Drug-evoked synaptic plasticity in addiction: from molecular changes to circuit remodeling

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.

Conditional Deletion of the AMPA-GluA1 and NMDA-GluN1 Receptor Subunit Genes in Midbrain D1 Neurons does not Alter Cocaine Reward in Mice

Synaptic plasticity in the mesolimbic dopamine (DA) system contributes to the neural adaptations underlying addictive behaviors and relapse. However, the specific behavioral relevance of glutamatergic excitatory drive onto dopamine D1 receptor (D1R)-expressing neurons in mediating the reinforcing effect of cocaine remains unclear. Here, we investigated how midbrain AMPAR and NMDAR function modulate cocaine reward-related behavior using mutant mouse lines lacking the glutamate receptor genes Gria1 or Grin1 in D1R-expressing neurons (GluA1D1CreERT2 or GluN1D1CreERT2, respectively). We found that conditional genetic deletion of either GluA1 or GluN1 within this neuronal sub-population did not impact the ability of acute cocaine injection to increase intracranial self-stimulation (ICSS) ratio or reduced brain reward threshold compared to littermate controls. Additionally, our data demonstrate that deletion of GluA1 and GluN1 receptor subunits within D1R-expressing neurons did not affect cocaine reinforcement in an operant self-administration paradigm, as mutant mice showed comparable cocaine responses and intake to controls. Given the pivotal role of glutamate receptors in mediating relapse behavior, we further explored the impact of genetic deletion of AMPAR and NMDAR onto D1R-expressing neurons on cue-induced reinstatement following extinction. Surprisingly, deletion of AMPAR and NMDAR onto these neurons did not impair cue-induced reinstatement of cocaine-seeking behavior. These findings suggest that glutamatergic activity via NMDAR and AMPAR in D1R-expressing neurons may not exclusively mediate the reinforcing effects of cocaine and cue-induced reinstatement.

A discrete subpopulation of PFC-LHb neurons govern cocaine place preference

Addiction is a complex behavioral disorder characterized by compulsive drug-seeking and drug use despite harmful consequences. The prefrontal cortex (PFC) plays a crucial role in cocaine addiction, involving decision-making, impulse control, memory, and emotional regulation. The PFC interacts with the brain's reward system, including the ventral tegmental area (VTA) and nucleus accumbens (NAc). The PFC also projects to the lateral habenula (LHb), a brain region critical for encoding negative reward and regulating the reward system. In the current study, we examined the role of PFC-LHb projections in regulating cocaine reward-related behaviors. We found that optogenetic stimulation of the PFC-LHb circuit during cocaine conditioning abolished cocaine preference without causing aversion. In addition, increased c-fos expression in LHb neurons was observed in animals that received optic stimulation during cocaine conditioning, supporting the circuit's involvement in cocaine preference regulation. Molecular analysis in animals that received optic stimulation revealed that cocaine-induced alterations in the expression of GluA1 subunit of AMPA receptor was normalized to saline levels in a region-specific manner. Moreover, GluA1 serine phosphorylation on S845 and S831 were differentially altered in LHb and VTA but not in the PFC. Together these findings highlight the critical role of the PFC-LHb circuit in controlling cocaine reward-related behaviors and shed light on the underlying mechanisms. Understanding this circuit's function may provide valuable insights into addiction and contribute to developing targeted treatments for substance use disorders.

Sign-tracking to non-drug reward is related to severity of alcohol-use problems in a sample of individuals seeking treatment

BACKGROUND

A prominent neuroscientific theory of drug addiction is the incentive sensitization model. Individual differences in the tendency to ascribe motivational salience to cues that predict reward, and involuntary "sign-tracking" (orientation towards) such cues have been identified as potentially important in understanding vulnerability to addiction and relapse. However, to date this behaviour has not been assessed in a treatment-seeking clinical population, who typically represent those most susceptible to alcohol-related harms and episodes of relapse. This highlights a significant gap in the literature pertaining to incentive sensitization and drug dependence.

METHODS

Individuals accessing inpatient drug and alcohol services with alcohol as primary drug of concern were recruited to participate in a Cognitive Bias Modification (CBM) intervention. At the baseline assessment, participants completed various self-report measures (including the Alcohol Use Disorders Identification Test; AUDIT) in addition to a visual search task measuring sign-tracking to cues signalling monetary reward. At 3-month follow up, abstinence from alcohol was the primary outcome measure. All analyses and hypotheses were pre-registered.

RESULTS

At baseline (57 participants), AUDIT scores correlated with sign-tracking to signals of monetary reward. In a subsequent regression analysis sign-tracking, gender and self-reported alcohol craving predicted abstinence at 3-month follow up (41 participants).

CONCLUSIONS

Our work demonstrates that involuntary sign-tracking to cues signalling non-drug reward is associated with problematic alcohol use and return to use at 3-month follow up, in a treatment-seeking sample. Whether this automatic prioritisation of cues signalling reward is a consequence or vulnerability for problematic alcohol use remains to be investigated.

PCSK9 inhibition attenuates alcohol-associated neuronal oxidative stress and cellular injury

Alcohol Use Disorder (AUD) is a persistent condition linked to neuroinflammation, neuronal oxidative stress, and neurodegenerative processes. While the inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9) has demonstrated effectiveness in reducing liver inflammation associated with alcohol, its impact on the brain remains largely unexplored. This study aimed to assess the effects of alirocumab, a monoclonal antibody targeting PCSK9 to lower systemic low-density lipoprotein cholesterol (LDL-C), on central nervous system (CNS) pathology in a rat model of chronic alcohol exposure. Alirocumab (50 mg/kg) or vehicle was administered weekly for six weeks in 32 male rats subjected to a 35 % ethanol liquid diet or a control liquid diet (n = 8 per group). The study evaluated PCSK9 expression, LDL receptor (LDLR) expression, oxidative stress, and neuroinflammatory markers in brain tissues. Chronic ethanol exposure increased PCSK9 expression in the brain, while alirocumab treatment significantly upregulated neuronal LDLR and reduced oxidative stress in neurons and brain vasculature (3-NT, p22phox). Alirocumab also mitigated ethanol-induced microglia recruitment in the cortex and hippocampus (Iba1). Additionally, alirocumab decreased the expression of pro-inflammatory cytokines and chemokines (TNF, CCL2, CXCL3) in whole brain tissue and attenuated the upregulation of adhesion molecules in brain vasculature (ICAM1, VCAM1, eSelectin). This study presents novel evidence that alirocumab diminishes oxidative stress and modifies neuroimmune interactions in the brain elicited by chronic ethanol exposure. Further investigation is needed to elucidate the mechanisms by which PCSK9 signaling influences the brain in the context of chronic ethanol exposure.

Long-term disruption of tissue levels of glutamate and glutamatergic neurotransmission neuromodulators, taurine and kynurenic acid induced by amphetamine

RATIONALE

Chronic amphetamine (AMPH) use leading to addiction results in adaptive changes within the central nervous system that persist well beyond the drug's elimination from the body and can precipitate relapse. Notably, alterations in glutamatergic neurotransmission play a crucial role in drug-associated behaviours.

OBJECTIVES

This study aimed to identify changes induced by amphetamine in glutamate levels and the neuromodulators of glutamatergic neurotransmission (taurine and kynurenic acid) observable after 14 and 28 days of abstinence in key brain regions implicated in addiction: the cortex (Cx), nucleus accumbens (Acb), and dorsolateral striatum (CPu-L).

