Post-treatment of dextromethorphan on methamphetamine-induced drug-seeking and behavioral sensitization in rats

In our previous study, we first demonstrated a significant effect of dextromethorphan (DM) on morphine‐seeking behavior in morphine‐dependent rats, when DM was given during morphine withdrawal. Using the same conditioned place preference (CPP) paradigm modified for measuring drug‐seeking‐related behavior, we further investigated the possible effect of DM on methamphetamine (MA)‐seeking in MA‐dependent rats. Our data showed that DM could also effectively suppress the drug‐seeking behavior for MA, when administered during MA withdrawal. This suggests that DM may possess a pharmacological property to prevent drug‐seeking behavior for addictive drugs in general. To examine the action sites of DM in the brain, DM was microinjected into the VTA or the NAc, and tested for its effect on MA‐seeking during withdrawal. Both intra‐VTA and intra‐NAc injections of DM were able to block the MA‐seeking, suggesting that DM has a dual action sites. In our neurochemical results, intra‐NAc injection of DM showed a clear reduction of DA turnover rate at the NAc and the mPFC in response to MA challenge during withdrawal, which matched with the behavioral results. However, intra‐VTA injection of DM reduced the DA turnover rate at the mPFC but did not have effect on the DA turnover rate at the NAc. Although further investigations may be needed to verify the connection between our neurochemical and behavioral results, the present study highlights the therapeutic potential of DM in antidrug‐seeking behavior of MA and that the mechanism could be related to its effect on the mesolimbic and mesocortical dopaminergic pathways. Synapse 2012. © 2012 Wiley Periodicals, Inc.     

The CaMKII-dependent phosphorylation of GABAB receptors in the nucleus accumbens was involved in cocaine-induced behavioral sensitization in rats

Background

Previous studies have established that the regulation of prolonged, distal neuronal inhibition by the GABA_B heteroreceptor (GABA_BR) is determined by its stability, and hence residence time, on the plasma membrane.

Aims

Here, we show that GABA_BR in the nucleus accumbens (NAc) of rats affects the development of cocaine-induced behavioral sensitization by mediating its perinucleus internalization and membrane expression.

Materials & Methods

By immunofluorescent labeling, flow cytometry analysis, Co-immunoprecipitation and open field test, we measured the role of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) to the control of GABA_BR membrane anchoring and cocaine induced-behavioral sensitization.

Results

Repeated cocaine treatment in rats (15 mg/kg) significantly decreases membrane levels of GABA_B1R and GABA_B2R in the NAc after day 3, 5 and 7. The membrane fluorescence and protein levels of GABA_BR was also decreased in NAc GAD₆₇⁺ neurons post cocaine (1 μM) treatment after 5 min. Moreover, the majority of internalized GABA_B1Rs exhibited perinuclear localization, a decrease in GABA_B1R-pHluroin signals was observed in cocaine-treated NAc neurons. By contrast, membrane expression of phosphorylated CaMKII (pCaMKII) post cocaine treatment was significantly increased after day 1, 3, 5 and 7. Baclofen blocked the cocaine induced behavioral sensitization via inhibition of cocaine enhanced-pCaMKII-GABA_B1R interaction.

Conclusion

These findings reveal a new mechanism by which pCaMKII-GABA_BR signaling can promote psychostimulant-induced behavioral sensitization.     

脑深部电刺激对吗啡心理依赖大鼠伏核多巴胺受体的影响

目的探讨脑深部电刺激(DBS)对大鼠双侧伏核多巴胺D1A受体(D1AR)和D2受体(D2R)表达的影响以及多巴胺受体(DAR)在DBS治疗吗啡心理依赖中的作用。方法将60只SD大鼠随机分为假刺激组(ShS组)、电刺激组(DBS组)和生理盐水对照组(NS组),20只/组。用免疫组化法和RT-PCR法检测各组大鼠伏核多巴胺D1AR和D2R表达的变化。结果ShS组伏核D1AR阳性细胞数较NS组、DBS组明显增多(P0.01),而DBS组与NS组比较,差异无统计学意义(P0.05);三组间D1ARmRNA比较,差异无统计学意义(P0.05)。DBS组大鼠D2R阳性细胞数较NS组明显下降(P0.01),但较ShS组明显上升(P0.01);ShS组大鼠伏核D2RmRNA较NS组及DBS组显著上升(P0.01),而DBS组与NS组比较,差异无统计学意义(P0.05)。结论DBS对吗啡心理依赖大鼠伏核D1AR和D2R的表达起反向调节作用。     

