Synaptic plasticity and 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.

Orbitostriatal encoding of reward delayed gratification and impulsivity in chronic pain

Central robust network functional rearrangement is a characteristic of several neurological conditions, including chronic pain. Preclinical and clinical studies have shown the importance of pain-induced dysfunction in both orbitofrontal cortex (OFC) and nucleus accumbens (NAc) brain regions for the emergence of cognitive deficits. Outcome information processing recruits the orbitostriatal circuitry, a pivotal pathway regarding context-dependent reward value encoding. The current literature reveals the existence of structural and functional changes in the orbitostriatal crosstalk in chronic pain conditions, which have emerged as a possible underlying cause for reward and time discrimination impairments observed in individuals affected by such disturbances. However, more comprehensive investigations are needed to elucidate the underlying disturbances that underpin disease development. In this review article, we aim to provide a comprehensive view of the orbitostriatal mechanisms underlying time-reward dependent behaviors, and integrate previous findings on local and network malplasticity under the framework of the chronic pain sphere.

Understanding methiopropamine, a new psychoactive substance: an in-depth review on its chemistry, pharmacology and implications to human health

Methiopropamine or 1-(thiophen-2-yl)-2-methylaminopropane (MPA) is a thiophene ring-based structural analogue of methamphetamine, first synthesized in 1942 but become popular when it started to be available for purchase on websites selling 'legal highs' since 2010. While it is legally controlled in many countries, it remains readily accessible and frequently encountered in recreational settings. The growing prevalence of MPA use results in new therapeutic challenges. Relatively few studies have focused on its pharmacodynamics and pharmacokinetics, making it important to better understand its potential risks and harmful effects in humans in terms of its toxicity. This review provides a comprehensive profiling of MPA toxicological properties, including its chemical properties, analytical methods, prevalence, patterns of use, and legal status. Additionally, it discusses the drug's effects on the central nervous system, its potential for addiction, and its adverse physical and mental health effects. Improving the understanding of safety aspects of MPA and how it imposes health threats for public health will guide the development of therapeutic approach of its intoxication and guide the authorities in deciding its legal status.

Sodium para-aminosalicylic acid attenuates combined manganese/iron-induced cortical synaptic damage in rats

We established experimental models of manganese (Mn) and iron (Fe) exposure in vitro and in vivo, and addressed the effects of manganese and iron combined exposure on the synaptic function of pheochromocytoma derived cell line 12 (PC12) cells and rat cortex, respectively. We investigated the protective effect of sodium para-aminosalicylate (PAS-Na) on manganese and iron combined neurotoxicity, providing a scientific basis for the prevention and treatment of ferromanganese combined neurotoxicity. Western blot and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) were performed to detect the expression levels of protein and mRNA related to synaptic damage. Y-maze novelty test and balance beam test were used to evaluate the motor and cognitive function of rats. Haematoxylin and eosin (H&E) and Nissl staining were performed to observe the cortical damage of rats. The results showed that the combined exposure of Mn and Fe in rats led to a synergistic effect, attenuating growth and development, and altering learning and memory as well as motor function. The combination of Mn and Fe also caused damage to the synaptic structure of PC12 cells, which is manifested as swelling of dendrites and axon terminals, and even lead to cell death. PAS-Na displayed some antagonistic effects against the Mn- and Fe-induced synaptic structural damage, growth, learning and memory impairment.

A cocaine-activated ensemble exerts increased control over behavior while decreasing in size

BACKGROUND

Substance use disorder (SUD) is characterized by long-lasting changes in reward-related brain regions, such as the nucleus accumbens (NAc). Previous work has shown that cocaine exposure induces plasticity in broad, genetically-defined cell types in the NAc; however, in response to a stimulus, only a small percent of neurons are transcriptionally active - termed an ensemble. Here, we identify an Arc-expressing neuronal ensemble that has a unique trajectory of recruitment and causally controls drug self-administration after repeated, but not acute, cocaine exposure.

METHOD

Using Arc-CreERT2 transgenic mice, we expressed transgenes in Arc+ ensembles activated by cocaine exposure [either acute (1 x 10mg/kg IP), or repeated (10 x 10mg/kg IP)]. Using genetic, optical, and physiological recording and manipulation strategies, we assessed the contribution of these ensembles to behaviors associated with SUD.

RESULTS

Repeated cocaine exposure reduced the size of the ensemble, while simultaneously increasing its control over behavior. Neurons within the repeated cocaine ensemble were hyperexcitable and their optogenetic excitation was sufficient for reinforcement. Finally, lesioning the repeated cocaine, but not acute cocaine, ensemble blunted cocaine self-administration. Thus, repeated cocaine exposure reduced the size of the ensemble while simultaneously increasing its contributions to drug reinforcement.

CONCLUSIONS

We show that repeated, but not acute, cocaine exposure induces a physiologically distinct ensemble characterized by the expression of the immediate early gene Arc, that is uniquely capable of modulating reinforcement behavior.

Learning and memory processes in behavioural addiction: A systematic review

Similar to addictive substances, addictive behaviours such as gambling and gaming are associated with maladaptive modulation of key brain areas and functional networks implicated in learning and memory. Therefore, this review sought to understand how different learning and memory processes relate to behavioural addictions and to unravel their underlying neural mechanisms. Adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we systematically searched four databases - PsycINFO, PubMed, Scopus, and Web of Science using the agreed-upon search string. Findings suggest altered executive function-dependent learning processes and enhanced habit learning in behavioural addiction. Whereas the relationship between working memory and behavioural addiction is influenced by addiction type, working memory aspect, and task nature. Additionally, long-term memory is incoherent in individuals with addictive behaviours. Consistently, neurophysiological evidence indicates alterations in brain areas and networks implicated in learning and memory processes in behavioural addictions. Overall, the present review argues that, like substance use disorders, alteration in learning and memory processes may underlie the development and maintenance of behavioural addictions.

Modulation of mGlu5 reduces rewarding associative properties of nicotine via changes in mesolimbic plasticity: Relevance to comorbid cigarette smoking in psychosis

RATIONALE

Antipsychotic medications that are used to treat psychosis are often limited in their efficacy by high rates of severe side effects. Treatment success in schizophrenia is further complicated by high rates of comorbid nicotine use. Dopamine D2 heteroreceptor complexes have recently emerged as targets for the development of more efficacious pharmaceutical treatments for schizophrenia.

OBJECTIVE

The current study sought to explore the use of the positive allosteric modulator of the mGlu5 receptor 3-Cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide (CDPPB) as a treatment to reduce symptoms related to psychosis and comorbid nicotine use.

METHODS

Neonatal treatment of animals with the dopamine D2-like receptor agonist quinpirole (NQ) from postnatal day (P)1-21 produces a lifelong increase in D2 receptor sensitivity, showing relevance to psychosis and comorbid tobacco use disorder. Following an 8-day conditioning paradigm, brain tissue in the mesolimbic pathway was analyzed for several plasticity markers, including brain derived neurotrophic factor (BDNF), phosphorylated p70 ribosomal S6 kinase (phospho-p70S6K), and cadherin-13 (Cdh13).

RESULTS

Pretreatment with CDPPB was effective to block enhanced nicotine conditioned place preference observed in NQ-treated animals. Pretreatment was additionally effective to block the nicotine-induced increase in BDNF and sex-dependent increases in cadherin-13 in the ventral tegmental area (VTA), as well as increased phospho-p70S6K in the nucleus accumbens (NAcc) shell found in NQ-treated animals.

CONCLUSION

In conjunction with prior work, the current study suggests positive allosteric modulation of the mGlu5 receptor, an emerging target for schizophrenia therapeutics, may be effective for the treatment of comorbid nicotine abuse in psychosis.

Psilocybin reduces heroin seeking behavior and modulates inflammatory gene expression in the nucleus accumbens and prefrontal cortex of male rats

Preclinical and human studies indicate psilocybin may reduce perseverant maladaptive behaviors, including nicotine and alcohol seeking. Such studies in the opioid field are lacking, though opioids are involved in more >50% of overdose deaths. Psilocybin is an agonist at the serotonin 2A receptor (5-HT2AR), a well-documented target for modulation of drug seeking, and evidence suggests 5-HT2AR agonists may dampen motivation for opioids. We sought to investigate the therapeutic efficacy of psilocybin in mediating cessation of opioid use and maintenance of long-lasting abstinence from opioid seeking behavior in a rat model of heroin self-administration (SA). Psilocybin or 5-HT2AR antagonists ketanserin and volinanserin were administered systemically to rats prior to SA of 0.075 mg/kg/infusion of heroin, or relapse following forced abstinence. Psilocybin did not alter heroin taking, but a single exposure to 3.0 mg/kg psilocybin 4-24 hours prior to a relapse test blunted cue-induced heroin seeking. Conversely, 5-HT2AR antagonists exacerbated heroin relapse. To begin to elucidate mechanisms of psilocybin, drug-naïve rats received psilocybin and/or ketanserin, and tissue was collected from the prefrontal cortex (PFC), a region critical for drug seeking and responsive to psilocybin, 24 hours later for RNA-sequencing. 3.0 mg/kg psilocybin regulated ~2-fold more genes in the PFC than 1.0 mg/kg, including genes involved in the cytoskeleton and cytokine signaling. Ketanserin blocked >90% of psilocybin-regulated genes, including the IL-17a cytokine receptor, Il17ra. Psychedelic compounds have reported anti-inflammatory properties, and therefore we performed a gene expression array to measure chemokine/cytokine molecules in the PFC of animals that displayed psilocybin-mediated inhibition of heroin seeking. Psilocybin regulated 4 genes, including Il17a, and a subset of genes correlated with relapse behavior. Selective inhibition of PFC IL-17a was sufficient to reduce heroin relapse. We conclude that psilocybin reduces heroin relapse and highlight IL-17a signaling as a potential downstream pathway of psilocybin that also reduces heroin seeking.

