Dissociable effects of kappa-opioid receptor activation on impulsive phenotypes in wistar rats

Dynorphin/kappa opioid receptor system regulation on amygdaloid circuitry: Implications for neuropsychiatric disorders

Amygdaloid circuits are involved in a variety of emotional and motivation-related behaviors and are impacted by stress. The amygdala expresses several neuromodulatory systems, including opioid peptides and their receptors. The Dynorphin (Dyn)/kappa opioid receptor (KOR) system has been implicated in the processing of emotional and stress-related information and is expressed in brain areas involved in stress and motivation. Dysregulation of the Dyn/KOR system has also been implicated in various neuropsychiatric disorders. However, there is limited information about the role of the Dyn/KOR system in regulating amygdala circuitry. Here, we review the literature on the (1) basic anatomy of the amygdala, (2) functional regulation of synaptic transmission by the Dyn/KOR system, (3) anatomical architecture and function of the Dyn/KOR system in the amygdala, (4) regulation of amygdala-dependent behaviors by the Dyn/KOR system, and (5) future directions for the field. Future work investigating how the Dyn/KOR system shapes a wide range of amygdala-related behaviors will be required to increase our understanding of underlying circuitry modulation by the Dyn/KOR system. We anticipate that continued focus on the amygdala Dyn/KOR system will also elucidate novel ways to target the Dyn/KOR system to treat neuropsychiatric disorders.

Release of endogenous dynorphin opioids in the prefrontal cortex disrupts cognition

Following repeated opioid use, some dependent individuals experience persistent cognitive deficits that contribute to relapse of drug-taking behaviors, and one component of this response may be mediated by the endogenous dynorphin/kappa opioid system in neocortex. In C57BL/6 male mice, we find that acute morphine withdrawal evokes dynorphin release in the medial prefrontal cortex (PFC) and disrupts cognitive function by activation of local kappa opioid receptors (KORs). Immunohistochemical analyses using a phospho-KOR antibody confirmed that both withdrawal-induced and optically evoked dynorphin release activated KOR in PFC. Using a genetically encoded sensor based on inert KOR (kLight1.2a), we revealed the in vivo dynamics of endogenous dynorphin release in the PFC. Local activation of KOR in PFC produced multi-phasic disruptions of memory processing in an operant-delayed alternation behavioral task, which manifest as reductions in response number and accuracy during early and late phases of an operant session. Local pretreatment in PFC with the selective KOR antagonist norbinaltorphimine (norBNI) blocked the disruptive effect of systemic KOR activation during both early and late phases of the session. The early, but not late phase disruption was blocked by viral excision of PFC KORs, suggesting an anatomically dissociable contribution of pre- and postsynaptic KORs. Naloxone-precipitated withdrawal in morphine-dependent mice or optical stimulation of pdyn^Cre neurons using Channelrhodopsin-2 disrupted delayed alternation performance, and the dynorphin-induced effect was blocked by local norBNI. Our findings describe a mechanism for control of cortical function during opioid dependence and suggest that KOR antagonism could promote abstinence.

The Neuropharmacology of Impulsive Behaviour, an Update

Neuropharmacological interventions in preclinical translational models of impulsivity have tremendously contributed to a better understanding of the neurochemistry and neural basis of impulsive behaviour. In this regard, much progress has been made over the last years, also due to the introduction of novel techniques in behavioural neuroscience such as optogenetics and chemogenetics. In this chapter, we will provide an update of how the behavioural pharmacology field has progressed and built upon existing data since an earlier review we wrote in 2008. To this aim, we will first give a brief background on preclinical translational models of impulsivity. Next, recent interesting evidence of monoaminergic modulation of impulsivity will be highlighted with a focus on the neurotransmitters dopamine and noradrenaline. Finally, we will close the chapter by discussing some novel directions and drug leads in the neuropharmacological modulation of impulsivity.