Silencing dopamine D3-receptors in the nucleus accumbens shell in vivo induces changes in cocaine-induced hyperlocomotion

The dopamine D(3) receptor (D(3)R) is an important pharmacotherapeutic target for its potential role in psychiatric disorders and drug dependence. To further explore its function in rats, a regulatable lentivirus, Lenti-D3, holding the rat D(3)R cDNA, has been constructed as well as three nonregulatable lentiviruses, Lenti-D3-siRNA1, Lenti-D3-siRNA2 and Lenti-D3-siRNA3, expressing small hairpin RNAs, aimed at silencing D(3)R expression and specifically targeted against different regions of the D(3)R mRNA. In vitro, Lenti-D3 expressed D(3)R and could efficiently be blocked with Lenti-D3-Sils. These viruses were stereotaxically injected into the shell part of the nucleus accumbens (NAcc) and effects of passive cocaine delivery on locomotor activity were assessed. Manipulations of D(3)R levels induced changes in the locomotor stimulant effects of cocaine as compared to control treatment. Suppression of dopamine (DA) D(3)R in the NAcc by means of local knockdown (with Lenti-D3-Sils) increased locomotor stimulant effects, whereas its overexpression with Lenti-D3 drastically reduced them. The latter effects could be reversed when animals were fed doxycycline, which prevented lentiviral-mediated DA D(3)R overexpression in the NAcc. Gene expression assessed by quantitative RT-PCR confirmed very efficient gene knockdown in vivo in animals treated with Lenti-D3-Sils (> 93% silencing of D(3)R gene). Thus D(3)R expression significantly contributes to behavioural changes associated with chronic cocaine delivery.     

Inputs from the basolateral amygdala to the nucleus accumbens shell control opiate reward magnitude via differential dopamine D1 or D2 receptor transmission

The basolateral amygdala (BLA), ventral tegmental area and nucleus accumbens (NAc) form a functionally connected neural circuit involved in the processing of opiate-related reward and memory. Dopamine (DA) projections from the ventral tegmental area to the BLA modulate associative plasticity mechanisms within the BLA. However, the role of DA receptor signaling in the BLA and its functional outputs to the NAc during opiate reward processing is not currently understood. Using an unbiased place conditioning procedure, we measured the rewarding effects of morphine following intra-BLA microinfusions of specific DA D1 or D2 receptor agonists in either opiate-naive or opiate-dependent/withdrawn rats. Activation of intra-BLA D1 receptors strongly potentiated the behaviorally rewarding effects of opiates, only in the opiate-naive state. However, once opiate dependence and withdrawal occurred, the intra-BLA DA-mediated potentiation of opiate reward salience switched to a D2 receptor-dependent substrate. We next performed single-unit, in-vivo extracellular neuronal recordings in the NAc shell (NA shell), to determine if intra-BLA D1/D2 receptor activation may modulate the NA shell neuronal response patterns to morphine. Consistent with our behavioral results, intra-BLA D1 or D2 receptor activation potentiated NAc 'shell' (NA shell) neuronal responses to sub-reward threshold opiate administration, following the same functional boundary between the opiate-naive and opiate-dependent/withdrawn states. Finally, blockade of N-methyl-d-aspartate transmission within the NA shell blocked intra-BLA DA D1 or D2 receptor-mediated opiate reward potentiation. Our findings demonstrate a novel and functional DA D1/D2 receptor-mediated opiate reward memory switch within the BLA→NA shell circuit that controls opiate reward magnitude as a function of opiate exposure state.     