METHODS

The rats were administered 12 doses of amphetamine (AMPH) intraperitoneally (i.p.) at 1.5 mg/kg. The behavioural response was evaluated through ultrasonic vocalizations (USV). High-performance liquid chromatography (HPLC) was used to measure the levels of glutamate, taurine, and kynurenic acid in the Cx, Acb, and CPu-L after 14 and 28 days of abstinence.

RESULTS

AMPH administration led to sensitisation towards AMPH's rewarding effects, as evidenced by changes in USV. There was a noticeable decrease in kynurenic acid levels and an increase in both taurine and glutamate in the CPu-L, along with an increase in glutamate levels in the Cx, 28 days following the final AMPH injection.

CONCLUSIONS

The most significant changes in the tissue levels of glutamate, taurine, and kynurenic acid were seen in the CPu-L 28 days after the last dose of AMPH. The emergence of these changes exclusively after 28 days suggests that the processes initiated by AMPH use and subsequent abstinence take time to become apparent and may be enduring. This could contribute to the incubation of craving and the risk of relapse. Developing pharmacological strategies to counteract the reduction in kynurenic acid induced by psychostimulants may provide new avenues for therapy development.

Cellular and circuit architecture of the lateral septum for reward processing

The lateral septum (LS) is composed of heterogeneous cell types that are important for various motivated behaviors. However, the transcriptional profiles, spatial arrangement, function, and connectivity of these cell types have not been systematically studied. Using single-nucleus RNA sequencing, we delineated diverse genetically defined cell types in the LS that play distinct roles in reward processing. Notably, we found that estrogen receptor 1 (Esr1)-expressing neurons in the ventral LS (LSEsr1) are key drivers of reward seeking via projections to the ventral tegmental area, and these neurons play an essential role in methamphetamine (METH) reward and METH-seeking behavior. Extended exposure to METH increases the excitability of LSEsr1 neurons by upregulating hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, thereby contributing to METH-induced locomotor sensitization. These insights not only elucidate the intricate molecular, circuit, and functional architecture of the septal region in reward processing but also reveal a neural pathway critical for METH reward and behavioral sensitization.

Analysis of the BDNF Gene rs6265 Polymorphism in a Group of Women with Alcohol Use Disorder, Taking into Account Personality Traits

It seems that BDNF has a direct influence on the brain pathways and is typically engaged during the processing of rewards. A surge in BDNF levels in the ventral tegmental area (the region from which the dopaminergic neurons of the mesocorticolimbic dopamine system originate and extend to the dorsolateral and ventromedial striatum) triggers a state of reward similar to that produced by opiates in animal studies. The aims of the study were (1) to analyze the association of the BDNF gene rs6265 polymorphism with AUD (alcohol use disorder) in women, (2) analyze personality and anxiety in alcohol-dependent and control woman, and (3) conduct an interaction analysis of rs6265 on personality, anxiety, and alcohol dependence. Our study found a notable interaction between the anxiety (trait and state), neuroticism, rs6265, and AUD. The alcohol AUD G/A genotype carriers revealed higher level of the anxiety trait (p < 0.0001) and neuroticism (p < 0.0001) compared to the control group with G/A and G/G genotypes. The alcohol use disorder subjects with the G/A genotype displayed higher levels of an anxiety state than the control group with G/A (p < 0.0001) and G/G (p = 0.0014) genotypes. Additionally, the alcohol use disorder subjects with the G/G genotype obtained lower levels of agreeability compared to the controls with G/A (p < 0.0001) and G/G (p < 0.0001) genotypes. Our study indicates that anxiety (trait and state) and neuroticism are interacting with the BDNF gene rs6265 polymorphism in alcohol-dependent women. Characteristics like anxiety (both as a trait and a state) and neuroticism could have a significant impact on the mechanism of substance dependency, particularly in females who are genetically susceptible. This is regardless of the reward system that is implicated in the emotional disruptions accompanying anxiety and depression.

Ventral tegmental area interneurons revisited: GABA and glutamate projection neurons make local synapses

The ventral tegmental area (VTA) contains projection neurons that release the neurotransmitters dopamine, GABA, and/or glutamate from distal synapses. VTA also contains GABA neurons that synapse locally on to VTA dopamine neurons, synapses widely credited to a population of so-called VTA interneurons. Interneurons in cortex, striatum, and elsewhere have well-defined morphological features, physiological properties, and molecular markers, but such features have not been clearly described in VTA. Indeed, there is scant evidence that local and distal synapses originate from separate populations of VTA GABA neurons. In this study we tested whether several markers expressed in non-dopamine VTA neurons are selective markers of interneurons, defined as neurons that synapse locally but not distally. Challenging previous assumptions, we found that VTA neurons genetically defined by expression of parvalbumin, somatostatin, neurotensin, or mu-opioid receptor project to known VTA targets including nucleus accumbens, ventral pallidum, lateral habenula, and prefrontal cortex. Moreover, we provide evidence that VTA GABA and glutamate projection neurons make functional inhibitory or excitatory synapses locally within VTA. These findings suggest that local collaterals of VTA projection neurons could mediate functions prior attributed to VTA interneurons. This study underscores the need for a refined understanding of VTA connectivity to explain how heterogeneous VTA circuits mediate diverse functions related to reward, motivation, or addiction.

Fiber-based Probes for Electrophysiology, Photometry, Optical and Electrical Stimulation, Drug Delivery, and Fast-Scan Cyclic Voltammetry In Vivo

Recording and modulation of neuronal activity enables the study of brain function in health and disease. While translational neuroscience relies on electrical recording and modulation techniques, mechanistic studies in rodent models leverage genetic precision of optical methods, such as optogenetics and imaging of fluorescent indicators. In addition to electrical signal transduction, neurons produce and receive diverse chemical signals which motivate tools to probe and modulate neurochemistry. Although the past decade has delivered a wealth of technologies for electrophysiology, optogenetics, chemical sensing, and optical recording, combining these modalities within a single platform remains challenging. This work leverages materials selection and convergence fiber drawing to permit neural recording, electrical stimulation, optogenetics, fiber photometry, drug and gene delivery, and voltammetric recording of neurotransmitters within individual fibers. Composed of polymers and non-magnetic carbon-based conductors, these fibers are compatible with magnetic resonance imaging, enabling concurrent stimulation and whole-brain monitoring. Their utility is demonstrated in studies of the mesolimbic reward pathway by simultaneously interfacing with the ventral tegmental area and nucleus accumbens in mice and characterizing the neurophysiological effects of a stimulant drug. This study highlights the potential of these fibers to probe electrical, optical, and chemical signaling across multiple brain regions in both mechanistic and translational studies.

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.