Association of variants of prodynorphin promoter 68-bp repeats in caucasians with opioid dependence diagnosis: Effect on age trajectory of heroin use

The dynorphin/kappa opioid receptor (Dyn/KOR) system is involved in reward processing and dysphoria/anhedonia. Exposure to mu-opioid receptor agonists such as heroin increases expression of the prodynorphin gene (PDYN) in the brain. In this study in a Caucasian cohort, we examined the association of the functional PDYN 68-bp repeat polymorphism with opioid use disorders. In this case-control study, 554 subjects with Caucasian ancestry (142 healthy controls, 153 opioid-exposed, but never opioid dependent, NOD, and 259 with an opioid dependence diagnosis, OD) were examined for association of the PDYN 68-bp repeats with the diagnosis of opioid dependence (DSM-IV criteria), with a dimensional measure of heroin exposure (KMSK scale), and age trajectory parameters of heroin use (age of heroin first use, and age of onset of heaviest use). The PDYN 68-bp repeat genotype (classified as: "short-short" [SS], "long-long" [LL], and "short-long" [SL], based on the number of repeats) was not associated with categorical opioid dependence diagnoses. However, the LL genotype was associated with later age of first heroin use than the SS + SL genotype (19 versus 18 years; p < 0.01). This was also confirmed by a significant positive correlation between the number of repeats and the age of first use of heroin, in volunteers with OD (Spearman r = 0.16; p = 0.01). This suggests that the functional PDYN 68-bp repeat genotype is associated with the age of first use of heroin in Caucasians diagnosed with opioid dependence.

Impact of Substance Use Disorder Pharmacotherapy on Executive Function: A Narrative Review

Substance use disorders are chronic, relapsing, and harmful conditions characterized by executive dysfunction. While there are currently no approved pharmacotherapy options for stimulant and cannabis use disorders, there are several evidence-based options available to help reduce symptoms during detoxification and aid long-term cessation for those with tobacco, alcohol and opioid use disorders. While these medication options have shown clinical efficacy, less is known regarding their potential to enhance executive function. This narrative review aims to provide a brief overview of research that has investigated whether commonly used pharmacotherapies for these substance use disorders (nicotine, bupropion, varenicline, disulfiram, acamprosate, nalmefene, naltrexone, methadone, buprenorphine, and lofexidine) effect three core executive function components (working memory, inhibitory control and cognitive flexibility). While pharmacotherapy-induced enhancement of executive function may improve cessation outcomes in dependent populations, there are limited and inconsistent findings regarding the effects of these medications on executive function. We discuss possible reasons for the mixed findings and suggest some future avenues of work that may enhance the understanding of addiction pharmacotherapy and cognitive training interventions and lead to improved patient outcomes.

Effect of chronic alcohol vapor exposure on reinstatement of alcohol seeking induced by U50,488

Alcohol dependence and stress are associated with relapse to alcohol during abstinence, but the underlying mechanisms are poorly understood. Kappa opioid receptors (KOR) are involved in alcohol reward and in the effects of stress. Previously, in non-dependent rats, we showed that KOR in the bed nucleus of the stria terminalis (BNST) mediate reinstatement of alcohol seeking induced by the selective KOR agonist U50,488. Here, we determine the effects of chronic, intermittent exposure to alcohol vapor on U50,488-induced reinstatement of alcohol seeking. We also study brain mechanisms involved using the neuronal activity marker Fos and phosphorylated p38 MAPK (p-p38), an intracellular messenger implicated in the effects of KOR stimulation. We trained male Long-Evans rats to self-administer alcohol (12% w/v) and exposed them to alcohol vapor (14 h vapor/10 h air) daily for 24 d or to the control condition, extinguished alcohol-reinforced responding and determined the dose response for U50,488-induced reinstatement. We then determined the effects of vapor exposure on U50,488-induced Fos and p-p38 expression. Vapor-exposed rats were more sensitive to U50,488-induced reinstatement. U50,488 increased Fos expression in brain areas involved in stress-induced relapse, and Fos activation in the ventral BNST was greater in vapor exposed rats. Vapor exposed rats had increased basal p-p38 expression in the dorsal BNST, LC and NTS. Our findings suggest that changes in the neuronal responses to KOR stimulation in the ventral BNST may be involved in the increased sensitivity to U50,488 accompanying dependence.

