Conditioned Place Preference Scores Research Articles

High frequency deep brain stimulation of the dorsal raphe nucleus prevents methamphetamine priming-induced reinstatement of drug seeking in rats

Drug addiction represents a multifaceted and recurrent brain disorder that possesses the capability to create persistent and ineradicable pathological memory. Deep brain stimulation (DBS) has shown a therapeutic potential for neuropsychological disorders, while the precise stimulation targets and therapeutic parameters for addiction remain deficient. Among the crucial brain regions implicated in drug addiction, the dorsal raphe nucleus (DRN) has been found to exert an essential role in the manifestation of addiction memory. Thus, we investigated the effects of DRN DBS in the treatment of addiction and whether it might produce side effects by a series of behavioral assessments, including methamphetamine priming-induced reinstatement of drug seeking behaviors, food-induced conditioned place preference (CPP), open field test and elevated plus-maze test, and examined brain activity and connectivity after DBS of DRN. We found that high-frequency DBS of the DRN significantly lowered the CPP scores and the number of active-nosepokes in the methamphetamine-primed CPP test and the self-administration model. Moreover, both high-frequency and sham DBS group rats were able to establish significant food-induced place preference, and no significant difference was observed in the open field test and in the elevated plus-maze test between the two groups. Immunofluorescence staining and functional magnetic resonance imaging revealed that high-frequency DBS of the DRN could alter the activity and functional connectivity of brain regions related to addiction. These results indicate that high-frequency DBS of the DRN effectively inhibits methamphetamine priming-induced relapse and seeking behaviors in rats and provides a new target for the treatment of drug addiction.

3'-Deoxyadenosin alleviates methamphetamine-induced aberrant synaptic plasticity and seeking behavior by inhibiting the NLRP3 inflammasome.

JOURNAL/nrgr/04.03/01300535-202410000-00028/figure1/v/2024-02-06T055622Z/r/image-tiff Methamphetamine addiction is a brain disorder characterized by persistent drug-seeking behavior, which has been linked with aberrant synaptic plasticity. An increasing body of evidence suggests that aberrant synaptic plasticity is associated with the activation of the NOD-like receptor family pyrin domain containing-3 (NLRP3) inflammasome. 3'-Deoxyadenosin, an active component of the Chinese fungus Cordyceps militaris, has strong anti-inflammatory effects. However, whether 3'-deoxyadenosin attenuates methamphetamine-induced aberrant synaptic plasticity via an NLRP3-mediated inflammatory mechanism remains unclear. We first observed that 3'-deoxyadenosin attenuated conditioned place preference scores in methamphetamine-treated mice and decreased the expression of c-fos in hippocampal neurons. Furthermore, we found that 3'-deoxyadenosin reduced the aberrant potentiation of glutamatergic transmission and restored the methamphetamine-induced impairment of synaptic plasticity. We also found that 3'-deoxyadenosin decreased the expression of NLRP3 and neuronal injury. Importantly, a direct NLRP3 deficiency reduced methamphetamine-induced seeking behavior, attenuated the impaired synaptic plasticity, and prevented neuronal damage. Finally, NLRP3 activation reversed the effect of 3'-deoxyadenosin on behavior and synaptic plasticity, suggesting that the anti-neuroinflammatory mechanism of 3'-deoxyadenosin on aberrant synaptic plasticity reduces methamphetamine-induced seeking behavior. Taken together, 3'-deoxyadenosin alleviates methamphetamine-induced aberrant synaptic plasticity and seeking behavior by inhibiting the NLRP3 inflammasome.

Quantifying conditioned place preference: a review of current analyses and a proposal for a novel approach.