Molecular and circuit determinants in the globus pallidus mediating control of cocaine-induced behavioral plasticity

The globus pallidus externus (GPe) is a central component of the basal ganglia circuit, receiving strong input from the indirect pathway and regulating a variety of functions, including locomotor output and habit formation. We recently showed that it also acts as a gatekeeper of cocaine-induced behavioral plasticity, as inhibition of parvalbumin-positive cells in the GPe (GPe PV ) prevents the development of cocaine-induced reward and sensitization. However, the molecular and circuit mechanisms underlying this function are unknown. Here we show that GPe PV cells control cocaine reward and sensitization by inhibiting GABAergic neurons in the substantia nigra pars reticulata (SNr GABA ), and ultimately, selectively modulating the activity of ventral tegmental area dopamine (VTA DA ) cells projecting to the lateral shell of the nucleus accumbens (NAcLat). A major input to GPe PV cells is the indirect pathway of the dorsomedial striatum (DMS D 2 ), which receives DAergic innervation from collaterals of VTA DA →NAcLat cells, making this a closed-loop circuit. Cocaine likely facilitates reward and sensitization not directly through actions in the GPe, but rather in the upstream DMS, where the cocaine-induced elevation of DA triggers a depression in DMS D 2 cell activity. This cocaine-induced elevation in DA levels can be blocked by inhibition of GPe PV cells, closing the loop. Interestingly, the level of GPe PV cell activity prior to cocaine administration is correlated with the extent of reward and sensitization that animals experience in response to future administration of cocaine, indicating that GPe PV cell activity is a key predictor of future behavioral responses to cocaine. Single nucleus RNA-sequencing of GPe cells indicated that genes encoding voltage-gated potassium channels KCNQ3 and KCNQ5 that control intrinsic cellular excitability are downregulated in GPe PV cells following a single cocaine exposure, contributing to the elevation in GPe PV cell excitability. Acutely activating channels containing KCNQ3 and/or KCNQ5 using the small molecule carnosic acid, a key psychoactive component of Salvia rosmarinus (rosemary) extract, reduced GPe PV cell excitability and also impaired cocaine reward, sensitization, and volitional cocaine intake, indicating its potential as a therapeutic to counteract psychostimulant use disorder. Our findings illuminate the molecular and circuit mechanisms by which the GPe orchestrates brain-wide changes in response to cocaine that are required for reward, sensitization, and self-administration behaviors.

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.

Acupuncture in the treatment of cocaine addiction: how does it work?

Cocaine is a frequently abused and highly addictive drug that damages brain health and imposes substantial social and economic costs. Acupuncture has been used in the treatment of cocaine addiction and has been shown to improve abnormal mental and motor states. This article mainly focuses on the neurobiological mechanisms involving the central nervous system (CNS) and peripheral nervous system (PNS) that underlie the effects of acupuncture in the treatment of cocaine addiction. The central dopamine system is a key player in acupuncture treatment of cocaine addiction; the ventral tegmental area (VTA)-nucleus accumbens (NAc) signaling pathway, which has a modulatory influence on behavior and psychology after chronic use of cocaine, is a significant target of acupuncture action. Moreover, acupuncture alleviates cocaine-induced seizures or acute psychomotor responses through the paraventricular thalamus and the lateral habenula (LHb)-rostromedial tegmental (RMTg) nucleus circuits. The data suggest that acupuncture can impact various cocaine-induced issues via stimulation of diverse brain areas; nevertheless, the interconnection of these brain regions and the PNS mechanisms involved remain unknown. In this review, we also discuss the effects of specific acupuncture protocols on cocaine addiction and note that variations in needling modalities, current intensities and traditional acupuncture point locations have led to different experimental results. Therefore, standardized acupuncture protocols (with respect to stimulation methods, point locations and number of sessions) may become particularly important in future studies.

Neural circuit basis of adolescent THC-induced potentiation of opioid responses in adult mice

Use of one drug of abuse typically influences the behavioral response to other drugs, either administered at the same time or a subsequent time point. The nature of the drugs being used, as well as the timing and dosing, also influence how these drugs interact. Here, we tested the effects of adolescent THC exposure on the development of morphine-induced behavioral adaptations following repeated morphine exposure during adulthood. We found that adolescent THC administration impacted morphine-induced behaviors across several dimensions, including potentiating reward and paradoxically impairing the development of morphine reward. We then mapped the whole-brain response to a reinstatement dose of morphine, finding that adolescent THC administration led to increased activity in the basal ganglia and increased functional connectivity between frontal cortical regions and the ventral tegmental area. Last, we show using rabies virus-based circuit mapping that adolescent THC exposure triggers a long-lasting elevation in connectivity from the frontal cortex regions onto ventral tegmental dopamine cells that has the potential to influence dopaminergic response to morphine administration during adulthood. Our study adds to the rich literature on the interaction between drugs of abuse and provides potential circuit substates by which adolescent THC exposure influences responses to morphine later in life.

Neuromarkers in addiction: definitions, development strategies, and recent advances

Substance use disorders (SUDs) are the most costly and prevalent psychiatric conditions. Recent calls emphasize a need for biomarkers-measurable, stable indicators of normal and abnormal processes and response to treatment or environmental agents-and, in particular, brain-based neuromarkers that will advance understanding of the neurobiological basis of SUDs and clinical practice. To develop neuromarkers, researchers must be grounded in evidence that a putative marker (i) is sensitive and specific to the psychological phenomenon of interest, (ii) constitutes a predictive model, and (iii) generalizes to novel observations (e.g., through internal cross-validation and external application to novel data). These neuromarkers may be used to index risk of developing SUDs (susceptibility), classify individuals with SUDs (diagnostic), assess risk for progression to more severe pathology (prognostic) or index current severity of pathology (monitoring), detect response to treatment (response), and predict individualized treatment outcomes (predictive). Here, we outline guidelines for developing and assessing neuromarkers, we then review recent advances toward neuromarkers in addiction neuroscience centering our discussion around neuromarkers of craving-a core feature of SUDs. In doing so, we specifically focus on the Neurobiological Craving Signature (NCS), which show great promise for meeting the demand of neuromarkers.

Tmod2 Is a Regulator of Cocaine Responses through Control of Striatal and Cortical Excitability and Drug-Induced Plasticity

Drugs of abuse induce neuroadaptations, including synaptic plasticity, that are critical for transition to addiction, and genes and pathways that regulate these neuroadaptations are potential therapeutic targets. Tropomodulin 2 (Tmod2) is an actin-regulating gene that plays an important role in synapse maturation and dendritic arborization and has been implicated in substance abuse and intellectual disability in humans. Here, we mine the KOMP2 data and find that Tmod2 knock-out mice show emotionality phenotypes that are predictive of addiction vulnerability. Detailed addiction phenotyping shows that Tmod2 deletion does not affect the acute locomotor response to cocaine administration. However, sensitized locomotor responses are highly attenuated in these knock-outs, indicating perturbed drug-induced plasticity. In addition, Tmod2 mutant animals do not self-administer cocaine indicating lack of hedonic responses to cocaine. Whole-brain MR imaging shows differences in brain volume across multiple regions, although transcriptomic experiments did not reveal perturbations in gene coexpression networks. Detailed electrophysiological characterization of Tmod2 KO neurons showed increased spontaneous firing rate of early postnatal and adult cortical and striatal neurons. Cocaine-induced synaptic plasticity that is critical for sensitization is either missing or reciprocal in Tmod2 KO nucleus accumbens shell medium spiny neurons, providing a mechanistic explanation of the cocaine response phenotypes. Combined, these data, collected from both males and females, provide compelling evidence that Tmod2 is a major regulator of plasticity in the mesolimbic system and regulates the reinforcing and addictive properties of cocaine.

Targeting the cytoskeleton as a therapeutic approach to substance use disorders

Substance use disorders (SUD) are chronic relapsing disorders governed by continually shifting cycles of positive drug reward experiences and drug withdrawal-induced negative experiences. A large body of research points to plasticity within systems regulating emotional, motivational, and cognitive processes as drivers of continued compulsive pursuit and consumption of substances despite negative consequences. This plasticity is observed at all levels of analysis from molecules to networks, providing multiple avenues for intervention in SUD. The cytoskeleton and its regulatory proteins within neurons and glia are fundamental to the structural and functional integrity of brain processes and are potentially the major drivers of the morphological and behavioral plasticity associated with substance use. In this review, we discuss preclinical studies that provide support for targeting the brain cytoskeleton as a therapeutic approach to SUD. We focus on the interplay between actin cytoskeleton dynamics and exposure to cocaine, methamphetamine, alcohol, opioids, and nicotine and highlight preclinical studies pointing to a wide range of potential therapeutic targets, such as nonmuscle myosin II, Rac1, cofilin, prosapip 1, and drebrin. These studies broaden our understanding of substance-induced plasticity driving behaviors associated with SUD and provide new research directions for the development of SUD therapeutics.

