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.

Stimuli predicting high-calorie reward increase dopamine release and drive approach to food in the absence of homeostatic need.

Animals and humans are motivated to consume high-fat, high-calorie foods by cues predicting such foods. The neural mechanisms underlying this effect are not well understood.Objective: We tested the hypothesis that cues paired with a food reward, as compared to explicitly unpaired cues, increase rats' food-seeking behavior by potentiating dopamine release in the nucleus accumbens, and that this effect would be less evident under satiety.Methods: We used a simple discriminative stimulus task and electrochemical recordings of dopamine release in freely moving rats.Results: We found that both food-predictive cue and hunger increased conditioned approaches to the receptacle (food-seeking behavior indicated by movement to the food receptacle). In addition, we observed dopamine release when the food-predictive cue (but not the unpaired cue) was presented, independent of hunger or satiety. Finally, we found a positive correlation between dopamine release amplitude and the number of conditioned approaches to the food receptacle in the sated condition, but not in the hungry condition.Discussion: Our results suggest that dopamine could drive seeking behavior for calorie-dense food in absence of homeostatic need, a core aspect of binge eating disorders.

An isotropic EPI database and analytical pipelines for rat brain resting-state fMRI.

Resting-state functional magnetic resonance imaging (fMRI) has drastically expanded the scope of brain research by advancing our knowledge about the topologies, dynamics, and interspecies translatability of functional brain networks. Several databases have been developed and shared in accordance with recent key initiatives in the rodent fMRI community to enhance the transparency, reproducibility, and interpretability of data acquired at various sites. Despite these pioneering efforts, one notable challenge preventing efficient standardization in the field is the customary choice of anisotropic echo planar imaging (EPI) schemes with limited spatial coverage. Imaging with anisotropic resolution and/or reduced brain coverage has significant shortcomings including reduced registration accuracy and increased deviation in brain feature detection. Here we proposed a high-spatial-resolution (0.4 mm), isotropic, whole-brain EPI protocol for the rat brain using a horizontal slicing scheme that can maintain a functionally relevant repetition time (TR), avoid high gradient duty cycles, and offer unequivocal whole-brain coverage. Using this protocol, we acquired resting-state EPI fMRI data from 87 healthy rats under the widely used dexmedetomidine sedation supplemented with low-dose isoflurane on a 9.4 T MRI system. We developed an EPI template that closely approximates the Paxinos and Watson's rat brain coordinate system and demonstrated its ability to improve the accuracy of group-level approaches and streamline fMRI data pre-processing. Using this database, we employed a multi-scale dictionary-learning approach to identify reliable spatiotemporal features representing rat brain intrinsic activity. Subsequently, we performed k-means clustering on those features to obtain spatially discrete, functional regions of interest (ROIs). Using Euclidean-based hierarchical clustering and modularity-based partitioning, we identified the topological organizations of the rat brain. Additionally, the identified group-level FC network appeared robust across strains and sexes. The "triple-network" commonly adapted in human fMRI were resembled in the rat brain. Through this work, we disseminate raw and pre-processed isotropic EPI data, a rat brain EPI template, as well as identified functional ROIs and networks in standardized rat brain coordinates. We also make our analytical pipelines and scripts publicly available, with the hope of facilitating rat brain resting-state fMRI study standardization.

Addiction history moderates the effect of prefrontal 10-Hz transcranial alternating current stimulation on habitual action selection.

