Persistent Alterations of Accumbal Cholinergic Interneurons and Cognitive Dysfunction after Adolescent Intermittent Ethanol Exposure

Cholinergic mu-opioid receptor deletion alters reward preference and aversion-resistance

The endogenous opioid system has been implicated in alcohol consumption and preference in both humans and animals. The mu opioid receptor (MOR) is expressed on multiple cells in the striatum, however little is known about the contributions of specific MOR populations to alcohol drinking behaviors. The current study used mice with a genetic deletion of MOR in cholinergic cells (ChAT-Cre/Oprm1fl/fl) to examine the role of MORs expressed in cholinergic interneurons (CINs) in home cage self-administration paradigms. Male and female ChAT-Cre/Oprm1fl/fl mice were generated and heterozygous Cre+ (knockout) and Cre- (control) mice were tested for alcohol consumption in two drinking paradigms: limited access "Drinking in the Dark" and intermittent access. Quinine was added to the drinking bottles in the DID experiment to test aversion-resistant, "compulsive" drinking. Nicotine and sucrose drinking were also assessed so comparisons could be made with other rewarding substances. Cholinergic MOR deletion did not influence consumption or preference for ethanol (EtOH) in either drinking task. Differences were observed in aversion-resistance in males with Cre + mice tolerating lower concentrations of quinine than Cre-. In contrast to EtOH, preference for nicotine was reduced following cholinergic MOR deletion while sucrose consumption and preference was increased in Cre+ (vs. Cre-) females. Locomotor activity was also greater in females following the deletion. These results suggest that cholinergic MORs participate in preference for rewarding substances. Further, while they are not required for consumption of alcohol alone, cholinergic MORs may influence the tendency to drink despite negative consequences.

Adolescent alcohol exposure persistently alters orbitofrontal cortical encoding of Pavlovian conditional stimulus components in female rats

Exposure to alcohol during adolescence impacts cortical and limbic brain regions undergoing maturation. In rodent models, long-term effects on behavior and neurophysiology have been described after adolescent intermittent ethanol (AIE), especially in males. We hypothesized that AIE in female rats increases conditional approach to a reward-predictive cue and corresponding neuronal activity in the orbitofrontal cortex (OFC) and nucleus accumbens (NAc). We evaluated behavior and neuronal firing after AIE (5 g/kg intragastric) or water (CON) in adult female rats. Both AIE and CON groups expressed a ST phenotype, and AIE marginally increased sign-tracking (ST) and decreased goal-tracking (GT) metrics. NAc neurons exhibited phasic firing patterns to the conditional stimulus (CS), with no differences between groups. In contrast, neuronal firing in the OFC of AIE animals was greater at CS onset and offset than in CON animals. During reward omission, OFC responses to CS offset normalized to CON levels, but enhanced OFC firing to CS onset persisted in AIE. We suggest that the enhanced OFC neural activity observed in AIE rats to the CS could contribute to behavioral inflexibility. Ultimately, AIE persistently impacts the neurocircuitry of reward-motivated behavior in female rats.

Alcohol Consumption During Adolescence Alters the Cognitive Function in Adult Male Mice by Persistently Increasing Levels of DUSP6

Binge alcohol drinking during adolescence has long-term effects on the adult brain that alter brain structure and behaviors, but the underlying mechanisms remain poorly understood. Extracellular signal-regulated kinase (ERK) is involved in the synaptic plasticity and pathological brain injury by regulating the expression of cyclic adenosine monophosphate response element binding protein (CREB) and brain-derived neurotrophic factor (BDNF). Dual-specificity phosphatase 6 (DUSP6) is a critical effector that dephosphorylates ERK1/2 to control the basal tone, amplitude, and duration of ERK signaling. To explore DUSP6 as a regulator of ERK signaling in the mPFC and its impact on long-term effects of alcohol, a male mouse model of adolescent intermittent alcohol (AIA) exposure was established. Behavioral experiments showed that AIA did not affect anxiety-like behavior or sociability in adulthood, but significantly damaged new object recognition and social recognition memory. Molecular studies further found that AIA reduced the levels of pERK-pCREB-BDNF-PSD95/NR2A involved in synaptic plasticity, while DUSP6 was significantly increased. Intra-mPFC infusion of AAV-DUSP6-shRNA restored the dendritic spine density and postsynaptic density thickness by reversing the level of p-ERK and its downstream molecular expression, and ultimately repaired adult cognitive impairment caused by chronic alcohol exposure during adolescence. These findings indicate that AIA exposure inhibits ERK-CREB-BDNF-PSD95/NR2A by increasing DUSP6 in the mPFC in adulthood that may be associated with long-lasting cognitive deficits.