Conditioned place preference (CPP) is used to measure the conditioned rewarding effects of a stimulus, including food, drugs, and social interaction. Because various analytic approaches can be used to quantify CPP, this can make direct comparisons across studies difficult. Common methods for analyzing CPP involve comparing the time spent in the CS+ compartment (e.g., compartment paired with drug) at posttest to the time spent in the CS+ compartment at pretest or to the CS- compartment (e.g., compartment paired with saline) at posttest. Researchers can analyze the time spent in the compartment(s), or they can calculate a difference score [(CS+post - CS+pre) or (CS+post - CS-post)] or a preference ratio (e.g., CS+post/(CS+post + CS-post)). While each analysis yields results that are, overall, highly correlated, there are situations in which different analyses can lead to discrepant interpretations. The current paper discusses some of the limitations associated with current analytic approaches and proposes a novel method for quantifying CPP, the adjusted CPP score, which can help resolve the limitations associated with current approaches. The adjusted CPP score is applied to both hypothetical and previously published data. Another major topic covered in this paper is methodologies for determining if individual subjects have met criteria for CPP. The paper concludes by highlighting ways in which researchers can increase transparency and replicability in CPP studies.

The effect of Varenicline on Betel nut dependence in Albino wistar rats

Betel nut is one of the most common addictive substance. Not many studies have explored the potential of varenicline as cessation therapy. We studied the benefits of varenicline in reducing the reward effects in rat model. Forty male albino rats of wistar strain weighing 150-250grams were used in the present study. Rats were randomized to 5 groups of 8 rats each to: Control; Betel nut group; Varenicline at doses of 0.5, 1 and 2mg/kg along with betel nut. Conditioned Place Preference (CPP) model was used for studying the drug seeking behavior. The CPP score was compared between the groups. Results showed a significant increase in body weight of rats at the end of the study compared to baseline in betel nut and varenicline groups. Compared to betel nut group (656.25±55) there was significant decrease in CPP score in Varenicline group at 0.5mg/kg (97.5±48); 1mg/kg (18.75±20) and at dose of 2mg/kg (-60±6). The study demonstrates the benefits of varenicline in betelnut dependence. There was dose dependent decrease in betel nut seeking behavior with varenicline in rat model of drug dependence.

Susceptibility to arecoline in male C57BL/6 J mice correlates with age factor

Epidemiological investigations and clinical studies have confirmed that human chewing of betel nut is an addictive behavior, and the proportion of teenagers chewing betel nut is increasing. Previous studies have shown that adolescence shows higher sensitivity to many addictive substances compared with adulthood, and that adult susceptibility to addictive substances is usually changed after exposure to addictive substances during adolescence. However, there are no reports of age-related animal experiments on betel nut or dependence to its active ingredients. Therefore, the two-bottle choice (TBC) (experiment 1 and 2) and conditioned place preference (CPP) (experiment 3 and 4) models with mice were used in this study to explore age-related differences in intake and preference of arecoline, the alkaloid in betel nut with highest content, and to explore the effect of arecoline exposure during adolescence on the re-exposure of arecoline in adulthood in mice. The results of experiment 1 showed that the intake of 80 μg/ml arecoline in adolescent mice was significantly higher than that in adult mice. However, there was no significant difference between adult and adolescent mice in preference for arecoline at any tested concentration (5–80 μg/ml), which may be due to the significantly higher intake of total fluid in adolescent mice compared to adult mice. The preference of arecoline in adolescent mice peaked at 20 μg/ml, and in adult mice peaked at 40 μg/ml. The results of experiment 2 showed that oral arecoline (5–80 μg/ml) in mice during adolescence caused a significant increase in the intake (days 3–16) and preference (days 5–8) for 40 μg/ml arecoline in adulthood. The results of experiment 3 showed that the doses of 0.03 or 0.1 mg/kg of arecoline produced the highest CPP response in adolescent or adult mice, respectively. The results of experiment 4 showed that mice exposed to arecoline in adolescence had significantly increased the CPP scores induced by arecoline in adulthood compared to mice that were not exposed. These data suggested that adolescent mice were more sensitive to arecoline, and exposure of mice to arecoline during adolescence increased the susceptibility to arecoline in adulthood.