Individuals with substance use disorders (SUDs) transition more quickly from goal-directed to habitual action-selection, but the neural mechanisms underlying this phenomenon remain unclear. Data from animal models suggest that drugs of abuse can modify the neurocircuits that regulate action-selection, enhancing circuits that drive inflexible, habit-based stimulus-response (S-R) action-selection and weakening circuits that drive flexible, goal-directed actions. Here, we tested the effect of bilateral 10-Hz transcranial alternating current stimulation (10Ηz-tACs) of the dorsolateral prefrontal cortex on action-selection in men and women with a SUD history and an age- and sex-matched control group. We tested the hypothesis that true 10Ηz-tACS versus active sham stimulation would reduce perseverative errors after changed response contingencies for well-learned S-R associations, reflecting reduced habit-based action-selection, specifically in the SUD group. We found that 10 Hz-tACS increased perseverative errors in the control group, but in the SUD group, 10 Hz-tACS effects on perseverative errors depended on substance abuse duration: a longer addiction history was associated with a greater reduction of perseverative errors. These results suggest that 10Ηz-tACs altered circuit level dynamics regulating behavioral flexibility, and provide a foundation for future studies to test stimulation site, frequency, and timing specificity. Moreover, these data suggest that chronic substance abuse is associated with altered circuit dynamics that are ameliorated by 10Ηz-tACs. Determining the generalizability of these effects and their duration merits investigation as a direction for novel therapeutic interventions. These findings are timely based on growing interest in transcranial stimulation methods for treating SUDs.NEW & NOTEWORTHY Treating the executive dysfunction associated with addiction is hampered by redundancies in pharmacological regulation of different behavioral control circuits. Thus, nonpharmacological interventions hold promise for addiction treatment. Here, we show that, among people with an addiction history, 10-Hz transcranial alternating current stimulation (10Hz-tACS) of the dorsolateral prefrontal cortex can reduce habitual actions. The fact that 10Hz-tACS can regulate behavioral flexibility suggests its possible utility in reducing harmful habitual actions.

Naltrexone Acutely Enhances Connectivity Between the Ventromedial Prefrontal Cortex and a Left Frontoparietal Network.

BACKGROUND: Naltrexone, an opioid receptor antagonist that is Food and Drug Administration approved for treating alcohol use disorder (AUD), reduces alcohol craving and intake. Despite known pharmacological properties, little is known regarding the effects of naltrexone on neural circuit function. Thus, a data-driven examination of the neural effects of naltrexone in human subjects may offer novel insight into its treatment mechanisms. METHODS: Twenty-one alcohol using males (22 to 39) participated in a double-blind, placebo-controlled crossover study of the effects of naltrexone on brain voxel-wise functional connectivity (FC) using intersubject FC correlation mapping. We first cross-correlated the time series from each gray matter voxel to produce a 6,356 × 6,356 FC matrix for each subject and session. We then subtracted the placebo FC matrix from the naltrexone FC matrix. To identify brain regions demonstrating significant reconfiguration of whole-brain FC patterns following naltrexone treatment, we statistically quantified the consistency of patterns of voxel FC changes across subjects. Permutation testing identified significant clusters of voxels undergoing significant reconfiguration. Using the identified clusters in a seed-based FC analysis, we then compared the FC patterns of affected brain areas on placebo versus naltrexone in a paired t-test. Ridge regression analyses identified self-report measures, including substance use, that significantly predicted individual differences in FC among naltrexone-modulated regions. RESULTS: Two clusters in the rostral anterior cingulate cortex (rACC)/ventromedial prefrontal cortex (vmPFC) demonstrated significant modulation of FC by naltrexone. Using these 2 proximal clusters as a single seed, specific FC changes were identified in regions associated with a left frontoparietal network (increasing), as well as visual and motor regions (decreasing). Stronger FC between the rACC/vmPFC and this set of regions on placebo was associated with more external locus of control, whereas weaker connectivity was associated with greater substance use problems. Naltrexone strengthened these connections most among individuals who reported greater drinking to cope. CONCLUSIONS: Enhancing connectivity between the rACC/vmPFC, implicated in alcohol craving, and components of a left frontoparietal network involved in executive control may represent an effective strategy for the treatment of AUD.

Mechanisms of Persistent Neurobiological Changes Following Adolescent Alcohol Exposure: NADIA Consortium Findings.