Kappa opioid receptors mediate yohimbine-induced increases in impulsivity in the 5-choice serial reaction time task

Dynorphin (DYN), and its receptor, the kappa opioid receptor (KOR) are involved in drug seeking and relapse but the mechanisms are poorly understood. One hypothesis is that DYN/KOR activation promotes drug seeking through increased impulsivity, because many stimuli that induce DYN release increase impulsivity. Here, we systematically compare the effects of drugs that activate DYN/KOR on performance on the 5-choice serial reaction time task (5-CSRTT), a test of sustained attention and impulsivity. In Experiment 1, we determined the effects of U50,488 (0, 2.5, 5 mg/kg), yohimbine (0, 1.25, 2.5 mg/kg), and nicotine (0, 0.15, 0.3 mg/kg) on 5-CSRTT performance. In Experiment 2, we determined the effects of alcohol (0, 0.5, 1.0, 1.5 g/kg) on 5-CSRTT performance before and after voluntary, intermittent alcohol exposure. In Experiment 3, we determined the potential role of KOR in the pro-impulsive effects of yohimbine (1.25 mg/kg) and nicotine (0.3 mg/kg) by the prior administration of the KOR antagonist nor-BNI (10 mg/kg). Premature responding, the primary measure of impulsivity, was reduced by U50,488 and alcohol, but these drugs had a general suppressive effect. Yohimbine and nicotine increased premature responding. Yohimbine-, but not nicotine-induced increases in premature responding were blocked by nor-BNI, suggesting that impulsivity induced by yohimbine is KOR dependent. This may suggests a potential role for KOR-mediated increases in impulsivity in yohimbine-induced reinstatement.

Opioid modulation of cognitive impairment in depression

The failure of traditional antidepressant medications to adequately target cognitive impairment is associated with poor treatment response, increased risk of relapse, and greater lifetime disability. Opioid receptor antagonists are currently under development as novel therapeutics for major depressive disorder (MDD) and other stress-related illnesses. Although it is known that dysregulation of the endogenous opioid system is observed in patients diagnosed with MDD, the impact of opioidergic neurotransmission on cognitive impairment has not been systematically evaluated. Here we review the literature indicating that opioid manipulations can alter cognitive functions in humans. Furthermore, we detail the preclinical studies that demonstrate the ability of mu-opioid receptor and kappa-opioid receptor ligands to modulate several cognitive processes. Specifically, this review focuses on domains within higher order cognitive processing, including attention and executive functioning, which can differentiate cognitive processes influenced by motivational state.

Maladaptive behavioral regulation in alcohol dependence: Role of kappa-opioid receptors in the bed nucleus of the stria terminalis

There is an important emerging role for the endogenous opioid dynorphin (DYN) and the kappa-opioid receptor (KOR) in the treatment of alcohol dependence. Evidence suggests that the DYN/KOR system in the bed nucleus of the stria terminalis (BNST) contributes to maladaptive behavioral regulation during withdrawal in alcohol dependence. The current experiments were designed to assess dysregulation of the BNST DYN/KOR system by evaluating alcohol dependence-induced changes in DYN/KOR gene expression (Pdyn and Oprk1, respectively), and the sensitivity of alcohol self-administration, negative affective-like behavior and physiological withdrawal to intra-BNST KOR antagonism during acute withdrawal. Wistar rats trained to self-administer alcohol, or not trained, were subjected to an alcohol dependence induction procedure (14 h alcohol vapor/10 h air) or air-exposure. BNST micropunches from air- and vapor-exposed animals were analyzed using RT-qPCR to quantify dependence-induced changes in Pdyn and Oprk1 mRNA expression. In addition, vapor- and air-exposed groups received an intra-BNST infusion of a KOR antagonist or vehicle prior to measurement of alcohol self-administration. A separate cohort of vapor-exposed rats was assessed for physiological withdrawal and negative affective-like behavior signs following intra-BNST KOR antagonism. During acute withdrawal, following alcohol dependence induction, there was an upregulation in Oprk1 mRNA expression in alcohol self-administering animals, but not non-alcohol self-administering animals, that confirmed dysregulation of the KOR/DYN system within the BNST. Furthermore, intra-BNST KOR antagonism attenuated escalated alcohol self-administration and negative affective-like behavior during acute withdrawal without reliably impacting physiological symptoms of withdrawal. The results confirm KOR system dysregulation in the BNST in alcohol dependence, illustrating the therapeutic potential of targeting the KOR to treat alcohol dependence.