Cholinergic mu-opioid receptor deletion alters reward preference and aversion-resistance

Heavy alcohol use and binge drinking are important contributors to alcohol use disorder (AUD). The endogenous opioid system has been implicated in alcohol consumption and preference in both humans and animals. The mu opioid receptor (MOR) is expressed on multiple cells in the striatum, however little is known about the contributions of specific MOR populations to alcohol drinking behaviors. The current study used mice with a genetic deletion of MOR in cholinergic cells (ChAT-Cre/Oprm1fl/fl) to examine the role of MORs expressed in cholinergic interneurons (CINs) in home cage self-administration paradigms. Male and female ChAT-Cre/Oprm1fl/fl mice were generated and heterozygous Cre+ (knockout) and Cre- (control) mice were tested for alcohol and nicotine consumption. In Experiment 1, binge-like and quinine-resistant drinking was tested using 15% ethanol (EtOH) in a two-bottle, limited-access Drinking in the Dark paradigm. Experiment 2 involved a six-week intermittent access paradigm in which mice received 20% EtOH, nicotine, and then a combination of the two drugs. Experiment 3 assessed locomotor activity, sucrose preference, and quinine sensitivity. Deleting MORs in cholinergic cells did not alter consumption of EtOH in Experiment 1 or 2. In Experiment 1, the MOR deletion resulted in greater consumption of quinine-adulterated EtOH in male Cre+ mice (vs. Cre-). In Experiment 2, Cre+ mice demonstrated a significantly lower preference for nicotine but did not differ from Cre- mice in nicotine or nicotine + EtOH consumption. Overall fluid consumption was also heightened in the Cre+ mice. In Experiment 3, Cre+ females were found to have greater locomotor activity and preference for sucrose vs. Cre- mice. These data suggest that cholinergic MORs are not required for EtOH, drinking behaviors but may contribute to aversion resistant EtOH drinking in a sex-dependent manner.

Modulation of the p75NTR during adolescent alcohol exposure prevents cholinergic neuronal atrophy and associated acetylcholine activity and behavioral dysfunction

Binge alcohol consumption during adolescence produces lasting deficits in learning and memory, while also increasing the susceptibility to substance use disorders. The adolescent intermittent ethanol (AIE) rodent model mimics human adolescent binge drinking and has identified the Nucleus Basalis Magnocellularis (NbM) as a key site of pathology. The NbM is a critical regulator of prefrontal cortical (PFC) cholinergic function and attention. The cholinergic phenotype is controlled pro/mature neurotrophin receptor activation. We sought to determine if p75NTR activity contributes to the loss of cholinergic phenotype in AIE by using a p75NTR modulator (LM11A-31) to inhibit prodegenerative signaling during ethanol exposure. Male and female rats underwent 5g/kg ethanol (AIE) or water (CON) exposure following 2-day-on 2-day-off cycles from PND 25-57. A subset of these groups also received a protective dose of LM11A-31 (50mg/kg) during adolescence. Rats were trained on a sustained attention task (SAT) while recording activity with a fluorescent acetylcholine indicator (AChGRAB 3.0). AIE produced learning deficits on the SAT, which were spared with LM11A-31. In addition, mPFC ACh activity was blunted by AIE, which LM11A-31 corrected. Investigation of NbM ChAT+ and TrkA+ neuronal expression found that AIE led to a reduction of ChAT+TrkA+ neurons, which again LM11A-31 protected. Taken together these findings demonstrate the p75NTR activity during AIE treatment is a key regulator of cholinergic degeneration.

Chronic intermittent ethanol exposure during adolescence produces sex- and age-dependent changes in anxiety and cognition without changes in microglia reactivity late in life

Binge-like ethanol exposure during adolescence has been shown to produce long lasting effects in animal models including anxiety-like behavior that can last into young adulthood and impairments in cognition that can last throughout most of the lifespan. However, little research has investigated if binge-like ethanol exposure during adolescence produces persistent anxiety-like behavior and concomitantly impairs cognition late in life. Furthermore, few studies have investigated such behavioral effects in both female and male rats over the lifespan. Finally, it is yet to be determined if binge-like ethanol exposure during adolescence alters microglia activation in relevant brain regions late in life. In the present study female and male adolescent rats were exposed to either 3.0 or 5.0 g/kg ethanol, or water control, in a chronic intermittent pattern before being tested in the elevated plus maze and open field task over the next ∼18 months. Animals were then trained in a spatial reference task via the Morris water maze before having their behavioral flexibility tested. Finally, brains were removed, sectioned and presumptive microglia activation determined using autoradiography for [3H]PK11195 binding. Males, but not females, displayed an anxiety-like phenotype initially following the chronic intermittent ethanol exposure paradigm which resolved in adulthood. Further, males but not females had altered spatial reference learning and impaired behavioral flexibility late in life. Conversely, [3H]PK11195 binding was significantly elevated in females compared to males late in life and the level of microglia activation interacted as a function of sex and brain regions, but there was no long-term outcome related to adolescent alcohol exposure. These data further confirm that binge-like ethanol exposure during adolescence produces alterations in behavior that can last throughout the lifespan. In addition, the data suggest that microglia activation late in life is not exacerbated by prior binge-like ethanol exposure during adolescence but the expression is sex- and brain region-dependent across the lifespan.

