Choi, Doo‐Sup

Abstract The external globus pallidus (GPe) has traditionally been viewed as a relay nucleus within the basal ganglia (BG), but accumulating evidence indicates a more dynamic role in reinforcement learning (RL). One key characteristic of GPe activity—transient pauses in high-frequency discharge (HFD) neurons—is preserved across species, yet its potential implications in RL remains unclear. Here, we developed a neurophysiologically grounded computational model to investigate the origin and role of GPe pauses in RL. Our model successfully replicated a range of empirical observations, including pause dynamics during learning and cue-related activity modulation. We demonstrated that the GPe-subthalamic nucleus (STN) circuit functions analogously to a denoising autoencoder, modulating baseline excitability in downstream BG circuits and that GPe pauses emerge as circuit-level consequences of strong, convergent inhibition from the GPe to STN. Simulations and in vivo recordings revealed that the activity of GPe-STN projecting neurons increases following sudden environmental changes, promoting adaptive exploration by disrupting action value contrast. Intriguingly, this same configuration impairs performance with extended training, suggesting that habitual behavior may benefit from weakened GPe-to-STN projections. These findings provide a unifying framework for understanding GPe pause dynamics and highlight circuit-level distinctions supporting the balance between flexibility and proficiency in RL.

AbstractBackgroundWorkforce engagement can provide structure, income, feelings of accomplishment, and personal contacts, growing an individual's recovery capital (RC). Employed individuals are also more likely to complete addiction treatment. We sought to investigate whether changes in employment status from alcohol treatment admission to discharge correlated with changes in alcohol use frequency over those time points.MethodsThe Treatment Episode Dataset—Discharges (2017–2021) provided the data. Employment status (full‐time, part‐time, unemployed, and not in labor force) and alcohol use frequency (daily use, some use, and no use in past month) were assessed at treatment admission and discharge. Changes in alcohol use frequency during treatment were recorded as Reduction or No reduction. Logistic regression using reduced alcohol use frequency as the dependent variable included employment status at admission and discharge separately. A second analysis included employment status at both admission and discharge and their interaction term. An adjusted model included all covariates (race, ethnicity, age, education, and referral source), with its results being used to derive the marginal probabilities of reduced alcohol use frequency.ResultsThere were 856,085 alcohol treatment admissions over the 5 years, with 221,724 (25.9%) first admissions. Transitioning from not in the labor force or unemployed to full‐time saw the largest percentage of encounters decreasing alcohol use frequency: 71.9% (95% CI: 70.0–73.7) and 69.3% (95% CI: 68.1–70.5), respectively. Those remaining unemployed had the lowest reduction at 26.7% (95% CI: 26.3–27.1), with a sample reduction of 42.7% (95% CI: 42.5–42.9) overall. Far more people (60.4%) completed treatment within the Reduction group than in the No reduction group (30.2%).ConclusionsFindings suggest that improving employment status may be relevant for reducing alcohol use frequency. This aligns with past work showing overall improved health outcomes with lower unemployment levels. Incorporating vocational training and workforce engagement activities into outpatient treatment may help augment traditional approaches to improve an individual's RC.

Abstract The dorsomedial striatum (DMS) is primarily recognized for regulating goal-directed reward-seeking behaviors, while the dorsolateral striatum (DLS) is predominantly associated with movement and habitual behaviors. In this study, we sought to investigate two pathways, direct medium spiny neuron (dMSN) and indirect medium spiny neuron (iMSN) in the two dorsal striatal subregions (DMS and DLS) in ethanol-seeking and drinking behaviors. Here, we selectively ablated iMSN DMS→GPe and iMSN DLS→GPe and trained mice to exhibit goal-directed and habitual reward-seeking behaviors using random ratio (RR) and random interval (RI) operant conditioning, respectively. We found that partial ablation of iMSN DLS→GPe exhibited increased resilience to bitter-tasting ethanol solution when subjected to quinine adulterated reward in operant conditioning paradigms, suggesting compulsive-like seeking behavior. Consistently, in a separate cohort of mice, we found that the iMSN DLS→GPe ablated mice show higher preference and consumption of quinine adulterated ethanol solution than control mice in two-bottle choice continuous access drinking, with increasing quinine concentration and exhibit more compulsive-like behavior. On the other hand, ablation of iMSN DMS→GPe resulted in insensitivity to satiety-based reward devaluation in RR-trained mice, consistent with a shift toward habitual behavior but no change in compulsive ethanol-seeking and drinking behavior. Together, our findings demonstrate that DLS iMSN function is essential in inhibiting compulsive-like behavior.

