Molecular basis of long-term plasticity underlying addiction

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.

The Effect of Antinociceptive Dose of Morphine on Cell Therapy in Rats with Spinal Cord Injury

Spinal cord injury (SCI) is a sensory-motor injury. Today, combined treatments such as cell therapy along with drug therapy and their interactions are of interest. Morphine is an opioid drug used to relieve intolerable pain. This study aims to evaluate the impact of an antinociceptive dose of morphine (with minimal tolerance/dependence but effective pain relief) on cell therapy in SCI. The antinociceptive dose of morphine was determined in rats with SCI through the Hargreaves and naloxone-induced morphine withdrawal tests. The rats were then allocated to 5 groups: laminectomy, SCI, SCI + Morphine, SCI + cell therapy, SCI + Morphine + cell therapy. The antinociceptive dose (5 mg/kg) was administered on days 1, 4, 10, and 13 (i.p.) post-SCI. On day 7, Neural-like stem cells derived from adipose tissue were transplanted intraspinally into the injured animals, and they were monitored for 12 weeks. The outcomes were assessed using the BBB test, somatosensory evoked potential (SSEP), and histology. The BBB test indicated that morphine significantly hindered functional recovery post-cell transplantation compared to animals receiving only cell therapy (p < 0.05). In the SSEP test, the analysis of amplitude and latency of waves did not reveal a significant difference (p > 0.05). The histological results showed that cell therapy reduced the cavity size post-SCI, while morphine had no significant impact on it. Morphine at the antinociceptive dose significantly impairs motor recovery despite cell therapy. Nonetheless, there was no significant difference between groups in terms of sensory pathway outcomes.

Preconception ethanol exposure changes anxiety, depressive and checking-like behavior and alter the expression levels of MAO-B in male offspring

Alcohol use, which alters the epigenome, increases the probability that it could affect subsequent generations, even if they were never directly exposed to ethanol or even in utero. We explored the effects of parental ethanol exposure before conception on behavioral changes in the offspring. Considering the role of Monoamine oxidase-B (MAO-B) in dopamine turnover in the prefrontal cortex (PFC) and its influence on behavior, and taking into account that ethanol exposure could alter MAO-B, we assessed the protein levels in the offspring. Male and female rats were exposed to ethanol for 30 days and then allowed ten days of abstinence. Afterward, they were mated with either control or ethanol-exposed rats. The F1 and F2 male offspring underwent tests to assess behavioral changes. Additionally, the levels of MAO-B in the PFC were evaluated. Results revealed that in the F1, anxiety increased only in the bi-parental ethanol-exposed male offspring in the elevated plus maze test (p < 0.05), while depressive-like behavior rose only in maternal and bi-parental ethanol-exposed offspring (p < 0.01). However, compulsive-like behavior increased in all ethanol-exposed offspring (p < 0.01). No significant phenotypic changes were observed in the F2. The levels of MAO-B in the PFC increased in the maternal (p < 0.05) and bi-parental ethanol-exposed offspring (p < 0.01). Our study demonstrates that parental ethanol exposure, even in the days preceding mating, adversely affects behaviors and induces molecular changes in the brain. Given these findings, it becomes imperative to monitor children exposed to parental (especially maternal) ethanol for the prevention of mental disorders.

Effects of social housing conditions on ethanol-induced behavioral sensitization in Swiss mice

RATIONALE

In previous animal model studies, it was shown that drug sensitization is dependent upon physical environmental conditions. However, the effects of social housing conditions on drug sensitization is much less known.

OBJECTIVE

The aim of the present study was to investigate the effects of social conditions, through the size of housing groups, on ethanol stimulant effects and ethanol-induced behavioral sensitization in mice.

MATERIALS AND METHODS

Male and female Swiss mice were housed in groups of different sizes (isolated mice, two mice per cage, four mice per cage and eight mice per cage) during a six-week period. A standard paradigm of ethanol-induced locomotor sensitization was then started with one daily injection of 2.5 g/kg ethanol for 8 consecutive days.

RESULTS

The results show that social housing conditions affect the acute stimulant effects of ethanol. The highest stimulant effects were observed in socially isolated mice and then gradually decreased as the size of the group increased. Although the rate of ethanol sensitization did not differ between groups, the ultimate sensitized levels of ethanol-induced stimulant effects were significantly reduced in mice housed in groups of eight.

CONCLUSIONS

These results are consistent with the idea that higher levels of acute and sensitized ethanol stimulant effects are observed in mice housed in stressful housing conditions, such as social isolation.

Drugs of abuse hijack a mesolimbic pathway that processes homeostatic need

Drugs of abuse are thought to promote addiction in part by "hijacking" brain reward systems, but the underlying mechanisms remain undefined. Using whole-brain FOS mapping and in vivo single-neuron calcium imaging, we found that drugs of abuse augment dopaminoceptive ensemble activity in the nucleus accumbens (NAc) and disorganize overlapping ensemble responses to natural rewards in a cell type-specific manner. Combining FOS-Seq, CRISPR-perturbation, and single-nucleus RNA sequencing, we identified Rheb as a molecular substrate that regulates cell type-specific signal transduction in NAc while enabling drugs to suppress natural reward consumption. Mapping NAc-projecting regions activated by drugs of abuse revealed input-specific effects on natural reward consumption. These findings characterize the dynamic, molecular and circuit basis of a common reward pathway, wherein drugs of abuse interfere with the fulfillment of innate needs.

Modulators of nicotine reward and reinforcement

Nicotine has been well-characterized for its ability to alter neurophysiology to promote rewarding and reinforcing properties. However, several exogenous chemicals possess properties that modulate or enhance nicotine's ability to alter neurophysiology. This chapter focuses on nicotine's impact on behavior through changes in neurophysiology and several chemical entities that in-turn modulate nicotine's ability to act as a neuromodulator.

DMHPpp1r17 neurons regulate aging and lifespan in mice through hypothalamic-adipose inter-tissue communication

Recent studies have shown that the hypothalamus functions as a control center of aging in mammals that counteracts age-associated physiological decline through inter-tissue communications. We have identified a key neuronal subpopulation in the dorsomedial hypothalamus (DMH), marked by Ppp1r17 expression (DMHPpp1r17 neurons), that regulates aging and longevity in mice. DMHPpp1r17 neurons regulate physical activity and WAT function, including the secretion of extracellular nicotinamide phosphoribosyltransferase (eNAMPT), through sympathetic nervous stimulation. Within DMHPpp1r17 neurons, the phosphorylation and subsequent nuclear-cytoplasmic translocation of Ppp1r17, regulated by cGMP-dependent protein kinase G (PKG; Prkg1), affect gene expression regulating synaptic function, causing synaptic transmission dysfunction and impaired WAT function. Both DMH-specific Prkg1 knockdown, which suppresses age-associated Ppp1r17 translocation, and the chemogenetic activation of DMHPpp1r17 neurons significantly ameliorate age-associated dysfunction in WAT, increase physical activity, and extend lifespan. Thus, these findings clearly demonstrate the importance of the inter-tissue communication between the hypothalamus and WAT in mammalian aging and longevity control.

Interface Engineering Enables Multilevel Resistive Switching in Ultra-Low-Power Chemobrionic Copper Silicate

Memristor is assuming prominence due to its exceptionally low power consumption, adaptable, and parallel signal processing capabilities that address the limitations of the von Neumann architecture to meet the growing demand for advanced technologies such as artificial intelligence, Internet of Things (IoTs), and neuromorphic computation. In this work, we demonstrate resistive switching in copper silicate-based hollow tube-forming self-organized membrane structures belonging to the category of chemobrionics or chemical gardens to demonstrate cost-effective and highly efficient memristor devices. The device architecture is configured as ITO/PEDOT:PSS/active layer (copper silicate)/PMMA/Ag, an arrangement that serves to stabilize current-voltage hysteresis and exhibit a low SET voltage ∼0.2 V with a 0.8 nJ power consumption while manifesting robust data endurance and multilevel resistive switching. The inherent self-rectifying behavior, characterized by a high rectification ratio of 60, underscores the potential utility of these devices across a spectrum of electronic applications. To emulate the functionality of biological synapses, fundamental synaptic characteristics are assessed, including paired-pulse facilitation (PPF) and potentiation and depression (P&D). We validate the potential of copper silicate chemical garden-based memristor devices for applications that require real-time synaptic processing. Importantly, the fabrication of these devices was accomplished through a comprehensive solution-based, low-temperature process conducted under ambient environmental conditions, obviating the need for specialized glovebox facilities.