κ-Opioid Receptor Activation in Dopamine Neurons Disrupts Behavioral Inhibition

The dynorphin/κ-opioid receptor (KOR) system has been previously implicated in the regulation of cognition, but the neural circuitry and molecular mechanisms underlying KOR-mediated cognitive disruption are unknown. Here, we used an operational test of cognition involving timing and behavioral inhibition and found that systemic KOR activation impairs performance of male and female C57BL/6 mice in the differential reinforcement of low response rate (DRL) task. Systemic KOR antagonism also blocked stress-induced disruptions of DRL performance. KOR activation increased 'bursts' of incorrect responses in the DRL task and increased marble burying, suggesting that the observed disruptions in DRL performance may be attributed to KOR-induced increases in compulsive behavior. Local inactivation of KOR by injection of the long-acting antagonist nor-BNI in the ventral tegmental area (VTA), but not the infralimbic prefrontal cortex (PFC) or dorsal raphe nucleus (DRN), prevented disruption of DRL performance caused by systemic KOR activation. Cre-dependent genetic excision of KOR from dopaminergic, but not serotonergic neurons, also blocked KOR-mediated disruption of DRL performance. At the molecular level, we found that these disruptive effects did not require arrestin-dependent signaling, because neither global deletion of G-protein receptor kinase 3 (GRK3) nor cell-specific deletion of GRK3/arrestin-dependent p38α MAPK from dopamine neurons blocked KOR-mediated DRL disruptions. We then showed that nalfurafine, a clinically available G-biased KOR agonist, could also produce DRL disruptions. Together, these studies demonstrate that KOR activation in VTA dopamine neurons disrupts behavioral inhibition in a GRK3/arrestin-independent manner and suggests that KOR antagonists could be beneficial for decreasing stress-induced compulsive behaviors.

Nalmefene for the management of alcohol dependence: review on its pharmacology, mechanism of action and meta-analysis on its clinical efficacy

Nalmefene, a mu- and delta-opioid receptor (MOR, DOR) antagonist and a partial kappa-opioid receptor (KOR) agonist, is approved in the European Union and other countries for the reduction of alcohol consumption in alcohol dependent patients with a high drinking risk level according to WHO ("target population"). This review presents an overview of nalmefene׳s pharmacology, its mechanisms of action and a meta-analysis on its efficacy in reducing alcohol consumption. The review was based on a systematic search of the literature. Random effects meta-analyses were performed on published and unpublished trials directed at drinking reduction using the changes in heavy drinking days (HDDs) and daily total alcohol consumption (TAC) from baseline to the primary endpoint. For each included study and each dose, Hedges' g was used as an unbiased estimator of the standardised mean differences between nalmefene and placebo. Preclinical data suggests that nalmefene counters alcohol-induced dysregulations of the MOR/endorphine and the KOR/dynorphin system. Evidence further suggests that reduced alcohol consumption is an effective treatment strategy that appeals to patients not ready for abstinence. Finally, meta-analyses confirmed the efficacy of 20mg nalmefene for reducing HDDs in the ITT population (Hedge׳s g=-0.20; 95% CI -0.30 to -0.09) and the target population (Hedge׳s g=-0.33; 95% CI -0.48 to -0.18). Similar results were seen for TAC. Several meta-analyses, including this new meta-analysis, support nalmefene׳s efficacy in reducing alcohol consumption. In conclusion, because it does not require abstinence, this treatment has the potential to motivate more patients for treatment and thus helps to address a major public health concern.

Does environmental exposure to the greenhouse gas, N2O, contribute to etiological factors in neurodevelopmental disorders? A mini-review of the evidence

BACKGROUND

Neurodevelopmental disorders are increasing in prevalence worldwide. Previous work suggests that exposure to the environmental air pollutant and greenhouse gas - nitrous oxide (N₂O) - may be an etiological factor in neurodevelopmental disorders through the targeting of several neural correlates.

METHODOLOGY

While a number of recent systematic reviews have addressed the role of general anesthesia in the surgical setting and neurodevelopmental outcomes, a narrative mini-review was conducted to first define and characterize the relevant variables (i.e., N₂O, attention-deficit hyperactivity disorder [ADHD] and autism spectrum disorders [ASD]) and their potential interactions into a coherent, hypothesis-generating work. The narrative mini-review merges basic principles in environmental science, anesthesiology, and psychiatry to more fully develop the novel hypotheses that neurodevelopmental impairment found in conditions like ADHD and ASD may be due to exposure to the increasing air pollutant, N₂O.