Cognitive Alterations in Addictive Disorders: A Translational Approach

The cognitive decline in people with substance use disorders is well known and can be found during both the dependence and drug abstinence phases. At the clinical level, cognitive decline impairs the response to addiction treatment and increases dropout rates. It can be irreversible, even after the end of drug abuse consumption. Improving our understanding of the molecular and cellular alterations associated with cognitive decline could be essential to developing specific therapeutic strategies for its treatment. Developing animal models to simulate drug abuse-induced learning and memory alterations is critical to continue exploring this clinical situation. The main aim of this review is to summarize the most recent evidence on cognitive impairment and the associated biological markers in patients addicted to some of the most consumed drugs of abuse and in animal models simulating this clinical situation. The available information suggests the need to develop more studies to further explore the molecular alterations associated with cognitive impairment, with the ultimate goal of developing new potential therapeutic strategies.

Adolescent intermittent ethanol exposure reduces astrocyte-synaptic proximity in the adult medial prefrontal cortex in rats: Reversal by gabapentin

Alcohol consumption in adolescence causes multiple acute negative changes in neural and behavioral function that persist well into adulthood and possibly throughout life. The medial prefrontal cortex (mPFC) and dorsal hippocampus are critical for executive function and memory and are especially vulnerable to adolescent ethanol exposure. We have reported that astrocytes, particularly in the mPFC, change both in morphology and synaptic proximity during adolescence. Moreover, adolescent intermittent ethanol (AIE) exposure produces enduring effects on both astrocyte function and synaptic proximity in the adult hippocampal formation, and the latter effect was reversed by the clinically used agent gabapentin (Neurontin), an anticonvulsant and analgesic that is an inhibitor of the VGCC α2δ1 subunit. These findings underscore the importance of investigating AIE effects on astrocytes in the mPFC, a region that undergoes marked changes in structure and connectivity during adolescence. Using astrocyte-specific viral labeling and immunohistochemistry, mPFC astrocytic morphology and colocalization with AMPA-(α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) glutamate receptor 1 (GluA1), an AMPA receptor subunit and established neuronal marker of excitatory synapses, were assessed to quantify the proximity of astrocyte processes with glutamatergic synaptic puncta. AIE exposure significantly reduced astrocyte-synaptic proximity in adulthood, an effect that was reversed by sub-chronic gabapentin treatment in adulthood. There was no effect of AIE on astrocytic glutamate homeostasis machinery or neuronal synaptic proteins in the mPFC. These findings indicate a possible glial-neuronal mechanism underlying the effects of AIE on frontal lobe-mediated behaviors and suggest a specific therapeutic approach for the amelioration of those effects.

Impact of adolescent intermittent ethanol exposure in male and female rats on social drinking and neuropeptide gene expression

BACKGROUND

Alcohol use during adolescence can alter maturational changes that occur in brain regions associated with social and emotional responding. Our previous studies have shown that adult male, but not female rats demonstrate social anxiety-like alterations and enhanced sensitivity to ethanol-induced social facilitation following adolescent intermittent ethanol exposure (AIE). These consequences of AIE may influence adult social drinking in a sex-specific manner.

METHODS

To test the effects of AIE on social drinking, male and female Sprague-Dawley rats exposed to water or ethanol (0 or 4 g/kg, intragastrically, every other day, between postnatal day [P] 25 and 45) were tested as adults (P72-83) in a social drinking paradigm (30-minute access to a 10% ethanol solution in supersac or supersac alone in groups of three same-sex littermates across two 4-day cycles separated by 4 days off). Social behavior was assessed during the last drinking session, along with assessment of oxytocin (OXT), oxytocin receptor (OXTR), vasopressin (AVP), and vasopressin receptors 1a and 1b (AVPR1a, AVPR1b) in the hypothalamus and lateral septum.

RESULTS

Males exposed to AIE consumed more ethanol than water-exposed controls during the second drinking cycle, whereas AIE did not affect supersac intake in males. AIE-exposed females consumed less ethanol and more supersac than water-exposed controls. Water-exposed females drinking ethanol showed more social investigation and significantly higher hypothalamic OXTR, AVP, and AVPR1b gene expression than their counterparts ingesting supersac and AIE females drinking ethanol. In males, hypothalamic AVPR1b gene expression was affected by drinking solution, with significantly higher expression evident in males drinking ethanol than those consuming supersac.

CONCLUSIONS

Collectively, these findings provide new evidence regarding sex-specific effects of AIE on social drinking and suggest that the hypothalamic OXT and AVP systems are implicated in the effects of ingested ethanol on social behavior in a sex- and adolescent-exposure-dependent manner.