The role of NMDA glutamate receptors in the lateral habenula on morphine-induced conditioned place preference in rats.

The lateral habenula (LHb) has received special attention due to its role in modulating motivated behavior, stress response, and rewarding and aversive stimuli through monoamine transmission. In the present study, the involvement of the N-methyl-d-aspartate (NMDA) receptors of the LHb in the expression and acquisition phases of morphine-induced conditioned place preference (CPP) was studied in male rats. Bilateral injections of agonist/antagonist (MK-801) of NMDA receptor were performed during the conditioning sessions of the acquisition phase. In other separate groups, drugs were also injected into the LHb before the test session during the expression phase of CPP. A 5-day CPP bias paradigm was used to study the effect of injections of NMDA and MK-801 into the LHb on morphine reward-related behavior. Different doses of NMDA plus morphine reduced the CPP score during the acquisition phase, whereas MK-801 significantly increased conditioning scores during the acquisition phase of CPP. The injection of agonists and antagonists of NMDA receptors in LHb had no significant effect on CPP scores and locomotion during the expression phase of CPP, whereas the motor activity in the acquisition phase was affected by the drugs. The reduction effect of NMDA on the CPP scores during the acquisition phase was blocked by pretreatment with MK-801. Our findings also suggest that NMDA receptors in the LHb may be involved in the acquisition phase of morphine-induced CPP.

Pharmacological evaluation of lateral habenula and rostromedial tegmental nucleus in the expression of ethanol-induced place preference.

Although ethanol administration produces a range of physiological effects, the rewarding aspect associated with its consumption is a major contributory factor to its abuse liability. Recently, lateral habenula (LHb) has been shown to be engaged by both rewarding and aversive stimuli. Its major glutamatergic output, the fasciculus retroflexus, projects to the rostromedial tegmental nucleus (RMTg) and controls the activity of the ventral tegmental area (VTA) dopaminergic system to promote reward circuitry. While several attempts have been made to understand the relationship between LHb and addiction, there is still a lack of knowledge in relation to ethanol addiction. In the present study, by pharmacologically exacerbating or inhibiting the LHb or RMTg neuronal activity during a post-conditioning test, we investigated the role of LHb-RMTg fasciculus retroflexus in ethanol-induced reward behavior using the conditioned place preference (CPP) test. We found that activation of LHb glutamatergic system by intra-LHb administration of l-trans-2,4-pyrrolidine dicarboxylate (PDC) (glutamate transporter inhibitor) significantly decreased CPP score; on the contrary, lamotrigine (inhibits glutamate release) significantly increased CPP score and showed a rewarding effect in CPP. Instead, intra-RMTg administration of muscimol (GABAA receptor agonist) significantly increased CPP score, whereas bicuculline (GABAA antagonist) treatment decreased CPP score. In immunohistochemistry, we found that PDC administration significantly decreased, whereas lamotrigine treatment significantly increased tyrosine hydroxylase immunoreactivity (TH-ir) in VTA and nucleus accumbens (NAc). Furthermore, while intra-RMTg administration of muscimol increased, the bicuculline treatment significantly decreased the TH-ir in VTA and NAc. Together, our behavioral and immunohistochemical results signify the role of LHb and RMTg in the expression of ethanol-conditioned reward behavior.

The Effects of Deep Brain Stimulation in Medial Prefrontal Cortex on Morphine Dependency and Electrical Recording of the Nucleus Accumbens