The ion channel TRPA1 is a modulator of the cocaine reward circuit in the nucleus accumbens

Drug addiction therapies commonly fail because continued drug use promotes the release of excessive and pleasurable dopamine levels. Because the connection between pleasure and drug use becomes hard-wired in the nucleus accumbens (NAc), which interfaces motivation, effective therapies need to modulate this mesolimbic reward system. Here, we report that mice with knockdown of the cation channel TRPA1 (transient receptor potential ankyrin 1) were resistant to the drug-seeking behavior and reward effects of cocaine compared to their wildtype litter mates. In our study, we demonstrate that TRPA1 inhibition in the NAc reduces cocaine activity and dopamine release, and conversely, that TRPA1 is critical for cocaine-induced synaptic strength in dopamine receptor 1-expressing medium spiny neurons. Taken together, our data support that cocaine-induced reward-related behavior and synaptic release of dopamine in the NAc are controlled by TRPA1 and suggest that TRPA1 has therapeutic potential as a target for drug misuse therapies.

Morphine-Driven m6A Epitranscriptomic Neuroadaptations in Primary Cortical Cultures

Opioid overdose is the leading cause of accidental death in the United States and remains a major public health concern, despite significant resources aimed at combating opioid misuse. Neurobiological research to elucidate molecular and cellular consequences of opioid exposure is required to define avenues to explore for reversal of opioid-induced neuroadaptations. Opioids impart well-documented regulation of the transcriptome and epigenetic modifications in the brain, but opioid-induced epitranscriptomic posttranscriptional regulation of RNA is vastly understudied. N6-methyladenosine (m6A) RNA methylation is significantly enriched in the brain and involved in learning, memory, and reward. m6A modifications have not been studied in opioid use disorder, despite being the most common RNA modification. We detected significant regulation of m6A-modifying enzymes in rat primary cortical cultures following morphine treatment, including AlkB Homolog 5 (Alkbh5). The m6a demethylase ALKBH5 functions as an m6A eraser, removing m6A modifications from mRNA. We hypothesized that chronic opioid treatment regulates m6A modifications through modulation of Alkbh5 and profiled m6A modifications in primary cortical cultures following chronic morphine treatment and Alkbh5 knock-down. We observed differential regulation of m6A modifications for a common set of transcripts following morphine or Alkbh5 knock-down, and the two treatments elicited concordant m6A epitranscriptomic profiles, suggesting that a subset of morphine-driven m6A modifications may be mediated through downregulation of Alkbh5 in cortical cultures. Gene Ontology terms of commonly regulated transcripts included serotonin secretion, synapse disassembly, neuron remodeling, and immune response. Thus, we conclude that morphine can drive epitranscriptomic changes, a subset of which may occur in an Alkbh5-dependent manner.

Anterior and Posterior Basolateral Amygdala Projections of Cell Type-Specific D1-Expressing Neurons From the Medial Prefrontal Cortex Differentially Control Alcohol-Seeking Behavior

BACKGROUND

Alcohol use disorder is characterized by compulsive alcohol-seeking behavior, which is associated with dysregulation of afferent projections from the medial prefrontal cortex to the basolateral amygdala (BLA). However, the contribution of the cell type-specific mechanism in this neuronal circuit to alcohol-seeking behavior remains unclear.

METHODS

Mice were trained with 2-bottle choice and operant alcohol self-administration procedures. Anterograde and retrograde viral methods traced the connection between dopamine type 1 receptor (D1R) neurons and BLA neurons. Electrophysiology and in vivo optogenetic techniques were used to test the function of neural circuits in alcohol-seeking behavior.

RESULTS

Chronic alcohol consumption preferentially changed the activity of posterior BLA (pBLA) neurons but not anterior BLA (aBLA) neurons and overexcited D1R neurons in the medial prefrontal cortex. Interestingly, we found that 2 populations of D1R neurons, anterior and posterior (pD1R) neurons, separately targeted the aBLA and pBLA, respectively, and only a few D1R neurons innervated both aBLA and pBLA neurons. Furthermore, pD1R neurons exhibited more excitability than anterior D1R neurons in alcohol-drinking mice. Moreover, we observed enhanced glutamatergic transmission and an increased NMDA/AMPA receptor ratio in the medial prefrontal cortex inputs from pD1R neurons to the pBLA. Optogenetic long-term depression induction of the pD1R-pBLA circuit reduced alcohol-seeking behavior, while optogenetic long-term depression or long-term potentiation induction of the anterior D1R-aBLA circuit produced no change in alcohol intake.

CONCLUSIONS

The pD1R-pBLA circuit mediates chronic alcohol consumption, which may suggest a cell type-specific neuronal mechanism underlying reward-seeking behavior in alcohol use disorder.

The behavioral relevance of a modular organization in the lateral habenula

Behavioral strategies for survival rely on the updates the brain continuously makes based on the surrounding environment. External stimuli-neutral, positive, and negative-relay core information to the brain, where a complex anatomical network rapidly organizes actions, including approach or escape, and regulates emotions. Human neuroimaging and physiology in nonhuman primates, rodents, and teleosts suggest a pivotal role of the lateral habenula in translating external information into survival behaviors. Here, we review the literature describing how discrete habenular modules-reflecting the molecular signatures, anatomical connectivity, and functional components-are recruited by environmental stimuli and cooperate to prompt specific behavioral outcomes. We argue that integration of these findings in the context of valence processing for reinforcing or discouraging behaviors is necessary, offering a compelling model to guide future work.

Neuromodulation for Atrial Fibrillation Control

Trigger and functional substrate are related to the tone of autonomic nervous system, and the role of the autonomic nerve is more significant in paroxysmal atrial fibrillation (AF) compared to non-paroxysmal AF. We have several options for neuromodulation to help to manage patients with AF. Neuromodulation targets can be divided into efferent and afferent pathways. On the efferent side, block would be an intuitive approach. However, permanent block is hard to achieve due to completeness of the procedure and reinnervation issues. Temporary block such as botulinum toxin injection into ganglionated plexi would be a possible option for post-cardiac surgery AF. Low-level subthreshold stimulation could also prevent AF, but the invasiveness of the procedure is the barrier for the general use. On the afferent side, block is also an option. Various renal denervation approaches are currently under investigation. Auditory vagus nerve stimulation is one of the representative low-level afferent stimulation methods. This technique is noninvasive and easy to apply, so it has the potential to be widely utilized if its efficacy is confirmed.

Current perspectives on brain circuits involved in food addiction-like behaviors

There is an emerging view that the increased availability of energy-dense foods in our society is contributing to excessive food consumption which could lead to food addiction-like behavior. Particularly, compulsive eating patterns are predominant in people suffering from eating disorders (binge-eating disorder, bulimia and anorexia nervosa) and obesity. Phenotypically, the behavioral pattern exhibits a close resemblance to individuals suffering from other forms of addiction (drug, sex, gambling). Growing body of evidence in neuroscience research is showing that excessive consumption of energy-dense foods alters the brain circuits implicated in reward, decision-making, control, habit formation, and emotions that are central to drug addiction. Here, we review the current understanding of the circuits of food addiction-like behaviors and highlight the future possibility of exploring those circuits to combat obesity and eating disorders.

Substance use and spine density: a systematic review and meta-analysis of preclinical studies

The elucidation of synaptic density changes provides valuable insights into the underlying brain mechanisms of substance use. In preclinical studies, synaptic density markers, like spine density, are altered by substances of abuse (e.g., alcohol, amphetamine, cannabis, cocaine, opioids, nicotine). These changes could be linked to phenomena including behavioral sensitization and drug self-administration in rodents. However, studies have produced heterogeneous results for spine density across substances and brain regions. Identifying patterns will inform translational studies given tools that now exist to measure in vivo synaptic density in humans. We performed a meta-analysis of preclinical studies to identify consistent findings across studies. PubMed, ScienceDirect, Scopus, and EBSCO were searched between September 2022 and September 2023, based on a protocol (PROSPERO: CRD42022354006). We screened 6083 publications and included 70 for meta-analysis. The meta-analysis revealed drug-specific patterns in spine density changes. Hippocampal spine density increased after amphetamine. Amphetamine, cocaine, and nicotine increased spine density in the nucleus accumbens. Alcohol and amphetamine increased, and cannabis reduced, spine density in the prefrontal cortex. There was no convergence of findings for morphine's effects. The effects of cocaine on the prefrontal cortex presented contrasting results compared to human studies, warranting further investigation. Publication bias was small for alcohol or morphine and substantial for the other substances. Heterogeneity was moderate-to-high across all substances. Nonetheless, these findings inform current translational efforts examining spine density in humans with substance use disorders.

