5-HT2 antagonist, ketanserin, significantly attenuated the reduction in 5-HT concentration in the striatum 3 h following MDMA administration and completely blocked 5-HT depletion at 7 days post administration. Moreover, ketanserin completely blocked MDMA-induced DOPA accumulation in the striatum. The results obtained in these studies suggest that MDMA activates nigrostriatal dopaminergic pathways via 5-HT2 receptors. In addition, these data are supportive of the hypothesis that dopamine plays a role in MDMA-induced 5-HT depletion.     

Methylenedioxymethamphetamine (MDMA; Ecstasy) suppresses IL-1beta and TNF-alpha secretion following an in vivo lipopolysaccharide challenge

In this study we examined the effects of methylenedioxymethamphetamine (MDMA) administration on responsiveness to an in vivo immune challenge with lipopolysaccharide (LPS; 100 microg/kg; i.p.). LPS produced an increase in circulating IL-1beta and TNF-alpha in control animals. MDMA (20 mg/kg; i.p.) significantly impaired LPS-induced IL-1beta and TNF-alpha secretion. The suppressive effect of MDMA on IL-1beta secretion was transient and returned to control levels within 3 hours of administration. In contrast, the MDMA-induced suppression of TNF-alpha secretion was evident for up to 12 hours following administration. In a second study we examined the effect of co-administration of MDMA (5, 10 and 20 mg/kg; i.p.) on LPS-induced IL-1beta and TNF-alpha secretion, and demonstrated that all three doses potently suppressed LPS-induced TNF-alpha secretion, but only MDMA 10 and 20 mg/kg suppressed LPS-induced IL-1beta secretion. In addition, serum MDMA concentrations displayed a dose-dependent increase, with the concentrations achieved following administration of 5 and 10 mg/kg being in the range reported in human MDMA abusers. In order to examine the possibility that the suppressive effect of MDMA on IL-1beta and TNF-alpha could be due to a direct effect of the drug on immune cells, the effect of in vitro exposure to MDMA on IL-1beta and TNF-alpha production in LPS-stimulated diluted whole blood was evaluated. However IL-1beta or TNF-alpha production were not altered by in vitro exposure to MDMA. In conclusion, these data demonstrate that acute MDMA administration impairs IL-1beta and TNF-alpha secretion following an in vivo LPS challenge, and that TNF-alpha is more sensitive to the suppressive effects of MDMA than is IL-1beta. However the suppressive effect of MDMA on IL-1beta and TNF-alpha could not be attributed to a direct effect on immune cells. The relevance of these findings to MDMA-induced immunomodulation is discussed.     

Enhancement of 3,4-methylenedioxymethamphetamine neurotoxicity by the energy inhibitor malonate

The acute and long-term effects of the local perfusion of 3,4-methylenedioxymethamphetamine (MDMA) and the interaction with the mitochondrial inhibitor malonate (MAL) were examined in the rat striatum. MDMA, MAL or the combination of MAL with MDMA was reverse dialyzed into the striatum for 8 h via a microdialysis probe while extracellular dopamine (DA) and serotonin (5-HT) were measured. One week later, tissue immediately surrounding the probe was assayed for DA and 5-HT tissue content. Local perfusion of MDMA increased DA and 5-HT release but did not produce long-term depletion of DA or 5-HT in tissue. Malonate also increased both DA and 5-HT release but, in contrast to MDMA, produced only long-term depletion of DA. The combined perfusion of MDMA/MAL synergistically increased the release of DA and 5-HT and produced long-term depletion of both DA and 5-HT in tissue. These results support the conclusion that DA, compared with 5-HT, neurons are more susceptible to mitochondrial inhibition. Moreover, MDMA, which does not normally produce DA depletion in the rat, exacerbated MAL-induced DA depletions. The effect of MDMA in combination with MAL to produce 5-HT depletion suggests a role for bio-energetic stress in MDMA-induced toxicity to 5-HT neurons. Overall, these results highlight the importance of energy balance to the function of DA and 5-HT neurons and to the toxic effects of MDMA.     

多巴胺D2受体拮抗剂、激动剂对SD大鼠条件化位置偏好的影响

通过慢性吗啡处理方式建立起SD大鼠吗啡依赖的条件化位置偏好(CPP)模型,用行为学手段研究多巴胺(DA)D2受体拮抗剂及激动剂对SD大鼠CPP的影响,探讨眶额叶DAD2受体在阿片精神依赖中的作用。通过腹腔注射吗啡同环境因素相结合,建立大鼠吗啡依赖的CPP模型;采用局部脑内微量注射法向额叶注射DAD2受体拮抗剂或激动剂或盐水(对照组),以得到SD大鼠在戒断期间的CPP的时间数据。CPP显示DAD2受体拮抗剂组与对照组相比,从戒断第2天起,前者表现出更明显的CPP增加现象,差异显著(P<0·05)。而DAD2受体激动剂组与对照组相比无显著差异(P>0·05)。采用腹腔小剂量注射吗啡,成功地建立了吗啡依赖SD大鼠的CPP模型;眶额叶微量注射DAD2受体拮抗剂增加了CPP时间,提示眶额叶多巴胺系统在吗啡依赖的过程中有着较为重要的作用;也提示了对于已经成瘾的动物,损伤其眶额叶,会使药物渴求增强。因而提示对于药物依赖患者进行手术干预治疗要极其慎重。     

Effect of rhynchophylline on conditioned place preference on expression of NR2B in methamphetamine-dependent mice

Objective

To study the effect of rhynchophylline on N-methyl d-aspartate receptor subtype 2B subunit in hippocampus of Methamphetamine-induced conditioned place preference (CPP) mice.