The Neurobiology of Adolescent Drinking in Adulthood (NADIA) Consortium has focused on the impact of adolescent binge drinking on brain development, particularly on effects that persist into adulthood. Adolescent binge drinking is common, and while many factors contribute to human brain development and alcohol use during adolescence, animal models are critical for understanding the specific consequences of alcohol exposure during this developmental period and the underlying mechanisms. Using adolescent intermittent ethanol (AIE) exposure models, NADIA investigators identified long-lasting AIE-induced changes in adult behavior that are consistent with observations in humans, such as increased alcohol drinking, increased anxiety (particularly social anxiety), increased impulsivity, reduced behavioral flexibility, impaired memory, disrupted sleep, and altered responses to alcohol. These behavioral changes are associated with multiple molecular, cellular, and physiological alterations in the brain that persist long after AIE exposure. At the molecular level, AIE results in long-lasting changes in neuroimmune/trophic factor balance and epigenetic-microRNA (miRNA) signaling across glia and neurons. At the cellular level, AIE history is associated in adulthood with reduced expression of cholinergic, serotonergic, and dopaminergic neuron markers, attenuated cortical thickness, decreased neurogenesis, and altered dendritic spine and glial morphology. This constellation of molecular and cellular adaptations to AIE likely contributes to observed alterations in neurophysiology, measured by synaptic physiology, EEG patterns, and functional connectivity. Many of these AIE-induced brain changes replicate findings seen in postmortem brains of humans with alcohol use disorder (AUD). NADIA researchers are now elucidating mechanisms of these adaptations. Emerging data demonstrate that exercise, antiinflammatory drugs, anticholinesterases, histone deacetylase inhibitors, and other pharmacological compounds are able to prevent (administered during AIE) and/or reverse (given after AIE) AIE-induced pathology in adulthood. These studies support hypotheses that adolescent binge drinking increases risk of adult hazardous drinking and influences brain development, and may provide insight into novel therapeutic targets for AIE-induced neuropathology and AUDs.

Adolescent Alcohol Exposure Persistently Impacts Adult Neurobiology and Behavior.

Adolescence is a developmental period when physical and cognitive abilities are optimized, when social skills are consolidated, and when sexuality, adolescent behaviors, and frontal cortical functions mature to adult levels. Adolescents also have unique responses to alcohol compared with adults, being less sensitive to ethanol sedative-motor responses that most likely contribute to binge drinking and blackouts. Population studies find that an early age of drinking onset correlates with increased lifetime risks for the development of alcohol dependence, violence, and injuries. Brain synapses, myelination, and neural circuits mature in adolescence to adult levels in parallel with increased reflection on the consequence of actions and reduced impulsivity and thrill seeking. Alcohol binge drinking could alter human development, but variations in genetics, peer groups, family structure, early life experiences, and the emergence of psychopathology in humans confound studies. As adolescence is common to mammalian species, preclinical models of binge drinking provide insight into the direct impact of alcohol on adolescent development. This review relates human findings to basic science studies, particularly the preclinical studies of the Neurobiology of Adolescent Drinking in Adulthood (NADIA) Consortium. These studies focus on persistent adult changes in neurobiology and behavior following adolescent intermittent ethanol (AIE), a model of underage drinking. NADIA studies and others find that AIE results in the following: increases in adult alcohol drinking, disinhibition, and social anxiety; altered adult synapses, cognition, and sleep; reduced adult neurogenesis, cholinergic, and serotonergic neurons; and increased neuroimmune gene expression and epigenetic modifiers of gene expression. Many of these effects are specific to adolescents and not found in parallel adult studies. AIE can cause a persistence of adolescent-like synaptic physiology, behavior, and sensitivity to alcohol into adulthood. Together, these findings support the hypothesis that adolescent binge drinking leads to long-lasting changes in the adult brain that increase risks of adult psychopathology, particularly for alcohol dependence.

Ethanol Exposure History and Alcoholic Reward Differentially Alter Dopamine Release in the Nucleus Accumbens to a Reward-Predictive Cue.