The role of orexin receptors within the CA1 area in the acquisition and expression of methamphetamine place preference

Treatment of Methamphetamine (METH) use disorder has become a crucial public health issue. The orexin system manipulation has provided promising evidence to attenuate addictive-like behaviors. This study explored the role of the orexin 1 receptor and orexin 2 receptor (OX1R and OX2R) in the CA1 area of the hippocampal formation in the acquisition and expression of METH-induced place preference. Animals were subjected to bilateral administration of different dosages (1, 3, 10, and 30 nmol/0.5 μl DMSO per side) of a selective OX1R antagonist, SB334867, or selective OX2R antagonist, TCS OX2 29 into the CA1 area throughout the conditioning phase or once on the post-conditioning phase in separate control and experimental groups. Behavioral data revealed that both OX1R (10 nmol; P < 0.01 and 30 nmol; P < 0.001) and OX2R (10 nmol; P < 0.05 and 30 nmol; P < 0.001) antagonism during the conditioning phase could block the formation of METH place preference dose-dependently. In addition, intra-CA1 microinjection of SB334867 on the post-conditioning phase attenuated the expression of METH place preference in a dose-dependent manner (3 nmol; P < 0.05, 10 nmol; P < 0.01 and 30 nmol; P < 0.001) whereas intra-CA1 administration of TCS OX2 29 only at the highest dosage (30 nmol) declined the expression of METH place preference (P < 0.01). It was also indicated that the suppressive effects of orexin receptor blockade on the METH-seeking behavior in the CA1 area were anatomically specific to this area. These findings support the possibility of targeting the orexin system to develop novel and successful pharmacological options for the treatment of METH dependence.

Adenosine and Cortical Plasticity

Brain plasticity is the ability of the nervous system to change its structure and functioning in response to experiences. These changes occur mainly at synaptic connections, and this plasticity is named synaptic plasticity. During postnatal development, environmental influences trigger changes in synaptic plasticity that will play a crucial role in the formation and refinement of brain circuits and their functions in adulthood. One of the greatest challenges of present neuroscience is to try to explain how synaptic connections change and cortical maps are formed and modified to generate the most suitable adaptive behavior after different external stimuli. Adenosine is emerging as a key player in these plastic changes at different brain areas. Here, we review the current knowledge of the mechanisms responsible for the induction and duration of synaptic plasticity at different postnatal brain development stages in which adenosine, probably released by astrocytes, directly participates in the induction of long-term synaptic plasticity and in the control of the duration of plasticity windows at different cortical synapses. In addition, we comment on the role of the different adenosine receptors in brain diseases and on the potential therapeutic effects of acting via adenosine receptors.

Distinct prefrontal projection activity and transcriptional state conversely orchestrate social competition and hierarchy

Social animals compete for limited resources, resulting in a social hierarchy. Although different neuronal subpopulations in the medial prefrontal cortex (mPFC), which has been mechanistically implicated in social dominance behavior, encode distinct social competition behaviors, their identities and associated molecular underpinnings have not yet been identified. In this study, we found that mPFC neurons projecting to the nucleus accumbens (mPFC-NAc) encode social winning behavior, whereas mPFC neurons projecting to the ventral tegmental area (mPFC-VTA) encode social losing behavior. High-throughput single-cell transcriptomic analysis and projection-specific genetic manipulation revealed that the expression level of POU domain, class 3, transcription factor 1 (Pou3f1) in mPFC-VTA neurons controls social hierarchy. Optogenetic activation of mPFC-VTA neurons increases Pou3f1 expression and lowers social rank. Together, these data demonstrate that discrete activity and gene expression in separate mPFC projections oppositely orchestrate social competition and hierarchy.

Intrinsic Functional Connectivity between the Anterior Insular and Retrosplenial Cortex as a Moderator and Consequence of Cocaine Self-Administration in Rats

While functional brain imaging studies in humans suggest that chronic cocaine use alters functional connectivity (FC) within and between key large-scale brain networks, including the default mode network (DMN), the salience network (SN), and the central executive network (CEN), cross-sectional studies in humans are challenging to obtain brain FC prior to cocaine use. Such information is critical to reveal the relationship between individual's brain FC and the subsequent development of cocaine dependence and brain changes during abstinence. Here, we performed a longitudinal study examining functional magnetic resonance imaging (fMRI) data in male rats (n = 7), acquired before cocaine self-administration (baseline), on 1 d of abstinence following 10 d of cocaine self-administration, and again after 30 d of experimenter-imposed abstinence. Using repeated-measures analysis of variance (ANOVA) with network-based statistics (NBS), significant connectivity changes were found between anterior insular cortex (AI) of the SN, retrosplenial cortex (RSC) of the DMN, somatosensory cortex, and caudate-putamen (CPu), with AI-RSC FC showing the most robust changes between baseline and 1 d of abstinence. Additionally, the level of escalated cocaine intake is associated with AI-RSC and AI-CPu FC changes between 1 d and 30 d of abstinence; further, the subjects' AI-RSC FC prior to cocaine intake is a significant moderator for the AI-RSC changes during abstinence. These results provide novel insights into the roles of AI-RSC FC before and after cocaine intake and suggest this circuit to be a potential target to modulate large-scale network and associated behavioral changes in cocaine use disorders.

Management of Impulse Control and Related Disorders in Parkinson's Disease: An Expert Consensus

BACKGROUND

Impulse-control and related behavioral disorders (ICBDs) significantly impact the lives of Parkinson's disease (PD) patients and caregivers, with lasting consequences if undiagnosed and untreated. While ICBD pathophysiology and risk factors are well-studied, a standardized severity definition and treatment evidence remain elusive.

OBJECTIVE

This work aimed to establish international expert consensus on ICBD treatment strategies. To comprehensively address diverse treatment availabilities, experts from various continents were included.

METHODS

From 2021 to 2023, global movement disorders specialists engaged in a Delphi process. A core expert group initiated surveys, involving a larger panel in three iterations, leading to refined severity definitions and treatment pathways.

RESULTS

Experts achieved consensus on defining ICBD severity, emphasizing regular PD patient screenings for early detection. General treatment recommendations focused on continuous monitoring, collaboration with significant others, and seeking specialist advice for legal or financial challenges. For mild to severe ICBDs, gradual reduction in dopamine agonists was endorsed, followed by reductions in other PD medications. Second-line treatment strategies included diverse approaches like reversing the last medication change, cognitive behavior therapy, subthalamic nucleus deep brain stimulation, and specific medications like quetiapine, clozapine, and antidepressants. The panel reached consensus on distinct treatment pathways for punding and dopamine dysregulation syndrome, formulating therapy recommendations. Comprehensive discussions addressed management strategies for the exacerbation of either motor or non-motor symptoms following the proposed treatments.

CONCLUSION

The consensus offers in-depth insights into ICBD management, presenting clear severity criteria and expert consensus treatment recommendations. The study highlights the critical need for further research to enhance ICBD management. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Identification of genes regulated by trait sensitivity to negative feedback and prolonged alcohol consumption in rats

BACKGROUND

The results of our previous studies demonstrated that low sensitivity to negative feedback (NF) is associated with increased vulnerability to the development of compulsive alcohol-seeking in rats. In the present study, we investigated the molecular underpinnings of this relationship.

METHODS

Using TaqMan Gene Expression Array Cards, we analyzed the expression of the genes related to NF sensitivity and alcohol metabolism in three cortical regions (medial prefrontal cortex [mPFC], anterior cingulate cortex [ACC], orbitofrontal cortex [OFC]) and two subcortical regions (nucleus accumbens [Nacc], amygdala [Amy]). Gene expression differences were confirmed at the protein level with Western blot.

RESULTS

Sensitivity to NF was characterized by differences in Gad2, Drd2, and Slc6a4 expression in the ACC, Maoa in the mPFC, and Gria1, Htr3a, and Maoa in the OFC. Chronic alcohol consumption was associated with differences in the expression of Comt and Maoa in the ACC, Comt, Adh1, and Htr2b in the mPFC, Adh1, and Slc6a4 in the Nacc, Gad2, and Htr1a in the OFC, and Drd2 in the Amy. Interactions between the sensitivity to NF and alcohol consumption were observed in the expression of Gabra1, Gabbr2, Grin2a, Grin2b, and Grm3 in the ACC, and Grin2a in the OFC. The observed differences were confirmed at the protein level for MAO-A in the mPFC, and ADH1 in the mPFC and Nacc.

