Factors Affecting the Short-Term Prognosis of Alcohol Dependent Patients Undergoing Inpatient Detoxification

Alcohol-induced damage to the fimbria/fornix reduces hippocampal-prefrontal cortex connection during early abstinence

INTRODUCTION

Alcohol dependence is characterized by a gradual reduction in cognitive control and inflexibility to contingency changes. The neuroadaptations underlying this aberrant behavior are poorly understood. Using an animal model of alcohol use disorders (AUD) and complementing diffusion-weighted (dw)-MRI with quantitative immunohistochemistry and electrophysiological recordings, we provide causal evidence that chronic intermittent alcohol exposure affects the microstructural integrity of the fimbria/fornix, decreasing myelin basic protein content, and reducing the effective communication from the hippocampus (HC) to the prefrontal cortex (PFC). Using a simple quantitative neural network model, we show how disturbed HC-PFC communication may impede the extinction of maladaptive memories, decreasing flexibility. Finally, combining dw-MRI and psychometric data in AUD patients, we discovered an association between the magnitude of microstructural alteration in the fimbria/fornix and the reduction in cognitive flexibility. Overall, these findings highlight the vulnerability of the fimbria/fornix microstructure in AUD and its potential contribution to alcohol pathophysiology. Fimbria vulnerability to alcohol underlies hippocampal-prefrontal cortex dysfunction and correlates with cognitive impairment.

The effects of acamprosate on prefrontal cortical function are mimicked by CaCl2 and they are influenced by the history of alcohol exposure

Alcohol use disorder is associated with functional changes in the medial prefrontal cortex (mPFC), which include altered glutamatergic transmission and deficits in executive functions that contribute to relapse. Acamprosate (calcium-bis N-acetylhomotaurinate) reduces alcohol craving and relapse, effects that are thought to be mediated by acamprosate's ability to ameliorate alcohol-induced dysregulation of glutamatergic signaling. Treatment with acamprosate and its active moiety calcium (CaCl2) both improve deficits in cognitive flexibility in postdependent mice following chronic intermittent ethanol (CIE) exposure. Here, we show that mice that self-administered alcohol under goal-directed conditions (i.e., operant responding on a fixed-ratio schedule) also display similar deficits in cognitive flexibility and altered glutamatergic signaling in the mPFC, both of which were improved with acamprosate or CaCl2. However, under conditions shown to bias behavior towards habitual responding (operant self-administration after CIE exposure, or on a variable interval schedule), alcohol-induced changes to glutamatergic transmission were unaffected by either acamprosate or CaCl2 treatment. Together, these findings suggest that the variable effects of acamprosate on synaptic signaling may reflect a shift in mPFC networks related to the loss of behavioral control in habitual alcohol-seeking.

Psilocybin targets a common molecular mechanism for cognitive impairment and increased craving in alcoholism

Alcohol-dependent patients commonly show impairments in executive functions that facilitate craving and can lead to relapse. However, the molecular mechanisms leading to executive dysfunction in alcoholism are poorly understood, and new effective pharmacological treatments are desired. Here, using a bidirectional neuromodulation approach, we demonstrate a causal link between reduced prefrontal mGluR2 function and both impaired executive control and alcohol craving. A neuron-specific prefrontal mGluR2 knockdown in rats generated a phenotype of reduced cognitive flexibility and excessive alcohol seeking. Conversely, virally restoring prefrontal mGluR2 levels in alcohol-dependent rats rescued these pathological behaviors. In the search for a pharmacological intervention with high translational potential, psilocybin was capable of restoring mGluR2 expression and reducing relapse behavior. Last, we propose a FDG-PET biomarker strategy to identify mGluR2 treatment-responsive individuals. In conclusion, we identified a common molecular pathological mechanism for both executive dysfunction and alcohol craving and provided a personalized mGluR2 mechanism-based intervention strategy for medication development for alcoholism.

Patterns of Relational Framing in Executive Function: An Investigation of the Wisconsin Card Sorting Test

Executive function (EF) is a concept widely used to describe higher order cognitive functioning. However, the concept seems to lack a precise definition upon which even experts in the area can agree. Examples of existing definitions describe EF as capacities for independent self-serving behavior and aspects of working memory, planning and organizational skills. It has been argued that the definition of EF is too imprecise, in terms of informing effective interventions. To possibly understand the range of behaviors termed EF in a more workable way, we administered a well-known computerized test (the Wisconsin Card Sorting Test; WCST) of EF to a sample of normal functioning participants (n = 11). During administration, they were asked questions about their ways of thinking. Transcriptions of questions and answers were analyzed in search of common patterns, using a behavioral theory of language and cognition (relational frame theory; RFT). The analysis suggested that a specific relationship between deictic and temporal framing, on the one hand, and coordination and spatial framing, on the other, was in effect when participants performed well on the WCST. At critical time points during the test (i.e., when need for EF was arguably most acute), deictic and temporal framing dominated participants’ behavior, whereas coordination and spatial framing were used relatively less.