BACKGROUND: Conditioned stimuli (CS) that predict reward delivery acquire the ability to induce phasic dopamine release in the nucleus accumbens (NAc). This dopamine release may facilitate conditioned approach behavior, which often manifests as approach to the site of reward delivery (called "goal-tracking") or to the CS itself (called "sign-tracking"). Previous research has linked sign-tracking in particular to impulsivity and drug self-administration, and addictive drugs may promote the expression of sign-tracking. Ethanol (EtOH) acutely promotes phasic release of dopamine in the accumbens, but it is unknown whether an alcoholic reward alters dopamine release to a CS. We hypothesized that Pavlovian conditioning with an alcoholic reward would increase dopamine release triggered by the CS and subsequent sign-tracking behavior. Moreover, we predicted that chronic intermittent EtOH (CIE) exposure would promote sign-tracking while acute administration of naltrexone (NTX) would reduce it. METHODS: Rats received 14 doses of EtOH (3 to 5 g/kg, intragastric) or water followed by 6 days of Pavlovian conditioning training. Rewards were a chocolate solution with or without 10% (w/v) alcohol. We used fast-scan cyclic voltammetry to measure phasic dopamine release in the NAc core in response to the CS and the rewards. We also determined the effect of NTX (1 mg/kg, subcutaneous) on conditioned approach. RESULTS: Both CIE and alcoholic reward, individually but not together, associated with greater dopamine to the CS than control conditions. However, this increase in dopamine release was not linked to greater sign-tracking, as both CIE and alcoholic reward shifted conditioned approach from sign-tracking behavior to goal-tracking behavior. However, they both also increased sensitivity to NTX, which reduced goal-tracking behavior. CONCLUSIONS: While a history of EtOH exposure or alcoholic reward enhanced dopamine release to a CS, they did not promote sign-tracking under the current conditions. These findings are consistent with the interpretation that EtOH can stimulate conditioned approach, but indicate that the conditioned response may manifest as goal-tracking.

Adolescent alcohol exposure decreases frontostriatal resting-state functional connectivity in adulthood.

Connectivity of the prefrontal cortex (PFC) matures through adolescence, coinciding with emergence of adult executive function and top-down inhibitory control over behavior. Alcohol exposure during this critical period of brain maturation may affect development of PFC and frontolimbic connectivity. Adult rats exposed to adolescent intermittent ethanol (AIE; 5 g/kg ethanol, 25 percent v/v in water, intragastrically, 2-day-on, 2-day-off, postnatal day 25-54) or water control underwent resting-state functional MRI to test the hypothesis that AIE induces persistent changes in frontolimbic functional connectivity under baseline and acute alcohol conditions (2 g/kg ethanol or saline, intraperitoneally administered during scanning). Data were acquired on a Bruker 9.4-T MR scanner with rats under dexmedetomidine sedation in combination with isoflurane. Frontolimbic network regions-of-interest for data analysis included PFC [prelimbic (PrL), infralimbic (IL), and orbitofrontal cortex (OFC) portions], nucleus accumbens (NAc), caudate putamen (CPu), dorsal hippocampus, ventral tegmental area, amygdala, and somatosensory forelimb used as a control region. AIE decreased baseline resting-state connectivity between PFC subregions (PrL-IL and IL-OFC) and between PFC-striatal regions (PrL-NAc, IL-CPu, IL-NAc, OFC-CPu, and OFC-NAc). Acute ethanol induced negative blood-oxygen-level-dependent changes within all regions of interest examined, along with significant increases in functional connectivity in control, but not AIE animals. Together, these data support the hypothesis that binge-like adolescent alcohol exposure causes persistent decreases in baseline frontolimbic (particularly frontostriatal) connectivity and alters sensitivity to acute ethanol-induced increases in functional connectivity in adulthood.

Sex and Adolescent Ethanol Exposure Influence Pavlovian Conditioned Approach.

