Chronic ethanol exposure produces long-lasting, subregion-specific physiological adaptations in RMTg-projecting mPFC neurons.

Chronic ethanol exposure produces neuroadaptations in the medial prefrontal cortex (mPFC) which facilitate the maladaptive behaviors interfering with recovery from alcohol use disorder. Despite evidence that different cortico-subcortical projections play distinct roles in behavior, few studies have examined the physiological effects of chronic ethanol at the circuit level. The rostromedial tegmental nucleus (RMTg) is a GABAergic midbrain region involved in aversive signaling and is functionally altered by chronic ethanol exposure. Our recent work identified a dense input from the mPFC to the RMTg, yet the effects of chronic ethanol exposure on this circuitry is unknown. In the current study, we examined physiological changes after chronic ethanol exposure in prelimbic (PL) and infralimbic (IL) mPFC neurons projecting to the RMTg. Adult male Long-Evans rats were injected with fluorescent retrobeads into the RMTg and rendered dependent using a 14-day chronic intermittent ethanol (CIE) vapor exposure paradigm. Whole-cell patch-clamp electrophysiological recordings were performed in fluorescently-labeled (RMTg-projecting) and -unlabeled (projection-undefined) layer 5 pyramidal neurons 7-10 days following ethanol exposure. CIE significantly increased intrinsic excitability as well as excitatory and inhibitory synaptic drive in RMTg-projecting IL neurons. In contrast, no lasting changes in excitability were observed in RMTg-projecting PL neurons, although a CIE-induced reduction in excitability was observed in projection-undefined PL neurons. CIE also increased excitatory synaptic drive in RMTg-projecting PL neurons. These data uncover novel subregion- and circuit-specific neuroadaptations in the mPFC following chronic ethanol exposure and reveal that the IL mPFC-RMTg projection is uniquely vulnerable to long-lasting effects of chronic ethanol.

Attenuated incubation of ethanol-induced conditioned taste aversion in a model of dependence.

RATIONALE: Preclinical studies report attenuated ethanol-induced conditioned taste aversion (CTA) following chronic ethanol exposure, suggesting that tolerance develops to the aversive properties of ethanol. However, these studies are confounded by pre-exposure to the unconditioned stimulus (US; ethanol), which is well known to hinder conditioning. OBJECTIVES: This study was designed to determine whether chronic ethanol exposure produces tolerance to the aversive properties of ethanol in the absence of a US pre-exposure confound. METHODS: CTA was performed in adult male and female Long-Evans rats by pairing 0.1% ingested saccharin with an intraperitoneal injection of ethanol (1.5 or 2.0 g/kg) or saline. Rats were then rendered ethanol dependent using chronic intermittent ethanol (CIE) vapor exposure. Controls were exposed to room air (AIR). The effect of chronic ethanol on CTA expression and reconditioning were examined following vapor exposure. RESULTS: Prior to vapor exposure, both sexes developed CTA to a comparable degree with 2.0 g/kg producing greater CTA than 1.5 g/kg ethanol. Following vapor exposure, AIR controls exhibited an increase in CTA magnitude compared to pre-vapor levels. This effect was largely absent in CIE-exposed rats. Re-conditioning after vapor exposure facilitated increased CTA magnitude to a similar degree in AIR- and CIE-exposed males. In contrast, CTA magnitude was unchanged by re-conditioning in females. CONCLUSIONS: These data suggest that chronic ethanol does not facilitate tolerance to the aversive properties of ethanol but rather attenuates incubation of ethanol-induced CTA. Loss of CTA incubation suggests that CIE exposure disrupts circuits encoding aversion.

A translational rodent model of individual differences in sensitivity to the aversive properties of ethanol.