Calcium-permeable AMPA and kainate receptors of GABAergic neurons

This Commentary presents a brief discussion of the action of glutamate calcium permeable receptors present with neurons on the release of the neurotransmitter gamma-aminobutyric acid (GABA). In particular, Glutamate sensitive Kainic Acid Receptors (KARs) and α-Amino-3-hydroxy-5-Methyl-4-isoxazole Propionic Acid Receptor (AMPARs) are Na+ channels that typically cause neuronal cells to depolarize and release GABA. Some of these receptors are also permeable to Ca2+ and are hence involved in the calcium-dependent release of GABA neurotransmitters. Calcium-permeable kainate and AMPA receptors (CP-KARs and CP-AMPARs) are predominantly located in GABAergic neurons in the mature brain and their primary role is to regulate GABA release. AMPARs which do not contain the GluA2 subunit are mainly localized in the postsynaptic membrane. CP-KAR receptors are located mainly in the presynapse. GABAergic neurons expressing CP-KARs and CP-AMPARs respond to excitation earlier and faster, suppressing hyperexcitation of other neurons by the advanced GABA release due to an early rapid [Ca2+]i increase. CP-AMPARs have demonstrated a more pronounced impact on plasticity compared to NMDARs because of their capacity to elevate intracellular Ca2+ levels independently of voltage. GABAergic neurons that express CP-AMPARs contribute to the disinhibition of glutamatergic neurons by suppressing GABAergic neurons that express CP-KARs. Hence, the presence of glutamate CP-KARs and CP-AMPARs is crucial in governing hyperexcitation and synaptic plasticity in GABAergic neurons.

Representational maps in the brain: concepts, approaches, and applications

Neural systems have evolved to process sensory stimuli in a way that allows for efficient and adaptive behavior in a complex environment. Recent technological advances enable us to investigate sensory processing in animal models by simultaneously recording the activity of large populations of neurons with single-cell resolution, yielding high-dimensional datasets. In this review, we discuss concepts and approaches for assessing the population-level representation of sensory stimuli in the form of a representational map. In such a map, not only are the identities of stimuli distinctly represented, but their relational similarity is also mapped onto the space of neuronal activity. We highlight example studies in which the structure of representational maps in the brain are estimated from recordings in humans as well as animals and compare their methodological approaches. Finally, we integrate these aspects and provide an outlook for how the concept of representational maps could be applied to various fields in basic and clinical neuroscience.

VTA Excitatory Neurons Control Reward-driven Behavior by Modulating Infralimbic Cortical Firing

The functional dichotomy of anatomical regions of the medial prefrontal cortex (mPFC) has been tested with greater certainty in punishment-driven tasks, and less so in reward-oriented paradigms. In the infralimbic cortex (IL), known for behavioral suppression (STOP), tasks linked with reward or punishment are encoded through firing rate decrease or increase, respectively. Although the ventral tegmental area (VTA) is the brain region governing reward/aversion learning, the link between its excitatory neuron population and IL encoding of reward-linked behavioral expression is unclear. Here, we present evidence that IL ensembles use a population-based mechanism involving broad inhibition of principal cells at intervals when reward is presented or expected. The IL encoding mechanism was consistent across multiple sessions with randomized rewarded target sites. Most IL neurons exhibit FR (Firing Rate) suppression during reward acquisition intervals (T1), and subsequent exploration of previously rewarded targets when the reward is omitted (T2). Furthermore, FR suppression in putative IL ensembles persisted for intervals that followed reward-linked target events. Pairing VTA glutamate inhibition with reward acquisition events reduced the weight of reward-target association expressed as a lower affinity for previously rewarded targets. For these intervals, fewer IL neurons per mouse trial showed FR decrease and were accompanied by an increase in the percentage of units with no change in FR. Together, we conclude that VTA glutamate neurons are likely involved in establishing IL inhibition states that encode reward acquisition, and subsequent reward-target association.

Activation of nucleus accumbens projections to the ventral tegmental area alters molecular signaling and neurotransmission in the reward system

The nucleus accumbens (NAc) and the ventral tegmental area (VTA) are integral brain regions involved in reward processing and motivation, including responses to drugs of abuse. Previously, we have demonstrated that activation of NAc-VTA afferents during the acquisition of cocaine conditioned place preference (CPP) reduces the rewarding properties of cocaine and diminished the activity of VTA dopamine neurons. In the current study, we examined the impact of enhancing these inhibitory inputs on molecular changes and neurotransmission associated with cocaine exposure. Our results unveiled significant reductions in extracellular signal-regulated kinase (ERK) levels in the VTA and medial prefrontal cortex (mPFC) of both cocaine-treated groups compared with the saline control group. Furthermore, optic stimulation of NAc-VTA inputs during cocaine exposure decreased the expression of GluA1 subunit of AMPA receptor in the VTA and mPFC. Notably, in the NAc, cocaine exposure paired with optic stimulation increased ERK levels and reduced GluA1 phosphorylation at Ser845 as compared with all other groups. Additionally, both cocaine-treated groups exhibited decreased levels of GluA1 phosphorylation at Ser831 in the NAc compared with the saline control group. Moreover, cocaine exposure led to reduced ERK, GluA1, and GluA1 phosphorylation at Ser845 and Ser831 in the mPFC. Augmentation of GABAergic tone from the NAc during cocaine conditioning mitigated changes in GluA1 phosphorylation at Ser845 in the mPFC but reduced ERK, GluA1, and GluA1 phosphorylation at Ser831 compared with the saline control group. Interestingly, enhancing GABAergic tone during saline conditioning decreased GluA1 phosphorylation at Ser831 compared with the saline control group in the mPFC. Our findings highlight the influence of modulating inhibitory inputs from the NAc to the VTA on molecular signaling and glutamatergic neurotransmission in cocaine-exposed animals. Activation of these inhibitory inputs during cocaine conditioning induced alterations in key signaling molecules and AMPA receptor, providing valuable insights into the neurobiological mechanisms underlying cocaine reward and cocaine use disorder. Further exploration of these pathways may offer potential therapeutic targets for the treatment of substance use disorder.

Accumulation of NMDA receptors in accumbal neuronal ensembles mediates increased conditioned place preference for cocaine after prolonged withdrawal

Cue-induced cocaine craving gradually intensifies following abstinence, a phenomenon known as the incubation of drug craving. Neuronal ensembles activated by initial cocaine use, are critically involved in this process. However, the mechanisms by which neuronal changes occurring in the ensembles after withdrawal contribute to incubation remain largely unknown. Here we labeled neuronal ensembles in the shell of nucleus accumbens (NAcSh) activated by cocaine conditioned place preference (CPP) training. NAcSh ensembles showed an increasing activity induced by CPP test after 21-day withdrawal. Inhibiting synaptic transmission of NAcSh ensembles suppressed the preference for cocaine paired-side after 21-day withdrawal, demonstrating a critical role of NAcSh ensembles in increased preference for cocaine. The density of dendritic spines in dopamine D1 receptor expressing ensembles was increased after 21-day withdrawal. Moreover, the expression of Grin1, a subunit of the N-methyl-D-aspartate (NMDA) receptor, specifically increased in the NAcSh ensembles after cocaine withdrawal in both CPP and self-administration (SA) mouse models. Targeted knockdown or dysfunction of Grin1 in NAcSh ensembles significantly suppressed craving for cocaine. Our results suggest that the accumulation of NMDA receptors in NAcSh ensembles mediates increased craving for cocaine after prolonged withdrawal, thereby providing potential molecular targets for treatment of drug addiction.