Distinct effects of enriched environment on dopamine clearance in nucleus accumbens shell and core following systemic nicotine administration

Environmental enrichment during development may reduce drug abuse liability by modulating dopamine transporter (DAT) function. Nucleus accumbens (NAc) shell and core respond differentially to regulate the rewarding properties and locomotor stimulant effects of psychostimulants. The current study evaluated dopamine (DA) clearance (CL_DA) in the NAc shell and core using in vivo voltammetry in rats raised in an enriched condition (EC) or an impoverished condition (IC) and determined the effect of nicotine (0.4 mg/kg) on CL_DA. Baseline CL_DA in NAc shell and core was not different between EC and IC rats. In the saline control group, CL_DA in NAc shell was greater across time in IC when compared with EC rats, whereas CL_DA in NAc core was greater in EC rats when compared with IC rats. Consistent with these findings, opposite effects of enrichment on DA clearance in shell and core were obtained following acute nicotine administration. In NAc shell, nicotine increased CL_DA in EC rats, but not in IC rats. Conversely, in NAc core, nicotine increased CL_DA in IC rats, but not in EC rats. The current results demonstrate that environmental enrichment differentially regulates the response to nicotine in NAc shell and core via alterations in DAT function, which may explain how environmental enrichment reduces the behavioral response to nicotine. Synapse, 2013. © 2012 Wiley Periodicals, Inc.     

The dopamine patchwork of the rat nucleus accumbens core

The dopamine (DA) terminal field in the rat dorsal striatum is organized as a patchwork of domains that show distinct DA kinetics. The rate and short‐term plasticity of evoked DA release, the rate of DA clearance and the actions of several dopaminergic drugs are all domain‐dependent. The patchwork arises in part from local variations in the basal extracellular concentration of DA, which establishes an autoinhibitory tone in slow but not fast domains. The present study addressed the hypothesis that a domain patchwork might also exist in the nucleus accumbens core (NAcc), a DA terminal field that is deeply involved in reward processing and the mechanisms underlying substance abuse. DA recordings in the NAcc by fast‐scan voltammetry during electrical stimulation of the medial forebrain bundle confirmed that the NAcc contains a patchwork of fast and slow domains showing significantly different rates of evoked DA release and DA clearance. Moreover, the NAcc domains are substantially different from those in the dorsal striatum. There were no signs in the NAcc of short‐term plasticity of DA release during multiple consecutive stimuli, and no signs of a domain‐dependent autoinhibitory tone. Thus, the NAcc domains are distinct from each other and from the domains of the dorsal striatum.     

Increased dopamine D3 receptor expression accompanying behavioral sensitization to nicotine in rats

Behavioral sensitization to nicotine, which appears following repeated nicotine administration, has been suggested to take part in the development of smoking habit in humans. The mesolimbic dopaminergic system plays a role in this process and a hypersensitivity of postsynaptic neurons of the nucleus accumbens as been proposed as a mechanism, but changes in dopamine D(1) or D(2) receptors have not been demonstrated to date. A challenge administration of nicotine (0.5 mg/kg s.c.) produced a strong increase in locomotor activity in rats repeatedly pretreated with nicotine (0.5 mg/kg s.c.), but not saline, once a day for 5 days. This behavioral sensitization was accompanied by an increase in D(3) receptor binding and mRNA in the shell of nucleus accumbens. D(3) receptor expression was unchanged in the core of nucleus accumbens and dorsal striatum, as it was in the shell of nucleus accumbens after an acute administration of nicotine to naive rats. In contrast, no changes were noticed in D(1) and D(2) receptor expressions in any brain region examined after chronic or acute treatment with nicotine. In addition, nicotine challenge decreased preprodynorphin and preprotachykinin mRNA levels in naive rats, but only preprotachykinin mRNA levels in rats pretreated with nicotine. These biochemical changes resemble those occurring during behavioral sensitization to levodopa of dopamine-denervated rats, which had been causally related to the induction of D(3) receptor expression. We propose that a similar mechanism is responsible for behavioral sensitization to nicotine.     