Abstract Behavioral flexibility allows animals to adjust actions to changing environments. While the basal ganglia are critical for adaptation, the specific role of the external globus pallidus (GPe) is unclear. This study examined the contributions of two major GPe cell types—prototypic neurons projecting to the subthalamic nucleus (Proto GPe→STN neurons) and astrocytes—to behavioral flexibility. Using longitudinal operant conditioning with context reversals, we found that Proto GPe→STN neurons dynamically represent contextual information correlating with behavioral optimality. In contrast, GPe astrocytes exhibited gradual contextual encoding independent of performance. Deleting Proto GPe→STN neurons impaired adaptive responses to changing action-outcome contingencies without altering initial reward-seeking acquisition, highlighting their specific role in enabling behavioral flexibility. Furthermore, we discovered that Proto GPe→STN neurons integrate inhibitory striatal and excitatory subthalamic inputs, modulating downstream basal ganglia circuits to support flexible behavior. This research elucidates the complementary roles of Proto GPe→STN neurons and astrocytes in cellular mechanisms of flexible reward-seeking behavior.

Abstract Aims Excessive alcohol use is associated with an increased risk of cognitive impairment. Since increased amyloid plaque burden exacerbates cognitive decline, we sought to assess the potential impact of alcohol use disorder (AUD) on cognition, memory, and amyloid burden corresponding with age. Methods We conducted the retrospective analysis with 6036 subjects, including 269 AUD+ subjects. A four-item CAGE (C—Cutting Down, A—Annoyance by Criticism, G—Guilty Feeling, E—Eye-openers) alcohol questionnaire was given during the recruitment to determine AUD in each participant. We assessed cognitive function, focusing on memory using neuropsychological testing. For 1038 participants, including 57 AUD+ subjects, we measured amyloid burden using the 11C Pittsburgh Compound B tracer-based positron emission tomography imaging. Results AUD+ was significantly associated with lower scores of cognition and memory function relative to AUD− individuals. No significant association was found with AUD and elevated brain amyloid under the age of 65. However, further analysis showed that those aged ≥65 showed greater odds for abnormal amyloid in AUD+ compared to AUD− participants. Conclusions Our results underscore AUD as a risk factor for cognitive decline and diminished memory, particularly in aging populations. The role of AUD in brain amyloid accumulation requires further study.

AbstractThis critical review summarizes the current state of omics‐based biomarkers in the alcohol research field. We first provide definitions and background information on alcohol and alcohol use disorder (AUD), biomarkers, and “omic” technologies. We next summarize using (1) genetic information as risk/prognostic biomarkers for the onset of alcohol‐related problems and the progression from regular drinking to problematic drinking (including AUD), (2) epigenetic information as diagnostic biomarkers for AUD and risk biomarkers for alcohol consumption, (3) transcriptomic information as diagnostic biomarkers for AUD, risk biomarkers for alcohol consumption, and (4) metabolomic information as diagnostic biomarkers for AUD, risk biomarkers for alcohol consumption, and predictive biomarkers for response to acamprosate in subjects with AUD. In the final section, the clinical implications of the findings are discussed, and recommendations are made for future research.

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the central nervous system (CNS). Most GABAergic neurons synthesize GABA from glutamate and release it in the synaptic cleft in the CNS. However, astrocytes can also synthesize and release GABA, activating GABA receptors in the neighboring neurons in physiological and pathological conditions. As the primary homeostatic glial cells in the brain, astrocytes play a crucial role in regulating GABA homeostasis and synaptic neurotransmission. Accumulating evidence demonstrates that astrocytic GABA dysregulation is implicated in psychiatric disorders, including alcohol use disorder (AUD) and major depressive disorder (MDD), the most prevalent co-occurring psychiatric disorders. Several current medications and emerging pharmacological agents targeting GABA levels are in clinical trials for treating AUD and MDD. This review offers a concise summary of the role of astrocytic GABA regulation in AUD and MDD. We also provide an overview of the current understanding and areas of debate regarding the mechanisms by which astrocytes regulate GABA in the CNS and their potential significance in the molecular basis of AUD and MDD, paving the way toward future research directions and potential therapeutic target areas within this field.