Unlocking the role of dorsal hippocampal α4β2 nicotinic acetylcholine receptors in Ethanol-Induced conditioned place preference in mice

Alcohol Use Disorder (AUD) presents a significant and challenging public health concern, marked by a dearth of effective pharmacological treatments. Understanding the neurobiological underpinnings of AUD is of paramount importance for the development of efficacious interventions. The process of addiction entails the acquisition of associative behaviors, prominently engaging the dorsal region of the hippocampus for encoding these associative memories. Nicotinic receptor systems have been implicated in mediating the rewarding effects of ethanol, as well as memory and learning processes. In our current investigation, we delved into the role of α4β2 nicotinic acetylcholine receptors (nAChRs) within the dorsal hippocampus in the context of ethanol-induced conditioned place preference (CPP), a robust model for scrutinizing the rewarding properties and drug-associated behaviors. To establish CPP, ethanol (2 g/kg) was administered intraperitoneally during a 8-day conditioning phase. Fos immunohistochemistry was employed to assess the involvement of discrete subregions within the dorsal hippocampus in ethanol-induced CPP. Additionally, we probed the influence of α4β2 nAChRs on CPP via microinjections of a selective nAChR antagonist, dihydro-β-erythroidine (DHBE, at dosages of 6, 12, and 18 µg/0.5 µL per hemisphere) within the hippocampus. Our results unveiled that ethanol-induced CPP was associated with an increase Fos -positive cells in various subregions of the dorsal hippocampus, including CA1, CA2, CA3, and the dentate gyrus. Intrahippocampal administration of DHBE (at doses of 6 and 18 µg/0.50 µL per hemisphere) effectively blocked ethanol-induced CPP, while leaving locomotor activity unaffected. These findings underscore the critical involvement of the dorsal hippocampus and α4β2 nAChRs in the acquisition of ethanol-associated learning and reward.

Mechanistic and structural studies reveal NRAP-1-dependent coincident activation of NMDARs

N-methyl-D-aspartate (NMDA)-type ionotropic glutamate receptors have essential roles in neurotransmission and synaptic plasticity. Previously, we identified an evolutionarily conserved protein, NRAP-1, that is required for NMDA receptor (NMDAR) function in C. elegans. Here, we demonstrate that NRAP-1 was sufficient to gate NMDARs and greatly enhanced glutamate-mediated NMDAR gating, thus conferring coincident activation properties to the NMDAR. Intriguingly, vertebrate NMDARs-and chimeric NMDARs where the amino-terminal domain (ATD) of C. elegans NMDARs was replaced by the ATD from vertebrate receptors-were spontaneously active when ectopically expressed in C. elegans neurons. Thus, the ATD is a primary determinant of NRAP-1- and glutamate-mediated gating of NMDARs. We determined the crystal structure of NRAP-1 at 1.9-Å resolution, which revealed two distinct domains positioned around a central low-density lipoprotein receptor class A domain. The NRAP-1 structure, combined with chimeric and mutational analyses, suggests a model where the three NRAP-1 domains work cooperatively to modify the gating of NMDARs.

BLA DBS improves anxiety and fear by correcting weakened synaptic transmission from BLA to adBNST and CeL in a mouse model of foot shock

Deep brain stimulation (DBS) in the basal lateral amygdala (BLA) has been established to correct symptoms of refractory post-traumatic stress disorder (PTSD). However, how BLA DBS operates in correcting PTSD symptoms and how the BLA elicits pathological fear and anxiety in PTSD remain unclear. Here, we discover that excitatory synaptic transmission from the BLA projection neurons (PNs) to the adBNST, and lateral central amygdala (CeL) is greatly suppressed in a mouse PTSD model induced by foot shock (FS). BLA DBS revises the weakened inputs from the BLA to these two areas to improve fear and anxiety. Optogenetic manipulation of the BLA-adBNST and BLA-CeL circuits shows that both circuits are responsible for anxiety but the BLA-CeL for fear in FS mice. Our results reveal that synaptic transmission dysregulation of the BLA-adBNST or BLA-CeL circuits is reversed by BLA DBS, which improves anxiety and fear in the FS mouse model.

Cajal, the neuronal theory and the idea of brain plasticity

This paper reviews the importance of Cajal's neuronal theory (the Neuron Doctrine) and the origin and importance of the idea of brain plasticity that emerges from this theory. We first comment on the main Cajal's discoveries that gave rise and confirmed his Neuron Doctrine: the improvement of staining techniques, his approach to morphological laws, the concepts of dynamic polarisation, neurogenesis and neurotrophic theory, his first discoveries of the nerve cell as an independent cell, his research on degeneration and regeneration and his fight against reticularism. Second, we review Cajal's ideas on brain plasticity and the years in which they were published, to finally focus on the debate on the origin of the term plasticity and its conceptual meaning, and the originality of Cajal's proposal compared to those of other authors of the time.

White matter integrity and medication response to antidepressants in major depressive disorder: a review of the literature

Major Depressive Disorder (MDD) is a severe psychiatric disorder characterized by selective impairments in mood regulation, cognition and behavior. Although it is well-known that antidepressants can effectively treat moderate to severe depression, the biochemical effects of these medications on white matter (WM) integrity are still unclear. Therefore, the aim of the study is to review the main scientific evidence on the differences in WM integrity in responders and non-responders to antidepressant medications. A record search was performed on three datasets (PubMed, Scopus and Web of Science) and ten records matched our inclusion criteria. Overall, the reviewed studies highlighted a good efficacy of antidepressants in MDD treatment. Furthermore, there were differences in WM integrity between responders and non-responders, mainly localized in cingulate cortices, hippocampus and corpus callosum, where the former group showed higher fractional anisotropy and lower axial diffusivity values. Modifications in WM integrity might be partially explained by branching and proliferation as well as neurogenesis of axonal fibers mediated by antidepressants, which in turn may have positively affected brain metabolism and increase the quantity of the serotonergic neurotransmitter within synaptic clefts. However, the reviewed studies suffer from some limitations, including the heterogeneity in treatment duration, antidepressant administration, medical posology, and psychiatric comorbidities. Therefore, future studies are needed to reduce confounding effects of antidepressant medications and to adopt longitudinal and multimodal approaches in order to better characterize the differences in WM integrity between responders and non-responders.

Sex dependence of opioid-mediated responses to subanesthetic ketamine in rats

Subanesthetic ketamine is increasingly used for the treatment of varied psychiatric conditions, both on- and off-label. While it is commonly classified as an N-methyl D-aspartate receptor (NMDAR) antagonist, our picture of ketamine's mechanistic underpinnings is incomplete. Recent clinical evidence has indicated, controversially, that a component of the efficacy of subanesthetic ketamine may be opioid dependent. Using pharmacological functional ultrasound imaging in rats, we found that blocking opioid receptors suppressed neurophysiologic changes evoked by ketamine, but not by a more selective NMDAR antagonist, in limbic regions implicated in the pathophysiology of depression and in reward processing. Importantly, this opioid-dependent response was strongly sex-dependent, as it was not evident in female subjects and was fully reversed by surgical removal of the male gonads. We observed similar sex-dependent effects of opioid blockade affecting ketamine-evoked postsynaptic density and behavioral sensitization, as well as in opioid blockade-induced changes in opioid receptor density. Together, these results underscore the potential for ketamine to induce its affective responses via opioid signaling, and indicate that this opioid dependence may be strongly influenced by subject sex. These factors should be more directly assessed in future clinical trials.