CONCLUSIONS

Our findings contribute to a better understanding of the molecular mechanisms underlying the relationship between trait sensitivity to NF and compulsive alcohol consumption.

Trait sensitivity to positive feedback is a predisposing factor for several aspects of compulsive alcohol drinking in male rats: behavioural, physiological, and molecular correlates

INTRODUCTION

Alcohol use disorder (AUD) is one of the most common psychiatric disorders and a leading cause of mortality worldwide. While the pathophysiology underlying AUD is relatively well known, the cognitive mechanisms of an individual's susceptibility to the development of alcohol dependence remain poorly understood. In this study, we investigated the theoretical claim that sensitivity to positive feedback (PF), as a stable and enduring behavioural trait, can predict individual susceptibility to the acquisition and maintenance of alcohol-seeking behaviour in rats.

METHODS

Trait sensitivity to PF was assessed using a series of probabilistic reversal learning tests. The escalation of alcohol intake in rats was achieved by applying a mix of intermittent free access and instrumental paradigms of alcohol drinking. The next steps included testing the influence of sensitivity to PF on the acquisition of compulsive alcohol-seeking behaviour in the seeking-taking punishment task, measuring motivation to seek alcohol, and comparing the speed of extinction and reinstatement of alcohol-seeking after a period of abstinence between rats expressing trait insensitivity and sensitivity to PF. Finally, trait differences in the level of stress hormones and in the expression of genes and proteins in several brain regions of interest were measured to identify potential physiological and neuromolecular mechanisms of the observed interactions.

RESULTS

We showed that trait sensitivity to PF in rats determines the level of motivation to seek alcohol following the experience of its negative consequences. They also revealed significant differences between animals classified as insensitive and sensitive to PF in their propensity to reinstate alcohol-seeking behaviours after a period of forced abstinence. The abovementioned effects were accompanied by differences in blood levels of stress hormones and differences in the cortical and subcortical expression of genes and proteins related to dopaminergic, serotonergic, and GABAergic neurotransmission.

CONCLUSION

Trait sensitivity to PF can determine the trajectory of alcohol addiction in rats. This effect is, at least partially, mediated via distributed physiological and molecular changes within cortical and subcortical regions of the brain.

Integrative Analysis of Morphine-Induced Differential Circular RNAs and ceRNA Networks in the Medial Prefrontal Cortex

Circular RNAs (circRNAs) are a novel type of non-coding RNAs. Despite the fact that the functional mechanisms of most circRNAs remain unknown, emerging evidence indicates that circRNAs could sponge microRNAs (miRNAs), bind to RNA binding proteins (RBP), and even be translated into protein. Recent research has demonstrated the crucial roles played by circRNAs in neuropsychiatric disorders. The medial prefrontal cortex (mPFC) is a crucial component of drug reward circuitry and exerts top-down control over cognitive functions. However, there is currently limited knowledge about the correlation between circRNAs and morphine-associated contextual memory in the mPFC. Here, we performed morphine-induced conditioned place preference (CPP) in mice and extracted mPFC tissue for RNA-sequencing. Our study represented the first attempt to identify differentially expressed circRNAs (DEcircRNAs) and mRNAs (DEmRNAs) in the mPFC after morphine-induced CPP. We identified 47 significantly up-regulated DEcircRNAs and 429 significantly up-regulated DEmRNAs, along with 74 significantly down-regulated DEcircRNAs and 391 significantly down-regulated DEmRNAs. Functional analysis revealed that both DEcircRNAs and DEmRNAs were closely associated with neuroplasticity. To further validate the DEcircRNAs, we conducted qRT-PCR, Sanger sequencing, and RNase R digestion assays. Additionally, using an integrated bioinformatics approach, we constructed ceRNA networks and identified critical circRNA/miRNA/mRNA axes that contributed to the development of morphine-associated contextual memory. In summary, our study provided novel insights into the role of circRNAs in drug-related memory, specifically from the perspective of ceRNAs.

Activation of Kv7 channels normalizes hyperactivity of the VTA-NAcLat circuit and attenuates methamphetamine-induced conditioned place preference and sensitization in mice

The brain circuit projecting from the ventral tegmental area (VTA) to the nucleus accumbens lateral shell (NAcLat) has a key role in methamphetamine (MA) addiction. As different dopamine (DA) neuron subpopulations in the VTA participate in different neuronal circuits, it is a challenge to isolate these DA neuron subtypes. Using retrograde tracing and Patch-seq, we isolated DA neurons in the VTA-NAcLat circuit in MA-treated mice and performed gene expression profiling. Among the differentially expressed genes, KCNQ genes were dramatically downregulated. KCNQ genes encode Kv7 channel proteins, which modulate neuronal excitability. Injection of both the Kv7.2/3 agonist ICA069673 and the Kv7.4 agonist fasudil into the VTA attenuated MA-induced conditioned place preference and locomotor sensitization and decreased neuronal excitability. Increasing Kv7.2/3 activity decreased neural oscillations, synaptic plasticity and DA release in the VTA-NacLat circuit in MA-treated mice. Furthermore, overexpression of only Kv7.3 channels in the VTA-NacLat circuit was sufficient to attenuate MA-induced reward behavior and decrease VTA neuron excitability. Activation of Kv7 channels in the VTA may become a novel treatment strategy for MA abuse.

Melatonin enhances the restoration of neurological impairments and cognitive deficits during drug withdrawal in methamphetamine-induced toxicity and endoplasmic reticulum stress in rats

Methamphetamine (METH) is a psychostimulant with a very high addiction rate. Prolonged use of METH has been observed as one of the root causes of neurotoxicity. Melatonin (Mel) has been found to have a significant role in METH-induced neurotoxicity. This study aimed to investigate the restorative effect of Mel on behavioral flexibility in METH-induced cognitive deficits. Male Sprague-Dawley rats were randomly assigned to be intraperitoneally injected with saline (control) or Meth at 5 mg/kg for 7 consecutive days. Then, METH injection was withdrawn and rats in each group were subcutaneously injected with saline or Mel at 10 mg/kg for 14 consecutive days. The stereotypic behavioral test and attentional set-shifting task (ASST) were used to evaluate neurological functions and cognitive flexibility, respectively. Rats developed abnormal features of stereotyped behaviors and deficits in cognitive flexibility after 7 days of METH administration. However, post-treatment with Mel for 14 days after METH withdrawal dramatically ameliorated the neurological and cognitive deficits in METH-treated rats. Blood biomarkers indicated METH-induced systemic low-grade inflammation. Moreover, METH-induced endoplasmic reticulum (ER) stress in the prefrontal cortex was diminished by melatonin supplementation. These findings might reveal the therapeutic potential of Mel in METH toxicity-induced neurological and cognitive deficits.

Alternating current stimulation promotes neurite outgrowth and plasticity in neurons through activation of the PI3K/AKT signaling pathway

As a commonly used physical intervention, electrical stimulation (ES) has been demonstrated to be effective in the treatment of central nervous system disorders. Currently, researchers are studying the effects of electrical stimulation on individual neurons and neural networks, which are dependent on factors such as stimulation intensity, duration, location, and neuronal properties. However, the exact mechanism of action of electrical stimulation remains unclear. In some cases, repeated or prolonged electrical stimulation can lead to changes in the morphology or function of the neuron. In this study, immunofluorescence staining and Sholl analysis are used to assess changes in the neurite number and axon length to determine the optimal pattern and stimulation parameters of ES for neurons. Neuronal death and plasticity are detected by TUNEL staining and microelectrode array assays, respectively. mRNA sequencing and bioinformatics analysis are applied to predict the key targets of the action of ES on neurons, and the identified targets are validated by western blot analysis and qRT-PCR. The effects of alternating current stimulation (ACS) on neurons are more significant than those of direct current stimulation (DCS), and the optimal parameters are 3 μA and 20 min. ACS stimulation significantly increases the number of neurites, the length of axons and the spontaneous electrical activity of neurons, significantly elevates the expression of growth-associated protein-43 (GAP-43) without significant changes in the expression of neurotrophic factors. Furthermore, application of PI3K/AKT-specific inhibitors significantly abolishes the beneficial effects of ACS on neurons, confirming that the PI3K/AKT pathway is an important potential signaling pathway in the action of ACS.

Blockade of the Dopamine D3 Receptor Attenuates Opioids-Induced Addictive Behaviours Associated with Inhibiting the Mesolimbic Dopamine System

Opioid use disorder (OUD) has become a considerable global public health challenge; however, potential medications for the management of OUD that are effective, safe, and nonaddictive are not available. Accumulating preclinical evidence indicates that antagonists of the dopamine D3 receptor (D3R) have effects on addiction in different animal models. We have previously reported that YQA14, a D3R antagonist, exhibits very high affinity and selectivity for D3Rs over D2Rs, and is able to inhibit cocaine- or methamphetamine-induced reinforcement and reinstatement in self-administration tests. In the present study, our results illustrated that YQA14 dose-dependently reduced infusions under the fixed-ratio 2 procedure and lowered the breakpoint under the progressive-ratio procedure in heroin self-administered rats, also attenuated heroin-induced reinstatement of drug-seeking behavior. On the other hand, YQA14 not only reduced morphine-induced expression of conditioned place preference but also facilitated the extinguishing process in mice. Moreover, we elucidated that YQA14 attenuated opioid-induced reward or reinforcement mainly by inhibiting morphine-induced up-regulation of dopaminergic neuron activity in the ventral tegmental area and decreasing dopamine release in the nucleus accumbens with a fiber photometry recording system. These findings suggest that D3R might play a very important role in opioid addiction, and YQA14 may have pharmacotherapeutic potential in attenuating opioid-induced addictive behaviors dependent on the dopamine system.