BACKGROUND: Alcohol use among adolescents is widespread and a growing concern due to long-term behavioral deficits, including altered Pavlovian behavior, that potentially contribute to addiction vulnerability. We tested the hypothesis that adolescent intermittent ethanol (AIE) exposure alters Pavlovian behavior in males and females as measured by a shift from goal-tracking to sign-tracking. Additionally, we investigated GLT-1, an astrocytic glutamate transporter, as a potential contributor to a sign-tracking phenotype. METHODS: Male and female Sprague-Dawley rats were exposed to AIE (5 g/kg, intragastric) or water intermittently 2 days on and 2 days off from postnatal day (P) 25 to 54. Around P70, animals began 20 daily sessions of Pavlovian conditioned approach (PCA), where they learned that a cue predicted noncontingent reward delivery. Lever pressing indicated interaction with the cue, or sign-tracking, and receptacle entries indicated approach to the reward delivery location, or goal-tracking. To test for effects of AIE on nucleus accumbens (NAcc) excitatory signaling, we isolated membrane subfractions and measured protein levels of the glutamate transporter GLT-1 after animals completed behavior as a measure of glutamate homeostasis. RESULTS: Females exhibited elevated sign-tracking compared to males with significantly more lever presses, faster latency to first lever press, and greater probability to lever press in a trial. AIE significantly increased lever pressing while blunting goal-tracking, as indicated by fewer cue-evoked receptacle entries, slower latency to receptacle entry, and lower probability to enter the receptacle in a trial. No significant sex-by-exposure interactions were observed in sign- or goal-tracking metrics. Moreover, we found no significant effects of sex or exposure on membrane GLT-1 expression in the NAcc. CONCLUSIONS: Females exhibited enhanced sign-tracking compared to males, while AIE decreased goal-tracking compared to control exposure. Our findings support the hypothesis that adolescent binge ethanol can shift conditioned behavior from goal- to cue-directed in PCA, especially in females.

Use of fast-scan cyclic voltammetry to assess phasic dopamine release in rat models of early postpartum maternal behavior and neglect.

Maternal behavior (MB) is a complex response to infant cues, orchestrated by postpartum neurophysiology. Although mesolimbic dopamine contributes toward MB, little is known about real-time dopamine fluctuations during the postpartum period. Thus, we used fast-scan cyclic voltammetry to measure individual dopamine transients in the nucleus accumbens of early postpartum rats and compared them with dopamine transients in virgins and in postpartum females exposed to cocaine during pregnancy, which is known to disrupt MB. We hypothesized that dopamine transients are normally enhanced postpartum and support MB. In anesthetized rats, electrically evoked dopamine release was larger and clearance was faster in postpartum females than in virgins and gestational cocaine exposure blocked the change in clearance. In awake rats, control mothers showed more dopamine transients than cocaine-exposed mothers during MB. Salient pup-produced stimuli may contribute toward differences in maternal phasic dopamine by evoking dopamine transients; supporting the feasibility of this hypothesis, urine composition (glucose, ketones, and leukocytes) differed between unexposed and cocaine-exposed infants. These data, resulting from the novel application of fast-scan cyclic voltammetry to models of MB, support the hypothesis that phasic dopamine signaling is enhanced postpartum. Future studies with additional controls can delineate which aspects of gestational cocaine reduce dopamine clearance and transient frequency.

Sex and the Lab: An Alcohol-Focused Commentary on the NIH Initiative to Balance Sex in Cell and Animal Studies.

In May 2014, Dr. Francis Collins, the director of U.S. National Institutes of Health (NIH), and Dr. Janine Clayton, the director of the U.S. National Institutes of Health Office of Research on Women's Health, published a commentary in the journal Nature announcing new policies to ensure that preclinical research funded by the NIH considers both males and females. While these policies are still developing, they have already generated great interest by the scientific community and triggered both criticism and applause. This review provides a description and interpretation of the NIH guidelines, and it traces the history that led to their implementation. As expected, this NIH initiative generated some anxiety in the scientific community. The use of female animals in the investigation of basic mechanisms is perceived to increase variability in the results, and the use of both sexes has been claimed to slow the pace of scientific discoveries and to increase the cost at a time characterized by declining research support. This review discusses issues related to the study of sex as a biological variable (SABV) in alcohol studies and provides examples of how researchers have successfully addressed some of them. A practical strategy is provided to include both sexes in biomedical research while maintaining control of the research direction. The inclusion of sex as an important biological variable in experimental design, analysis, and reporting of preclinical alcohol research is likely to lead to a better understanding of alcohol pharmacology and the development of alcohol use disorder, may promote drug discovery for new pharmacotherapies by increasing scientific rigor, and may provide clinical benefit to women's health. This review aims to promote the understanding of the NIH's SABV guidelines and to provide alcohol researchers with a theoretical and practical framework for working with both sexes in preclinical research.