Effect of lead exposure on dopaminergic receptors in rat striatum and nucleus accumbens

Haloperidol- and sulpiride-displaceable [3H]spiroperidol binding and the dopamine-inhibited adenylate cyclase were measured in rats chronically exposed to lead acetate. Haloperidol-displaceable [3H]spiroperidol binding was unmodified while sulpiride-displaceable binding was increased in striatum and decreased in nucleus accumbens. In addition, the decrease of sulpiride-displaceable binding in nucleus accumbens was paralleled by a reduced ability of bromocriptine to inhibit cAMP formation in presence of the D1 receptor antagonist SCH 23390. The results support the concept that in vivo lead treatment affects dopaminergic receptors and that the binding sites labelled by [3H]spiroperidol displaced by haloperidol may be different from those which recognize sulpiride.     

Neonatal ventral hippocampal lesions potentiate amphetamine-induced increments in dopamine efflux in the core, but not the shell, of the nucleus accumbens.

BACKGROUND: In rats, neonatal ventral hippocampal lesions (NVHLs) result in the postpubertal emergence of alterations reminiscent of several features of schizophrenia, including increased responsivity to the behavioral effects of amphetamine (AMPH). The precise nature of presynaptic aspects of accumbal dopamine (DA) function in these alterations is however uncertain: previous studies have found that the exacerbated responses to AMPH of NVHL rats are associated with either decreased or unchanged DA efflux in the nucleus accumbens (NAc) as compared with shams. Because these studies investigated DA output in the whole NAc, it was considered of interest to examine the impact of NVHLs on DA transmission in NAc subregions involved in distinct aspects of goal-directed behavior. METHODS: The effects of AMPH (.25 mg/kg, subcutaneous) on the accumbal DA efflux of adult rats were evaluated using brain microdialysis, and motor activity was recorded alongside dialysate sample collection. RESULTS: The enhanced behavioral responsivity to AMPH of NVHL rats is associated with potentiation of AMPH-induced DA output in the NAc core and a concomitant attenuation of DA overflow in the NAc shell. CONCLUSIONS: The functional alterations in the NAc core induced by NVHLs provide a link between the hippocampal damage and striatal DA hyperactivity in schizophrenia.     

Stressor controllability modulates stress-induced serotonin but not dopamine efflux in the nucleus accumbens shell

The ability of an organism to control a stressor can modulate many of the consequences of stress. Previous research indicates that uncontrollable stress (inescapable shock, IS) activates serotonergic (5-HT) neurons of the dorsal raphe nucleus (DRN) to a greater degree than controllable stress (escapable shock, ES), potentiating 5-HT efflux in the DRN and in target regions. Previous research also indicates that IS selectively affects dopamine (DA) efflux. The present study measured 5-HT and DA efflux in the NAc shell during IS or ES using in vivo microdialysis. Male Sprague Dawley rats with probes in the NAc shell were dialysed while subjected to 100 1.0 mA tailshocks. Rats were run in yoked pairs in wheel-turn boxes such that one rat (ES) in the pair could terminate the shock received by both himself and his yoked (IS) partner by a behavioral response. No stress controls remained in the dialysis bowls. 5-HT efflux selectively increased during IS, and remained increased throughout as well as after the stress session. There was no effect of stress on DA efflux. These results indicate that the NAc 5-HT response is preferentially sensitive to stress and can be modulated by stressor controllability.     