Impact of miR-29c-3p in the Nucleus Accumbens on Methamphetamine-Induced Behavioral Sensitization and Neuroplasticity-Related Proteins

Methamphetamine (METH) abuse inflicts both physical and psychological harm. While our previous research has established the regulatory role of miR-29c-3p in behavior sensitization, the underlying mechanisms and target genes remain incompletely understood. In this study, we employed the isobaric tags for relative and absolute quantitation (iTRAQ) technique in conjunction with Ingenuity pathway analysis (IPA) to probe the putative molecular mechanisms of METH sensitization through miR-29c-3p inhibition. Through a microinjection of AAV-anti-miR-29c-3p into the nucleus accumbens (NAc) of mice, we observed the attenuation of METH-induced locomotor effects. Subsequent iTRAQ analysis identified 70 differentially expressed proteins (DEPs), with 22 up-regulated potential target proteins identified through miR-29c-3p target gene prediction and IPA analysis. Our focus extended to the number of neuronal branches, the excitatory synapse count, and locomotion-related pathways. Notably, GPR37, NPC1, and IREB2 emerged as potential target molecules for miR-29c-3p regulation, suggesting their involvement in the modulation of METH sensitization. Quantitative PCR confirmed the METH-induced aberrant expression of Gpr37, Npc1, and Ireb2 in the NAc of mice. Specifically, the over-expression of miR-29c-3p led to a significant reduction in the mRNA level of Gpr37, while the inhibition of miR-29c-3p resulted in a significant increase in the mRNA level of Gpr37, consistent with the regulatory principle of miRNAs modulating target gene expression. This suggests that miR-29c-3p potentially influences METH sensitization through its regulation of neuroplasticity. Our research indicates that miR-29c-3p plays a crucial role in regulating METH-induced sensitization, and it identified the potential molecular of miR-29c-3p in regulating METH-induced sensitization.

Memantine and SKF82958 but not an enriched environment modulate naloxone-precipitated morphine abstinence syndrome without affecting hippocampal tPA mRNA levels in rats

There is accumulating evidence supporting the involvement of tissue-plasminogen activator (tPA) in the mechanisms underlying the effects of morphine and an enriched environment. This study was designed to investigate possible interactive roles of the glutamatergic and the dopaminergic systems regarding hippocampal tPA in the neurobiology of morphine dependence. For this purpose, Wistar albino rats, housed in either a standard- (SE) or an enriched environment (EE) were implanted subcutaneously with morphine (150 mg base) or placebo pellets. Behavioral and somatic signs of morphine abstinence precipitated by an opioid-receptor antagonist naloxone (1 mg/kg, i.p.) 72 h after the pellet implantation were observed individually for 15 min in all groups. Memantine (10 mg/kg i.p.), an antagonist of N-methyl-D-aspartic acid class of glutamatergic receptor-subtype decreased teeth-chattering, ptosis, diarrhea and the loss of body weight. SKF82958 (1 mg/kg, i.p.), a dopamine D1-receptor agonist decreased jumping and ptosis but increased rearing and loss of body weight. On the other hand, co-administration of SKF82958 with memantine prevented some of their effects that occur when administered alone at the same doses. Furthermore, the EE did not change the intensity of morphine abstinence. The level of hippocampal tPA mRNA was found to be lower in the SE morphine abstinence group than in the placebo group and close to the EE morphine abstinence group, whereas there was no significant alteration of its level in the memantine or SKF82958 groups. These findings suggest that the interaction between the glutamatergic and the dopaminergic systems may be an important component of the neurobiology of morphine dependence, and the role of tPA in this interaction should be further investigated.

Analysis of the Methylation Level of the DAT1 Dopamine Transporter Gene in Patients Addicted to Stimulants, Taking into Account an Analysis of Personality Traits

Drug addiction is a chronic biochemical drug use disorder that affects the human brain and behavior and leads to the uncontrolled use of legal or illicit drugs. It has been shown that three factors are involved in the development of addiction: genetic factors, a diverse environment, and the effect of medication on gene expression. The comprehensive approach and holistic analysis of the problem are due to the multigenic and multifactorial nature of addiction. Dopamine, one of the major neurotransmitters in the brain, is believed to be the "culprit" that leads to a drug abuse-induced "high". That is why, in our research, we focused mainly on the genes related to dopaminergic reuptake. In the present study, we chose methylation of the DAT1 dopamine transporter gene based on molecular reasons related to the dopaminergic theory of addiction. This study included two groups: 226 stimulant-dependent and 290 non-stimulant-dependent subjects. The analysis consisted of a case-control comparison of people addicted to psychostimulants compared to a control group of healthy and non-addicted people. There were differences in the levels of statistical significance between the groups. Our research shows lower methylation of islands 1, 9, and 14 in addicted people and greater methylation of islands 32 and 33. The difference in individual CpG methylation islands of the gene under study provides valuable information about the DNA methylation process in patients addicted to psychostimulants. Pearson's linear correlation analysis in stimulant dependence showed a negative correlation between total methylation island levels and the NEO-FFI Neuroticism scale. In subjects with neuroticism, the methylation level was statistically significantly lower. Pearson's linear correlation analysis of stimulant-dependent subjects showed a positive correlation between total methylation island levels and the NEO-FFI Openness scale and the NEO-FFI Conscientiousness scale.

Sex differences in mouse infralimbic cortex projections to the nucleus accumbens shell

BACKGROUND

The nucleus accumbens (NAc) is an important region in motivation and reward. Glutamatergic inputs from the infralimbic cortex (ILC) to the shell region of the NAc (NAcSh) have been implicated in driving the motivation to seek reward through repeated action-based behavior. While this has primarily been studied in males, observed sex differences in motivational circuitry and behavior suggest that females may be more sensitive to rewarding stimuli. These differences have been implicated for the observed vulnerability in women to substance use disorders.

METHODS

We used an optogenetic self-stimulation task in addition to ex vivo electrophysiological recordings of NAcSh neurons in mouse brain slices to investigate potential sex differences in ILC-NAcSh circuitry in reward-seeking behavior. Glutamatergic neurons in the ILC were infected with an AAV delivering DNA encoding for channelrhodopsin. Entering the designated active corner of an open field arena resulted in photostimulation of the ILC terminals in the NAcSh. Self-stimulation occurred during two consecutive days of testing over three consecutive weeks: first for 10 Hz, then 20 Hz, then 30 Hz. Whole-cell recordings of medium spiny neurons in the NAcSh assessed both optogenetically evoked local field potentials and intrinsic excitability.

RESULTS

Although both sexes learned to seek the active zone, within the first day, females entered the zone more than males, resulting in a greater amount of photostimulation. Increasing the frequency of optogenetic stimulation amplified female reward-seeking behavior. Males were less sensitive to ILC stimulation, with higher frequencies and repeated days required to increase male reward-seeking behavior. Unexpectedly, ex vivo optogenetic local field potentials in the NAcSh were greater in slices from male animals. In contrast, female medium-spiny neurons (MSNs) displayed significantly greater intrinsic neuronal excitability.

CONCLUSIONS

Taken together, these data indicate that there are sex differences in the motivated behavior driven by glutamate within the ILC-NAcSh circuit. Though glutamatergic signaling was greater in males, heightened intrinsic excitability in females appears to drive this sex difference.

Reactive Oxygen Species Mediate Transcriptional Responses to Dopamine and Cocaine in Human Cerebral Organoids

Dopamine signaling in the adult ventral forebrain regulates behavior, stress response, and memory formation and in neurodevelopment regulates neural differentiation and cell migration. Excessive dopamine levels, including those due to cocaine use in utero and in adults, could lead to long-term adverse consequences. The mechanisms underlying both homeostatic and pathological changes remain unclear, in part due to the diverse cellular responses elicited by dopamine and the reliance on animal models that exhibit species-specific differences in dopamine signaling. In this study, we use the human-derived ventral forebrain organoid model of Xiang-Tanaka and characterize their response to cocaine or dopamine. We explore dosing regimens of dopamine or cocaine to simulate acute or chronic exposure. We then use calcium imaging, cAMP imaging, and bulk RNA-sequencing to measure responses to cocaine or dopamine exposure. We observe an upregulation of inflammatory pathways in addition to indicators of oxidative stress following exposure. Using inhibitors of reactive oxygen species (ROS), we then show ROS to be necessary for multiple transcriptional responses of cocaine exposure. These results highlight novel response pathways and validate the potential of cerebral organoids as in vitro human models for studying complex biological processes in the brain.

Antidepressant Medication Does Not Contribute to the Elevated Circulating Concentrations of Acylethanolamides Found in Substance Use Disorder Patients

Circulating acylethanolamides (NAEs) are bioactive signaling molecules that modulate multiple homeostatic functions including mood and hedonic responses. Variations in their plasma concentrations are associated with substance use disorders (SUD) and recent studies suggest that psychotropic medication might influence its circulating levels, limiting its use as a clinical biomarker of addiction. In addition, they might have a role as mediators of the pharmacological effects of psychotropic drugs. Thus, in mild depression, the response to selective serotonin reuptake inhibitor-type antidepressants (SSRI) is associated with a marked increase in circulating NAEs. To further investigate if antidepressants are able to modify the plasma concentration of NAEs in SUD patients, we analyzed the circulating levels of NAEs in 333 abstinent and 175 healthy controls on the basis of the treatment with SSRI antidepressants. As described previously, SUD patients display higher concentrations of NAEs than those measured in a control population. This increase was not further modified by antidepressant therapy. Only marginal increases in palmitoylethanolamide (PEA), oleoylethanolamide (OEA), or docosatetraenoyl-ethanolamide (DEA) were found, and the net effect was very small. Thus, our study shows that treatment with SSRI-type antidepressants does not modify the clinical utility of monitoring enhanced NAE production as biomarkers of SUD. In addition, the possibility that a blunted NAE response to antidepressant therapy might be related to the loss of efficacy of SSRIs in dual depression emerges as an attractive hypothesis that needs to be addressed in future studies.

