Role of prefrontal cortex in the extinction of drug memories

Modulation of neuronal excitability by binge alcohol drinking

Drug use poses a serious threat to health systems throughout the world. The number of consumers rises every year being alcohol the drug of abuse most consumed causing 3 million deaths (5.3% of all deaths) worldwide and 132.6 million disability-adjusted life years. In this review, we present an up-to-date summary about what is known regarding the global impact of binge alcohol drinking on brains and how it affects the development of cognitive functions, as well as the various preclinical models used to probe its effects on the neurobiology of the brain. This will be followed by a detailed report on the state of our current knowledge of the molecular and cellular mechanisms underlying the effects of binge drinking on neuronal excitability and synaptic plasticity, with an emphasis on brain regions of the meso-cortico limbic neurocircuitry.

Epigenetic mechanisms involved in methamphetamine addiction

Methamphetamine (METH) is an illicit psychostimulant that is widely abused. The molecular mechanism of METH addiction is complicated and still unknown. METH causes the release of the neurotransmitters including dopamine, glutamate, norepinephrine and serotonin, which activate various brain areas in the central nervous system. METH also induces synaptic plasticity and pathological memory enhancement. Epigenetics plays the important roles in regulating METH addiction. This review will briefly summarize the studies on epigenetics involved in METH addiction.

Binge Alcohol Drinking Alters Synaptic Processing of Executive and Emotional Information in Core Nucleus Accumbens Medium Spiny Neurons

The nucleus accumbens (NAc) is a forebrain region mediating the positive-reinforcing properties of drugs of abuse, including alcohol. It receives glutamatergic projections from multiple forebrain and limbic regions such as the prefrontal cortex (PFCx) and basolateral amygdala (BLA), respectively. However, it is unknown how NAc medium spiny neurons (MSNs) integrate PFCx and BLA inputs, and how this integration is affected by alcohol exposure. Because progress has been hampered by the inability to independently stimulate different pathways, we implemented a dual wavelength optogenetic approach to selectively and independently stimulate PFCx and BLA NAc inputs within the same brain slice. This approach functionally demonstrates that PFCx and BLA inputs synapse onto the same MSNs where they reciprocally inhibit each other pre-synaptically in a strict time-dependent manner. In alcohol-naïve mice, this temporal gating of BLA-inputs by PFCx afferents is stronger than the reverse, revealing that MSNs prioritize high-order executive processes information from the PFCx. Importantly, binge alcohol drinking alters this reciprocal inhibition by unilaterally strengthening BLA inhibition of PFCx inputs. In line with this observation, we demonstrate that in vivo optogenetic stimulation of the BLA, but not PFCx, blocks binge alcohol drinking escalation in mice. Overall, our results identify NAc MSNs as a key integrator of executive and emotional information and show that this integration is dysregulated during binge alcohol drinking.

Effects of N-acetylcysteine treatment on ethanol's rewarding properties and dopaminergic alterations in mesocorticolimbic and nigrostriatal pathways

Recent reports have shown that N-acetylcysteine (N-AC) has beneficial effects in the treatment of cocaine and nicotine abuse. Considering the similar neurobiologic mechanisms involved in the development of addiction to different drugs, N-AC treatment could be useful in the treatment of ethanol abuse. The rewarding properties of the drugs of abuse plays an important role in the development of addiction and can be studied using the conditioned place preference (CPP) paradigm. Thus, to study the effects of N-AC treatment in the rewarding effects of ethanol, we investigated the effects of N-AC administration in the ethanol-induced CPP and neurochemical alterations within the mesocorticolimbic and the nigrostriatal dopaminergic pathways. Adult male Swiss mice were pretreated with N-AC (60 or 120 mg/kg intraperitoneal) and tested for the development, expression, or extinction of the ethanol-induced CPP. Another cohort of animals received N-AC (60 or 120 mg/kg intraperitoneal) 2-h before an acute administration of ethanol and had their brains removed for dopamine and its metabolites quantification in the mesocorticolimbic and nigrostriatal pathways. Pretreatment with N-AC (120 mg/kg) blocked the development of ethanol-induced CPP. On the other hand, N-AC at both doses did not alter the expression nor the extinction of ethanol-induced CPP. N-AC increased 3,4-dihydroxyphenylacetic acid content in the medial prefrontal cortex and dopaminergic turnover within the substantia nigra. Besides that, there was an increase in dopamine content in the nucleus accumbens of ethanol-treated animals. In summary, N-AC treatment blocked the development of ethanol CPP, without altering ethanol effects on dopaminergic neurotransmission.