Background: Addiction is known as a gradual process leading to the uncontrolled abuse of a substance. The main problem facing the practitioners is the high rate of return among abusers after stopping substance consumption. Deep brain stimulation (DBS) is considered as one of the methods for treating stimulant substance abuse, in which an electrical current is passed, typically at frequencies above 100 Hz, through electrodes implanted surgically in the subcortical brain nuclei. Objectives: The present study aimed to investigate the effects of high-frequency DBS (HF-DBS) applied to the medial prefrontal cortex (mPFC) on the electrical response of the accumbens nucleus as well as on the motor activity and dependency in morphine-addicted male rats. Methods: Experimental rats (n = 40) were assigned to five groups (n = 8), including saline, sham, morphine, saline+DBS, and morphine+DBS groups. The rats received DBS with a frequency of 130 Hz, amplitude of 0.2 to 0.5 mA, and repeated periods of 15 minutes with an interval of 45 minutes for 3 hours during the conditioning period in the conditioned place preference (CPP) box. Then, they were treated with saline or morphine and were subjected to stereotaxic surgery for insertion of the stimulator electrode in mPFC and the recorder electrode in AC. The electrical response of AC neurons to DBS was determined adopting the single unit recording method. Then, motor activities of different groups were assessed in order to evaluate the effects of DBS on animal movement activities. Finally, data analysis was performed using GraphPad Prism 8.1. Results: The injection of morphine enhanced the CPP score and reduced the average of spikes in the cortical neurons of the AC compared to those obtained in the sham group. These parameters were significantly decreased and increased in the animals receiving morphine+DBS compared to the morphine group, respectively. Moreover, a significant difference was observed between morphine+DBS group and morphine group in terms of the total traveled distance. Conclusions: The stimulation of the AC nucleus at high frequency reduced the addiction preference as well as enhanced the locomotor activity and primary neuron activity in the cortex of AC nucleus.

Amelioration of Nicotine-Induced Conditioned Place Preference Behaviors in Mice by an FABP3 Inhibitor

We previously demonstrated that fatty acid-binding protein 3 null (FABP3-/-) mice exhibit resistance to nicotine-induced conditioned place preference (CPP). Here, we confirm that the FABP3 inhibitor, MF1 ((4-(2-(1-(2-chlorophenyl)-5-phenyl-1H-pyrazol-3-yl)phenoxy) butanoic acid), successfully reduces nicotine-induced CPP scores in mice. MF1 (0.3 or 1.0 mg/kg) was orally administered 30 min before nicotine, and CPP scores were assessed in the conditioning, withdrawal, and relapse phases. MF1 treatment decreased CPP scores in a dose-dependent manner. Failure of CPP induction by MF1 (1.0 mg/kg, p.o.) was associated with the inhibition of both CaMKII and ERK activation in the nucleus accumbens (NAc) and hippocampal CA1 regions. MF1 treatment reduced nicotine-induced increases in phosphorylated CaMKII and cAMP-response element-binding protein (CREB)-positive cells. Importantly, the increase in dopamine D2 receptor (D2R) levels following chronic nicotine exposure was inhibited by MF1 treatment. Moreover, the quinpirole (QNP)-induced increase in the level of CaMKII and ERK phosphorylation was significantly inhibited by MF1 treatment of cultured NAc slices from wild type (WT) mice; however, QNP treatment had no effect on CaMKII and ERK phosphorylation levels in the NAc of D2R null mice. Taken together, these results show that MF1 treatment suppressed D2R/FABP3 signaling, thereby preventing nicotine-induced CPP induction. Hence, MF1 can be used as a novel drug to block addiction to nicotine and other drugs by inhibiting the dopaminergic system.

Low Current Intensity Plus an Ineffective Dose of Morphine Affect Conditioning Place Preference Through Different Pathways in the Lateral Habenula.