Methamphetamine-induced region-specific transcriptomic and epigenetic changes in the brain of male rats

Psychostimulant methamphetamine (METH) is neurotoxic to the brain and, therefore, its misuse leads to neurological and psychiatric disorders. The gene regulatory network (GRN) response to neurotoxic METH binge remains unclear in most brain regions. Here we examined the effects of binge METH on the GRN in the nucleus accumbens, dentate gyrus, Ammon's horn, and subventricular zone in male rats. At 24 h after METH, ~16% of genes displayed altered expression and over a quarter of previously open chromatin regions - parts of the genome where genes are typically active - showed shifts in their accessibility. Intriguingly, most changes were unique to each area studied, and independent regulation between transcriptome and chromatin accessibility was observed. Unexpectedly, METH differentially impacted gene activity and chromatin accessibility within the dentate gyrus and Ammon's horn. Around 70% of the affected chromatin-accessible regions in the rat brain have conserved DNA sequences in the human genome. These regions frequently act as enhancers, ramping up the activity of nearby genes, and contain mutations linked to various neurological conditions. By sketching out the gene regulatory networks associated with binge METH in specific brain regions, our study offers fresh insights into how METH can trigger profound, region-specific molecular shifts.

Hypoxia-inducible factor upregulation by roxadustat attenuates drug reward by altering brain iron homoeostasis

Substance use disorder remains a major challenge, with an enduring need to identify and evaluate new, translational targets for effective treatment. Here, we report the upregulation of Hypoxia-inducible factor-1α (HIF-1α) expression by roxadustat (Rox), a drug developed for renal anemia that inhibits HIF prolyl hydroxylase to prevent degradation of HIF-1α, administered either systemically or locally into selected brain regions, suppressed morphine (Mor)-induced conditioned place preference (CPP). A similar effect was observed with methamphetamine (METH). Moreover, Rox also inhibited the expression of both established and reinstated Mor-CPP and promoted the extinction of Mor-CPP. Additionally, the elevation of HIF-1α enhanced hepcidin/ferroportin 1 (FPN1)-mediated iron efflux and resulted in cellular iron deficiency, which led to the functional accumulation of the dopamine transporter (DAT) in plasma membranes due to iron deficiency-impaired ubiquitin degradation. Notably, iron-deficient mice generated via a low iron diet mimicked the effect of Rox on the prevention of Mor- or METH-CPP formation, without affecting other types of memory. These data reveal a novel mechanism for HIF-1α and iron involvement in substance use disorder, which may represent a potential novel therapeutic strategy for the treatment of drug abuse. The findings also repurpose Rox by suggesting a potential new indication for the treatment of substance use disorder.

Drugs of abuse hijack a mesolimbic pathway that processes homeostatic need

Addiction prioritizes drug use over innate needs by "hijacking" brain circuits that direct motivation, but how this develops remains unclear. Using whole-brain FOS mapping and in vivo single-neuron calcium imaging, we find that drugs of abuse augment ensemble activity in the nucleus accumbens (NAc) and disorganize overlapping ensemble responses to natural rewards in a cell-type-specific manner. Combining "FOS-Seq", CRISPR-perturbations, and snRNA-seq, we identify Rheb as a shared molecular substrate that regulates cell-type-specific signal transductions in NAc while enabling drugs to suppress natural reward responses. Retrograde circuit mapping pinpoints orbitofrontal cortex which, upon activation, mirrors drug effects on innate needs. These findings deconstruct the dynamic, molecular, and circuit basis of a common reward circuit, wherein drug value is scaled to promote drug-seeking over other, normative goals.

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.

Cannabidiol modulates chronic neuropathic pain aversion behavior by attenuation of neuroinflammation markers and neuronal activity in the corticolimbic circuit in male Wistar rats

Chronic neuropathic pain (CNP) is a vast world health problem often associated with the somatosensory domain. This conceptualization is problematic because, unlike most other sensations that are usually affectively neutral and may present emotional, affective, and cognitive impairments. Neuronal circuits that modulate pain can increase or decrease painful sensitivity based on several factors, including context and expectation. The objective of this study was to evaluate whether subchronic treatment with Cannabidiol (CBD; 0.3, 3, and 10 mg/kg intraperitoneal route - i.p., once a day for 3 days) could promote pain-conditioned reversal, in the conditioned place preference (CPP) test, in male Wistar rats submitted to chronic constriction injury (CCI) of the sciatic nerve. Then, we evaluated the expression of astrocytes and microglia in animals treated with CBD through the immunofluorescence technique. Our results demonstrated that CBD promoted the reversal of CPP at 3 and 10 mg/kg. In CCI animals, CBD was able to attenuate the increase in neuronal hyperactivity, measured by FosB protein expression, in the regions of the corticolimbic circuit: anterior cingulate cortex (ACC), complex basolateral amygdala (BLA), granular layer of the dentate gyrus (GrDG), and dorsal hippocampus (DH) - adjacent to subiculum (CA1). CBD also prevented the increased expression of GFAP and IBA-1 in CCI animals. We concluded that CBD effects on CNP are linked to the modulation of the aversive component of pain. These effects decrease chronic neuronal activation and inflammatory markers in regions of the corticolimbic circuit.

Theoretical Frameworks and Mechanistic Aspects of Alcohol Addiction: Alcohol Addiction as a Reward Deficit/Stress Surfeit Disorder

Alcohol use disorder (AUD) can be defined by a compulsion to seek and take alcohol, the loss of control in limiting intake, and the emergence of a negative emotional state when access to alcohol is prevented. Alcohol use disorder impacts multiple motivational mechanisms and can be conceptualized as a disorder that includes a progression from impulsivity (positive reinforcement) to compulsivity (negative reinforcement). Compulsive drug seeking that is associated with AUD can be derived from multiple neuroadaptations, but the thesis argued herein is that a key component involves the construct of negative reinforcement. Negative reinforcement is defined as drug taking that alleviates a negative emotional state. The negative emotional state that drives such negative reinforcement is hypothesized to derive from the dysregulation of specific neurochemical elements that are involved in reward and stress within basal forebrain structures that involve the ventral striatum and extended amygdala, respectively. Specific neurochemical elements in these structures include decreases in reward neurotransmission (e.g., decreases in dopamine and opioid peptide function in the ventral striatum) and the recruitment of brain stress systems (e.g., corticotropin-releasing factor [CRF]) in the extended amygdala, which contributes to hyperkatifeia and greater alcohol intake that is associated with dependence. Glucocorticoids and mineralocorticoids may play a role in sensitizing the extended amygdala CRF system. Other components of brain stress systems in the extended amygdala that may contribute to the negative motivational state of withdrawal include norepinephrine in the bed nucleus of the stria terminalis, dynorphin in the nucleus accumbens, hypocretin and vasopressin in the central nucleus of the amygdala, and neuroimmune modulation. Decreases in the activity of neuropeptide Y, nociception, endocannabinoids, and oxytocin in the extended amygdala may also contribute to hyperkatifeia that is associated with alcohol withdrawal. Such dysregulation of emotional processing may also significantly contribute to pain that is associated with alcohol withdrawal and negative urgency (i.e., impulsivity that is associated with hyperkatifeia during hyperkatifeia). Thus, an overactive brain stress response system is hypothesized to be activated by acute excessive drug intake, to be sensitized during repeated withdrawal, to persist into protracted abstinence, and to contribute to the compulsivity of AUD. The combination of the loss of reward function and recruitment of brain stress systems provides a powerful neurochemical basis for a negative emotional state that is responsible for the negative reinforcement that at least partially drives the compulsivity of AUD.