Alterations of Glucose Uptake and Protein Expression Related to the Insulin Signaling Pathway in the Brain of Phenobarbital-Addictive Rats by 18F-FDG PET/CT and Proteomic Analysis

Drug addiction is a chronic relapsing brain disease. Alterations of glucose uptake and metabolism are found in the brain of drug addicts. Insulin mediates brain glucose metabolism and its abnormality could induce brain injury and cognitive impairment. Here, we established a rat model of phenobarbital addiction by 90 days of dose escalation and evaluated addiction-related symptoms. We also performed ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) to detect glucose uptake in the brain and proteomic analysis of the function of the differentially expressed (DE) proteins via bioinformatics in brain tissues by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) on days 60 and 90 of phenobarbital or 0.5% carboxymethyl cellulose sodium (CMC-Na) (vehicle) administration. The results showed that phenobarbital-addictive rats developed severe withdrawal symptoms after abstinence and glucose uptake was significantly increased in the brain. Proteomics analysis showed that numerous DE proteins were enriched after phenobarbital administration, among which CALM1, ARAF, and Cbl proteins (related to the insulin signaling pathway) were significantly downregulated on day 60 but not day 90. However, SLC27A3 and NF-κB1 proteins (related to insulin resistance) were significantly upregulated on day 90 (data are available via ProteomeXchange with identifier PXD021101). Our data indicate that the insulin signaling pathway and insulin resistance may play a role in the development of phenobarbital addiction and brain injury, so the findings may have important clinical implications.

Long-term exposure to ephedrine leads to neurotoxicity and neurobehavioral disorders accompanied by up-regulation of CRF in prefrontal cortex and hippocampus in rhesus macaques

Drug addiction continues to threaten the health and welfare of people worldwide, and ephedrine abuse is a serious drug problem in many areas of the world. Ephedrine toxicity is thought to induce behavioral effects primarily through actions on the central nervous system. The corticotropin-releasing factor (CRF) system plays an important role in regulating behavioral effects induced by addictive drugs, but whether CRF is related to ephedrine toxicity remains unclear. This study seeks to examine whether there is a correlation between the CRF and chronic ephedrine neurotoxicity. To this end, we established a chronic ephedrine (0.4-1.6 mg/kg/d) exposure model in rhesus macaques, assessed its effects on body weight and behavior, examined neuronal changes in the prefrontal cortex and hippocampus, and measured the CRF expression in the prefrontal cortex and hippocampus. After 8-weeks of exposure to ephedrine, the toxic effects of ephedrine included significant weight loss and induction of behavioral changes in rhesus macaques. In particular, in the modeling group, the abnormal behavioral changes mainly manifested as irritability and behavioral sensitization. Meanwhile, the histological abnormalities included neuronal morphological changes, pyknosis and irregular shapes of neurons in the prefrontal cortex and hippocampus. In addition, the expression levels of CRF mRNA and protein were increased in the prefrontal cortex and hippocampus of ephedrine-treated animals. In summary, the finding of this study indicated that ephedrine neurotoxicity can cause neuronal damage in cerebral cortex, which in turn can result in certain neurobehavioral abnormalities, and that CRF expression in prefrontal cortex and hippocampus is elevated in response to ephedrine exposure. These observations suggested that long-term exposure to ephedrine might be causing neurotoxicity and leading to neurobehavioral disorders accompanied by up-regulation of CRF in prefrontal cortex and hippocampus.

Susceptibility to extinction and reinstatement of ethanol-induced conditioned place preference is related to differences in astrocyte cystine-glutamate antiporter content

Individual susceptibility to alcohol effects plays an important role in the development of alcohol addiction and studies have shown that glutamate release is altered after chronic ethanol consumption. The cystine-glutamate antiporter (xCT) is a protein that regulates glutamate release. However, little is known about the relationship between xCT levels and this individual susceptibility. Thus, this study aimed to evaluate the relationship between the extinction and stress-induced reinstatement of ethanol conditioned place preference (CPP) and xCT levels in the medial prefrontal cortex (mPFC), nucleus accumbens (NAcc) and amygdala (Amy). Male Swiss mice were submitted to a CPP procedure followed by an extinction protocol and then identified as those which extinguished the CPP and those that did not. In another cohort, mice that extinguished the CPP were submitted to a protocol of stress-induced reinstatement. Immediately after the tests, brains were removed for xCT quantification. The xCT levels were significantly lower in the mPFC and NAcc of mice that did not extinguish CPP. Moreover, mice that were susceptible to stress-induced reinstatement of CPP had lower levels of xCT in the NAcc. Our results suggest that individual susceptibility to the extinction and reinstatement of ethanol CPP is related to alterations in xCT levels.