Impact of adolescent intermittent ethanol exposure on interneurons and their surrounding perineuronal nets in adulthood

BACKGROUND

Binge alcohol exposure during adolescence results in long-lasting alterations in the brain and behavior. For example, adolescent intermittent ethanol (AIE) exposure in rodents results in long-term loss of functional connectivity among prefrontal cortex (PFC) and striatal regions as well as a variety of neurochemical, molecular, and epigenetic alterations. Interneurons in the PFC and striatum play critical roles in behavioral flexibility and functional connectivity. For example, parvalbumin (PV) interneurons are known to contribute to neural synchrony and cholinergic interneurons contribute to strategy selection. Furthermore, extracellular perineuronal nets (PNNs) that surround some interneurons, particularly PV+ interneurons, further regulate cellular plasticity. The effect of AIE exposure on the expression of these markers within the PFC is not well understood.

METHODS

The present study tested the hypothesis that AIE exposure reduces the expression of PV+ and choline acetyltransferase (ChAT)+ interneurons in the adult PFC and striatum and increases the related expression of PNNs (marked by binding of Wisteria floribunda agglutinin lectin) in adulthood. Male rats were exposed to AIE (5 g/kg/day, 2-days-on/2-days-off, i.e., P25 to P54) or water (CON), and brain tissue was harvested in adulthood (>P80). Immunohistochemistry and co-immunofluorescence were used to assess the expression of ChAT, PV, and PNNs within the adult PFC and striatum following AIE exposure.

RESULTS

ChAT and PV interneuron densities in the striatum and PFC were unchanged after AIE exposure. However, PNN density in the PFC of AIE-exposed rats was greater than in CON rats. Moreover, significantly more PV neurons were surrounded by PNNs in AIE-exposed subjects than controls in both PFC subregions assessed: orbitofrontal cortex (CON = 34%; AIE = 40%) and medial PFC (CON = 10%; AIE = 14%).

CONCLUSIONS

These findings indicate that, following AIE exposure, PV interneuron expression in the adult PFC and striatum is unaltered, while PNNs surrounding these neurons are increased. This increase in PNNs may restrict the plasticity of the ensheathed neurons, thereby contributing to impaired microcircuitry in frontostriatal connectivity and related behavioral impairments.

The Effect of Chronic Alcohol on Cognitive Decline: Do Variations in Methodology Impact Study Outcome? An Overview of Research From the Past 5 Years

Excessive alcohol use is often associated with accelerated cognitive decline, and extensive research using animal models of human alcohol consumption has been conducted into potential mechanisms for this relationship. Within this literature there is considerable variability in the types of models used. For example, alcohol administration style (voluntary/forced), length and schedule of exposure and abstinence period are often substantially different between studies. In this review, we evaluate recent research into alcohol-induced cognitive decline according to methodology of alcohol access, as well as cognitive behavioral task employed. Our aim was to query whether the nature and severity of deficits observed may be impacted by the schedule and type of alcohol administration. We furthermore examined whether there is any apparent relationship between the amount of alcohol consumed and the severity of the deficit, as well as the potential impact of abstinence length, and other factors such as age of administration, and sex of subject. Over the past five years, researchers have overwhelmingly used non-voluntary methods of intake, however deficits are still found where intake is voluntary. Magnitude of intake and type of task seem most closely related to the likelihood of producing a deficit, however even this did not follow a consistent pattern. We highlight the importance of using systematic and clear reporting styles to facilitate consistency across the literature in this regard. We hope that this analysis will provide important insights into how experimental protocols might influence findings, and how different patterns of consumption are more or less likely to produce an addiction-vulnerable cognitive phenotype in animal models.

Altered Cortico-Subcortical Network After Adolescent Alcohol Exposure Mediates Behavioral Deficits in Flexible Decision-Making

Behavioral flexibility, the ability to modify behavior according to changing conditions, is essential to optimize decision-making. Deficits in behavioral flexibility that persist into adulthood are one consequence of adolescent alcohol exposure, and another is decreased functional connectivity in brain structures involved in decision-making; however, a link between these two outcomes has not been established. We assessed effects of adolescent alcohol and sex on both Pavlovian and instrumental behaviors and resting-state functional connectivity MRI in adult animals to determine associations between behavioral flexibility and resting-state functional connectivity. Alcohol exposure impaired attentional set reversals and decreased functional connectivity among cortical and subcortical regions-of-interest that underlie flexible behavior. Moreover, mediation analyses indicated that adolescent alcohol-induced reductions in functional connectivity within a subnetwork of affected brain regions statistically mediated errors committed during reversal learning. These results provide a novel link between persistent reductions in brain functional connectivity and deficits in behavioral flexibility resulting from adolescent alcohol exposure.