Alprazolam exposure during adolescence induces long-lasting dysregulation in reward sensitivity to morphine and second messenger signaling in the VTA-NAc pathway

Increased use of benzodiazepines in adolescents have been reported, with alprazolam (ALP) being the most abused. Drug abuse during adolescence can induce changes with lasting consequences. This study investigated the neurobiological consequences of ALP exposure during adolescence in C57BL/6J male mice. Mice received ALP (0, 0.5, 1.0 mg/kg) once/daily (postnatal day 35-49). Changes in responsiveness to morphine (2.5, 5.0 mg/kg), using the conditioned place preference paradigm, were assessed 24-h and 1-month after ALP exposure. In a separate experiment, mice received ALP (0, 0.5 mg/kg) and then sacrificed 24-h or 1-month after treatment to assess levels of extracellular signal regulated kinase 1/2 (ERK1/2) gene expression, protein phosphorylation, and downstream targets (CREB, AKT) within the ventral tegmental area (VTA) and nucleus accumbens (NAc). ALP-pretreated mice developed a strong preference to the compartment(s) paired with a subthreshold dose (2.5 mg/kg) of MOR short-term, and this effect was also present in the 1-month group. Adolescent ALP exposure resulted in dysregulation of ERK-signaling within the VTA-NAc pathway 24-h and 1-month after ALP exposure. Results indicate ALP exposure during adolescence potentiates the rewarding properties of MOR and induces persistent changes in ERK-signaling within the VTA-NAc pathway, a brain circuit highly implicated in the regulation of both drug reward and mood- related behaviors.

Does Morphine Exposure Before Gestation Change Anxiety-Like Behavior During Morphine Dependence in Male Wistar Rats?

Background

Anxiety is one of the comorbid disorders of opioid addiction, which leads to opioid abuse or persuades people to engage in opioid abuse. Evidence revealed that morphine exposure before conception changes the offspring's phenotype. The current study aimed to investigate the influence of morphine dependence and abstinence on anxiety-like behavior in morphine-exposed and drug-naïve offspring.

Methods

Adult male and female rats were treated with morphine or vehicle for 21 days. Then, all rats were left without drug treatment for 10 days. A morphine-exposed female rat was mated with either a vehicle-exposed or morphine-abstinent male. According to parental morphine exposure, the offspring were categorized into four distinct groups: (1) control (both drug-naïve parents), (2) paternal morphine-exposed, (3) maternal morphine-exposed, and (4) biparental morphine-exposed. The anxiety-like behavior was measured in adult male offspring using open field and elevated plus-maze tests before morphine exposure (naïve), 21 days after morphine exposure (dependence), and ten days after the last morphine exposure (abstinence).

Findings

The results indicated that anxiety-like behavior increased before morphine exposure in maternal and biparental morphine-exposed offspring (P<0.05). However, after morphine exposure, the anxiety level did not change among the groups. Ten days after the last morphine exposure, anxiety-like behavior increased only in biparental morphine-exposed offspring (P<0.05).

Conclusion

The offspring of morphine-abstinent parents exhibited an anxious phenotype. Disruption of the HPA axis was seen in the progeny of maternal and biparental morphine-exposed rats. Indeed, morphine exposure for 21 days did not change anxiety-like behavior in these offspring which might be correlated to disruption of HPA axis in them.

Effect of transcranial direct current stimulation over the left dorsolateral prefrontal cortex on the aggressive behavior in methamphetamine addicts

Aggressive behavior of drug addicts threatens human security and social stability, and Methamphetamine (MA) addicts show especially aggressive behavior. Researches showed that the decreased activity of dorsolateral prefrontal cortex (DLPFC) is closely related to violence and aggression, and continuous transcranial direct current stimulation (tDCS) on DLPFC can increase the activity of this position. So, the purpose of this study was to investigate the effect of tDCS on DLPFC for the aggressive behavior of MA addicts. Ninety MA addicts were recruited and randomly divided into anodal tDCS group, cathode tDCS group and sham tDCS group (current intensity was set as 2 mA, 2 mA and 0 mA, respectively). The tDCS intervention was conducted twice a day for five consecutive days. Taylor Aggression Paradigm (TAP) was used to measure the proactive aggressiveness and reactive aggressiveness of MA addicts at different time points (Pretest, Day 1, and Day 5). At the same time, we also recruited 30 healthy adult males as healthy controls, and measured their aggressiveness through TAP for comparative analysis. The results showed that the aggressiveness of MA addicts was significantly higher than that of healthy controls. The aggressiveness of MA addicts was effectively reduced by the anode intervention of tDCS on the left DLPFC, especially when they were subjected to high-intensity provocation, the 2-way interaction between time and tDCS group was statistically significant (F_4,164 = 2.939, P = 0.022, η_p² = 0.067). This study can provide a reference for how to correct the aggressive behavior of MA addicts.

Understanding health behavior change by motivation and reward mechanisms: a review of the literature

The global rise of lifestyle-related chronic diseases has engendered growing interest among various stakeholders including policymakers, scientists, healthcare professionals, and patients, regarding the effective management of health behavior change and the development of interventions that facilitate lifestyle modification. Consequently, a plethora of health behavior change theories has been developed with the intention of elucidating the mechanisms underlying health behavior change and identifying key domains that enhance the likelihood of successful outcomes. Until now, only few studies have taken into account neurobiological correlates underlying health behavior change processes. Recent progress in the neuroscience of motivation and reward systems has provided further insights into the relevance of such domains. The aim of this contribution is to review the latest explanations of health behavior change initiation and maintenance based on novel insights into motivation and reward mechanisms. Based on a systematic literature search in PubMed, PsycInfo, and Google Scholar, four articles were reviewed. As a result, a description of motivation and reward systems (approach/wanting = pleasure; aversion/avoiding = relief; assertion/non-wanting = quiescence) and their role in health behavior change processes is presented. Three central findings are discussed: (1) motivation and reward processes allow to distinguish between goal-oriented and stimulus-driven behavior, (2) approach motivation is the key driver of the individual process of behavior change until a new behavior is maintained and assertion motivation takes over, (3) behavior change techniques can be clustered based on motivation and reward processes according to their functional mechanisms into facilitating (= providing external resources), boosting (= strengthening internal reflective resources) and nudging (= activating internal affective resources). The strengths and limitations of these advances for intervention planning are highlighted and an agenda for testing the models as well as future research is proposed.

Effects of acid-sensing ion channel-1A (ASIC1A) on cocaine-induced synaptic adaptations

Chronic drug abuse is thought to induce synaptic changes in nucleus accumbens medium spiny neurons (MSNs) that promote subsequent craving and drug-seeking behavior. Accumulating data suggest acid-sensing ion channels (ASICs) may play a critical role. In drug naïve mice, disrupting the ASIC1A subunit produced a variety of synaptic changes reminiscent of wild-type mice following cocaine withdrawal, including increased AMPAR/NMDAR ratio, increased AMPAR rectification, and increased dendrite spine density. Importantly, these changes in Asic1a -/- mice were normalized by a single dose of cocaine. Here we sought to understand the temporal effects of cocaine exposure in Asic1a -/- mice and the cellular site of ASIC1A action. Six hours after cocaine exposure, there was no effect. However, 15 h, 24 h and 4 days after cocaine exposure there was a significant reduction in AMPAR/NMDAR ratio in Asic1a -/- mice. Within 7 days the AMPAR/NMDAR ratio had returned to baseline levels. Cocaine-evoked changes in AMPAR rectification and dendritic spine density followed a similar time course with significant reductions in rectification and dendritic spines 24 h after cocaine exposure in Asic1a -/- mice. To test the cellular site of ASIC1A action on these responses, we disrupted ASIC1A specifically in a subpopulation of MSNs. We found that effects of ASIC1A disruption were cell autonomous and restricted to neurons in which the channels are disrupted. We further tested whether ASIC1A disruption differentially affects MSNs subtypes and found AMPAR/NMDAR ratio was elevated in dopamine receptor 1-expressing MSNs, suggesting a preferential effect for these cells. Finally, we tested if protein synthesis was involved in synaptic adaptations that occurred after ASIC1A disruption, and found the protein synthesis inhibitor anisomycin normalized AMPAR-rectification and AMPAR/NMDAR ratio in drug-naïve Asic1a -/- mice to control levels, observed in wild-type mice. Together, these results provide valuable mechanistic insight into the effects of ASICs on synaptic plasticity and drug-induced effects and raise the possibility that ASIC1A might be therapeutically manipulated to oppose drug-induced synaptic changes and behavior.

Reactive Oxygen Species Mediate Transcriptional Responses to Dopamine and Cocaine in Human Cerebral Organoids

Dopamine signaling in the adult ventral forebrain regulates behavior, stress response, and memory formation and in neurodevelopment regulates neural differentiation and cell migration. Excessive dopamine levels including due to cocaine use both in utero and in adults could lead to long-term adverse consequences. The mechanisms underlying both homeostatic and pathological changes remain unclear, partly due to the diverse cellular responses elicited by dopamine and the reliance on animal models that exhibit species-specific differences in dopamine signaling. To address these limitations, 3-D cerebral organoids have emerged as human-derived models, recapitulating salient features of human cell signaling and neurodevelopment. Organoids have demonstrated responsiveness to external stimuli, including substances of abuse, making them valuable investigative models. In this study we utilize the Xiang-Tanaka ventral forebrain organoid model and characterize their response to acute and chronic dopamine or cocaine exposure. The findings revealed a robust immune response, novel response pathways, and a potential critical role for reactive oxygen species (ROS) in the developing ventral forebrain. These results highlight the potential of cerebral organoids as in vitro human models for studying complex biological processes in the brain.