The involvement of lateral habenula and the ineffective dose of morphine on reward-related learning and memory is less well-known. This study looked into the effects of electrical stimulation, GABAB receptor blockade, and a combination of both with morphine on conditioned place preference. In this experiment, male rats were anesthetized with ketamine/xylazine (six rats in each group). A 5-day biased conditioned place preference paradigm was used for the behavioral test. The effects of electrical stimulation and phaclofen plus a low dose of morphine on the acquisition and expression phases were examined during conditioning sessions and before the test phase, respectively. The conditioning scores were reduced by antagonist injection during the acquisition phase. Interestingly, different intensities exhibited opposite effects on the acquisition phase. Conditioned place preference scores during the acquisition phase were significantly induced by 25 μA electrical stimulation, while conditioning scores were suppressed by electrical stimulation at 150 μA. Phaclofen (2 μg/rat) combined with high intensity induced aversion during the acquisition phase, while inhibiting expression. In contrast, high intensity with phaclofen (1 μg/rat) inhibited only the acquisition session. However, low intensity during the acquisition phase had an additive effect that was prevented by pretreatment with phaclofen (2 μg/rat), but this response was modified by the antagonist's low dose. A behavioral technique called conditioned place preference is frequently used to evaluate learning that is related to rewards. Therefore, lateral habenula electrical stimulation and phaclofen plus morphine could affect place preference through the involvement of the reward system.

Non-nicotine constituents in cigarette smoke extract enhance nicotine addiction through monoamine oxidase A inhibition.

Tobacco addiction has been largely attributed to nicotine, a component in tobacco leaves and smoke. However, extensive evidence suggests that some non-nicotine components of smoke should not be overlooked when considering tobacco dependence. Yet, their individual effect and synergistic effect on nicotine reinforcement remain poorly understood. The study herein focused on the role of non-nicotine constituents in promoting the effects of nicotine and their independent reinforcing effects. Denicotinized cigarettes were prepared by chemical extracting of cut tobacco, and the cigarette smoke extracts (CSE, used as a proxy for non-nicotine ingredients) were obtained by machine-smoking the cigarettes and DMSO extraction. The compositions of harmful components, nicotine, and other minor alkaloids in both cut tobacco and the CSE of experimental denicotinized cigarettes were examined by GC-MS, and compared with 3R4F reference cigarettes. individually and in synergy with nicotine were determined by conditioned place preference (CPP), dopamine (DA) level detection, the open field test (OFT), and the elevated plus maze (EPM). Finally, the potential enhancement mechanism of non-nicotinic constituents was investigated by nicotine metabolism and monoamine oxidase A (MAOA) activity inhibition in the striatum of mice and human recombinant MAOA. Thenicotine content in smoke from the experimental denicotinized cigarettes (under ISO machine-smoking conditions) was reduced by 95.1% and retained most minor alkaloids, relative to the 3R4F reference cigarettes. It was found that non-nicotine constituents increased acute locomotor activities. This was especially pronounced for DA levels in NAc and CPP scores, decreased the time in center zone. There were no differences in these metrics with DNC group when compared to the NS group. Non-nicotine constituents alone did not show reinforcing effects in CPP or striatum DA levels in mice. However, in the presence of nicotine, non-nicotine constituents further increased the reinforcing effects. Furthermore, non-nicotine constituents may enhance nicotine's reinforcing effects by inhibiting striatum MAOA activity rather than affecting nicotine metabolism or total striatum DA content in mice. These findings expand our knowledge of the effect on smoking reinforcement of non-nicotine constituents found in tobacco products.

Involvement of AMPA receptors of lateral habenula in the expression and acquisition phases of morphine-induced place preference

The lateral habenula (LHb), known as the brain structure of the epithalamic, plays the main role in depression and drug addiction. The glutamatergic system influences morphine reward. The effect of activation/inhibition of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptors (AMPARs) in the LHb on different phases of morphine-induced conditioned place preference (CPP) remains unknown. In this research, the effect of bilateral intra-LHb microinjection of AMPARs agonist and antagonist on the acquisition and expression phases of CPP in male rats has been investigated. Different doses of NBQX, the antagonist of AMPARs, in combination with the effective dose of morphine, increased the CPP score during the acquisition phase. While AMPA, the agonist of AMPARs, significantly reduced the conditioning scores in the acquisition phase. Pretreatment with NBQX (0.5 and 1 μg/rat) reversed the inhibitory effect of AMPA (1 μg/rat) on the acquisition phase of morphine-induced CPP. The antagonist (1 μg/rat) increased the effect of a high dose of agonist (2 μg/rat) on CPP. On the other hand, NBQX significantly increased CPP scores during the expression phase. AMPA did not significantly affect CPP scores in the expression phase, but significantly reduced locomotor activity in the test phase. These results confirmed the importance of AMPARs in the LHb in morphine reward. Our data also suggest that injection of an AMPARs antagonist into the LHb may alter the AMPA-induced morphine response in a dose-dependent manner.