Anatomical and pharmacological characterization of catecholamine transients in the medial prefrontal cortex evoked by ventral tegmental area stimulation.

Voltammetric measurements of catecholamines in the medial prefrontal cortex (mPFC) are infrequent because of lack of chemical selectivity between dopamine and norepinephrine and their overlapping anatomical inputs. Here, we examined the contribution of norepinephrine to the catecholamine release in the mPFC evoked by electrical stimulation of the ventral tegmental area (VTA). Initially, electrical stimulation was delivered in the midbrain at incremental depths of -5 to -9.4 mm from bregma while catecholamine release was monitored in the mPFC. Although catecholamine release was observed at dorsal stimulation sites that may correspond to the dorsal noradrenergic bundle (DNB, containing noradrenergic axonal projections to the mPFC), maximal release was evoked by stimulation of the VTA (the source of dopaminergic input to the mPFC). Next, VTA-evoked catecholamine release was monitored in the mPFC before and after knife incision of the DNB, and no significant changes in the evoked catecholamine signals were found. These data indicated that DNB fibers did not contribute to the VTA-evoked catecholamine release observed in the mPFC. Finally, while the D2-receptor antagonist raclopride significantly altered VTA-evoked catecholamine release, the α2-adrenergic receptor antagonist idazoxan did not. Specifically, raclopride reduced catecholamine release in the mPFC, opposite to that observed in the striatum, indicating differential autoreceptor regulation of mesocortical and mesostriatal neurons. Together, these findings suggest that the catecholamine release in the mPFC arising from VTA stimulation was predominately dopaminergic rather than noradrenergic.

Ethanol reduces evoked dopamine release and slows clearance in the rat medial prefrontal cortex.

BACKGROUND: Ethanol (EtOH) intoxication affects cognitive performance, contributing to attentional deficits and poor decision making, which may occur via actions in the medial prefrontal cortex (mPFC). mPFC function is modulated by the catecholamines dopamine and norepinephrine. In this study, we examine the acute effects of EtOH on electrically evoked dopamine release and clearance in the mPFC of anesthetized rats naïve to alcohol or chronically exposed to alcohol during adolescence. METHODS: Dopamine release and clearance was evoked by electrical stimulation of the ventral tegmental area (VTA) and measured in the mPFC of anesthetized rats with fast-scan cyclic voltammetry. In Experiments 1 and 2, effects of a high dose of EtOH (4 g/kg, intraperitoneally) on dopamine neurotransmission in the mPFC of EtOH-naïve rats and rats given EtOH exposure during adolescence were investigated. Effects of cumulative dosing of EtOH (0.5 to 4 g/kg) on the dopamine release and clearance were investigated in Experiment 3. Experiment 4 studied effects of EtOH locally applied to the VTA on the dopamine neurotransmission in the mPFC of EtOH-naïve rats. RESULTS: A high dose of EtOH decreased evoked dopamine release within 10 minutes of administration in EtOH-naïve rats. When tested via cumulative dosing from 0.5 to 4 g/kg, both 2 and 4 g/kg EtOH inhibited evoked dopamine release in the mPFC of EtOH-naïve rats, while 4 g/kg EtOH also slowed dopamine clearance. A similar effect on electrically evoked dopamine release in the mPFC was observed after infusion of EtOH into the VTA. Interestingly, intermittent EtOH exposure during adolescence had no effect on observed changes in mPFC dopamine release and clearance induced by acute EtOH administration. CONCLUSIONS: Taken together, these data describe EtOH-induced reductions in the dynamics of VTA-evoked mPFC dopamine release and clearance, with the VTA contributing to the attenuation of evoked mPFC dopamine release induced by EtOH.