Disrupted Dynamic Interactions Between Large-Scale Brain Networks in Cocaine Users Are Associated With Dependence Severity

BACKGROUND

Substance use disorder is conceptualized as a neuropsychiatric disease with multifaceted phenotypic manifestations including disrupted interactions between brain networks. While the current understanding of brain network interactions is mostly based on static functional connectivity, accumulating evidence suggests that temporal dynamics of these network interactions may better reflect brain function and disease-related dysfunction. We thus investigated brain dynamics in cocaine use disorder and assessed their relationship with cocaine dependence severity.

METHODS

Using a time frame analytical approach on resting-state functional magnetic resonance imaging data of 54 cocaine users and 54 age- and sex-matched healthy control participants, we identified temporally recurring brain network configuration patterns, termed brain states. With Menon's triple network model as a guide, we characterized these state dynamics by quantifying their occurrence rate and transition probability. Group differences in the state dynamics and their association with cocaine dependence were assessed.

RESULTS

Three recurrent brain states with spatial patterns resembling the default mode, salience, and executive control networks were identified. Compared with healthy control subjects, cocaine users showed a higher default mode state occurrence rate and higher probability of transitioning from the salience state to the default mode state, with the former being attributed to the latter. A composite state transition probability negatively correlated with cocaine dependence severity.

CONCLUSIONS

Our results provide novel evidence supporting the triple network model. While confirming hyperactivity of default mode network in cocaine users, our findings indicate the failure of salience network in toggling between default mode and executive control networks in cocaine use disorder.

Increased Excitability and Synaptic Plasticity of Drd1- and Drd2-Expressing Prelimbic Neurons Projecting to Nucleus Accumbens after Heroin Abstinence Are Reversed by Cue-Induced Relapse and Protein Kinase A Inhibition

Dysregulation of the input from the prefrontal cortex (PFC) to the nucleus accumbens (NAc) contributes to cue-induced opioid seeking but the heterogeneity in, and regulation of, prelimbic (PL)-PFC to NAc (PL->NAc) neurons that are altered has not been comprehensively explored. Recently, baseline and opiate withdrawal-induced differences in intrinsic excitability of Drd1+ (D1+) versus Drd2+ (D2+) PFC neurons have been demonstrated. Thus, here we investigated physiological adaptations of PL->NAc D1+ versus D2+ neurons after heroin abstinence and cue-induced relapse. Drd1-Cre+ and Drd2-Cre+ transgenic male Long-Evans rats with virally labeled PL->NAc neurons were trained to self-administer heroin followed by 1 week of forced abstinence. Heroin abstinence significantly increased intrinsic excitability in D1+ and D2+ PL->NAc neurons and increased postsynaptic strength selectively in D1+ neurons. These changes were normalized by cue-induced relapse to heroin seeking. Based on protein kinase A (PKA)-dependent changes in the phosphorylation of plasticity-related proteins in the PL cortex during abstinence and cue-induced relapse to cocaine seeking, we assessed whether the electrophysiological changes in D1+ and D2+ PL->NAc neurons during heroin abstinence were regulated by PKA. In heroin-abstinent PL slices, application of the PKA antagonist (R)-adenosine, cyclic 3',5'-(hydrogenphosphorothioate) triethylammonium (RP-cAMPs) reversed intrinsic excitability in both D1+ and D2+ neurons and postsynaptic strength in only D1+ neurons. Additionally, in vivo bilateral intra-PL infusion of RP-cAMPs after abstinence from heroin inhibited cue-induced relapse to heroin seeking. These data reveal that PKA activity in D1+ and D2+ PL->NAc neurons is not only required for abstinence-induced physiological adaptations but is also required for cue-induced relapse to heroin seeking.SIGNIFICANCE STATEMENT Neuronal plasticity in the medial prefrontal cortex is thought to underlie relapse to drug seeking, yet the subpopulation of neurons that express this plasticity to functionally guide relapse is unclear. Here we show cell type-specific adaptations in Drd1-expressing versus Drd2-expressing prelimbic pyramidal neurons with efferent projections to nucleus accumbens. These adaptations are bidirectionally regulated during abstinence versus relapse and involve protein kinase A (PKA) activation. Furthermore, we show that disruption of the abstinence-associated adaptations via site-specific PKA inhibition abolishes relapse. These data reveal the promising therapeutic potential of PKA inhibition for preventing relapse to heroin seeking and suggest that cell type-specific pharmacologies that target subpopulations of prefrontal neurons would be ideal for future therapeutic developments.

Antipsychotic Medication Influences the Discriminative Value of Acylethanolamides as Biomarkers of Substance Use Disorder

Plasma acylethanolamides (NAEs), including the endocannabinoid anandamide (AEA), have been proposed as circulating biomarkers of substance use disorders. However, the concentration of these lipid transmitters might be influenced by the use of drugs prescribed for either the treatment of addiction or the associated psychiatric co-morbidities such as psychosis. As an example, neuroleptics, used for attenuation of psychotic symptoms and sedation, might theoretically interfere with the monoamine-mediated production of NAEs, obstructing the interpretation of plasma NAEs as clinical biomarkers. To solve the lack of information on the impact of neuroleptics on the concentration of NAEs, we evaluated the concentrations of NAEs in a control group and compared them to those present in (a) substance use disorders (SUD) patients that are not prescribed with neuroleptics, and (b) SUD patients (both alcohol use disorder and cocaine use disorder patients) using neuroleptics. The results demonstrate that SUD patients exhibited greater concentrations of NAEs than the control population, affecting all species with the exception of stearoylethanolamide (SEA) and palmitoleoylethanolamide (POEA). Neuroleptic treatment enhanced the concentrations of NAEs, especially those of AEA, linoleoylethanolamide (LEA), and oleoylethanolamide (OEA). This effect of neuroleptic treatment was observed independently of the drug addiction that motivated the demand for treatment (either alcohol or cocaine). This study remarks the need to control the current use of psychotropic medication as a potential confounding variable when considering the use of NAEs as biomarkers in SUD.

Autophosphorylation of αCaMKII regulates alcohol consumption by controlling sedative effects of alcohol and alcohol-induced loss of excitatory synapses

Calcium/calmodulin-dependent kinase II (CaMKII) is a key enzyme at the glutamatergic synapses. CAMK2A gene variants have been linked with alcohol use disorder (AUD) by an unknown mechanism. Here, we looked for the link between αCaMKII autophosphorylation and the AUD aetiology. Autophosphorylation-deficient heterozygous αCaMKII mutant mice (T286A^+/- ) were trained in the IntelliCages to test the role of αCaMKII activity in AUD-related behaviours. The glutamatergic synapses morphology in CeA was studied in the animals drinking alcohol using 3D electron microscopy. We found that T286A^+/- mutants consumed less alcohol and were more sensitive to sedating effects of alcohol, as compared to wild-type littermates (WT). After voluntary alcohol drinking, T286A^+/- mice had less excitatory synapses in the CeA, as compared to alcohol-naive animals. This change correlated with alcohol consumption was not reversed after alcohol withdrawal and not observed in WT mice. Our study suggests that αCaMKII autophosphorylation affects alcohol consumption by controlling sedative effects of alcohol and preventing synaptic loss in the individuals drinking alcohol. This finding advances our understanding of the molecular processes that regulate alcohol dependence.

Orbitofrontal cortex microRNAs support long-lasting heroin seeking behavior in male rats

Recovery from opioid use disorder (OUD) and maintenance of abstinence from opioid use is hampered by perseverant drug cravings that may persist for months after cessation of drug use. Drug cravings can intensify during the abstinence period, a phenomenon referred to as the 'incubation of craving' that has been well-described in preclinical studies. We previously reported that animals that self-administered heroin at a dosage of 0.075 mg/kg/infusion (HH) paired with discrete drug cues displayed robust incubation of heroin craving behavior after 21 days (D) of forced abstinence, an effect that was not observed with a lower dosage (0.03 mg/kg/infusion; HL). Here, we sought to elucidate molecular mechanisms underlying long-term heroin seeking behavior by profiling microRNA (miRNA) pathways in the orbitofrontal cortex (OFC), a brain region that modulates incubation of heroin seeking. miRNAs are small noncoding RNAs with long half-lives that have emerged as critical regulators of drug seeking behavior but their expression in the OFC has not been examined in any drug exposure paradigm. We employed next generation sequencing to detect OFC miRNAs differentially expressed after 21D of forced abstinence between HH and HL animals, and proteomics analysis to elucidate miRNA-dependent translational neuroadaptations. We identified 55 OFC miRNAs associated with incubation of heroin craving, including miR-485-5p, which was significantly downregulated following 21D forced abstinence in HH but not HL animals. We bidirectionally manipulated miR-485-5p in the OFC to demonstrate that miR-485-5p can regulate long-lasting heroin seeking behavior after extended forced abstinence. Proteomics analysis identified 45 proteins selectively regulated in the OFC of HH but not HL animals that underwent 21D forced abstinence, of which 7 were putative miR-485-5p target genes. Thus, the miR-485-5p pathway is dysregulated in animals with a phenotype of persistent heroin craving behavior and OFC miR-485-5p pathways may function to support long-lasting heroin seeking.