Reprogramming of mPFC transcriptome and function in alcohol dependence

Despite its limited immediate reinforcement value, alcohol has a potent ability to induce neuroadaptations that promote its incentive salience, escalation of voluntary alcohol intake and aversion-resistant alcohol seeking. A constellation of these traits, collectively called 'post-dependent', emerges following brain exposure to repeated cycles of intoxication and withdrawal. The medial prefrontal cortex (mPFC) and its subdivisions exert top-down regulation of approach and avoidance behaviors, including those that lead to alcohol intake. Here, we review an emerging literature which indicates that a reprogramming of mPFC function occurs with prolonged exposure of the brain to cycles of alcohol intoxication and withdrawal. This reprogramming results in molecular dysregulations that contribute to the post-dependent syndrome. Convergent evidence has identified neuroadaptations resulting in altered glutamatergic and BDNF-mediated signaling, and for these pathways, direct evidence for a mechanistic role has been obtained. Additional evidence points to a dysregulation of pathways involving calcium homeostasis and neurotransmitter release. Recent findings indicate that global DNA hypermethylation is a key factor in reprogramming the mPFC genome after a history of dependence. As one of the results of this epigenetic remodeling, several histone modifying epigenetic enzymes are repressed. Among these, PR-domain zinc-finger protein 2, a methyltransferase that selectively mono-methylates histone H3 at lysine 9 has been functionally validated to drive several of the molecular and behavioral long-term consequences of alcohol dependence. Information processing within the mPFC involves formation of dynamic neuronal networks, or functional ensembles that are shaped by transcriptional responses. The epigenetic dysregulations identified by our molecular studies are likely to alter this dynamic processing in multiple ways. In summary, epigenetic molecular switches in the mPFC appear to be turned on as alcoholism develops. Strategies to reverse these processes may offer targets for disease-modifying treatments.

Deficits in the extinction of ethanol-seeking behavior following chronic intermittent ethanol exposure are attenuated with positive allosteric modulation of mGlu5

Alcoholism is a chronic relapsing disorder characterized by periods of heavy alcohol consumption and unsuccessful attempts at abstinence. Relapse is one of the most problematic aspects in the treatment of alcoholism and is triggered by ethanol-associated cues. Extinction-based cue exposure therapies have proven ineffective in the treatment of alcoholism. However, positive allosteric modulation of mGlu5 with CDPPB enhances the extinction learning of alcohol-seeking behavior. The current study investigated the impact of chronic alcohol exposure on the extinction of ethanol-seeking behavior. Adult Wistar rats were trained to self-administer alcohol with a light/tone stimulus serving as the alcohol cue. After training, one group of rats was exposed to chronic intermittent ethanol (CIE) daily for a period of 2 weeks to induce ethanol dependence. Control rats were exposed to air for the same period of time. Both groups were then retrained to self-administer ethanol and subsequently tested for changes in extinction learning. CIE exposed rats consumed more ethanol compared to their pre-CIE levels and to control rats. During extinction training, CIE rats responded significantly more on the previously active lever and required more sessions to reach extinction criteria compared to control rats. Treatment with CDPPB facilitated extinction in control rats and attenuated the increased resistance to extinction in CIE-exposed rats. These results demonstrate that chronic ethanol exposure not only alters ethanol intake, but also the extinction of ethanol-seeking behaviors. The ability to attenuate deficits through modulation of mGlu5 provides a potential target for pharmacological manipulation that could ultimately reduce relapse in alcoholics.

Chronic alcohol disrupts dopamine receptor activity and the cognitive function of the medial prefrontal cortex

Dopamine (DA) receptors in the medial prefrontal cortex (mPFC) exert powerful effects on cognition by modulating the balance between excitatory and inhibitory neurotransmission. The present study examined the impact of chronic intermittent ethanol (CIE) exposure on cognitive function and DA receptor-mediated neurotransmission in the rat mPFC. Consistent with alterations in executive function in alcoholics, CIE-exposed rats exhibited deficits in behavioral flexibility in an operant set-shifting task. Since alterations in dopaminergic neurotransmission in the mPFC have been implicated in a number of behavioral disorders including addiction, studies were then performed in the adult acute slice preparation to examine changes in DA receptor function in the mPFC following CIE exposure. In slices obtained from control rats, DA receptor stimulation was observed to exert complex actions on neuronal firing and synaptic neurotransmission that were not only dependent upon the particular receptor subtype but also whether it was a pyramidal cell or a fast-spiking interneuron. In contrast to slices from control rats, there was a near complete loss of the modulatory actions of D2/D4 receptors on cell firing and neurotransmission in slices obtained immediately, 1 and 4 weeks after the last day of CIE exposure. This loss did not appear to be associated with changes in receptor expression. In contrast, CIE exposure did not alter D1 receptor function or mGluR1 modulation of firing. These studies are consistent with the suggestion that chronic alcohol exposure disrupts cognitive function at least in part through disruption of D2 and D4 receptor signaling in mPFC.