RESULTS

The results of the present mini-review indicate that exposure to N₂O, even at non-toxic doses, may modulate central neurotransmission and target many neural substrates directly implicated in neurodevelopmental disorders, including the glutamatergic, opioidergic, cholinergic, and dopaminergic systems. Epidemiological studies also indicate that early and repeated exposure to general anesthesia, including N₂O, may contribute to later adverse neurodevelopmental outcomes in children.

CONCLUSIONS

The current evidence and subsequent hypotheses suggest that a renewed interest be taken in the toxicological assessment of environmental N₂O exposure using validated biomarkers and psychiatric endpoints. Given the relevance of N₂O as a greenhouse gas, societies may also wish to engage in a more robust monitoring and reporting of N₂O levels in the environment for climactic benefit as well.

Lifespan Changes in the Countermanding Performance of Young and Middle Aged Adult Rats

Inhibitory control can be investigated with the countermanding task, which requires subjects to make a response to a go signal and cancel that response when a stop signal is presented occasionally. Adult humans performing the countermanding task typically exhibit impaired response time (RT), stop signal response time (SSRT) and response accuracy as they get older, but little change in post-error slowing. Rodent models of the countermanding paradigm have been developed recently, yet none have directly examined age-related changes in performance throughout the lifespan. Male Wistar rats (N = 16) were trained to respond to a visual stimulus (go signal) by pressing a lever directly below an illuminated light for food reward, but to countermand the lever press subsequent to a tone (stop signal) that was presented occasionally (25% of trials) at a variable delay. Subjects were tested in 1 h sessions at approximately 7 and 12 months of age with intermittent training in between. Rats demonstrated longer go trial RT, a higher proportion of go trial errors and performed less total trials at 12, compared to 7 months of age. Consistent SSRT and post-error slowing were observed for rats at both ages. These results suggest that the countermanding performance of rats does vary throughout the lifespan, in a manner similar to humans, suggesting that rodents may provide a suitable model for behavioral impairment related to normal aging. These findings also highlight the importance of indicating the age at which rodents are tested in countermanding investigations.

Prefrontal Cortical Kappa Opioid Receptors Attenuate Responses to Amygdala Inputs

Kappa opioid receptors (KORs) have been implicated in anxiety and stress, conditions that involve activation of projections from the basolateral amygdala (BLA) to the medial prefrontal cortex (mPFC). Although KORs have been studied in several brain regions, their role on mPFC physiology and on BLA projections to the mPFC remains unclear. Here, we explored whether KORs modify synaptic inputs from the BLA to the mPFC using in vivo electrophysiological recordings with electrical and optogenetic stimulation. Systemic administration of the KOR agonist U69,593 inhibited BLA-evoked synaptic responses in the mPFC without altering hippocampus-evoked responses. Intra-mPFC U69,593 inhibited electrical and optogenetic BLA-evoked synaptic responses, an effect blocked by the KOR antagonist nor-BNI. Bilateral intra-mPFC injection of the KOR antagonist nor-BNI increased center time in the open field test, suggesting an anxiolytic effect. The data demonstrate that mPFC KORs negatively regulate glutamatergic synaptic transmission in the BLA-mPFC pathway and anxiety-like behavior. These findings provide a framework whereby KOR signaling during stress and anxiety can regulate the flow of emotional state information from the BLA to the mPFC.

Maturational alterations in constitutive activity of medial prefrontal cortex kappa-opioid receptors in Wistar rats