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.

DNA Methylation of the Dopamine Transporter DAT1 Gene—Bliss Seekers in the Light of Epigenetics

DNA methylation (leading to gene silencing) is one of the best-studied epigenetic mechanisms. It is also essential in regulating the dynamics of dopamine release in the synaptic cleft. This regulation relates to the expression of the dopamine transporter gene (DAT1). We examined 137 people addicted to nicotine, 274 addicted subjects, 105 sports subjects and 290 people from the control group. After applying the Bonferroni correction, our results show that as many as 24 out of 33 examined CpG islands had statistically significantly higher methylation in the nicotine-dependent subjects and athletes groups compared to the control group. Analysis of total DAT1 methylation revealed a statistically significant increase in the number of total methylated CpG islands in addicted subjects (40.94%), nicotine-dependent subjects (62.84%) and sports subjects (65.71%) compared to controls (42.36%). The analysis of the methylation status of individual CpG sites revealed a new direction of research on the biological aspects of regulating dopamine release in people addicted to nicotine, people practicing sports and people addicted to psychoactive substances.

Role of the mesolimbic dopamine pathway in the antidepressant effects of ketamine

Depression is a complex and highly heterogeneous disorder which diagnosis is based on an exceedingly variable set of clinical symptoms. Current treatments focus almost exclusively on the manipulation of monoamine neurotransmitter systems, but despite considerable efforts, these remain inadequate for a significant proportion of those afflicted by the disorder. The emergence of racemic (R, S)-ketamine as a fast-acting antidepressant has provided an exciting new path for the study of major depressive disorder (MDD) and the search for better therapeutics for its treatment. Previous work suggested that ketamine's mechanism of action is primarily mediated via blockaded of N-methyl-d-aspartate (NMDA) receptors, however, this is an area of active research and clinical and preclinical evidence now indicate that ketamine acts on multiple systems. The last couple of decades have cemented the mesolimbic dopamine reward pathway's involvement in the pathogenesis of MDD and related mood disorders. Exposure to negative stress dysregulates dopamine neuronal activity disrupting reward and motivational processes resulting in anhedonia (lack of pleasure), a hallmark symptom of depression. Although the mechanism(s) underlying ketamine's antidepressant activity continue to be elucidated, current evidence indicate that its therapeutic effects are mediated, at least in part, via long-lasting synaptic changes and subsequent molecular adaptations in brain regions within the mesolimbic dopamine system. Notwithstanding, ketamine is a drug of abuse, and this liability may pose limitations for long term use as an antidepressant. This review outlines the current knowledge of ketamine's actions within the mesolimbic dopamine system and its abuse potential. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Repeated dosing with cocaine produces strain-dependent effects on responding for conditioned reinforcement in Collaborative Cross mice

RATIONALE

Cocaine use disorder (CUD) is a highly heritable form of substance use disorder, with genetic variation accounting for a substantial proportion of the risk for transitioning from recreational use to a clinically impairing addiction. With repeated exposures to cocaine, psychomotor and incentive sensitization are observed in rodents. These phenomena are thought to model behavioral changes elicited by the drug that contribute to the progression into addiction, but little is known about how genetic variation may moderate these consequences.

OBJECTIVES

Here, we describe the use of two Collaborative Cross (CC) recombinant inbred mouse strains that either exhibit high (CC018/UncJ) or no (CC027/GeniUncJ) psychomotor sensitization in response to cocaine to measure phenotypes related to incentive sensitization after repeated cocaine exposures; given the relationship of incentive motivation to nucleus accumbens core (NAc) dopamine release and reuptake, we also assessed these neurochemical mechanisms.

METHODS

Adult male and female CC018/UncJ and CC027/GeniUncJ mice underwent Pavlovian conditioning to associate a visual cue with presentation of a palatable food reward, then received five, every-other-day injections of cocaine or vehicle. Following Pavlovian re-training, they underwent testing acquisition of a new operant response for the visual cue, now serving as a conditioned reinforcer. Subsequently, electrically evoked dopamine release was assessed using fast-scan cyclic voltammetry from acute brain slices containing the NAc.

RESULTS

While both strains acquired the Pavlovian association, only CC018/UncJ mice showed conditioned reinforcement and incentive sensitization in response to cocaine, while CC027/GeniUncJ mice did not. Voltammetry data revealed that CC018/UncJ, compared to CC027/GeniUnc, mice exhibited higher baseline dopamine release and uptake. Moreover, chronic cocaine exposure blunted tonic and phasic dopamine release in CC018/UncJ, but not CC027/GeniUncJ, mice.

CONCLUSIONS

Genetic background is a moderator of cocaine-induced neuroadaptations in mesolimbic dopamine signaling, which may contribute to both psychomotor and incentive sensitization and indicate a shared biological mechanism of variation.

Cocaine regulates sensory filtering in cortical pyramidal neurons

Exposure to cocaine leads to robust changes in the structure and function of neurons within the mesocorticolimbic pathway. However, little is known about how cocaine influences the processing of information within the sensory cortex. We address this by using patch-clamp and juxtacellular voltage recordings and two-photon Ca2+ imaging in vivo to investigate the influence of acute cocaine exposure on layer 2/3 (L2/3) pyramidal neurons within the primary somatosensory cortex (S1). Here, cocaine dampens membrane potential state transitions and decreases spontaneous somatic action potentials and Ca2+ transients. In contrast to the uniform decrease in background spontaneous activity, cocaine has a heterogeneous influence on sensory encoding, increasing tactile-evoked responses in dendrites that do not typically encode sensory information and decreasing responses in those dendrites that are more reliable sensory encoders. Combined, these findings suggest that cocaine acts as a filter that suppresses background noise to selectively modulate incoming sensory information.

Cav1.3 L-type Ca2+ channel-activated CaMKII/ERK2 pathway in the ventral tegmental area is required for cocaine conditioned place preference

We have previously demonstrated that pharmacological blockade of ventral tegmental area (VTA) Cav1.3 L-type calcium channels (LTCCs) using Cav1.2 dihydropyridine insensitive (Cav1.2DHP-/-) mutant mice attenuates cocaine conditioned place preference (CPP). However, the molecular mechanisms by which Cav1.3 channels mediate the effects of cocaine in the VTA remain largely unknown. In this study using Cav1.2DHP-/- male mice, we find that cocaine place preference increases CaM kinase IIα, ERK2, and CREB phosphorylation in the VTA, proteins strongly linked to cocaine behaviors. To further explore the causal role of these intracellular signaling proteins in cocaine preference, the CaM kinase II inhibitor, KN93 was directly injected into the VTA of male mice before each cocaine conditioning session. We found that KN93 attenuates conditioned preference for cocaine compared to vehicle treated mice and decreased VTA ERK2 and CREB phosphorylation. Additionally, blockade of the ERK pathway with the MEK inhibitor, U0126 or knockdown of ERK2 using siRNA, attenuated cocaine preference and VTA CREB phosphorylation but not CaMKIIα phosphorylation, suggesting that ERK is activated downstream of CaMKIIα. Examination of postsynaptic density (PSD) GluA1 subunit of AMPA receptors in the nucleus accumbens (NAc) that we have previously shown to be upregulated following long withdrawal periods, was blunted by KN93, U0126 and ERK2 siRNA when examined 30 days following cocaine CPP. Taken together, these findings demonstrate that Cav1.3 channels in the VTA are required for cocaine reward behavior and activation of the CaMKIIα/ERK/CREB signaling pathway in the VTA is necessary for long-lasting changes in the NAc. This article is part of the Special Issue on 'L-type calcium channel mechanisms in neuropsychiatric disorders'.

Methylphenidate cross-sensitization with amphetamine is dose dependent but not age dependent

Psychostimulants such as methylphenidate (MPD) and amphetamine (AMP) are often prescribed to young children and adolescents to treat behavioral disorders, or used to improve their intellectual performance in our competitive society. This is concerning as the temporal effects of how MPD exposure at a young age influences the response to MPD and AMP administration later in adulthood remains unclear. The objective of this study was to test whether MPD has the characteristics of substances that elicit behavioral symptoms of dependence and whether those effects are influenced by the initial age of MPD exposure. Three control and nine experimental groups of male rats were used. They were exposed to repetitive (chronic) 0.6, 2.5, or 10.0 mg/kg MPD in adolescence only, adulthood only, or adolescence and adulthood respectively. Then all groups were subsequently re-challenged with a single AMP dose in adulthood to test whether cross-sensitization between MPD and AMP was expressed, potentially as a result of prior MPD consumption. Exposure to 2.5 mg/kg and 10.0 mg/kg MPD in adolescence and adulthood or in adulthood alone led to cross-sensitization with AMP while exposure to 0.6 mg/kg MPD in adolescence and adulthood or in adulthood alone did not lead to cross-sensitization with AMP. Thus, these results indicate that MPD cross-sensitization with AMP is dose dependent.