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.

From learned value to sustained bias: how reward conditioning changes attentional priority.

Introduction: Attentional bias to reward-associated stimuli can occur even when it interferes with goal-driven behavior. One theory posits that dopaminergic signaling in the striatum during reward conditioning leads to changes in visual cortical and parietal representations of the stimulus used, and this, in turn, sustains attentional bias even when reward is discontinued. However, only a few studies have examined neural activity during both rewarded and unrewarded task phases. Methods: In the current study, participants first completed a reward-conditioning phase, during which responses to certain stimuli were associated with monetary reward. These stimuli were then included as non-predictive cues in a spatial cueing task. Participants underwent functional brain imaging during both task phases. Results: The results show that striatal activity during the learning phase predicted increased visual cortical and parietal activity and decreased ventro-medial prefrontal cortex activity in response to conditioned stimuli during the test. Striatal activity was also associated with anterior cingulate cortex activation when the reward-conditioned stimulus directed attention away from the target. Discussion: Our findings suggest that striatal activity during reward conditioning predicts the degree to which reward history biases attention through learning-induced changes in visual and parietal activities.

Acute, but not repeated, cocaine exposure alters allopregnanolone levels in the midbrain of male and female rats.

RATIONALE: Multiple psychiatric disorders are associated with altered brain and serum levels of neuroactive steroids, including the endogenous GABAergic steroid, allopregnanolone. Clinically, chronic cocaine use was correlated with decreased levels of pregnenolone. Preclinically, the effect of acute cocaine on allopregnanolone levels in rodents has had mixed results, showing an increase or no change in allopregnanolone levels in some brain regions. OBJECTIVE: We hypothesized that cocaine acutely increases allopregnanolone levels, but repeated cocaine exposure decreases allopregnanolone levels compared to controls. METHODS: We performed two separate studies to determine how systemic administration of 15 mg/kg cocaine (1) acutely or (2) chronically alters brain (olfactory bulb, frontal cortex, dorsal striatum, and midbrain) and serum allopregnanolone levels in adult male and female Sprague-Dawley rats. RESULTS: Cocaine acutely increased allopregnanolone levels in the midbrain, but not in olfactory bulb, frontal cortex, or dorsal striatum. Repeated cocaine did not persistently (24 h later) alter allopregnanolone levels in any region in either sex. However, allopregnanolone levels varied by sex across brain regions. In the acute study, we found that females had significantly higher allopregnanolone levels in serum and olfactory bulb relative to males. In the repeated cocaine study, females had significantly higher allopregnanolone levels in olfactory bulb, frontal cortex, and serum. Finally, acute cocaine increased allopregnanolone levels in the frontal cortex of females in proestrus, relative to non-proestrus stages. CONCLUSION: Collectively these results suggest that allopregnanolone levels vary across brain regions and by sex, which may play a part in differential responses to cocaine by sex.

A Multi-Institutional Description of Processes and Outcomes of Postbaccalaureate Research Education Programs in the Mid-Atlantic Region.

ABSTRACT: Outcome data from 6 National Institutes of Health-funded Postbaccalaureate Research Education Programs (PREPs) in the Mid-Atlantic region were combined to give a multi-institutional perspective on their scholars' characteristics and progress through biomedical research training. The institutions hosting these programs were Johns Hopkins University School of Medicine, the Medical University of South Carolina, the University of Maryland School of Medicine, the University of North Carolina at Chapel Hill, Virginia Commonwealth University, and Virginia Polytechnic Institute and State University. The authors summarize the institutional pathways, demographics, undergraduate institutions, and graduate institutions for a total of 384 PREP scholars who completed the programs by June 2021. A total of 228 (59.4%) of these PREP scholars identified as Black or African American, 116 (30.2%) as Hispanic or Latinx, and 269 (70.0%) as female. The authors found that 376 of 384 scholars (97.9%) who started PREP finished their program, 319 of 376 (84.8%) who finished PREP matriculated into PhD or MD/PhD programs, and 284 of 319 (89.0%) who matriculated have obtained their PhD or are successfully making progress toward their PhD.