A 1:1 ratio of cannabidiol: tetrahydrocannabinol attenuates methamphetamine conditioned place preference in mice: A prospective study of antidopaminergic mechanism

A 1:1 ratio of cannabidiol to tetrahydrocannabinol (CT) was suggested to be safer for therapeutic purposes in many illnesses. However, CT effects on methamphetamine (METH) conditioned place preference (CPP) remained largely unexplored. This study aimed to examine the effects of CT on METH CPP mice evaluated by animal behaviors accompanied by local field potential (LFP) signals analysis. Male ICR mice were implanted with the LFP electrode in the ventral tegmental area (VTA) and the nucleus accumbens (NAc). Animals were next subjected to induce METH CPP by peritoneal injection with 1 mg/kg METH and 0.9 % NaCl on an alternate day for ten sessions and confined to the corresponding compartment for 30 min meanwhile control mice were given normal saline all day for both compartments. On testing day, either 10 mg/kg CT or 20 mg/kg bupropion (BP), a dopamine reuptake inhibitor, and VTA GABAergic suppressor were orally administered before CPP testing. The results revealed that CPP scores elevation was observed in the METH+vehicle and METH+BP mice, but this was reversed by CT treatment. Although both METH+vehicle and METH+BP enhanced the VTA delta power, NAc gamma I power, NAc delta-gamma coupling, and VTA-NAc gamma I coherence, changes in opposite trends of all mentioned parameters were seen by CT application. These improvements were postulated to involve the antidopaminergic effects of CT via modulations of neural signaling in the VTA and NAc. Altogether, the evidence-based study may suggest the use of CT as alternative drug for METH-seeking and craving therapy.

Astrocyte-derived lactate/NADH alters methamphetamine-induced memory consolidation and retrieval by regulating neuronal synaptic plasticity in the dorsal hippocampus.

Drug memory is associated with drug-taking experience and environmental cues, which mainly contribute to addiction. Recent studies report that glycogenolysis-derived lactate from astrocyte transport to neurons is necessary for long-term potentiation and memory formation instead of its function as an energy substrate. However, the role of astrocyte-neuron lactate transfer in neuronal plasticity and methamphetamine (METH)-induced addiction memory consolidation and retrieval, especially the underlying mechanisms, are not clear. C57BL/6J mice trained for METH-induced conditioned place preference (CPP) were stereotaxically injected with the glycogen phosphorylaseinhibitor 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) into the dorsal hippocampus (dHPC) 15 minbeforetraining. The CPP score was recorded, and neuronal synaptic plasticity was detected with Golgi staining. The neuronal Ca2+ levels were examined using AAV-GCaMP6 injection. Moreover, monocarboxylate transporters (MCT1, MCT2, MCT4) were inhibited with oligodeoxynucleotides in the dHPC to further prove the METH appetitive memory changes. The data showed that inhibiting lactate transport by microinjection with DAB or monocarboxylate transporter oligodeoxynucleotides in the dHPC completely destroyed METH-induced CPP, reduced Npas4 and other plasticity-associated gene expression and decreased neuronal Ca2+ levels and neuronal arborization and spine density, all of which were fully rescued by L-lactate coadministration except for MCT2-ODN administration. Furthermore, the downstream signaling molecule NADH could mimic lactate's effects and trigger METH CPP by influencing the redox state of neurons and regulating NMDA receptor activity. Collectively, these findings indicate that astrocyte-neuron lactate transfer is crucial for METH-induced memory consolidation and retrieval.