Adolescent Ethanol Exposure Alters Cholinergic Function and Apical Dendritic Branching Within the Orbital Frontal Cortex

During adolescence, heavy binge-like ethanol consumption can lead to frontocortical structural and functional impairments. These impairments are likely driven by adolescence being a critical time point for maturation of brain regions associated with higher-order cognitive functioning. Rodent models of heavy binge-like ethanol exposure show consistent disruptions to the typical development of the prefrontal cortex (PFC). All deep cortical layers receive cholinergic projections that originate from the Nucleus basalis of Meynert (NbM) complex. These cholinergic projections are highly involved in learning, memory, and attention. Adolescent intermittent ethanol exposure (AIE) induces cholinergic dysfunction as a result of an epigenetic suppression of the genes that drive the cholinergic phenotype. The current study used a model of AIE to assess structural and functional changes to the frontal cortex and NbM following binge-like ethanol exposure in adolescence. Western blot analysis revealed long-term disruptions of the cholinergic circuit following AIE: choline acetyltransferase (ChAT) was suppressed in the NbM and vesicular acetylcholine transporter (VAChT) was suppressed in the orbitofrontal cortex (OFC). In vivo microdialysis for acetylcholine efflux during a spatial memory task determined changes in cholinergic modulation within the PFC following AIE. However, AIE spared performance on the spatial memory task and on an operant reversal task. In a second study, Golgi-Cox staining determined that AIE increased apical dendritic complexity in the OFC, with sex influencing whether the increase in branching occurred near or away from the soma. Spine density or maturity was not affected, likely compensating for a disruption in neurotransmitter function following AIE.

Increased Endogenous GDNF in Mice Protects Against Age-Related Decline in Neuronal Cholinergic Markers

Gradual decline in cholinergic transmission and cognitive function occurs during normal aging, whereas pathological loss of cholinergic function is a hallmark of different types of dementia, including Alzheimer’s disease (AD), Lewy body dementia (LBD), and Parkinson’s disease dementia (PDD). Glial cell line-derived neurotrophic factor (GDNF) is known to modulate and enhance the dopamine system. However, how endogenous GDNF influences brain cholinergic transmission has remained elusive. In this study, we explored the effect of a twofold increase in endogenous GDNF (Gdnf hypermorphic mice, Gdnf^wt/hyper) on cholinergic markers and cognitive function upon aging. We found that Gdnf^wt/hyper mice resisted an overall age-associated decline in the cholinergic index observed in the brain of Gdnf^wt/wt animals. Biochemical analysis revealed that the level of nerve growth factor (NGF), which is important for survival and function of central cholinergic neurons, was significantly increased in several brain areas of old Gdnf^wt/hyper mice. Analysis of expression of genes involved in cholinergic transmission in the cortex and striatum confirmed modulation of cholinergic pathways by GDNF upon aging. In line with these findings, Gdnf^wt/hyper mice did not undergo an age-related decline in cognitive function in the Y-maze test, as observed in the wild type littermates. Our results identify endogenous GDNF as a potential modulator of cholinergic transmission and call for future studies on endogenous GDNF function in neurodegenerative disorders characterized by cognitive impairments, including AD, LBD, and PDD.

The role of sex in the persistent effects of adolescent alcohol exposure on behavior and neurobiology in rodents

Alcohol drinking is often initiated during adolescence, and this frequently escalates to binge drinking. As adolescence is also a period of dynamic neurodevelopment, preclinical evidence has highlighted that some of the consequences of binge drinking can be long lasting with deficits persisting into adulthood in a variety of cognitive-behavioral tasks. However, while the majority of preclinical work to date has been performed in male rodents, the rapid increase in binge drinking in adolescent female humans has re-emphasized the importance of addressing alcohol effects in the context of sex as a biological variable. Here we review several of the consequences of adolescent ethanol exposure in light of sex as a critical biological variable. While some alcohol-induced outcomes, such as non-social approach/avoidance behavior and sleep disruption, are generally consistent across sex, others are variable across sex, such as alcohol drinking, sensitivity to ethanol, social anxiety-like behavior, and induction of proinflammatory markers.

Relationship between voluntary ethanol drinking and approach-avoidance biases in the face of motivational conflict: novel sex-dependent associations in rats

RATIONALE

Aberrant approach-avoidance conflict processing may contribute to compulsive seeking that characterizes addiction. Exploration of the relationship between drugs of abuse and approach-avoidance behavior remains limited, especially with ethanol.

OBJECTIVES

To investigate the effects of voluntary ethanol consumption on approach-avoidance conflict behavior and to examine the potential approach/avoidance bias to predict drinking in male and female rats.

METHODS

Long-Evans rats consumed ethanol for 5 weeks under the intermittent access two-bottle choice (IA2BC) paradigm. Approach-avoidance tendencies were assessed before and after IA2BC drinking using a previously established cued approach-avoidance conflict maze task and the elevated plus maze (EPM).

RESULTS

Female rats displayed higher consumption of and preference for ethanol than males. In the conflict task, males showed greater approach bias towards cues predicting conflict than females. In females only, a median split and regression analysis of cued-conflict preference scores revealed that the more conflict-avoidant group displayed higher intake and preference for ethanol in the first few weeks of drinking. In both sexes, ethanol drinking did not affect cued-conflict preference, but ethanol exposure led to increased time spent in the central hub in the males only. Finally, anxiety levels in EPM predicted subsequent onset of ethanol drinking in males only.

CONCLUSIONS

Our results highlight sex and individual differences in both drinking and approach-avoidance bias in the face of cued conflict and further suggest that cued-conflict preference should be examined as a potential predictor of ethanol drinking. Ethanol exposure may also affect the timing of decision-making in the face of conflict.