Acute inhibition of AMPA receptors by perampanel reduces amyloid β-protein levels by suppressing β-cleavage of APP in Alzheimer's disease models

Hippocampal hyperexcitability is a promising therapeutic target to prevent Aβ deposition in AD since enhanced neuronal activity promotes presynaptic Aβ production and release. This article highlights the potential application of perampanel (PER), an AMPA receptor (AMPAR) antagonist approved for partial seizures, as a therapeutic agent for AD. Using transgenic AD mice combined with in vivo brain microdialysis and primary neurons under oligomeric Aβ-evoked neuronal hyperexcitability, the acute effects of PER on Aβ metabolism were investigated. A single oral administration of PER rapidly decreased ISF Aβ40 and Aβ42 levels in the hippocampus of J20, APP transgenic mice, without affecting the Aβ40 /Aβ42 ratio; 5 mg/kg PER resulted in declines of 20% and 31%, respectively. Moreover, PER-treated J20 manifested a marked decrease in hippocampal APP βCTF levels with increased FL-APP levels. Consistently, acute treatment of PER reduced sAPPβ levels, a direct byproduct of β-cleavage of APP, released to the medium in primary neuronal cultures under oligomeric Aβ-induced neuronal hyperexcitability. To further evaluate the effect of PER on ISF Aβ clearance, a γ-secretase inhibitor was administered to J20 1 h after PER treatment. PER did not influence the elimination of ISF Aβ, indicating that the acute effect of PER is predominantly on Aβ production. In conclusion, acute treatment of PER reduces Aβ production by suppressing β-cleavage of amyloid-β precursor protein effectively, indicating a potential effect of PER against Aβ pathology in AD.

Cdc42GAP deficiency contributes to the Alzheimer's disease phenotype

Alzheimer's disease, the most common cause of dementia, is a chronic degenerative disease with typical pathological features of extracellular senile plaques and intracellular neurofibrillary tangles and a significant decrease in the density of neuronal dendritic spines. Cdc42 is a member of the small G protein family that plays an important role in regulating synaptic plasticity and is regulated by Cdc42GAP, which switches Cdc42 from active GTP-bound to inactive GDP-bound states regulating downstream pathways via effector proteins. However, few studies have focused on Cdc42 in the progression of Alzheimer's disease. In a heterozygous Cdc42GAP mouse model that exhibited elevated Cdc42-GTPase activity accompanied by increased Cdc42-PAK1-cofilin signalling, we found impairments in cognitive behaviours, neuron senescence, synaptic loss with depolymerization of F-actin and the pathological phenotypes of Alzheimer's disease, including phosphorylated tau (p-T231, AT8), along with increased soluble and insoluble Aβ1-42 and Aβ1-40, which are consistent with typical Alzheimer's disease mice. Interestingly, these impairments increased significantly with age. Furthermore, the results of quantitative phosphoproteomic analysis of the hippocampus of 11-month-old GAP mice suggested that Cdc42GAP deficiency induces and accelerates Alzheimer's disease-like phenotypes through activation of GSK-3β by dephosphorylation at Ser9, Ser389 and/or phosphorylation at Tyr216. In addition, overexpression of dominant-negative Cdc42 in the primary hippocampal and cortical neurons of heterozygous Cdc42GAP mice reversed synaptic loss and tau hyperphosphorylation. Importantly, the Cdc42 signalling pathway, Aβ1-42, Aβ1-40 and GSK-3β activity were increased in the cortical sections of Alzheimer's disease patients compared with those in healthy controls. Together, these data indicated that Cdc42GAP is involved in regulating Alzheimer's disease-like phenotypes such as cognitive deficits, dendritic spine loss, phosphorylated tau (p-T231, AT8) and increased soluble and insoluble Aβ1-42 and Aβ1-40, possibly through the activation of GSK-3β, and these impairments increased significantly with age. Thus, we provide the first evidence that Cdc42 is involved in the progression of Alzheimer's disease-like phenotypes, which may provide new targets for Alzheimer's disease treatment.

N-Oleoyl Glycine and Its Derivatives Attenuate the Acquisition and Expression of Cocaine-Induced Behaviors

Introduction: The endocannabinoid system (ECS) plays a key modulatory role during synaptic plasticity and homeostatic processes in the brain and plays an important role in the neurobiological processes underlying drug addiction. Impaired endocannabinoid (eCB) signaling contributes to dysregulated synaptic plasticity, increased stress responsivity, and craving that propel addiction. Therefore, we hypothesized that boosting the ECS by exogenous administration of selective eCBs will attenuate cocaine-induced behaviors. Materials and Methods: The behavioral paradigms included psychomotor sensitization (PS) and conditioned place preference (CPP). Liquid chromatography-mass spectrometry analysis was used for quantitative profiling of eCBs in mouse brain. Results: We first measured the levels of eCBs in different brain areas of the reward system following chronic cocaine treatment. We found that following daily administration of cocaine, the levels of N-oleoyl glycine (OlGly) were significantly elevated in the nucleus accumbens (NAc) in a region-specific manner. We next tested whether administration of OlGly will attenuate cocaine-induced behaviors. We found that administration of OlGly during withdrawal, but not during acquisition of PS, attenuated the expression of cocaine sensitization. In addition, the administration of OlGly during the acquisition of cocaine CPP, but not during withdrawal, attenuated the expression of cocaine-conditioned reward. To enhance the stability of OlGly and its duration of action, two methylated derivatives of OlGly were synthesized, the monomethylated OlGly (HU-595) and dimethylated OlGly (HU-596). We found that the effect of administration of HU-595 or HU-596 during cocaine conditioning did not differ from the OlGly-induced decrease in the expression of CPP. Conclusion: Our findings suggest that the ECS is involved in the common neurobiological mechanisms underlying the development and expression of cocaine reward and drug-seeking. Boosting the ECS exogenously has beneficial effects against cocaine-induced behaviors.

A visual circuit related to the habenula mediates the prevention of cocaine relapse by bright light treatment

Despite significant advancements in our understanding of addiction at the neurobiological level, a highly effective extinction procedure for preventing relapse remains elusive. In this study, we report that bright light treatment (BLT) administered during cocaine withdrawal with extinction training prevents cocaine-driven reinstatement by acting through the thalamic-habenular pathway. We found that during cocaine withdrawal, the lateral habenula (LHb) was recruited, and inhibition of the LHb via BLT prevented cocaine-driven reinstatement. We also demonstrated that the effects of BLT were mediated by activating LHb-projecting neurons in the ventral lateral geniculate nucleus and intergeniculate leaflet (vLGN/IGL) or by inhibiting postsynaptic LHb neurons. Furthermore, BLT was found to improve aversive emotional states induced by drug withdrawal. Our findings suggest that BLT administered during the cocaine withdrawal may be a promising strategy for achieving drug abstinence.

Kappa opioid receptor in nucleus accumbens regulates depressive-like behaviors following prolonged morphine withdrawal in mice

Prolonged withdrawal from opioids leads to negative emotions. Kappa opioid receptor (KOR) plays an important role in opioid addiction and affective disorders. However, the underlying mechanism of KOR in withdrawal-related depression is still lacking. We found that escitalopram treatment had a limited effect in improving depression symptoms in heroin-dependent patients. In mice, we demonstrated prolonged (4 weeks) but not acute (24 h) withdrawal from morphine induced depressive-like behaviors. The number of c-Fos positive cells and the expression of KOR in the nucleus accumbens (NAc), were significantly increased in the prolonged morphine withdrawal mice. Conditional KOR knockdown in NAc significantly improved depressive-like behaviors. Repeated but not acute treatment with the KOR antagonist norBNI improved depressive-like behaviors and reversed PSD95, synaptophysin, p-ERK, p-CREB, and BDNF in NAc. This study demonstrated the important role of striatal KOR in morphine withdrawal-related depressive-like behaviors and offered therapeutic potential for the treatment of withdrawal-related depression.