Dorsomedial and dorsolateral striatum exhibit distinct phasic neuronal activity during alcohol self-administration in rats.

The development of alcoholism may involve a shift from goal-directed to habitual drinking. These action control systems are distinct in the dorsal striatum, with the dorsomedial striatum (DMS) important for goal-directed behavior and the dorsolateral striatum (DLS) required for habit formation. Goal-directed behavior can be modeled in rats with a fixed ratio (FR) reinforcement schedule, while a variable interval (VI) schedule promotes habitual behavior (e.g. insensitivity to contingency degradation). Using extracellular recordings from chronically implanted electrodes, we investigated how DMS and DLS neurons encoded lever-press responses and conditioned cues during operant alcohol self-administration in these two models. In rats self-administering 10% alcohol on an FR schedule, the DMS neuronal population showed increased firing at the onset of start-of-session stimuli. During self-administration, the most prominent phasic firing patterns in the DMS occurred at the time of reinforcement and reinforcement-associated cues, while the most prominent phasic activity in the DLS surrounded the lever response. Neural recordings from an additional cohort of rats trained on a VI schedule revealed a similar pattern of results; however, phasic changes in firing were smaller and differences between the medial and lateral dorsal striatum were less marked. In summary, the DMS and DLS exhibited overlapping but specialized phasic firing patterns: DMS excitations were typically time-locked to reinforcement, while DLS excitations were generally associated with lever responses. Furthermore, the regional specificities and magnitudes of phasic firing differed between reinforcement schedules, which may reflect differences in behavioral flexibility, reward expectancy and the action sequences required to procure reinforcement.

Specific and nonspecific effects of naltrexone on goal-directed and habitual models of alcohol seeking and drinking.

BACKGROUND: The opioid-receptor antagonist naltrexone (NTX) reduces goal-directed alcohol drinking in rats presumably by blunting alcohol reward. However, different operant conditioning behavior can be produced by different reinforcement schedules, with goal-directed operant behavior being more sensitive to changes in reward value than less flexible, habit-associated models. We tested the hypothesis that NTX more effectively reduces alcohol drinking and seeking in a goal-directed than in a habit-associated operant model, and more effectively reduces alcohol versus sucrose self-administration, consistent with diminished alcohol reward. METHODS: Rats were trained to self-administer 10% alcohol or 1.5% sucrose in a lever-press task and then underwent a within-subject assessment of NTX (0.1 to 1 mg/kg) effects on operant behavior. A fixed-ratio (FR5) reinforcement schedule was used to model goal-directed behavior, and a variable-interval (VI30) schedule was used to model habitual behavior. RESULTS: As predicted, NTX reduced fluid deliveries earned by the FR5-alcohol group significantly more than all other groups. However, NTX reduced lever presses during self-administration sessions in VI30-trained rats without reducing earned deliveries, due to the low contingency between rate of pressing and fluid deliveries under that schedule. Interestingly, when fluid delivery was withheld (extinction), NTX reduced reward-seeking in all rats. Finally, NTX blocked reinstatement of reward-seeking upon presentation of 0.2 ml alcohol or sucrose and associated cues in the FR5-trained but not VI30-trained rats. CONCLUSIONS: NTX reduced goal-directed alcohol drinking compared with other operant conditions. In addition, NTX blocked reinstatement of reward-seeking in rats trained on the goal-directed FR5 reinforcement schedule but not in rats trained on the habit-like VI30 reinforcement schedule. However, NTX also exerted nonspecific effects on reward-seeking that were revealed under low-effort contingency conditions or absence of reward. Together, these data support the hypothesis that NTX is less effective in conditioning models that are more habit-associated.