Activation of RMTg projections to the VTA reverse cocaine-induced molecular adaptation in the reward system

The rostromedial tegmental nucleus (RMTg) plays a crucial role in regulating reward-related behavior by exerting inhibitory control over the ventral tegmental area (VTA). This modulation of dopamine neuron activity within the VTA is essential for maintaining homeostasis in the reward system. Recently we have shown that activation of RMTg projections to the VTA during the acquisition of cocaine-conditioned place preference (CPP) reduces the rewarding properties of cocaine and decreases VTA dopamine neuron activity. By inhibiting dopamine neurons in the VTA, we hypothesized that RMTg projections hold the potential to restore reward system homeostasis disrupted by repeated cocaine use, and attenuate molecular adaptations in the reward system, including alterations in signaling pathways. Our study demonstrates that enhancing the GABAergic inputs from the RMTg to the VTA can mitigate cocaine-induced molecular changes in key regions, namely the VTA, nucleus accumbens (NAc), and prefrontal cortex (PFC). Specifically, we found that cocaine-induced alteration in the phosphorylation state of ERK (pERK) and GluA1 on serine 845 (S845) and serine 831 (S831), that play a major role in plasticity by controlling the activity and trafficking of AMPA receptors, were significantly reversed following optic stimulation of RMTg afferents to the VTA. These findings highlight the therapeutic potential of targeting the RMTg-VTA circuitry for mitigating cocaine reward. Ultimately, this research may pave the way for novel therapeutic interventions that restore balance in the reward system and alleviate the detrimental effects of cocaine.

Targeting mitochondrial dynamics of morphine-responsive dopaminergic neurons ameliorates opiate withdrawal

Converging studies demonstrate the dysfunction of the dopaminergic neurons following chronic opioid administration. However, the therapeutic strategies targeting opioid-responsive dopaminergic ensembles that contribute to the development of opioid withdrawal remain to be elucidated. Here, we used the neuronal activity-dependent Tet-Off system to label dopaminergic ensembles in response to initial morphine exposure (Mor-Ens) in the ventral tegmental area (VTA). Fiber optic photometry recording and transcriptome analysis revealed downregulated spontaneous activity and dysregulated mitochondrial respiratory, ultrastructure, and oxidoreductase signal pathways after chronic morphine administration in these dopaminergic ensembles. Mitochondrial fragmentation and the decreased mitochondrial fusion gene mitofusin 1 (Mfn1) were found in these ensembles after prolonged opioid withdrawal. Restoration of Mfn1 in the dopaminergic Mor-Ens attenuated excessive oxidative stress and the development of opioid withdrawal. Administration of Mdivi-1, a mitochondrial fission inhibitor, ameliorated the mitochondrial fragmentation and maladaptation of the neuronal plasticity in these Mor-Ens, accompanied by attenuated development of opioid withdrawal after chronic morphine administration, without affecting the analgesic effect of morphine. These findings highlighted the plastic architecture of mitochondria as a potential therapeutic target for opioid analgesic-induced substance use disorders.

Therapeutic mechanisms of psychedelics and entactogens

Recent clinical and preclinical evidence suggests that psychedelics and entactogens may produce both rapid and sustained therapeutic effects across several indications. Currently, there is a disconnect between how these compounds are used in the clinic and how they are studied in preclinical species, which has led to a gap in our mechanistic understanding of how these compounds might positively impact mental health. Human studies have emphasized extra-pharmacological factors that could modulate psychedelic-induced therapeutic responses including set, setting, and integration-factors that are poorly modelled in current animal experiments. In contrast, animal studies have focused on changes in neuronal activation and structural plasticity-outcomes that are challenging to measure in humans. Here, we describe several hypotheses that might explain how psychedelics rescue neuropsychiatric disease symptoms, and we propose ways to bridge the gap between human and rodent studies. Given the diverse pharmacological profiles of psychedelics and entactogens, we suggest that their rapid and sustained therapeutic mechanisms of action might best be described by the collection of circuits that they modulate rather than their actions at any single molecular target. Thus, approaches focusing on selective circuit modulation of behavioral phenotypes might prove more fruitful than target-based methods for identifying novel compounds with rapid and sustained therapeutic effects similar to psychedelics and entactogens.

Pre-mating administration of theophylline could prevent the transgenerational effects of maternal morphine dependence on offspring anxiety behavior: The role of dopamine receptors

Opioid addiction causes some molecular alterations in the brain reward pathway, such as changes in gene expression that may be transferred to the next generation via epigenetic mechanisms such as histone acetylation. This study aimed to evaluate the effect of theophylline as an HDAC (Histone deacetylases) activator on D1 and D2 dopamine receptor expression in the nucleus accumbens (NAc) and anxiety behavior in the offspring of morphine-dependent female rats. Female rats were exposed to escalating doses of morphine for six days and were then treated with theophylline (20 mg/kg) or saline for 10 days before mating with normal male rats. Male and female offspring were tested for anxiety behavior using an elevated plus maze apparatus. Besides, the expression of D1 and D2 dopamine receptors in the NAc was evaluated by real-time PCR (polymerase chain reaction). Results showed that offspring of morphine-dependent female rats had increased expression of both D1 and D2 receptors in the NAc, as well as decreased anxiety behavior, compared to control offspring. However, the mentioned effects were returned to normal levels in the offspring whose morphine-dependent mothers had received theophylline for 10 days before mating. It is concluded that theophylline may be therapeutically effective in minimizing the adverse consequences of maternal morphine dependence on offspring behavior by restoring normal dopamine receptor expression levels and modulating anxiety. To completely comprehend the underlying mechanisms of this phenomenon, more research is required.

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.

Beyond the 5-HT2A Receptor: Classic and Nonclassic Targets in Psychedelic Drug Action

Serotonergic psychedelics, such as psilocybin and LSD, have garnered significant attention in recent years for their potential therapeutic effects and unique mechanisms of action. These compounds exert their primary effects through activating serotonin 5-HT2A receptors, found predominantly in cortical regions. By interacting with these receptors, serotonergic psychedelics induce alterations in perception, cognition, and emotions, leading to the characteristic psychedelic experience. One of the most crucial aspects of serotonergic psychedelics is their ability to promote neuroplasticity, the formation of new neural connections, and rewire neuronal networks. This neuroplasticity is believed to underlie their therapeutic potential for various mental health conditions, including depression, anxiety, and substance use disorders. In this mini-review, we will discuss how the 5-HT2A receptor activation is just one facet of the complex mechanisms of action of serotonergic psychedelics. They also interact with other serotonin receptor subtypes, such as 5-HT1A and 5-HT2C receptors, and with neurotrophin receptors (e.g., tropomyosin receptor kinase B). These interactions contribute to the complexity of their effects on perception, mood, and cognition. Moreover, as psychedelic research advances, there is an increasing interest in developing nonhallucinogenic derivatives of these drugs to create safer and more targeted medications for psychiatric disorders by removing the hallucinogenic properties while retaining the potential therapeutic benefits. These nonhallucinogenic derivatives would offer patients therapeutic advantages without the intense psychedelic experience, potentially reducing the risks of adverse reactions. Finally, we discuss the potential of psychedelics as substrates for post-translational modification of proteins as part of their mechanism of action.