Nucleus accumbens D1/D2 circuits control opioid withdrawal symptoms in mice

The nucleus accumbens (NAc) is the most promising target for drug use disorder treatment. Deep brain stimulation (DBS) of NAc is effective for drug use disorder treatment. However, the mechanisms by which DBS produces its therapeutic effects remain enigmatic. Here, we define a behavioral cutoff criterion to distinguish depressive-like behaviors and non-depressive-like behaviors in mice after morphine withdrawal. We identified a basolateral amygdala (BLA) to NAc D1 medium spiny neuron (MSN) pathway that controls depressive-like behaviors after morphine withdrawal. Furthermore, the paraventricular nucleus of thalamus (PVT) to NAc D2 MSN pathway controls naloxone-induced acute withdrawal symptoms. Optogenetically induced long-term potentiation with κ-opioid receptor (KOR) antagonism enhanced BLA to NAc D1 MSN signaling and also altered the excitation/inhibition balance of NAc D2 MSN signaling. We also verified that a new 50 Hz DBS protocol reversed morphine withdrawal-evoked abnormal plasticity in NAc. Importantly, this refined DBS treatment effectively alleviated naloxone-induced withdrawal symptoms and depressive-like behaviors and prevented stress-induced reinstatement. Taken together, the results demonstrated that input- and cell type-specific synaptic plasticity underlies morphine withdrawal, which may lead to novel targets for the treatment of opioid use disorder.

The ubiquitin-proteasome system and learning-dependent synaptic plasticity - A 10 year update

Over 25 years ago, a seminal paper demonstrated that the ubiquitin-proteasome system (UPS) was involved in activity-dependent synaptic plasticity. Interest in this topic began to expand around 2008 following another seminal paper showing that UPS-mediated protein degradation controlled the "destabilization" of memories following retrieval, though we remained with only a basic understanding of how the UPS regulated activity- and learning-dependent synaptic plasticity. However, over the last 10 years there has been an explosion of papers on this topic that has significantly changed our understanding of how ubiquitin-proteasome signaling regulates synaptic plasticity and memory formation. Importantly, we now know that the UPS controls much more than protein degradation, is involved in plasticity underlying drugs of abuse and that there are significant sex differences in how ubiquitin-proteasome signaling is used for memory storage processes. Here, we aim to provide a critical 10-year update on the role of ubiquitin-proteasome signaling in synaptic plasticity and memory formation, including updated cellular models of how ubiquitin-proteasome activity could be regulating learning-dependent synaptic plasticity in the brain.

Non-Opioid Anesthetics Addiction: A Review of Current Situation and Mechanism

Drug addiction is one of the major worldwide health problems, which will have serious adverse consequences on human health and significantly burden the social economy and public health. Drug abuse is more common in anesthesiologists than in the general population because of their easier access to controlled substances. Although opioids have been generally considered the most commonly abused drugs among anesthesiologists and nurse anesthetists, the abuse of non-opioid anesthetics has been increasingly severe in recent years. The purpose of this review is to provide an overview of the clinical situation and potential molecular mechanisms of non-opioid anesthetics addiction. This review incorporates the clinical and biomolecular evidence supporting the abuse potential of non-opioid anesthetics and the foreseeable mechanism causing the non-opioid anesthetics addiction phenotypes, promoting a better understanding of its pathogenesis and helping to find effective preventive and curative strategies.

Sex-specific adaptations to VTA circuits following subchronic stress

Dysregulation of the mesolimbic reward circuitry is implicated in the pathophysiology of stress-related illnesses such as depression and anxiety. These disorders are more frequently diagnosed in females, and sex differences in the response to stress are likely to be one factor that leads to enhanced vulnerability of females. In this study, we use subchronic variable stress (SCVS), a model in which females are uniquely vulnerable to behavioral disturbances, to investigate sexually divergent mechanisms of regulation of the ventral tegmental area by stress. Using slice electrophysiology, we find that female, but not male mice have a reduction in the ex vivo firing rate of VTA dopaminergic neurons following SCVS. Surprisingly, both male and female animals show an increase in inhibitory tone onto VTA dopaminergic neurons and an increase in the firing rate of VTA GABAergic neurons. In males, however, this is accompanied by a robust increase in excitatory synaptic tone onto VTA dopamine neurons. This supports a model by which SCVS recruits VTA GABA neurons to inhibit dopaminergic neurons in both male and female mice, but males are protected from diminished functioning of the dopaminergic system by a compensatory upregulation of excitatory synapses.

Acute adolescent morphine exposure improves dark avoidance memory and enhances long-term potentiation of ventral hippocampal CA1 during adulthood in rats

Adolescence represents a distinctive vulnerable period when exposure to stressful situations including opioid exposure can entail lasting effects on brain and can change neural mechanisms involved in memory formation for drug-associated cues, possibly increasing vulnerability of adolescents to addiction. Herein, the effects of acute adolescent morphine exposure (AAME, two injections of 2.5 mg/kg SC morphine on PND 31) were therefore investigated 6 weeks later (adulthood) on avoidance memory and hippocampal long-term potentiation (LTP) at Schaffer collateral-CA1 synapses in transvers slices from the ventral hippocampus in adult male rats using field recordings technique. Animal body weight was measured from PND 31 throughout PND 40 and also in four time points with 1 week intervals from adolescence to adulthood (PNDs 48, 55, 62 and 69) to evaluate the effect of AAME on the weight gain. We showed that there were no effects on body weight, anxiety-like behaviour and locomotor activity, even until adulthood. There was an improved dark avoidance memory during adulthood. Finally, AAME had no effects on baseline synaptic responses and resulted in a decrease in the mean values of the field excitatory postsynaptic potential slopes required to evoke the half-maximal population spike amplitude and an enhancement of LTP magnitude (%) in the ventral CA1 during adulthood. Briefly, our results suggest long-lasting effects of acute adolescent morphine exposure on the ventral hippocampus, which begin the enhancing of synaptic plasticity and the improving of emotional memory in adulthood.

Identification of PROK2 gene polymorphisms as predictors of methamphetamine use disorder risk and indicators of craving scale in the Chinese Han population

Background: Methamphetamine use disorder (MUD) has become a global problem due to the highly addictive nature of methamphetamine. Earlier research have demonstrated that PROK2 functions as a compensatory and protective response against neurotoxic stress by stimulating astrocyte reactivity. The aim of our study was to evaluate the correlation between the PROK2 gene and both MUD risk susceptibility and craving scale in the Chinese Han population. Methods: A total of 5,282 participants (1,796 MUD patients and 3,486 controls) were recruited. Seven tag SNPs of the PROK2 gene were chosen and genotyped in the samples. Genetic association analyses were performed to capture the significant SNPs. To investigate the relationship between PROK2 levels and craving scores with the associated-SNP genotypes, we conducted a linear model. Results: SNP rs75433452 was significantly linked with MUD risk (p-value = 1.54 × 10^-8), with the A allele being positively correlated with an increased risk of MUD. Moreover, the average serum level of PROK2 decreased when more copies of the A allele were presented in both MUD patients (p-value = 4.57 × 10^-6) and controls (p-value = 1.13 × 10^-5). Furthermore, the genotypes of SNP rs75433452 were strongly correlated with the craving scores in MUD patients (p-value = 4.05 × 10^-4). Conclusion: Our study identified a significant association signal of the PROK2 gene with MUD risk susceptibility and methamphetamine craving scores in the Chinese Han population, providing potential valuable insights into the underlying mechanisms of METH dependence.

Functional neuroanatomy of craving in heroin use disorder: voxel-based meta-analysis of functional magnetic resonance imaging (fMRI) drug cue reactivity studies

Background: The neuroanatomy of craving, typically investigated using the functional magnetic resonance imaging (fMRI) drug cue reactivity (FDCR) paradigm, has been shown to involve the mesocorticolimbic, nigrostriatal, and corticocerebellar systems in several substances. However, the neuroanatomy of craving in heroin use disorder is still unclear.Objective: The current meta-analysis examines previous research on the neuroanatomy of craving in abstinent individuals with opioid use disorder (OUD).Method: Seven databases were searched for studies comparing abstinent OUD versus healthy controls on drug > neutral contrast interaction at the whole-brain level. Voxel-based meta-analysis was performed using seed-based d mapping with permuted subject images (SDM-PSI). Thresholds were set at a family-wise error rate of less than 5% with the default pre-processing parameters of SDM-PSI.Results: A total of 10 studies were included (296 OUD and 187 controls). Four hyperactivated clusters were identified with Hedges' g of peaks that ranged from 0.51 to 0.82. These peaks and their associated clusters correspond to the three systems identified in the previous literature: a) mesocorticolimbic, b) nigrostriatal, and c) corticocerebellar. There were also newly revealed hyperactivation regions including the bilateral cingulate, precuneus, fusiform gyrus, pons, lingual gyrus, and inferior occipital gyrus. The meta-analysis did not reveal areas of hypoactivation.Conclusion: Recommendations based on the functional neuroanatomical findings of this meta-analysis include pharmacological interventions such as buprenorphine/naloxone and cognitive-behavioral treatments such as cue-exposure combined with HRV biofeedback. In addition, research should utilize FDCR as pre- and post-measurement to determine the effectiveness and mechanism of action of such interventions.