Hyperpolarizing and depolarizing actions of dopamine via D-1 and D-2 receptors on nucleus accumbens neurons

The effect of dopamine (DA) on the nucleus accumbens neurons in guinea-pig brain slices was studied by intracellular recordings. DA caused a hyperpolarization in 28% of the neurons tested, a depolarization in 11%, and a hyperpolarization followed by a depolarization in 53%. The remaining neurons were unaffected. Analyses of the responses revealed that the DA hyperpolarization was produced by activation of the D-1 receptor and associated with an increase in potassium conductance, whereas the DA depolarization was generated by activation of the D-2 receptor and accompanied by a decrease in potassium conductance. DA uptake inhibitors augmented both the hyperpolarizing and depolarizing responses, while cyclic adenosine monophosphate selectively enhanced the former.     

Group III metabotropic glutamate receptors and D1-like and D2-like dopamine receptors interact in the rat nucleus accumbens to influence locomotor activity

Evidence for functional interactions between metabotropic glutamate (mGlu) receptors and dopamine (DA) neurotransmission is now clearly established. In the present study, we investigated interactions between group III mGlu receptors and D1- and D2-like receptors in the nucleus accumbens (NAcc). Administration, into the NAcc, of the selective group III mGlu receptor agonist, AP4, resulted in an increase in locomotor activity, which was blocked by pretreatment with the group III mGlu receptor antagonist, MPPG. In addition, pretreatment with AP4 further blocked the increase in motor activity induced by the D1-like receptor agonist, SKF 38393, but potentiated the locomotor responses induced by either the D2-like receptor agonist, quinpirole, or coinfusion of SKF 38393 and quinpirole. MPPG reversed the effects of AP4 on the motor responses induced by D1-like and/or D2-like receptor activation. These results confirm that glutamate transmission may control DA-dependent locomotor function through mGlu receptors and further indicate that group III mGlu receptors oppose the behavioural response produced by D1-like receptor activation and favour those produced by D2-like receptor activation.     

Chronic bupropion attenuated the anhedonic component of nicotine withdrawal in rats via inhibition of dopamine reuptake in the nucleus accumbens shell

Bupropion, a dopamine reuptake inhibitor, is an effective therapy for smoking cessation, but the behavioral and neurochemical mechanisms mediating its antismoking properties are relatively unknown. To explore the hypothesis that bupropion ameliorates nicotine withdrawal partly by a dopamine-dependent mechanism, we investigated the effects of chronic bupropion on potassium-stimulated dopamine overflow in the nucleus accumbens shell in nicotine-withdrawing rats. We also assessed the effects of chronic bupropion on behavioral aspects of nicotine withdrawal measured by elevations in brain reward thresholds and somatic signs of withdrawal. Rats were treated with nicotine or saline for 7 days and then coadministration of bupropion or saline was initiated. After 14 days of coadministration of bupropion/saline and nicotine/saline, nicotine/saline administration was terminated, whereas bupropion/saline administration continued. These conditions mimic bupropion administration in human smokers. Cessation of nicotine administration in non-bupropion-treated rats elevated reward thresholds reflecting a reward deficit, increased somatic signs and diminished potassium-evoked dopamine overflow in the nucleus accumbens shell. Chronic bupropion lowered reward thresholds and increased potassium-evoked dopamine release regardless of previous nicotine exposure, possibly by inhibition of dopamine reuptake, and thus attenuated the anhedonic and neurochemical effects of nicotine withdrawal. Chronic bupropion blocked withdrawal-associated increased somatic signs. Finally, acute experimenter-administered nicotine enhanced brain reward function equally in all groups, indicating that bupropion does not alter the reward-facilitating effects of experimenter-administered nicotine. In conclusion, the bupropion-induced increase in extracellular dopamine in the nucleus accumbens shell may ameliorate the anhedonia associated with nicotine withdrawal, which in turn may facilitate smoking cessation.     