Reaction Time and Visual Memory in Connection with Alcohol Use in Schizophrenia and Schizoaffective Disorder

The purpose of this study was to explore the association between cognition and hazardous drinking and alcohol use disorder in schizophrenia and schizoaffective disorder. Cognition is more or less compromised in schizophrenia, and schizoaffective disorder and alcohol use might aggravate this phenomenon. The study population included 3362 individuals from Finland with diagnoses of schizophrenia or schizoaffective disorder. Hazardous drinking was screened with the AUDIT-C (Alcohol Use Disorders Identification Test for Consumption) screening tool. Alcohol use disorder (AUD) diagnoses were obtained from national registrar data. Participants performed two computerized tasks from the Cambridge Automated Neuropsychological Test Battery (CANTAB) on a tablet computer: The Five-Choice Serial Reaction Time Task (5-CSRTT) or the reaction time (RT) test and the Paired Associative Learning (PAL) test. The association between alcohol use and the RT and PAL tests was analyzed with log-linear regression and logistic regression, respectively. After adjustment for age, education, housing status, and the age at which the respondents had their first psychotic episodes, hazardous drinking was associated with a lower median RT in females and less variable RT in males, while AUD was associated with a poorer PAL test performance in terms of the total errors adjusted scores (TEASs) in females. Our findings of positive associations between alcohol and cognition in schizophrenia and schizoaffective disorder are unique.

Alcohol Consumption during Adulthood Does Not Impair Later Go/No-Go Reversal Learning in Male Rats

Reversal learning tasks are used to model flexible decision-making in laboratory animals, and exposure to drugs of abuse can cause long-term impairments in reversal learning. However, the long-term effects of alcohol on reversal learning have varied. We evaluated whether six weeks of voluntary alcohol consumption through chronic intermittent alcohol access (elevated by food restriction) in adult male rats would impair rats in a go/no-go reversal learning task when tested at an interval beyond acute withdrawal. In our go/no-go task, rats were reinforced for pressing one lever or withholding from pressing another lever, and the identities of the two levers were switched twice (once rats reached an accuracy criterion). We found no evidence that prior alcohol consumption altered discrimination or reversal learning in our task. This replicates previous patterns from our laboratory that higher alcohol consumption in food-restricted rats did not impair discrimination or reversal learning in a different go/no-go task and that alcohol consumption in free-fed adolescent/early adult rats did not impair go/no-go discrimination or reversal learning in the same task. It is unclear whether this represents an insensitivity of this task to alcohol exposure generally or whether an alcohol exposure procedure that leads to higher blood ethanol concentration (BEC) levels would impair learning. More research is needed to investigate these possibilities.

Rats exposed to intermittent ethanol during late adolescence exhibit enhanced habitual behavior following reward devaluation

The brain undergoes substantial maturation during adolescence, and repeated exposure to ethanol at this time has been shown to result in long-lasting behavioral and neural consequences. During the broad period of adolescence, different neuronal populations and circuits are refined between early and late adolescence, suggesting the possibility that ethanol exposure at these differing times may lead to differential outcomes. The goal of the current study was to evaluate the impact of adolescent intermittent ethanol (AIE) during early and late adolescence on the formation of goal-directed and habitual behavior in adulthood. Male and female Sprague-Dawley rats were exposed to ethanol via intragastric gavage (4.0 g/kg, 25% v/v) every other day from postnatal day (P) 25-45 or P45-65, considered early and late adolescence, respectively. In adulthood (~P70 early or ~ P90 late), rats were gradually food-restricted and began operant training on a fixed ratio 1 schedule. Rats were then transitioned onto random interval schedules and eventually underwent a sensory-specific satiation procedure as a model of reward devaluation. Few differences as a result of adolescent ethanol exposure were found during instrumental training. Following reward devaluation, rats exposed to water and ethanol during early adolescence exhibited reductions in lever pressing, suggestive of a goal-directed response pattern. In contrast, late AIE males and females demonstrated persistent responding following both devalued and non-devalued trials, findings representative of a habitual behavior pattern. The shifts from goal-directed to habitual behavior noted only following late AIE contribute to the growing literature identifying specific behavioral consequences as a result of ethanol exposure during distinct developmental periods within adolescence. More work is needed to determine whether the greater habit formation following late AIE is also associated with elevated habitual ethanol consumption.