Behavioral State-Dependent Modulation of Prefrontal Cortex Activity by Respiration

Respiration-rhythmic oscillations in the local field potential emerge in the mPFC, a cortical region with a key role in the regulation of cognitive and emotional behavior. Respiration-driven rhythms coordinate local activity by entraining fast γ oscillations as well as single-unit discharges. To what extent respiration entrainment differently engages the mPFC network in a behavioral state-dependent manner, however, is not known. Here, we compared the respiration entrainment of mouse PFC local field potential and spiking activity (23 male and 2 female mice) across distinct behavioral states: during awake immobility in the home cage (HC), during passive coping in response to inescapable stress under tail suspension (TS), and during reward consumption (Rew). Respiration-driven rhythms emerged during all three states. However, prefrontal γ oscillations were more strongly entrained by respiration during HC than TS or Rew. Moreover, neuronal spikes of putative pyramidal cells and putative interneurons showed significant respiration phase-coupling throughout behaviors with characteristic phase preferences depending on the behavioral state. Finally, while phase-coupling dominated in deep layers in HC and Rew conditions, TS resulted in the recruitment of superficial layer neurons to respiration. These results jointly suggest that respiration dynamically entrains prefrontal neuronal activity depending on the behavioral state.SIGNIFICANCE STATEMENT The mPFC, through its extensive connections (e.g., to the amygdala, the striatum, serotoninergic and dopaminergic nuclei), flexibly regulates cognitive behaviors. Impairment of prefrontal functions can lead to disease states, such as depression, addiction, or anxiety disorders. Deciphering the complex regulation of PFC activity during defined behavioral states is thus an essential challenge. Here, we investigated the role of a prefrontal slow oscillation that has recently attracted rising interest, the respiration rhythm, in modulating prefrontal neurons during distinct behavioral states. We show that prefrontal neuronal activity is differently entrained by the respiration rhythm in a cell type- and behavior-dependent manner. These results provide first insight into the complex modulation of prefrontal activity patterns by rhythmic breathing.

Changes in synaptic markers after administration of ketamine or psychedelics: a systematic scoping review

Background

Ketamine and psychedelics have abuse liability. They can also induce "transformative experiences" where individuals experience enhanced states of awareness. This enhanced awareness can lead to changes in preexisting behavioral patterns which could be beneficial in the treatment of substance use disorders (SUDs). Preclinical and clinical studies suggest that ketamine and psychedelics may alter markers associated with synaptic density, and that these changes may underlie effects such as sensitization, conditioned place preference, drug self-administration, and verbal memory performance. In this scoping review, we examined studies that measured synaptic markers in animals and humans after exposure to ketamine and/or psychedelics.

Methods

A systematic search was conducted following PRISMA guidelines, through PubMed, EBSCO, Scopus, and Web of Science, based on a published protocol (Open Science Framework, DOI: 10.17605/OSF.IO/43FQ9). Both in vivo and in vitro studies were included. Studies on the following synaptic markers were included: dendritic structural changes, PSD-95, synapsin-1, synaptophysin-1, synaptotagmin-1, and SV2A.

Results

Eighty-four studies were included in the final analyses. Seventy-one studies examined synaptic markers following ketamine treatment, nine examined psychedelics, and four examined both. Psychedelics included psilocybin/psilocin, lysergic acid diethylamide, N,N-dimethyltryptamine, 2,5-dimethoxy-4-iodoamphetamine, and ibogaine/noribogaine. Mixed findings regarding synaptic changes in the hippocampus and prefrontal cortex (PFC) have been reported when ketamine was administered in a single dose under basal conditions. Similar mixed findings were seen under basal conditions in studies that used repeated administration of ketamine. However, studies that examined animals during stressful conditions found that a single dose of ketamine counteracted stress-related reductions in synaptic markers in the hippocampus and PFC. Repeated administration of ketamine also counteracted stress effects in the hippocampus. Psychedelics generally increased synaptic markers, but results were more consistently positive for certain agents.

Conclusion

Ketamine and psychedelics can increase synaptic markers under certain conditions. Heterogeneous findings may relate to methodological differences, agents administered (or different formulations of the same agent), sex, and type of markers. Future studies could address seemingly mixed results by using meta-analytical approaches or study designs that more fully consider individual differences.

Role of α6-Nicotinic Receptors in Alcohol-Induced GABAergic Synaptic Transmission and Plasticity to Cholinergic Interneurons in the Nucleus Accumbens

The prevailing view is that enhancement of dopamine (DA) transmission in the mesolimbic system, consisting of DA neurons in the ventral tegmental area (VTA) that project to the nucleus accumbens (NAc), underlies the reward properties of ethanol (EtOH) and nicotine (NIC). We have shown previously that EtOH and NIC modulation of DA release in the NAc is mediated by α6-containing nicotinic acetylcholine receptors (α6*-nAChRs), that α6*-nAChRs mediate low-dose EtOH effects on VTA GABA neurons and EtOH preference, and that α6*-nAChRs may be a molecular target for low-dose EtOH. However, the most sensitive target for reward-relevant EtOH modulation of mesolimbic DA transmission and the involvement of α6*-nAChRs in the mesolimbic DA reward system remains to be elucidated. The aim of this study was to evaluate EtOH effects on GABAergic modulation of VTA GABA neurons and VTA GABAergic input to cholinergic interneurons (CINs) in the NAc. Low-dose EtOH enhanced GABAergic input to VTA GABA neurons that was blocked by knockdown of α6*-nAChRs. Knockdown was achieved either by α6-miRNA injected into the VTA of VGAT-Cre/GAD67-GFP mice or by superfusion of the α-conotoxin MII[H9A;L15A] (MII). Superfusion of MII blocked EtOH inhibition of mIPSCs in NAc CINs. Concomitantly, EtOH enhanced CIN firing rate, which was blocked by knockdown of α6*-nAChRs with α6-miRNA injected into the VTA of VGAT-Cre/GAD67-GFP mice. The firing rate of CINs was not enhanced by EtOH in EtOH-dependent mice, and low-frequency stimulation (LFS; 1 Hz, 240 pulses) caused inhibitory long-term depression at this synapse (VTA-NAc CIN-iLTD) which was blocked by knockdown of α6*-nAChR and MII. Ethanol inhibition of CIN-mediated evoked DA release in the NAc was blocked by MII. Taken together, these findings suggest that α6*-nAChRs in the VTA-NAc pathway are sensitive to low-dose EtOH and play a role in plasticity associated with chronic EtOH.

Negative modulation of AMPA receptors bound to transmembrane AMPA receptor regulatory protein γ-8 blunts the positive reinforcing properties of alcohol and sucrose in a brain region-dependent manner in male mice

RATIONALE

The development and progression of alcohol use disorder (AUD) are widely viewed as maladaptive neuroplasticity. The transmembrane alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) regulatory protein γ8 (TARP γ-8) is a molecular mechanism of neuroplasticity that has not been evaluated in AUD or other addictions.

OBJECTIVE

To address this gap in knowledge, we evaluated the mechanistic role of TARP γ-8 bound AMPAR activity in the basolateral amygdala (BLA) and ventral hippocampus (vHPC) in the positive reinforcing effects of alcohol, which drive repetitive alcohol use throughout the course of AUD, in male C57BL/6 J mice. These brain regions were selected because they exhibit high levels of TARP γ-8 expression and send glutamate projections to the nucleus accumbens (NAc), which is a key nucleus in the brain reward pathway.

METHODS AND RESULTS

Site-specific pharmacological inhibition of AMPARs bound to TARP γ-8 in the BLA via bilateral infusion of the selective negative modulator JNJ-55511118 (0-2 µg/µl/side) significantly decreased operant alcohol self-administration with no effect on sucrose self-administration in behavior-matched controls. Temporal analysis showed that reductions in alcohol-reinforced response rate occurred > 25 min after the onset of responding, consistent with a blunting of the positive reinforcing effects of alcohol in the absence of nonspecific behavioral effects. In contrast, inhibition of TARP γ-8 bound AMPARs in the vHPC selectively decreased sucrose self-administration with no effect on alcohol.

CONCLUSIONS

This study reveals a novel brain region-specific role of TARP γ-8 bound AMPARs as a molecular mechanism of the positive reinforcing effects of alcohol and non-drug rewards.

Reinstatement of nicotine conditioned place preference in a transgenerational model of drug abuse vulnerability in psychosis: Impact of BDNF on the saliency of drug associations

RATIONALE

Psychotic disorders such as schizophrenia are often accompanied by high rates of cigarette smoking, reduced quit success, and high relapse rates, negatively affecting patient outcomes. However, the mechanisms underlying altered relapse-like behaviors in psychosis are poorly understood.

OBJECTIVES

The present study analyzed changes in extinction and reinstatement of nicotine conditioned place preference (CPP) and resulting changes in brain-derived neurotrophic factor (BDNF) in a novel heritable rodent model of psychosis, demonstrating increased dopamine D₂ receptor sensitivity, to explore mechanisms contributing to changes in relapse-like behaviors.