Involvement of GABAA receptors of lateral habenula in the acquisition and expression phases of morphine-induced place preference in male rats.

The lateral habenula (LHb) is a critical brain structure involved in the aversive response to drug abuse. It has been determined that the gamma-aminobutyric acid (GABA)-ergic system plays the main role in morphine dependency. The role of GABA type A receptors (GABAARs) in LHb on morphine-induced conditioned place preference (CPP) remains unknown. In this study, the effect of bilateral intra-LHb microinjection of GABAAR agonist and antagonist on the acquisition and expression phases of CPP, utilizing a 5-day CPP paradigm in male rats, was evaluated. Subcutaneous administration of different doses of morphine caused a dose-dependent CPP. Intra-LHb microinjection of the GABAAR agonist, muscimol, in combination with morphine (5 mg/kg; subcutaneously) enhanced CPP scores in the acquisition phase of morphine CPP, whereas the GABAAR antagonist, bicuculline, significantly reduced the conditioning scores in the acquisition phase. Furthermore, pretreatment with a high dose of bicuculline reversed the additive effect of muscimol during the acquisition phase, yet the low dose of antagonist had no significant effect on agonist-induced CPP scores. On the other hand, muscimol (3 µg/rat) significantly increased CPP scores in the expression phase but bicuculline did not induce a significant effect on CPP scores. Bicuculline and muscimol microinjections did not affect locomotor activity in the testing sessions. Our results confirm that GABAARs in LHb play an active role in morphine reward. In addition, microinjections of bicuculline/muscimol may alter the morphine response through the GABAergic system.

Differential Aspects of Natural and Morphine Reward-related Behaviors in Conditioned Place Preference Paradigm.

Natural rewards are essential for survival. However, drug-seeking behaviors can be maladaptive and endanger survival. The present study was conducted to enhance our understanding of how animals respond to food and morphine as natural and drug rewards, respectively, in a conditioned place preference (CPP) paradigm. We designed a protocol to induce food CPP and compare it as a natural reward with morphine CPP in rats. The protocol for reward induction in both groups (foods and morphine) consisted of three phases: pre-test, conditioning, and post-test. In morphine groups, we injected morphine as a reward (5 mg/kg, SC). To induce natural reward, we used two different protocols. In the first one, the rats were deprived of food for 24 h. In the other method, the rats were restricted to food for 14 days. During the conditioning period, the animals received daily chow, biscuits, or popcorn as a reward inducer. Results revealed that CPP was not induced in food-deprived rats. A combination of food restriction (as a facilitator) and a biscuit or popcorn-induced reward using CPP. In contrast, food deprivation did not facilitate food CPP in response to regular food. Interestingly the CPP score of the group which received biscuits during a 7-day conditioning period was more than that of the morphine group. In conclusion, food restriction could be a better protocol than food deprivation to facilitate food reward.

Exploring the role and mechanism of gut microbiota in methamphetamine addiction using antibiotic treatment followed by fecal microbiota transplantation.

Recently, the role of the gut microbiota in the context of drug addiction has attracted the attention of researchers; however, the specific effects and underlying mechanisms require further exploration. To accomplish this, C57BL/6 mice were firstly treated with methamphetamine (MA). Conditioned place preference (CPP) behavior changes, gut permeability and function, microglial activation, and inflammatory cytokine expression were systematically analyzed in antibiotics-treated mice with microbiota depletion and in fecal microbiota transplantation mice with microbiota reconstitution. MA treatment altered microbiota composition and caused gut dysbiosis. Depletion of gut microbiota with antibiotics inhibited MA-induced CPP formation, and fecal microbiota transplantation reversed this inhibition. Mechanistic analyses indicated that antibiotic treatment decreased gut permeability and neuroinflammation, while fecal microbiota transplantation offset the impact of antibiotic treatment. Additionally, MA-induced microglial activation was suppressed by antibiotics but restored by microbiota transplantation, and this correlated well with the CPP score. Compared to antibiotic treatment, microbiota transplantation significantly increased 5-HT4 receptor expression in both the nucleus accumbens and the hippocampus. Furthermore, when fecal microbiota from healthy mice was transplanted into MA-treated mice, the CPP scores decreased. Our results provide a novel avenue for understanding MA addiction and suggest a potential future intervention strategy.