Neurocognitive performance, alcohol withdrawal, and effects of a combination of flumazenil and gabapentin in alcohol dependence

BACKGROUND

Among some alcohol-dependent individuals, early alcohol abstinence is marked by alcohol withdrawal (AW), a phenomenon mediated by GABA and glutamate signaling. We previously reported that a combination of 2 medications that affect GABA and glutamate tone, gabapentin and flumazenil, more effectively reduced drinking among individuals with higher pretreatment AW (Anton et al., 2009). This study evaluated whether this finding is related to changes in neurocognitive performance, which is also affected by cortical GABA and glutamate tone.

METHODS

Neurocognitive performance was assessed at baseline and twice during the first week of treatment among 60 alcohol-dependent participants in the previously published clinical trial.

RESULTS

AW was associated with poorer baseline performance on 4 of 8 measures, and individuals with higher baseline AW who received the gabapentin and flumazenil combination demonstrated greater improvement on a measure of response inhibition than those with lower AW or those who received a combination of placebos. Improvement in response inhibition during the first week and medication group interacted in their effect on subsequent drinking, such that improvement predicted greater abstinence only among individuals who received gabapentin and flumazenil. Improvement on other neurocognitive measures was neither differentially impacted by medication or baseline AW nor related to subsequent drinking.

CONCLUSIONS

Taken together, these data suggest that acute AW accounts for a small proportion of variance in neurocognitive performance, that gabapentin and flumazenil slightly improve response inhibition during early abstinence, and that such improvement may somewhat reduce later drinking. However, these medications may not affect other neurocognitive domains.

Long-term suppression of forebrain neurogenesis and loss of neuronal progenitor cells following prolonged alcohol dependence in rats

Alcohol dependence leads to persistent neuroadaptations, potentially related to structural plasticity. Previous work has shown that hippocampal neurogenesis is modulated by alcohol, but effects of chronic alcohol on neurogenesis in the forebrain subventricular zone (SVZ) have not been reported. Effects in this region may be relevant for the impairments in olfactory discrimination present in alcoholism. Here, we examined the effects of prolonged alcohol dependence on neurogenesis. Rats were sacrificed directly after 7 wk of intermittent alcohol vapour exposure, or 3, 7 or 21 d into abstinence. Proliferation was assessed using BrdU and Ki67 immunoreactivity, newly differentiated neurons (neurogenesis) as doublecortin-immunoreactivity (DCX-IR), and neural stem cells using the SOX2 marker. In the dentate gyrus, chronic dependence resulted in a pattern similar to that previously reported for acute alcohol exposure: proliferation and neurogenesis were suppressed by the end of exposure, rebounded on day 3 of abstinence, and returned to control levels by days 7 and 21. In the SVZ, proliferation was also suppressed at the end of alcohol exposure, followed by a proliferation burst 3 d into abstinence. However, in this area, there was a trend for reduced proliferation on days 7 and 21 of abstinence, and this was accompanied by significant suppression of DCX-IR, indicating a long-term suppression of forebrain neurogenesis. Finally, a decrease in the SOX2 stem cell marker was detected at days 7 and 21, suggesting long-term reduction of the SVZ stem cell pool. While suppression of hippocampal neurogenesis by alcohol dependence is transient, the suppression in the forebrain SVZ appears long-lasting.

Neuropsychological assessment of impulsive behavior in abstinent alcohol-dependent subjects

OBJECTIVE: Poor impulse control is thought to be one of the characteristics of alcohol addiction. The capacity to remain abstinent may be linked to cognitive bias related to three dimensions of impulsivity: motor, non-planning, and attentional impulsivity. The aim of this study was to evaluate the neuropsychological profile related to these impulsivity dimensions in alcohol-dependent patients within 15 -120 days of abstinence. METHOD: We compared 31 alcohol-dependent patients to 30 matched healthy controls regarding their performances on the Continuous Performance Task, the Iowa Gambling Test, and the Wisconsin Card Sorting Test, each of which is thought to tax primarily one of the three dimensions of impulsivity just outlined. RESULTS: When compared to controls, alcohol-dependent patients presented more commission errors on the Continuous Performance Task; made more disadvantageous choices on the Iowa Gambling Test; and made more perseverative errors on the Wisconsin Card Sorting Test. There was no significant correlation between performance on these tests and the length of abstinence. CONCLUSIONS: These results suggest that deficits related to motor, non-planning and attentional components of impulsivity exist in alcohol-dependent patients, in the period immediately after acute alcohol withdrawal. These results may help guide interventions designed to prevent the risk of relapse in alcohol-abstinent patients.