Short- and Long-Term Effects of Cocaine on Enteric Neuronal Functions

Cocaine is one of the most consumed illegal drugs among (young) adults in the European Union and it exerts various acute and chronic negative effects on psychical and physical health. The central mechanism through which cocaine initially leads to improved performance, followed by addictive behavior, has already been intensively studied and includes effects on the homeostasis of the neurotransmitters dopamine, partly mediated via nicotinic acetylcholine receptors, and serotonin. However, effects on the peripheral nervous system, including the enteric nervous system, are much less understood, though a correlation between cocaine consumption and gastrointestinal symptoms has been reported. The aim of the present study was to gain more information on the effects of cocaine on enteric neuronal functions and the underlying mechanisms. For this purpose, functional experiments using an organ bath, Ussing chamber and neuroimaging techniques were conducted on gastrointestinal tissues from guinea pigs. Key results obtained are that cocaine (1) exhibits a stimulating, non-neuronal effect on gastric antrum motility, (2) acutely (but not chronically) diminishes responses of primary cultured enteric neurons to nicotinic and serotonergic stimulation and (3) reversibly attenuates neuronal-mediated intestinal mucosal secretion. It can be concluded that cocaine, among its central effects, also alters enteric neuronal functions, providing potential explanations for the coexistence of cocaine abuse and gastrointestinal complaints.

Chronic Ethanol Exposure Modulates Periaqueductal Gray to Extended Amygdala Dopamine Circuit

The bed nucleus of the stria terminalis (BNST) is a component of the extended amygdala that regulates motivated behavior and affective states and plays an integral role in the development of alcohol-use disorder (AUD). The dorsal subdivision of the BNST (dBNST) receives dense dopaminergic input from the ventrolateral periaqueductal gray (vlPAG)/dorsal raphe (DR). To date, no studies have examined the effects of chronic alcohol on this circuit. Here, we used chronic intermittent ethanol exposure (CIE), a well-established rodent model of AUD, to functionally interrogate the vlPAG/DR-BNST dopamine (DA) circuit during acute withdrawal. We selectively targeted vlPAG/DR^DA neurons in tyrosine hydroxylase-expressing transgenic adult male mice. Using ex vivo electrophysiology, we found hyperexcitability of vlPAG/DR^DA neurons in CIE-treated mice. Further, using optogenetic approaches to target vlPAG/DR^DA terminals in the dBNST, we revealed a CIE-mediated shift in the vlPAG/DR-driven excitatory-inhibitory (E/I) ratio to a hyperexcitable state in dBNST. Additionally, to quantify the effect of CIE on endogenous DA signaling, we coupled optogenetics with fast-scan cyclic voltammetry to measure pathway-specific DA release in dBNST. CIE-treated mice had significantly reduced signal half-life, suggestive of faster clearance of DA signaling. CIE treatment also altered the ratio of vlPAG/DR^DA-driven cellular inhibition and excitation of a subset of dBNST neurons. Overall, our findings suggest a dysregulation of vlPAG/DR to BNST dopamine circuit, which may contribute to pathophysiological phenotypes associated with AUD.SIGNIFICANCE STATEMENT The dorsal bed nucleus of the stria terminalis (dBNST) is highly implicated in the pathophysiology of alcohol-use disorder and receives dopaminergic inputs from ventrolateral periaqueductal gray/dorsal raphe regions (vlPAG/DR). The present study highlights the plasticity within the vlPAG/DR to dBNST dopamine (DA) circuit during acute withdrawal from chronic ethanol exposure. More specifically, our data reveal that chronic ethanol strengthens vlPAG/DR-dBNST glutamatergic transmission while altering both DA transmission and dopamine-mediated cellular inhibition of dBNST neurons. The net result is a shift toward a hyperexcitable state in dBNST activity. Together, our findings suggest chronic ethanol may promote withdrawal-related plasticity by dysregulating the vlPAG/DR-dBNST DA circuit.

Role of KCC2 in the Regulation of Brain-Derived Neurotrophic Factor on Ethanol Consumption in Rats

Alcohol use disorder (AUD) is a common and complex disorder resulting from repetitive alcohol drinking. The mesocorticolimbic dopamine (DA) system, originating from the ventral tegmental area (VTA) in the midbrain, is involved in the rewarding effect of ethanol. The γ-aminobutyric acid (GABA) neurons in VTA appear to be key substrates of acute and chronic ethanol, which regulates DA neurotransmission indirectly in the mesocorticolimbic system. Despite significant research on the relationship between brain-derived neurotrophic factor (BDNF) and reduced alcohol consumption in male rats involving tropomyosin-related kinase B (TrkB), the mechanisms of BDNF-TrkB regulating alcohol behavior remain scarce. K⁺-Cl^- cotransporter 2 (KCC2) plays a crucial role in synaptic function in GABAergic neurons by modulating intracellular chlorine homeostasis. Here, we found that 4-week intermittent alcohol exposure impaired the function of KCC2 in VTA, evidenced by a lower expression level of phosphorylated KCC2 and decreased ratio of phosphorylated KCC2 to total KCC2, especially 72 h after withdrawal from 4-week ethanol exposure in male rats. CLP290 (a KCC2 activator) reduced excessive alcohol consumption after alcohol withdrawal, whereas VU0240551 (a specific KCC2 inhibitor) further enhanced alcohol intake. Importantly, VU0240551 reversed the attenuating effects of BDNF and 7,8-dihydroxyflavone (7,8-DHF) on alcohol consumption after withdrawal. Moreover, intraperitoneal injection of 7,8-DHF upregulated KCC2 expression and phosphorylated KCC2 in VTA 72 h after withdrawal from ethanol exposure in male rats. Collectively, our data indicate that KCC2 may be critical in the regulating action of BDNF-TrkB on ethanol consumption in AUD.

Functional consequences of short-term exposure to opioids versus cannabinoids in nonhuman primates

Opioids provide pain relief but are associated with several adverse effects. Researchers are exploring cannabis-based medicine as an alternative. However, little is known about the tendency for physical dependence on cannabinoids in comparison with that on opioids in primates. The aim of this study was to compare the potency of heroin and delta-9-tetrahydrocannabinol (THC) in eliciting analgesic effects and the development of physical dependence between opioids and cannabinoids in both male and female rhesus monkeys. Systemic administration of either heroin (0.03-0.18 mg/kg) or THC (0.3-1.8 mg/kg) in a dose-dependent manner produced antinociceptive effects against an acute thermal nociceptive stimulus. The μ-opioid receptor antagonist naltrexone (0.01 mg/kg) and the cannabinoid receptor antagonist SR141716A (0.3 mg/kg) produced the same degree of rightward shift in the dose-response curves for heroin- and THC-induced antinociception, respectively. Monkeys implanted with telemetry devices were subjected to short-term repeated administrations (two injections per day for 1-3 days) of either heroin (0.18 mg/kg), morphine (1.8 mg/kg), THC (1.8 mg/kg), or CP 55,940 (0.032 mg/kg). Administration of naltrexone (0.01 mg/kg) increased respiration, heart rate, and blood pressure in heroin- or morphine-treated monkeys. In contrast, administration of SR141716A (0.3 mg/kg) did not cause a significant change in these physiological parameters in THC- or CP 55,940-treated monkeys. Additionally, morphine, but not CP 55,940, enhanced the monkeys' hypersensitivity to the algogen capsaicin. Collectively, these results demonstrate that in nonhuman primates, both opioids and cannabinoids exert comparable antinociception; however, physical dependence on opioids, but not cannabinoids, at their antinociceptive doses, occurs following short-term exposures.

Whole-brain tracking of cocaine and sugar rewards processing

Natural rewards, such as food, and sex are appetitive stimuli available for animals in their natural environment. Similarly, addictive rewards such as drugs of abuse possess strong, positive valence, but their action relies on their pharmacological properties. Nevertheless, it is believed that both of these kinds of rewards activate similar brain circuitry. The present study aimed to discover which parts of the brain process the experience of natural and addictive rewards. To holistically address this question, we used a single-cell whole-brain imaging approach to find patterns of activation for acute and prolonged sucrose and cocaine exposure. We analyzed almost 400 brain structures and created a brain-wide map of specific, c-Fos-positive neurons engaged by these rewards. Acute but not prolonged sucrose exposure triggered a massive c-Fos expression throughout the brain. Cocaine exposure on the other hand potentiated c-Fos expression with prolonged use, engaging more structures than sucrose treatment. The functional connectivity analysis unraveled an increase in brain modularity after the initial exposure to both types of rewards. This modularity was increased after repeated cocaine, but not sucrose, intake. To check whether discrepancies between the processing of both types of rewards can be found on a cellular level, we further studied the nucleus accumbens, one of the most strongly activated brain structures by both sucrose and cocaine experience. We found a high overlap between natural and addictive rewards on the level of c-Fos expression. Electrophysiological measurements of cellular correlates of synaptic plasticity revealed that natural and addictive rewards alike induce the accumulation of silent synapses. These results strengthen the hypothesis that in the nucleus accumbens drugs of abuse cause maladaptive neuronal plasticity in the circuitry that typically processes natural rewards.