Opioid receptors can display spontaneous agonist-independent G-protein signaling (basal signaling/constitutive activity). While constitutive κ-opioid receptor (KOR) activity has been documented in vitro, it remains unknown if KORs are constitutively active in native systems. Using [(35) S] guanosine 5'-O-[gamma-thio] triphosphate coupling assay that measures receptor functional state, we identified the presence of medial prefrontal cortex KOR constitutive activity in young rats that declined with age. Furthermore, basal signaling showed an age-related decline and was insensitive to neutral opioid antagonist challenge. Collectively, the present data are first to demonstrate age-dependent alterations in the medial prefrontal cortex KOR constitutive activity in rats and changes in the constitutive activity of KORs can differentially impact KOR ligand efficacy. These data provide novel insights into the functional properties of the KOR system and warrant further consideration of KOR constitutive activity in normal and pathophysiological behavior. Opioid receptors exhibit agonist-independent constitutive activity; however, kappa-opioid receptor (KOR) constitutive activity has not been demonstrated in native systems. Our results confirm KOR constitutive activity in the medial prefrontal cortex (mPFC) that declines with age. With the ability to presynaptically inhibit multiple neurotransmitter systems in the mPFC, maturational or patho-logical alterations in constitutive activity could disrupt corticofugal glutamatergic pyramidal projection neurons mediating executive function. Regulation of KOR constitutive activity could serve as a therapeutic target to treat compromised executive function.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Convergent pharmacological mechanisms in impulsivity and addiction: insights from rodent models

Research over the last two decades has widely demonstrated that impulsivity, in its various forms, is antecedent to the development of drug addiction and an important behavioural trait underlying the inability of addicts to refrain from continued drug use. Impulsivity describes a variety of rapidly and prematurely expressed behaviours that span several domains from impaired response inhibition to an intolerance of delayed rewards, and is a core symptom of attention deficit hyperactivity disorder (ADHD) and other brain disorders. Various theories have been advanced to explain how impulsivity interacts with addiction both causally and as a consequence of chronic drug abuse; these acknowledge the strong overlaps in neural circuitry and mechanisms between impulsivity and addiction and the seemingly paradoxical treatment of ADHD with stimulant drugs with high abuse potential. Recent years have witnessed unprecedented progress in the elucidation of pharmacological mechanisms underpinning impulsivity. Collectively, this work has significantly improved the prospect for new therapies in ADHD as well as our understanding of the neural mechanisms underlying the shift from recreational drug use to addiction. In this review, we consider the extent to which pharmacological interventions that target impulsive behaviour are also effective in animal models of addiction. We highlight several promising examples of convergence based on empirical findings in rodent-based studies.

The role of the opioid system in alcohol dependence

The role of the brain opioid system in alcohol dependence has been the subject of much research for over 25 years. This review explores the evidence: firstly describing the opioid receptors in terms of their individual subtypes, neuroanatomy, neurophysiology and ligands; secondly, summarising emerging data from specific neurochemical, behavioural and neuroimaging studies, explaining the characteristics of addiction with a focus on alcohol dependence and connecting the opioid system with alcohol dependence; and finally reviewing the known literature regarding opioid antagonists in clinical use for alcohol dependence. Further interrogation of how modulation of the opioid system, via use of MOP (mu), DOP (delta) and KOP (kappa) agents, restores the balance of a dysregulated system in alcohol dependence should increase our insight into this disease process and therefore guide better methods for understanding and treating alcohol dependence in the future.

Upregulated dynorphin opioid peptides mediate alcohol-induced learning and memory impairment

The dynorphin opioid peptides control glutamate neurotransmission in the hippocampus. Alcohol-induced dysregulation of this circuit may lead to impairments in spatial learning and memory. This study examines whether changes in the hippocampal dynorphin and glutamate systems are related, and contribute to impairment of spatial learning and memory in a rat model of cognitive deficit associated with alcohol binge drinking. Hippocampal dynorphins (radioimmunoassay) and glutamate (in vivo microdialysis) were analyzed in Wistar rats exposed to repeated moderate-dose ethanol bouts that impair spatial learning and memory in the Water Maze Task (WMT). The highly selective, long-acting κ-opioid receptor (KOR) antagonist nor-binaltorphimine (nor-BNI) was administered systemically or into the hippocampal CA3 region to test a role of dynorphins in alcohol-induced dysregulations in glutamate neurotransmission and behavior in the WMT. The ethanol treatment impaired learning and memory, upregulated dynorphins and increased glutamate overflow in the CA3 region. Administration of nor-BNI after cessation of ethanol exposure reversed ethanol-induced changes in glutamate neurotransmission in animals exposed to ethanol and normalized their performance in the WMT. The findings suggest that impairments of spatial learning and memory by binge-like ethanol exposure are mediated through the KOR activation by upregulated dynorphins resulting in elevation in glutamate levels. Selective KOR antagonists may correct alcohol-induced pathological processes, thus representing a novel pharmacotherapy for treating of ethanol-related cognitive deficits.