METHODS

Male and female offspring of two neonatal quinpirole-treated (1 mg/kg quinpirole from postnatal day (P)1-21; QQ) and two neonatal saline-treated (SS) Sprague-Dawley rats (F1 generation) were tested on an extended CPP paradigm to analyze extinction and nicotine-primed reinstatement. Brain tissue was analyzed 60 min after the last nicotine injection for BDNF response in the ventral tegmental area (VTA), the infralimbic (IfL) and prelimbic (PrL) cortices.

RESULTS

F1 generation QQ offspring demonstrated delayed extinction and more robust reinstatement compared to SS control animals. In addition, QQ animals demonstrated an enhanced BDNF response to nicotine in the VTA, IfL and Prl cortices compared to SS offspring.

CONCLUSIONS

This study is the first to demonstrate altered relapse-like behavior in a heritable rodent model with relevance to comorbid drug abuse and psychosis. This altered pattern of behavior is hypothesized to be related to elevated activity-dependent BDNF in brain areas associated with drug reinforcement during conditioning that persists through the extinction phase, rendering aberrantly salient drug associations resistant to extinction and enhancing relapse vulnerability.

Future perspectives of emerging novel drug targets and immunotherapies to control drug addiction

Substance Use Disorder (SUD) is one of the major mental illnesses that is terrifically intensifying worldwide. It is becoming overwhelming due to limited options for treatment. The complexity of addiction disorders is the main impediment to understanding the pathophysiology of the illness. Hence, unveiling the complexity of the brain through basic research, identification of novel signaling pathways, the discovery of new drug targets, and advancement in cutting-edge technologies will help control this disorder. Additionally, there is a great hope of controlling the SUDs through immunotherapeutic measures like therapeutic antibodies and vaccines. Vaccines have played a cardinal role in eliminating many diseases like polio, measles, and smallpox. Further, vaccines have controlled many diseases like cholera, dengue, diphtheria, Haemophilus influenza type b (Hib), human papillomavirus, influenza, Japanese encephalitis, etc. Recently, COVID-19 was controlled in many countries by vaccination. Currently, continuous effort is done to develop vaccines against nicotine, cocaine, morphine, methamphetamine, and heroin. Antibody therapy against SUDs is another important area where serious attention is required. Antibodies have contributed substantially against many serious diseases like diphtheria, rabies, Crohn's disease, asthma, rheumatoid arthritis, and bladder cancer. Antibody therapy is gaining immense momentum due to its success rate in cancer treatment. Furthermore, enormous advancement has been made in antibody therapy due to the generation of high-efficiency humanized antibodies with a long half-life. The advantage of antibody therapy is its instant outcome. This article's main highlight is discussing the drug targets of SUDs and their associated mechanisms. Importantly, we have also discussed the scope of prophylactic measures to eliminate drug dependence.

Insights into the mechanisms underlying opioid use disorder and potential treatment strategies

Opioid use disorder is a worldwide societal problem and public health burden. Strategies for treating opioid use disorder can be divided into those that target the opioid receptor system and those that target non-opioid receptor systems, including the dopamine and glutamate receptor systems. Currently, the clinical drugs used to treat opioid use disorder include the opioid receptor agonists methadone and buprenorphine, which are limited by their abuse liability, and the opioid receptor antagonist naltrexone, which is limited by poor compliance. Therefore, the development of effective medications with lower abuse liability and better potential for compliance is urgently needed. Based on recent advances in the understanding of the neurobiological mechanisms underlying opioid use disorder, potential treatment strategies and targets have emerged. This review focuses on the progress made in identifying potential targets and developing medications to treat opioid use disorder, including progress made by our laboratory, and provides insights for future medication development. LINKED ARTICLES: This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Intravenous Injection of GluR2-3Y Inhibits Repeated Morphine-Primed Reinstatement of Drug Seeking in Rats

Studies have demonstrated that the α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor is essential to drug addiction. In this study, we explored the influence of GluR2-3Y, an interfering peptide to prevent the endocytosis of AMPA receptors containing the GluR2 subunit, on morphine-seeking behavior in the rat self-administration model. After self-administration was established, the rats received intravenous injections of GluR2-3Y during the extinction sessions. There were no significant differences in both active and inactive pokes compared to the control group of rats that received GluR2-3S, indicating that GluR2-3Y has no significant influences on the extinction of morphine self-administration. The other two groups of rats were trained, extinguished, and reinstated by repeated morphine priming (respectively, called Prime 1, Prime 2, and Prime 3). Only one intravenous injection of GluR2-3Y was performed before Prime 1. Compared to the control group, GluR2-3Y did not affect Prime 1, but significantly attenuated the morphine-seeking behavior during repeated morphine-primed reinstatement, indicating an inhibitory after effect of GluR2-3Y on morphine-seeking behavior in rats. The long-term depression (LTD) in the nucleus accumbens (NAc) shell was also assessed. Pretreatment with GluR2-3Y altered the ability of LTD induction to the level of that in the naive group, while pretreatment with GluR2-3S had no effects on LTD. Our results demonstrated that the intravenous injection of GluR2-3Y, to block the endocytosis of AMPA receptors, inhibited the reinstatement of morphine-seeking behavior, which may be induced by modulating the neuronal plasticity in the NAc shell of rats.

VU0155041, a positive allosteric modulator of mGluR4, in the nucleus accumbens facilitates extinction and inhibits the reinstatement of morphine-induced conditioned place preference in male rats

Nucleus accumbens (NAc) neurons appear to be at the hub of the reward circuit. New evidence suggests that the behavioural effects of morphine substances may be significantly regulated by glutamate-mediated transmission, notably by metabotropic glutamate (mGlu) receptors. Here, we examined the hypothesis that the mGlu4 receptor within that NAc has a role in the extinction and reinstatement of morphine-induced conditioned place preference (CPP). The animals received bilaterally microinjections of VU0155041, a positive allosteric modulator (PAM) and partial agonist of mGlu4 receptor, into the NAc. In Experiment 1, the rats received VU0155041 (10, 30 and 50μg/0.5μL) during the extinction period. In Experiment 2, the CPP extinguished rats received VU0155041 (10, 30 and 50μg/0.5μL) five minutes prior to the administration of morphine (1mg/kg) in order to reinstate the extinguished CPP. The results showed that the intra-accumbal administration of VU0155041 reduced the extinction period of CPP. Furthermore, the administration of VU0155041 into the NAc dose-dependently inhibited the reinstatement of CPP. The findings suggested that the mGluR4 in the NAc facilitates the extinction and inhibits the reinstatement of the morphine-induced CPP, which could be mediated by an increase in the release of extracellular glutamate.

Deletion of Cryab increases the vulnerability of mice to the addiction-like effects of the cannabinoid JWH-018 via upregulation of striatal NF-κB expression

Synthetic cannabinoids have exhibited unpredictable abuse liabilities, especially self-administration (SA) responses in normal rodent models, despite seemingly inducing addiction-like effects in humans. Thus, an efficient pre-clinical model must be developed to determine cannabinoid abuse potential in animals and describe the mechanism that may mediate cannabinoid sensitivity. The Cryab knockout (KO) mice were recently discovered to be potentially sensitive to the addictive effects of psychoactive drugs. Herein, we examined the responses of Cryab KO mice to JWH-018 using SA, conditioned place preference, and electroencephalography. Additionally, the effects of repeated JWH-018 exposure on endocannabinoid- and dopamine-related genes in various addiction-associated brain regions were examined, along with protein expressions involving neuroinflammation and synaptic plasticity. Cryab KO mice exhibited greater cannabinoid-induced SA responses and place preference, along with divergent gamma wave alterations, compared to wild-type (WT) mice, implying their higher sensitivity to cannabinoids. Endocannabinoid- or dopamine-related mRNA expressions and accumbal dopamine concentrations after repeated JWH-018 exposure were not significantly different between the WT and Cryab KO mice. Further analyses revealed that repeated JWH-018 administration led to possibly greater neuroinflammation in Cryab KO mice, which may arise from upregulated NF-κB, accompanied by higher expressions of synaptic plasticity markers, which might have contributed to the development of cannabinoid addiction-related behavior in Cryab KO mice. These findings signify that increased neuroinflammation via NF-κB may mediate the enhanced addiction-like responses of Cryab KO mice to cannabinoids. Altogether, Cryab KO mice may be a potential model for cannabinoid abuse susceptibility.

Exploring psilocybin-assisted psychotherapy in the treatment of methamphetamine use disorder

Methamphetamine use disorder is a chronic relapsing condition associated with substantial mental, physical, and social harms and increasing rates of mortality. Contingency management and psychotherapy interventions are the mainstays of treatment but are modestly effective with high relapse rates, while pharmacological treatments have shown little to no efficacy. Psilocybin-assisted psychotherapy is emerging as a promising treatment for a range of difficult-to-treat conditions, including substance use disorders; however, no studies have yet been published looking at psilocybin-assisted psychotherapy in the treatment of methamphetamine use disorder. Here we review the rationale for psilocybin-assisted psychotherapy as a potential treatment for this indication, and describe practical considerations based on our early experience designing and implementing four separate clinical trials of psilocybin-assisted psychotherapy for methamphetamine use disorder.