Inactivation of the Lateral Hypothalamus Attenuates Methamphetamine-Induced Conditioned Place Preference through Regulation of Kcnq3 Expression.

Repeated administration of methylamphetamine (MA) induces MA addiction, which is featured by awfully unpleasant physical and emotional experiences after drug use is terminated. Neurophysiological studies show that the lateral hypothalamus (LH) is involved in reward development and addictive behaviors. Here, we show that repeated administration of MA activates the expression of c-Fos in LH neurons responding to conditioned place preference (CPP). Chemogenetic inhibition of the LH can disrupt the addiction behavior, demonstrating that the LH plays an important role in MA-induced reward processing. Critically, MA remodels the neurons of LH synaptic plasticity, increases intracellular calcium level, and enhances spontaneous current and evoked potentials of neurons compared to the saline group. Furthermore, overexpression of the potassium voltage-gated channel subfamily Q member 3 (Kcnq3) expression can reverse the CPP score and alleviate the occurrence of addictive behaviors. Together, these results unravel a new neurobiological mechanism underlying the MA-induced addiction in the lateral hypothalamus, which could pave the way toward new and effective interventions for this addiction disease.

Effect of Testosterone on the Extinction Period of Morphine-induced CPP in Male Rats

Background: Sex-related differences in the incidence, prevalence, symptoms, and side effects of drug use, especially narcotics, have been previously shown in animal models and human studies. Objectives: In the presents study, the effects of different doses of testosterone on morphine extinction period were investigated in a rat model. Methods: Forty mature male Wistar rats were randomly allocated to four categories (10 in each group), including control (received intramuscular injection of vehicle) and testosterone (received intramuscular injection of testosterone at 1, 2.5 and 5 mg/kg) during the extinction period. Conditioned place preference (CPP) test was done to assess the psychological phenomena of drug craving and relapse. The CPP score was calculated in four stages, including the baseline (preconditioning), expression (postconditioning), extinction, and reinstatement. Results: Our results demonstrated that testosterone (1, 2.5 and 5 mg/kg) significantly extended morphine extinction duration compared to the control group. Conclution: It has been shown that dopamine neurotransmission in mesocorticolimbic system is affected by testosterone through androgen receptors in adolescence and alteration in testosterone level could affect drug use vulnerability. It seems that normalization of testosterone levels reduces the symptoms of opioid withdrawal syndrome and have important clinical implication for clinicians to understand the effects of testosterone dysregulation on the extinction and withdrawal periods.

Effects of Different Extinction for Morphine-CPP on Hippocampal EEG Power Spectrum in Mice

The relationship between hippocampal electroencephalogram (EEG) power spectrum and the extinction of addiction memory was investigated. Forty KM mice (Kunming mice) that had successfully established morphine (MOR)-conditioned place preference (CPP) were divided into four groups: saline-training extinction (SAL-TE), SAL-natural extinction (SAL-NE), MOR-TE, MOR-NE, for extinction treatment and EEG recording in the dorsal and ventral hippocampus (DH/VH). Results show that the CPP score of MOR-TE significantly decreased and the total, β and γ bands power spectrum of MOR-TE was suppressed. Notably, the total power from the VH was more correlated with the extinction method, and the TE total power was always lower than NE in SAL or MOR group. Naloxone enhanced the EEG total power and all bands (DH) or β and γ bands (VH) power in the SAL group. However, in the MOR-TE group, only β and γ bands power in VH increased (P<0.05). The results suggest that TE can promote the extinction of opiate addictive memory more effectively than NE, and the extinction of MOR-CPP may have a stronger correlation with changes of VH-EEG power spectrum.