Differential alterations of insular cortex excitability after adolescent or adult chronic intermittent ethanol administration in male rats

Adolescent alcohol drinking, primarily in the form of binge-drinking episodes, is a serious public health concern. Binge drinking in laboratory animals has been modeled by a procedure involving chronic intermittent ethanol (CIE) administration, as compared with chronic intermittent water (CIW). The prolonged effects of adolescent binge alcohol exposure in adults, such as high risk of developing alcohol use disorder, are severe but available treatments in the clinic are limited. One reason is the lack of sufficient understanding about the associated neuronal alterations. The involvement of the insular cortex, particularly the anterior agranular insula (AAI), has emerged as a critical region to explain neuronal mechanisms of substance abuse. This study was designed to evaluate the functional output of the AAI by measuring the intrinsic excitability of pyramidal neurons from male rats 2 or 21 days after adolescent or adult CIE treatment. Decreases in intrinsic excitability in AAI pyramidal neurons were detected 21 days, relative to 2 days, after adolescent CIE. Interestingly, the decreased intrinsic excitability in the AAI pyramidal neurons was observed 2 days after adult CIE, compared to adult CIW, but no difference was found between 2 versus 21 days after adult CIE. These data indicate that, although the AAI is influenced within a limited period after adult but not adolescent CIE, neuronal alterations in AAI are affected during the prolonged period of withdrawal from adolescent but not adult CIE. This may explain the prolonged vulnerability to mental disorders of subjects with an alcohol binge history during their adolescent stage.

Aberrations in Incentive Learning and Responding to Heroin in Male Rats After Adolescent or Adult Chronic Binge-Like Alcohol Exposure

BACKGROUND AND PURPOSE

Binge drinking is a serious problem among adolescents and young adults despite its adverse consequences on the brain and behavior. One area that remains poorly understood concerns the impact of chronic intermittent ethanol (CIE) exposure on incentive learning.

METHODS

Here, we examined the effects of CIE exposure during different developmental stages on conditioned approach and conditioned reward learning in rats experiencing acute or protracted withdrawal from alcohol. Two or 21 days after adolescent or adult CIE exposure, male rats were exposed to pairings of a light stimulus (CS) and food pellets for 3 consecutive daily sessions (30 CS-food pellet pairings per session). This was followed by conditioned approach testing measuring responses (food trough head entries) to the CS-only presentations and by conditioned reward testing measuring responses on a lever producing the CS and on another producing a tone. We then measured behavioral sensitization to repeated injections of heroin (2 mg/kg/d for 9 days).

RESULTS

Adolescent and adult alcohol-treated rats showed significantly impaired conditioned reward learning regardless of withdrawal period (acute or prolonged). We found no evidence of changes to conditioned approach learning after adolescent or adult exposure to CIE. Finally, in addition to producing long-term impairments in incentive learning, CIE exposure enhanced locomotor activity in response to heroin and had no effect on behavioral sensitization to heroin regardless of age and withdrawal period.

CONCLUSIONS

Our work sets a framework for identifying CIE-induced alterations in incentive learning and inducing susceptibility to subsequent opioid effects.

Adolescent drug exposure: A review of evidence for the development of persistent changes in brain function

Over the past decade, many studies have indicated that adolescence is a critical period of brain development and maturation. The refinement and maturation of the central nervous system over this prolonged period, however, makes the adolescent brain highly susceptible to perturbations from acute and chronic drug exposure. Here we review the preclinical literature addressing the long-term consequences of adolescent exposure to common recreational drugs and drugs-of-abuse. These studies on adolescent exposure to alcohol, nicotine, opioids, cannabinoids and psychostimulant drugs, such as cocaine and amphetamine, reveal a variety of long-lasting behavioral and neurobiological consequences. These agents can affect development of the prefrontal cortex and mesolimbic dopamine pathways and modify the reward systems, socio-emotional processing and cognition. Other consequences include disruption in working memory, anxiety disorders and an increased risk of subsequent drug abuse in adult life. Although preventive and control policies are a valuable approach to reduce the detrimental effects of drugs-of-abuse on the adolescent brain, a more profound understanding of their neurobiological impact can lead to improved strategies for the treatment and attenuation of the detrimental neuropsychiatric sequelae.

Chronic voluntary alcohol consumption causes persistent cognitive deficits and cortical cell loss in a rodent model

Chronic alcohol use is associated with cognitive decline that impedes behavioral change during rehabilitation. Despite this, addiction therapy does not address cognitive deficits, and there is poor understanding regarding the mechanisms that underlie this decline. We established a rodent model of chronic voluntary alcohol use to measure ensuing cognitive effects and underlying pathology. Rats had intermittent access to alcohol or an isocaloric solution in their home cage under voluntary 2-bottle choice conditions. In Experiments 1 and 2 cognition was assessed using operant touchscreen chambers. We examined performance in a visual discrimination and reversal task (Experiment 1), and a 5-choice serial reaction time task (Experiment 2). For Experiment 3, rats were perfused immediately after cessation of alcohol access period, and volume, cell density and microglial populations were assessed in the prefrontal cortex and striatum. Volume was assessed using the Cavalieri probe, while cell and microglial counts were estimated using unbiased stereology with an optical fractionator. Alcohol-exposed and control rats showed comparable acquisition of pairwise discrimination; however, performance was impaired when contingencies were reversed indicating reduced behavioral flexibility. When tested in a 5-choice serial reaction time task alcohol-exposed rats showed increased compulsivity and increased attentional bias towards a reward associated cue. Consistent with these changes, we observed decreased cell density in the prefrontal cortex. These findings confirm a detrimental effect of chronic alcohol and establish a model of alcohol-induced cognitive decline following long-term voluntary intake that may be used for future intervention studies.