Methods

Place preference mice models were established by methamphetamine; the expression of NR2B was observed by immunohistochemistry technique and Western blot.

Results

Methamphetamine (4 mg/kg)-induced place preference mice model was successfully established; ketamine (15 mg/kg), rhynchophylline (40 mg/kg) and rhynchophylline (80 mg/kg) can eliminate place preference; Immunohistochemistry showed that the number of NR2B-positive neurons in hippocampus was increased in the methamphetamine model group, whereas less NR2B-positive neurons were found in the ketamine group, low and high dosage rhynchophylline group. Western blot showed that the expression of NR2B protein was significantly increased in the model group, whereas less expression was found in the ketamine group, low and high dosage rhynchophylline group.

Conclusions

NR2B plays an important role in the formation of methamphetamine-induced place preference in mice. Rhynchophylline reversed the expression of NR2B in the hippocampus demonstrates the potential effect of mediates methamphetamine induced rewarding effect.     

Effect of Atomoxetine on Hyperactivity in an Animal Model of Attention-Deficit/Hyperactivity Disorder (ADHD)

Background

Hyperactivity related behaviors as well as inattention and impulsivity are regarded as the nuclear symptoms of attention-deficit/hyperactivity disorder (ADHD).

Purpose

To investigate the therapeutic effects of atomoxetine on the motor activity in relation to the expression of the dopamine (DA) D2 receptor based on the hypothesis that DA system hypofunction causes ADHD symptoms, which would correlate with extensive D2 receptor overproduction and a lack of DA synthesis in specific brain regions: prefrontal cortex (PFC), striatum, and hypothalamus.

Methods

Young male spontaneously hypertensive rats (SHR), animal models of ADHD, were randomly divided into four groups according to the daily dosage of atomoxetine and treated for 21 consecutive days. The animals were assessed using an open-field test, and the DA D2 receptor expression was examined.

Results

The motor activity improved continuously in the group treated with atomoxetine at a dose of 1 mg/Kg/day than in the groups treated with atomoxetine at a dose of 0.25 mg/Kg/day or 0.5 mg/Kg/day. With respect to DA D₂ receptor immunohistochemistry, we observed significantly increased DA D₂ receptor expression in the PFC, striatum, and hypothalamus of the SHRs as compared to the WKY rats. Treatment with atomoxetine significantly decreased DA D₂ expression in the PFC, striatum, and hypothalamus of the SHRs, in a dose-dependent manner.

Conclusion

Hyperactivity in young SHRs can be improved by treatment with atomoxetine via the DA D2 pathway.     

Effects of Ifenprodil on Morphine-Induced Conditioned Place Preference and Spatial Learning and Memory in Rats

Drug addiction, as well as learning and memory, share common mechanisms in terms of neural circuits and intracellular signaling pathways. In the present study, the role of N-methyl-D-aspartate (NMDA) receptors, particularly those containing NR2B subunits, in morphine-induced conditioned place preference (CPP) and Morris water maze (MWM) learning and memory task was investigated. CPP was used as a paradigm for assessing the rewarding effect of morphine, and MWM was used to measure spatial learning and memory in male Sprague–Dawley rats. We found that ifenprodil, an antagonist highly selective for NR2B-containing NMDA receptors, dose-dependently blocked the development, maintenance and reinstatement of morphine-induced CPP, without evident impairment of the acquisition and retrieval of spatial memory in the MWM task. However, the consolidation of spatial memory was disrupted by a high dose (10 mg/kg) of ifenprodil. These results clearly demonstrate that NR2B-containing NMDA receptors are actively involved in addiction memory induced by morphine conditioning, but not in the acquisition and retrieval of spatial learning and memory. In conclusion, NR2B-containing NMDA receptors can be considered potential targets for the treatment of opiate addiction.     

Neurochemical Interactions of Competitive N-Methyl-D-Aspartate Antagonists with Dopaminergic Neurotransmission and the Cerebellar Cyclic GMP System: Functional Evidence for a Phasic Glutamatergic Control of the Nigrostriatal Dopaminergic Pathway

Direct intrastriatal injection of N-methyl-D-aspartate (NMDA; 100 micrograms/rat) increased striatal dopamine (DA) release in vivo. However, parenteral administration of (+/-)-3-(2-carboxypiperizin-4-yl)propyl-1-phosphonic acid (CPP) and cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS-19755) did not alter DA metabolism and release in several brain regions in the rat and mouse. Intracerebroventricular administration of the competitive NMDA antagonists CPP, CGS-19755, 2-amino-5-phosphonopentanoate, and 2-amino-7-phosphonoheptanoate did not alter rat striatal DA metabolism and release but profoundly reduced cerebellar cyclic GMP (cGMP) levels in the same animals. CPP and CGS-19755 decreased basal cerebellar cGMP levels in the mouse with ED50 values of 6 and 1 mg/kg, i.p., respectively. CPP antagonized the harmaline-induced increases in cGMP levels with an ED50 value of 5.0 mg/kg, i.p. CPP (25 mg/kg, i.p.) also decreased basal cGMP levels in mouse cerebellum for up to 3 h, a result suggesting brain bioavailability and a long duration of NMDA receptor antagonism in vivo. These contrasting patterns suggest that NMDA receptors exert a tonic excitatory tone on the guanine nucleotide signal transduction pathway in the cerebellum while exerting a phasic control over nigrostriatal dopaminergic neurotransmission. These results also indicate that competitive NMDA antagonists, unlike phencyclidine receptor agonists, may not mediate biochemical and behavioral effects via dopaminergic mechanisms.