Plasma endocannabinoids in cocaine dependence and their relation to cerebral metabotropic glutamate receptor 5 density

Animal models indicate that the endocannabinoid system (ECS) plays a modulatory role in stress and reward processing, both crucially impaired in addictive disorders. Preclinical findings showed endocannabinoid-modulated synaptic plasticity in reward brain networks linked to the metabotropic-glutamate-5 receptor (mGluR5), contributing to drug-reinforcing effects and drug-seeking behavior. Although animal models postulate a link between ECS and cocaine addiction, human translational studies are lacking. Here, we tested previous preclinical findings by investigating plasma endocannabinoids (eCBs) anandamide (AEA), 2-arachidonoylglycerol (2-AG), and the related N-acylethanolamines (NAEs) palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), including their interaction with cerebral mGluR5, in chronic cocaine users (CU). We compared basal plasma concentrations between chronic CU (N = 103; 69 recreational CU and 34 dependent CU) and stimulant-naïve healthy controls (N = 92). Follow-up basal eCB/NAE plasma levels after 12 months were used for reliability and stability check (CU: N = 33; controls: N = 43). In an additional analysis using 11C-ABP688 positron emission tomography (PET) in a male subsample (CU: N = 18; controls: N = 16), we investigated the relationships between eCBs/NAEs and mGluR5 density in the brain. We found higher 2-AG plasma levels in dependent CU compared to controls and recreational CU. 2-AG levels were stable over time across all groups. In the PET-subsample, a positive association between 2-AG and mGluR5 brain density only in CU was found. Our results corroborate animal findings suggesting an alteration of the ECS in cocaine dependence and an association between peripheral 2-AG levels and cerebral mGluR5 in humans. Therefore, the ECS might be a promising pharmaco-therapeutic target for novel treatments of cocaine dependence.

Shared GABA transmission pathology in dopamine agonist- and antagonist-induced dyskinesia

Dyskinesia is involuntary movement caused by long-term medication with dopamine-related agents: the dopamine agonist 3,4-dihydroxy-L-phenylalanine (L-DOPA) to treat Parkinson's disease (L-DOPA-induced dyskinesia [LID]) or dopamine antagonists to treat schizophrenia (tardive dyskinesia [TD]). However, it remains unknown why distinct types of medications for distinct neuropsychiatric disorders induce similar involuntary movements. Here, we search for a shared structural footprint using magnetic resonance imaging-based macroscopic screening and super-resolution microscopy-based microscopic identification. We identify the enlarged axon terminals of striatal medium spiny neurons in LID and TD model mice. Striatal overexpression of the vesicular gamma-aminobutyric acid transporter (VGAT) is necessary and sufficient for modeling these structural changes; VGAT levels gate the functional and behavioral alterations in dyskinesia models. Our findings indicate that lowered type 2 dopamine receptor signaling with repetitive dopamine fluctuations is a common cause of VGAT overexpression and late-onset dyskinesia formation and that reducing dopamine fluctuation rescues dyskinesia pathology via VGAT downregulation.

The activity-regulated cytoskeleton-associated protein, Arc, functions in the nucleus accumbens shell to limit multiple triggers of cocaine-seeking behaviour

Use of addictive substances like cocaine produces enduring associations between the drug experience and cues in the drug-taking environment. In individuals with a substance use disorder (SUD) and attempting to remain abstinent, these powerful drug-cue associations can trigger a return to active drug use, but the molecular mechanisms regulating drug-cue associations remain poorly understood. The activity-regulated cytoskeleton-associated protein (Arc) is induced by cocaine in the nucleus accumbens (NAc), an important brain reward region, but Arc's NAc function in SUD-related behaviour remains unclear. We show here that cocaine self-administration (SA) in rats produced a significant upregulation of Arc protein in both the core and shell subregions of the NAc. Subregion-specific Arc reduction (shRNA) in the medial NAc Shell enhanced both context-associated and cue-reinstated cocaine seeking, but without altering the motivation to work for cocaine, the sensitivity to the reinforcing effects of cocaine or the ability of cocaine priming to reinstate drug seeking. In contrast, we observed no effects of Arc knockdown in the NAc core on any aspect of cocaine SA, extinction or reinstated cocaine seeking, suggesting that Arc functions within the medial NAc shell, but not NAc core, to limit the strength of drug-context and drug-cue associations that promote cocaine-seeking behaviour.

Maladaptive plasticity induced by morphine is mediated by hippocampal astrocytic Connexin-43

AIMS

Drug addiction is an aberrant learning process that involves the recruitment of memory systems. We have previously demonstrated that morphine exposure causes maladaptive synaptic plasticity which involved hippocampal glial cells, especially astrocytes. Morphine addiction has been associated with astrocytic connexin 43 (Cx43), which plays a role in synaptic homeostasis. This study aimed to examine the role of hippocampal astrocytic Cx43 in morphine-induced maladaptive plasticity as a mechanism of addiction.

MAIN METHODS

Male rats were injected with morphine (10 mg/kg) subcutaneously every 12 h for nine days to induce dependence. Cx43 was inhibited by TAT-Gap19 (1 μl/1 nmol) microinjection in the CA1 region of the hippocampus 30 min before each morning morphine injection. Field potential recordings were used to assess synaptic plasticity. fEPSP was recorded from the CA1 area following CA3 stimulation.

KEY FINDINGS

Electrophysiological results showed that morphine treatment altered baseline synaptic responses. It also appears that morphine treatment augmented long-term potentiation (LTP) compared with the control group. Hippocampal astrocytic Cx43 inhibition, with the TAT-Gap19, undermines these effects of morphine on baseline synaptic responses and LTP. Despite this, long-term depression (LTD) did not differ significantly between the groups. Additionally, in the morphine-receiving group, inhibition of Cx43 significantly reduced the paired-pulse index at an 80-millisecond inter-pulse interval when assessing short-term plasticity.

SIGNIFICANCE

The results of this study demonstrated that inhibiting Cx43 reduced synaptic plasticity induced by morphine. It can be concluded that hippocampal astrocytes through Cx43 are involved in morphine-induced metaplasticity.

Obesity-mediated Lipoinflammation Modulates Food Reward Responses

Accumulation of white adipose tissue (WAT) during obesity is associated with the development of chronic low-grade inflammation, a biological process known as lipoinflammation. Systemic and central lipoinflammation accumulates pro-inflammatory cytokines including IL-6, IL-1β and TNF-α in plasma and also in brain, disrupting neurometabolism and cognitive behavior. Obesity-mediated lipoinflammation has been reported in brain regions of the mesocorticolimbic reward circuit leading to alterations in the perception and consumption of ultra-processed foods. While still under investigation, lipoinflammation targets two major outcomes of the mesocorticolimbic circuit during food reward: perception and motivation ("Wanting") and the pleasurable feeling of feeding ("Liking"). This review will provide experimental and clinical evidence supporting the contribution of obesity- or overnutrition-related lipoinflammation affecting the mesocorticolimbic reward circuit and enhancing food reward responses. We will also address neuroanatomical targets of inflammatory profiles that modulate food reward responses during obesity and describe potential cellular and molecular mechanisms of overnutrition linked to addiction-like behavior favored by brain lipoinflammation.