Adolescent neurodevelopment and substance use: Receptor expression and behavioral consequences

Adolescence is the transitional period between childhood and adulthood, during which extensive brain development occurs. Since this period also overlaps with the initiation of drug use, it is important to consider how substance use during this time might produce long-term neurobiological alterations, especially against the backdrop of developmental changes in neurotransmission. Alcohol, cannabis, nicotine, and opioids all produce marked changes in the expression and function of the neurotransmitter and receptor systems with which they interact. These acute and chronic alterations also contribute to behavioral consequences ranging from increased addiction risk to cognitive or neuropsychiatric behavioral dysfunctions. The current review provides an in-depth overview and update of the developmental changes in neurotransmission during adolescence, as well as the impact of drug exposure during this neurodevelopmental window. While most of these factors have been studied in animal models, which are the focus of this review, future longitudinal studies in humans that assess neural function and behavior will help to confirm pre-clinical findings. Furthermore, the neural changes induced by each drug should also be considered in the context of other contributing factors, such as sex. Further understanding of these consequences can help in the identification of novel approaches for preventing and reversing the neurobiological effects of adolescent substance use.

Aging with alcohol-related brain damage: Critical brain circuits associated with cognitive dysfunction

Alcoholism is associated with brain damage and impaired cognitive functioning. The relative contributions of different etiological factors, such as alcohol, thiamine deficiency and age vulnerability, to the development of alcohol-related neuropathology and cognitive impairment are still poorly understood. One reason for this quandary is that both alcohol toxicity and thiamine deficiency produce brain damage and cognitive problems that can be modulated by age at exposure, aging following alcohol toxicity or thiamine deficiency, and aging during chronic alcohol exposure. Pre-clinical models of alcohol-related brain damage (ARBD) have elucidated some of the contributions of ethanol toxicity and thiamine deficiency to neuroinflammation, neuronal loss and functional deficits. However, the critical variable of age at the time of exposure or long-term aging with ARBD has been relatively ignored. Acute thiamine deficiency created a massive increase in neuroimmune genes and proteins within the thalamus and significant increases within the hippocampus and frontal cortex. Chronic ethanol treatment throughout adulthood produced very minor fluctuations in neuroimmune genes, regardless of brain region. Intermittent "binge-type" ethanol during the adolescent period established an intermediate neuroinflammatory response in the hippocampus and frontal cortex, that can persist into adulthood. Chronic excessive drinking throughout adulthood, adolescent intermittent ethanol exposure, and thiamine deficiency all led to a loss of the cholinergic neuronal phenotype within the basal forebrain, reduced hippocampal neurogenesis, and alterations in the frontal cortex. Only thiamine deficiency results in gross pathological lesions of the thalamus. The behavioral impairment following these types of treatments is hierarchical: Thiamine deficiency produces the greatest impairment of hippocampal- and prefrontal-dependent behaviors, chronic ethanol drinking ensues mild impairments on both types of tasks and adolescent intermittent ethanol exposure leads to impairments on frontocortical tasks, with sparing on most hippocampal-dependent tasks. However, our preliminary data suggest that as rodents age following adolescent intermittent ethanol exposure, hippocampal functional deficits began to emerge. A necessary requirement for the advancement of understanding the neural consequences of alcoholism is a more comprehensive assessment and understanding of how excessive alcohol drinking at different development periods (adolescence, early adulthood, middle-aged and aged) influences the trajectory of the aging process, including pathological aging and disease.

Adolescent intermittent ethanol impairs behavioral flexibility in a rat foraging task in adulthood

Alcohol exposure is linked to behavioral flexibility deficits in humans, but it is unclear when the critical exposure occurred or if alcohol exposure alone is sufficient to produce behavior deficits. Increasing evidence shows that binge levels of alcohol during adolescence are particularly harmful to the brain, producing physiological and behavioral effects that can persist into adulthood. The present study determined whether adolescent intermittent ethanol (AIE) in rats impaired action selection in a discriminative stimulus task using a foraging response. Rats were exposed to ethanol during adolescence (5 g/kg/day, IG, 2-days-on/2-days-off, postnatal day 25-54). In adulthood, they learned to dig for food reward buried in one of two media, cued with one of two odors. AIE and control rats both learned to discriminate between olfactory cues, but AIE rats were impaired when reversing that learned association (first intra-dimensional reversal). However, AIE rats were faster to reinstate the original odor discrimination rule (second reversal), suggesting perseverative behavior. Next, the reward location was cued by digging media rather than odor. Both groups learned this extra-dimensional shift; however, control rats were slower to reach criterion. These findings are consistent with studies of people with substance abuse disorder, who learn new stimulus-response associations similarly to, or better than, control subjects, but perseverate when attempting to replace a well-learned association. These data suggest that adolescent binge-alcohol exposure contributes to behavioral flexibility deficits observed in adulthood.