Mobility Coupled with Motivation Promotes Survival: The Evolution of Cognition as an Adaptive Strategy

Morphine plays a critical regulatory role in both simple and complex plant species. Dopamine is a critical chemical intermediate in the morphine biosynthetic pathway and may have served as a primordial agonist in developing catecholamine signaling pathways. While dopamine remains the preeminent catecholamine in invertebrate neural systems, epinephrine is the major product of catecholamine synthetic pathways in vertebrate species. Given that the enzymatic steps leading to the generation of morphine are similar to those constraining the evolutionary adaptation of the biosynthesis of catecholamines, we hypothesize that the emergence of these more advanced signaling pathways was based on conservation and selective "retrofitting" of pre-existing enzyme activities. This is consistent with observations that support the recruitment of enzymatically synthesized tetrahydrobiopterin (BH4), which is a cofactor for tyrosine hydroxylase, the enzyme responsible for dopamine production. BH4 is also an electron donor involved in the production of nitric oxide (NO). The links that coordinate BH4-mediated NO and catecholaminergic-mediated processes provide these systems with the capacity to regulate numerous downstream signaling pathways. We hypothesize that the evolution of catecholamine signaling pathways in animal species depends on the acquisition of a mobile lifestyle and motivationally driven feeding, sexual, and self-protective responses.

Persistent increase of accumbens cocaine ensemble excitability induced by IRK downregulation after withdrawal mediates the incubation of cocaine craving

The incubation phenomenon, cue-induced drug craving progressively increasing over prolonged withdrawal, accounts for persistent relapse, leading to a dilemma in the treatment of cocaine addiction. The role of neuronal ensembles activated by initial cocaine experience in the incubation phenomenon was unclear. In this study, with cocaine self-administration (SA) models, we found that neuronal ensembles in the nucleus accumbens shell (NAcSh) showed increasing activation induced by cue-induced drug-seeking after 30-day withdrawal. Inhibition or activation of NAcSh cocaine-ensembles suppressed or promoted craving for cocaine, demonstrating a critical role of NAcSh cocaine-ensembles in incubation for cocaine craving. NAcSh cocaine-ensembles showed a specific increase of membrane excitability and a decrease of inward rectifying channels Kir_2.1 currents after 30-day withdrawal. Overexpression of Kir_2.1 in NAcSh cocaine-ensembles restored neuronal membrane excitability and suppressed cue-induced drug-seeking after 30-day withdrawal. Expression of dominant-negative Kir_2.1 in NAcSh cocaine-ensembles enhanced neuronal membrane excitability and accelerated incubation of cocaine craving. Our results provide a cellular mechanism that the downregulation of Kir_2.1 functions in NAcSh cocaine-ensembles induced by prolonged withdrawal mediates the enhancement of ensemble membrane excitability, leading to incubation of cocaine craving.

Sleep-mediated regulation of reward circuits: implications in substance use disorders

Our modern society suffers from both pervasive sleep loss and substance abuse-what may be the indications for sleep on substance use disorders (SUDs), and could sleep contribute to the individual variations in SUDs? Decades of research in sleep as well as in motivated behaviors have laid the foundation for us to begin to answer these questions. This review is intended to critically summarize the circuit, cellular, and molecular mechanisms by which sleep influences reward function, and to reveal critical challenges for future studies. The review also suggests that improving sleep quality may serve as complementary therapeutics for treating SUDs, and that formulating sleep metrics may be useful for predicting individual susceptibility to SUDs and other reward-associated psychiatric diseases.

The translational genetics of ADHD and related phenotypes in model organisms

Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent neurodevelopmental disorder resulting from the interaction between genetic and environmental risk factors. It is well known that ADHD co-occurs frequently with other psychiatric disorders due, in part, to shared genetics factors. Although many studies have contributed to delineate the genetic landscape of psychiatric disorders, their specific molecular underpinnings are still not fully understood. The use of animal models can help us to understand the role of specific genes and environmental stimuli-induced epigenetic modifications in the pathogenesis of ADHD and its comorbidities. The aim of this review is to provide an overview on the functional work performed in rodents, zebrafish and fruit fly and highlight the generated insights into the biology of ADHD, with a special focus on genetics and epigenetics. We also describe the behavioral tests that are available to study ADHD-relevant phenotypes and comorbid traits in these models. Furthermore, we have searched for new models to study ADHD and its comorbidities, which can be useful to test potential pharmacological treatments.

Evaluation of microRNA let-7b-3p expression levels in methamphetamine abuse

OBJECTIVE

In this study, we aimed to identify a microRNA expression signature that could be used to distinguish methamphetamine from control samples. We also utilized the existing bioinformatics tools in order to predict the candidate microRNAs that could play potential key roles in regulating drug addiction-related genes.

METHODS

Methamphetamine samples from 21 ventral tegmental area and 21 nucleus accumbens samples and their control regions were obtained from the Council of Forensic Medicine (Istanbul). Quantitative analysis of let-7b-3p was studied using quantitative reverse transcription PCR. Statistical analysis was carried out using Student's t-test. The receiver operating characteristic curves were plotted with Statistical Package for the Social Sciences (SPSS 20.0).

RESULTS

Our quantitative reverse transcription PCR results revealed that let-7b-3p was significantly overexpressed in brain tissues of the methamphetamine-user group. Let-7b-3p had significant power to discriminate methamphetamine from control samples in the ventral tegmental area (AUC; 0.922) and nucleus accumbens (AUC; 0.899) regions.

CONCLUSION

We have shown for the first time in the literature the differential expression of let-7b-3p in samples from methamphetamine-addicted individuals. We suggest that let-7b-3p could be a powerful marker for the diagnosis of methamphetamine addiction. Our results showed that differentially expressed let-7b-3p in methamphetamine users could be used as a diagnostic and therapeutic marker.

The interaction of membrane estradiol receptors and metabotropic glutamate receptors in adaptive and maladaptive estradiol-mediated motivated behaviors in females

Estrogen receptors were initially identified as intracellular, ligand-regulated transcription factors that result in genomic change upon ligand binding. However, rapid estrogen receptor signaling initiated outside of the nucleus was also known to occur via mechanisms that were less clear. Recent studies indicate that these traditional receptors, estrogen receptor α and estrogen receptor β, can also be trafficked to act at the surface membrane. Signaling cascades from these membrane-bound estrogen receptors (mERs) can rapidly alter cellular excitability and gene expression, particularly through the phosphorylation of CREB. A principal mechanism of neuronal mER action has been shown to occur through glutamate-independent transactivation of metabotropic glutamate receptors (mGlu), which elicits multiple signaling outcomes. The interaction of mERs with mGlu has been shown to be important in many diverse functions in females, including driving motivated behaviors. Experimental evidence suggests that a large part of estradiol-induced neuroplasticity and motivated behaviors, both adaptive and maladaptive, occurs through estradiol-dependent mER activation of mGlu. Herein we will review signaling through estrogen receptors, both "classical" nuclear receptors and membrane-bound receptors, as well as estradiol signaling through mGlu. We will focus on how the interactions of these receptors and their downstream signaling cascades are involved in driving motivated behaviors in females, discussing a representative adaptive motivated behavior (reproduction) and maladaptive motivated behavior (addiction).

Medication overuse headache and substance use disorder: A comparison based on basic research and neuroimaging

It has yet to be determined whether medication overuse headache (MOH) is an independent disorder or a combination of primary headache and substance addiction. To further explore the causes of MOH, we compared MOH with substance use disorder (SUD) in terms of the brain regions involved to draw more targeted conclusions. In this review, we selected alcohol use disorder (AUD) as a representative SUD and compared MOH and AUD from two aspects of neuroimaging and basic research. We found that in neuroimaging studies, there were many overlaps between AUD and MOH in the reward circuit, but the extensive cerebral cortex damage in AUD was more serious than that in MOH. This difference was considered to reflect the sensitivity of the cortex structure to alcohol damage. In future research, we will focus on the central amygdala (CeA), prefrontal cortex (PFC), orbital-frontal cortex (OFC), hippocampus, and other brain regions for interventions, which may have unexpected benefits for addiction and headache symptoms in MOH patients.