Linking input- and cell-type-specific synaptic plasticity to the reinforcement of alcohol-seeking behavior

The reinforcement of voluntary alcohol-seeking behavior requires dopamine-dependent long-term synaptic plasticity in the striatum. Specifically, the long-term potentiation (LTP) of direct-pathway medium spiny neurons (dMSNs) in the dorsomedial striatum (DMS) promotes alcohol drinking. However, it remains unclear whether alcohol induces input-specific plasticity onto dMSNs and whether this plasticity directly drives instrumental conditioning. In this study, we found that voluntary alcohol intake selectively strengthened glutamatergic transmission from the medial prefrontal cortex (mPFC) to DMS dMSNs in mice. Importantly, mimicking this alcohol-induced potentiation by optogenetically self-stimulating mPFC→dMSN synapse with an LTP protocol was sufficient to drive the reinforcement of lever pressing in operant chambers. Conversely, induction of a post-pre spike timing-dependent LTD at this synapse time-locked to alcohol delivery during operant conditioning persistently decreased alcohol-seeking behavior. Our results establish a causal relationship between input- and cell-type-specific corticostriatal plasticity and the reinforcement of alcohol-seeking behavior. This provides a potential therapeutic strategy to restore normal cortical control of dysregulated basal ganglia circuitries in alcohol use disorder.

Role of sex hormones in the effects of sleep deprivation on methamphetamine reward memory

Sleep deficiency is known as an important risk factor for relapse to drug abuse, especially for the powerful psychostimulant methamphetamine (METH). On the other hand, both drug addiction and sleep neurobiology are affected by sex hormones. We, therefore, aimed to examine the probable effects of sleep deprivation (SD) on methamphetamine (METH) reward memory in male and female rats. Moreover, we asked if sex hormones influence the effects of SD on METH reward memory. Adult male and female Wistar rats were divided into two main groups, sham and gonadectomized groups. Three weeks later, they were conditioned to receive METH (2 mg/kg, i.p.) in the conditioned place preference. METH reward memory was then reinstated following a 10-day extinction period. SD was induced for 72 h, either before or after extinction, in different groups. In gonadectomized animals, they daily received either subcutaneous administration of estrogen (5 μg/0.1 ml oil) or progesterone (2 mg/0.1 ml oil) or dihydrotestosterone (25 mg/0.1 ml oil) for thirteen days, from post-conditioning day to reinstatement session. We found that SD facilitated relapse to METH reward memory, depending on the time interval between SD and METH reinstatement. Furthermore, we found that estrogen and SD showed synergistic effects to facilitate METH reward memory, whereas testosterone and progesterone revealed inhibitory effects in the controls, but not in the SD, animals. Our findings would seem to suggest that sex hormones should be considered as determinant factors to manage METH abuse and relapse to METH seeking/taking behavior, especially for those with sleep deficiency.

Voluntary wheel running during adolescence prevents the increase in ethanol intake induced by social defeat in male mice

RATIONALE

Exposure to social defeat (SD) induces a depressive phenotype, increased ethanol seeking and consumption, accompanied by activation of the neuroinflammatory response. However, a resilient response can be potentiated through physical exercise in the form of voluntary wheel running (VWR) during or after exposure to social stress. Therefore, the aim of this study was to test whether physical exercise during adolescence prior to being exposed to SD can enhance resilience to the increase in ethanol intake.

METHODS

Male mice had access to VWR during adolescence and the effects of social defeat (4 sessions every 72 h) on oral ethanol self-administration (SA) was evaluated. Based on the social interaction test, mice were classified as resilient or susceptible to depressive-like behavior. Two weeks after the last encounter, mice were subjected to the drinking in the dark and oral ethanol SA paradigms. Mice were then sacrificed to measure brain-derived neurotrophic factor (BDNF) levels in the striatum and hippocampus.

RESULTS

As expected, susceptible mice increased ethanol intake in the oral SA protocol. However, susceptible mice in the exercise condition did not increase ethanol intake, showing similar consumption and motivation for ethanol than the control and resilient groups. On the other hand, decreased BDNF levels were observed in susceptible mice in both experimental conditions compared to the control groups after ethanol SA.

CONCLUSIONS

The pre-exposure of VWR prevented the increase in consumption and motivation for ethanol induced by SD in susceptible mice. On the other hand, it appears that VWR did not exhibit any significant long-term effects on BDNF signaling, which is mainly affected in susceptible mice after ethanol intake.

Synaptic and cellular endocannabinoid signaling mechanisms regulate stress-induced plasticity of nucleus accumbens somatostatin neurons

Interneuron populations within the nucleus accumbens (NAc) orchestrate excitatory-inhibitory balance, undergo experience-dependent plasticity, and gate-motivated behavior, all biobehavioral processes heavily modulated by endogenous cannabinoid (eCB) signaling. While eCBs are well known to regulate synaptic plasticity onto NAc medium spiny neurons and modulate NAc function at the behavioral level, how eCBs regulate NAc interneuron function is less well understood. Here, we show that eCB signaling differentially regulates glutamatergic and feedforward GABAergic transmission onto NAc somatostatin-expressing interneurons (NAcSOM+) in an input-specific manner, while simultaneously increasing postsynaptic excitability of NAcSOM+ neurons, ultimately biasing toward vHPC (ventral hippocampal), and away from BLA (basolateral amygdalalar), activation of NAcSOM+ neurons. We further demonstrate that NAcSOM+ are activated by stress in vivo and undergo stress-dependent plasticity, evident as a global increase in intrinsic excitability and an increase in excitation-inhibition balance specifically at vHPC, but not BLA, inputs onto NAcSOM+ neurons. Importantly, both forms of stress-induced plasticity are dependent on eCB signaling at cannabinoid type 1 receptors. These findings reveal eCB-dependent mechanisms that sculpt afferent input and excitability of NAcSOM+ neurons and demonstrate a key role for eCB signaling in stress-induced plasticity of NAcSOM+-associated circuits.

Accumbal-thalamic connectivity and associated glutamate alterations in human cocaine craving: A state-dependent rs-fMRI and 1H-MRS study

Craving is a core symptom of cocaine use disorder and a major factor for relapse risk. To date, there is no pharmacological therapy to treat this disease or at least to alleviate cocaine craving as a core symptom. In animal models, impaired prefrontal-striatal signalling leading to altered glutamate release in the nucleus accumbens appear to be the prerequisite for cocaine-seeking. Thus, those network and metabolic changes may constitute the underlying mechanisms for cocaine craving and provide a potential treatment target. In humans, there is recent evidence for corresponding glutamatergic alterations in the nucleus accumbens, however, the underlying network disturbances that lead to this glutamate imbalance remain unknown. In this state-dependent randomized, placebo-controlled, double-blinded, cross-over multimodal study, resting state functional magnetic resonance imaging in combination with small-voxel proton magnetic resonance spectroscopy (voxel size: 9.4 × 18.8 × 8.4 mm3) was applied to assess network-level and associated neurometabolic changes during a non-craving and a craving state, induced by a custom-made cocaine-cue film, in 18 individuals with cocaine use disorder and 23 healthy individuals. Additionally, we assessed the potential impact of a short-term challenge of N-acetylcysteine, known to normalize disturbed glutamate homeostasis and to thereby reduce cocaine-seeking in animal models of addiction, compared to a placebo. We found increased functional connectivity between the nucleus accumbens and the dorsolateral prefrontal cortex during the cue-induced craving state. However, those changes were not linked to alterations in accumbal glutamate levels. Whereas we additionally found increased functional connectivity between the nucleus accumbens and a midline part of the thalamus during the cue-induced craving state. Furthermore, obsessive thinking about cocaine and the actual intensity of cocaine use were predictive of cue-induced functional connectivity changes between the nucleus accumbens and the thalamus. Finally, the increase in accumbal-thalamic connectivity was also coupled with craving-related glutamate rise in the nucleus accumbens. Yet, N-acetylcysteine had no impact on craving-related changes in functional connectivity. Together, these results suggest that connectivity changes within the fronto-accumbal-thalamic loop, in conjunction with impaired glutamatergic transmission, underlie cocaine craving and related clinical symptoms, pinpointing the thalamus as a crucial hub for cocaine craving in humans.

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.