Berberine Facilitates Extinction of Drug-Associated Behavior and Inhibits Reinstatement of Drug Seeking

A high rate of relapse is a major clinical problem among drug-addicted individuals. Persistent traces of drug-associated reward memories contribute to intense craving and often trigger relapse. A number of interventions on drug-associated memories have shown significant benefits in relapse prevention. Among them are pre- or post-extinction pharmacological manipulations that facilitate the extinction of drug-associated behavior. Berberine, a bioactive isoquinoline alkaloid, has been recently reported to provide therapeutic benefits for a number of central nervous system (CNS) disorders, including morphine addiction. The present study aimed to investigate whether berberine could serve as a post-extinction pharmacological intervention agent to reduce risks of reinstatement of drug seeking. We found that an intragastric administration of berberine at doses of 25 and 50 mg/kg during the critical time window significantly facilitated the extinction of morphine-reward related behavior in free access and confined conditioned place preference (CPP) extinction paradigms, and subsequently, it prevented reinstatement and spontaneous recovery of morphine-induced CPP in mice. Intriguingly, the berberine treatment with or without extinction training altered expression of plasticity-related proteins such as brain-derived neurotrophic factor (BDNF), AMPA receptors (GluA1 and GluA2) in the nucleus accumbens (NAc). Moreover, the post-extinction berberine treatment significantly reduced reinstatement of cocaine-induced CPP and operant intravenous self-administration (IVSA) memories in rats. Altogether, our findings suggest that extinction training combined with the post-extinction berberine treatment can facilitate extinction of drug-associated behavior making it an attractive therapeutic candidate in relapse prevention.

Altered brain activities associated with cue reactivity during forced break in subjects with Internet gaming disorder

BACKGROUND

Studies have proven that forced break can elicit strong psychological cravings for addictive behaviors. This phenomenon could create an excellent situation to study the neural underpinnings of addiction. The current study explores brain features during a cue-reactivity task in Internet gaming disorder (IGD) when participants were forced to stop their gaming behaviors.

METHODS

Forty-nine IGD subjects and forty-nine matched recreational Internet game users (RGU) were asked to complete a cue-reactivity task when their ongoing gaming behaviors were forced to break. We compared their brain responses to gaming cues and tried to find specific features associated with IGD.

RESULTS

Compared with RGU, the IGD subjects showed decreased activation in the anterior cingulate cortex (ACC), parahippocampal gyrus, and dorsolateral prefrontal cortex (DLPFC). Significant negative correlations were observed between self-reported gaming cravings and the baseline activation level (bate value) of the ACC, DLPFC, and parahippocampal gyrus.

CONCLUSIONS

IGD subjects were unable to suppress their gaming cravings after unexpectedly forced break. This result could also explain why RGU subjects are able to play online games without developing dependence.

Region-specific interneuron demyelination and heightened anxiety-like behavior induced by adolescent binge alcohol treatment

Adolescent binge drinking represents a major public health challenge and can lead to persistent neurological and mental conditions, but the underlying pathogenic mechanisms remain poorly understood. Using a mouse model of adolescent binge ethanol treatment (ABET), we found that this treatment induced behavioral changes associated with demyelination in different brain regions. After ABET, adolescent mice exhibited anxiogenic behaviors with no change in locomotion on the elevated plus maze, and impaired spatial memory indicated by a significant reduction in spontaneous alternation in the Y maze test. Both effects persisted into adulthood. Anatomical studies further showed that ABET induced a significant reduction of parvalbumin-positive (PV+) GABAergic interneurons and myelin density in the hippocampus and medial prefrontal cortex (mPFC). While these deficits in PV+ interneurons and myelin persisted into early adulthood in the hippocampus, the myelin density recovered in the mPFC. Moreover, whereas ABET mainly damaged myelin of PV+ axons in the hippocampus, it primarily damaged myelin of PV-negative axons in the mPFC. Thus, our findings reveal that an adolescent binge alcohol treatment regimen disrupts spatial working memory, increases anxiety-like behaviors, and exerts unique temporal and spatial patterns of gray matter demyelination in the hippocampus and mPFC.

Altered Activity of SK Channel Underpins Morphine Withdrawal Relevant Psychiatric Deficiency in Infralimbic to Accumbens Shell Pathway

Drug addiction can be viewed as a chronic psychiatric disorder that is related to dysfunction of neural circuits, including reward deficits, stress surfeits, craving changes, and compromised executive function. The nucleus accumbens (NAc) plays a crucial role in regulating craving and relapse, while the medial prefrontal cortex (mPFC) represents a higher cortex projecting into the NAc that is active in the management of executive function. In this study, we investigated the role of the small conductance calcium-activated potassium channels (SK channels) in NAc and mPFC after morphine withdrawal. Action potential (AP) firing of neurons in the NAc shell was enhanced via the downregulations of the SK channels after morphine withdrawal. Furthermore, the expression of SK2 and SK3 subunits in the NAc was significantly reduced after 3 weeks of morphine withdrawal, but was not altered in the dorsal striatum. In mPFC, the SK channel subunits were differentially expressed. To be specific, the expression of SK3 was upregulated, while the expression of SK2 was unchanged. Furthermore, the AP firing in layer 5 pyramidal neurons of the infralimbic (IL) cortex was decreased via the upregulations of the SK channel-related tail current after 3 weeks of morphine withdrawal. These results suggest that the SK channel plays a specific role in reward circuits following morphine exposure and a period of drug withdrawal, making it a potential target for the prevention of relapse.