Abstract Background Alcohol use disorder (AUD) has been associated with the development of neurodegenerative diseases, including Alzheimer's disease (AD). However, recent studies demonstrate that moderate alcohol consumption may be protective against dementia and cognitive decline. Methods We examined astrocyte function, low-density lipoprotein (LDL) receptor-related protein 1 (LRP1), and the NF-κB p65 and IKK-α/β signaling pathways in modulating neuroinflammation and amyloid beta (Aβ) deposition. We assessed apolipoprotein E (ApoE) in the mouse brain using IHC and ELISA in response to moderate ethanol exposure (MEE). First, to confirm the intracerebral distribution of ApoE, we co-stained with GFAP, a marker for astrocytes that biosynthesize ApoE. We sought to investigate whether the ethanol-induced upregulation of LRP1 could potentially inhibit the activity of IL-1β and TNF-α induced IKK-α/β towards NF-κB p65, resulting in a reduction of pro-inflammatory cytokines. To evaluate the actual Aβ load in the brains of APP/PS1 mice, we performed with a specific antibody Aβ (Thioflavin S) on both air- and ethanol-exposed groups, subsequently analyzing Aβ levels. We also measured glucose uptake activity using 18F-FDG in APP/PS1 mice. Finally, we investigated whether MEE induced cognitive and memory changes using the Y maze, noble objective recognition (NOR) test, and Morris water maze (MWM). Results Our findings demonstrate that MEE reduced astrocytic glial fibrillary acidic protein (GFAP) and ApoE levels in the cortex and hippocampus in presymptomatic APP/PS1 mice. Interestingly, increased LRP1 protein expression is accompanied by dampening the IKK-α/β-NF-κB p65 pathway, resulting in decreased IL-1β and TNF-α levels in male mice. Notably, female mice show reduced anti-inflammatory cytokines, IL-4, and IL-10 levels without altering IL-1β and TNF-α concentrations. In both males and females, Aβ plaques, a hallmark of AD, were reduced in the cortex and hippocampus of ethanol-exposed presymptomatic APP/PS1 mice. Consistently, MEE increased fluorodeoxyglucose (FDG)-positron emission tomography (PET)-based brain activities and normalized cognitive and memory deficits in the APP/PS1 mice. Conclusions Our findings suggest that MEE may benefit AD pathology via modulating LRP1 expression, potentially reducing neuroinflammation and attenuating Aβ deposition. Our study implies that reduced astrocyte derived ApoE and LDL cholesterol levels are critical for attenuating AD pathology.

Mice lacking the ethanol‐sensitive equilibrative nucleoside adenosine transporter 1 (ENT1 –/– ) display enhanced goal‐directed behaviors due to decreased adenosine A 2A R function. However, the role of A 2A R signaling in the regulation of impulsivity remains unknown. Using Pavlovian conditioning, second‐order schedule discrimination, and the 5‐choice serial reaction time task (5‐CSRTT), which incorporates differential‐reward of low rate (DRL) schedules, we reveal that deficits in A 2A R function promote impulsivity. ENT1 –/– mice display exaggerated impulsive responses and faster reaction times to retrieve reward during conditioning and extinction. Interestingly, our results show that basal ERK1/2 phosphorylation is reduced in the dorsal hippocampus (dHPC) of ENT1 –/– mice and that impulsive Pavlovian conditioning significantly increases ERK1/2 phosphorylation. Subsequently, we validate that inhibition of A 2A R promotes impulsivity during Pavlovian conditioning and the 5‐CSRTT. In addition to increased ERK1/2 phosphorylation, mice demonstrating exaggerated impulsivity as a result of A 2A R inhibition exhibit enhanced expression of doublecortin and increased incorporation of BrdU within the HPC. Taken together, these findings indicate that impaired ENT1/A 2A R signaling promotes impulsivity during cue‐induced conditioning and contributes to reward seeking during extinction. More importantly, these results demonstrate that impulsive behavior is associated with aberrant hippocampal neurogenesis, which may contribute to the development of maladaptive reward‐seeking behaviors. Support or Funding Information NIH R01 AA018779