Methylphenidate dose–response behavioral and neurophysiological study of the ventral tegmental area and nucleus accumbens in adolescent rats

The psychostimulant methylphenidate (MPD) is the most common medication used in treating ADHD in children. Studies have shown an increasing prevalence among adolescents without ADHD to take MPD as a cognitive booster and recreational drug, even though it is a Schedule II drug and has a high potential for abuse. The objective of this study is to explore if there is an association between the animals’ behavioral and neurophysiological responses to acute and/or chronic methylphenidate exposure within the ventral tegmental area and the nucleus accumbens, and to compare how these two brain structures fire in response to methylphenidate. Freely moving adolescent rats implanted with semimicroelectrodes within the VTA and NAc were divided into three MPD dosing groups: 0.6, 2.5, and 10 mg/kg i.p., as well as a saline control group. The animals were divided into two groups based on their behavioral responses to chronic MPD, behavioral sensitization and tolerance, and the neuronal responses of the two groups were compared for each MPD dosing. Significant differences in the proportion of neuronal units in the VTA and NAc responding to MPD were observed at the 0.6 and 10.0 mg/kg MPD dosing groups. Moreover, the same doses of 0.6, 2.5, and 10.0 mg/kg MPD elicited behavioral sensitization in some animals and behavioral tolerance in others. This specific study shows that the VTA and NAc neurons respond differently to the same doses of MPD. MPD has different neuronal and behavioral effects depending on the individual, the dosage of MPD, and the brain structure studied.     

Changes in dendritic spine density in the nucleus accumbens do not underlie ethanol sensitization

Behavioral sensitization to various drugs of abuse has been shown to change dendritic spine density and/or morphology of nucleus accumbens (NAc) medium spiny neurons, an effect seen across drug classes. However, is it not known whether behavioral sensitization to ethanol (EtOH) is also associated with structural changes in this region. Here we compared dendritic spine density and morphology between mice showing High vs. Low levels of EtOH sensitization and found that high levels of EtOH sensitization were not associated with changes in dendritic spine density or spine type. Unexpectedly, however, a significant increase in the density of stubby‐type spines was seen in mice that were resistant to sensitization. Since the presence of this spine type has been associated with long‐term depression and cognitive/learning deficits this may explain why these mice fail to sensitize and why they show poor performance in conditioning tasks, as previously shown. A possible causal role for structural plasticity in behavioral sensitization to various drugs has been debated. In the case of EtOH sensitization, our results suggest that drug‐induced changes in structural plasticity in the accumbens neurons may not be the cause of sensitized behavior. Synapse 69:607–610, 2015 . © 2015 Wiley Periodicals, Inc.     

Interactions of cholecystokinin octapeptide and dopamine on nucleus accumbens neurons

Local microiontophoretic administration of cholecystokinin octapeptide (CCK) increased the firing rates of neurons in the dorsomedial nucleus accumbens (NAc), but exerted little to no effect on lateral NAc neurons. This regionally defined CCK-effect corresponds to the topographical distribution of CCK-like immunoreactive nerve terminal fiber networks and CCK receptors within the NAc. The excitatory effects of CCK were selectively antagonized by the CCK antagonist proglumide. Dopamine (DA) decreased the firing of NAc cells and reversed CCK-induced excitation. These results suggest that CCK and DA may interact to influence the activity of neurons within the dorsomedial NAc.     

伏隔核毁损对MAP模型大鼠行为及脑内DA受体的影响

目的 探讨立体定向伏隔核毁损对甲基苯丙胺（MAP）模型大鼠行为学及不同脑区多巴胺D2受体表达的影响。方法 将80只SD大鼠随机分为对照组、模型组、假手术组和手术组，每组各20只。经腹腔注射MAP制备精神分裂症模型，采用立体定向一直流电毁损伏隔核，观察大鼠刻板行为变化；并采用原位杂交法观察额叶、颞叶、边缘区及脑干部位的D2受体表达。结果 与对照组比较，模型组及假手术组大鼠刻板行为评分及各个脑区D2受体表达均显著性增加；与模型组及假手术组比较，手术组大鼠刻板行为评分及各脑区DA受体阳性细胞数目均显著性减少。结论 伏隔核毁损可能通过抑制MAP诱发的脑内D2表达亢进而改变其行为学异常。