BACKGROUND: A strong relationship exists between individual sensitivity to the aversive properties of ethanol and risk for alcohol use disorder (AUD). Despite this, our understanding of the neurobiological mechanisms underlying the subjective response to ethanol is limited. A major contributor to this lack of knowledge is the absence of preclinical models that enable exploration of this individual variability such as is possible in studies of humans. METHODS: Adult male and female Long-Evans rats were trained to associate a novel tastant (saccharin) with acute exposure to either saline or ethanol (1.5 g/kg or 2.0 g/kg i.p.) over three conditioning days using a standard conditioned taste aversion (CTA) procedure. Variability in sensitivity to ethanol-induced CTA was phenotypically characterized using a median split across the populations studied. RESULTS: When examining group averages, both male and female rats exposed to saccharin paired with either dose of ethanol exhibited lower saccharin intake relative to saline controls indicative of ethanol-induced CTA. Examination of individual data revealed a bimodal distribution of responses uncovering two distinct phenotypes present in both sexes. CTA-sensitive rats exhibited a rapid and progressive reduction in saccharin intake with each successive ethanol pairing. In contrast, saccharin intake was unchanged or maintained after an initial decrease from baseline levels in CTA-resistant rats. While CTA magnitude was similar between male and female CTA-sensitive rats, among CTA-resistant animals females were more resistant to the development of ethanol-induced CTA than males. Phenotypic differences were not driven by differences in baseline saccharin intake. CONCLUSIONS: These data parallel work in humans by revealing individual differences in sensitivity to the aversive properties of ethanol that emerge immediately after initial exposure to ethanol in both sexes. This model can be used in future studies to investigate the neurobiological mechanisms that confer risk for AUD.

Transcriptional Dysregulation of Cholesterol Synthesis Underlies Hyposensitivity to GABA in the Ventral Tegmental Area During Acute Alcohol Withdrawal.

BACKGROUND: The ventral tegmental area (VTA) is a dopaminergic brain area that is critical in the development and maintenance of addiction. During withdrawal from chronic ethanol exposure, the response of VTA neurons to GABA (gamma-aminobutyric acid) is reduced through an epigenetically regulated mechanism. In the current study, a whole-genome transcriptomic approach was used to investigate the underlying molecular mechanism of GABA hyposensitivity in the VTA during withdrawal after chronic ethanol exposure. METHODS: We performed RNA sequencing of the VTA of Sprague Dawley male rats withdrawn for 24 hours from a chronic ethanol diet as well as sequencing of the VTA of control rats fed the Lieber-DeCarli diet. RNA sequencing data were analyzed using weighted gene coexpression network analysis to identify modules that contained coexpressed genes. Validation was performed with quantitative polymerase chain reaction, gas chromatography-mass spectrometry, and electrophysiological assays. RESULTS: Pathway and network analysis of weighted gene coexpression network analysis module 1 revealed a significant downregulation of genes associated with the cholesterol synthesis pathway. Consistent with this association, VTA cholesterol levels were significantly decreased during withdrawal. Chromatin immunoprecipitation indicated a decrease in levels of acetylated H3K27 at the transcriptional control regions of these genes. Electrophysiological studies in VTA slices demonstrated that GABA hyposensitivity during withdrawal was normalized by addition of exogenous cholesterol. In addition, inhibition of cholesterol synthesis produced GABA hyposensitivity, which was reversed by adding exogenous cholesterol to VTA slices. CONCLUSIONS: These results suggest that decreased expression of cholesterol synthesis genes may regulate GABA hyposensitivity of VTA neurons during alcohol withdrawal. Increasing cholesterol levels in the brain may be a novel avenue for therapeutic intervention to reverse detrimental effects of chronic alcohol exposure.

Attenuated incubation of ethanol-induced conditioned taste aversion in a model of dependence.

Rationale: Preclinical studies report attenuated ethanol-induced conditioned taste aversion (CTA) following chronic ethanol exposure, suggesting that tolerance develops to the aversive properties of ethanol. However, these studies are confounded by pre-exposure to the unconditioned stimulus (US; ethanol), which is well known to hinder conditioning. Objectives: This study was designed to determine whether chronic ethanol exposure produces tolerance to the aversive properties of ethanol in the absence of a US pre-exposure confound. Methods: CTA was performed in adult male and female Long-Evans rats by pairing 0.1% ingested saccharin with an intraperitoneal injection of ethanol (1.5 or 2.0 g/kg) or saline. Rats were then rendered ethanol dependent using chronic intermittent ethanol (CIE) vapor exposure. Controls were exposed to room air (AIR). The effect of chronic ethanol on CTA expression and reconditioning were examined following vapor exposure. Results: Prior to vapor exposure, both sexes developed CTA to a comparable degree with 2.0 g/kg producing greater CTA than 1.5 g/kg ethanol. Following vapor exposure, AIR controls exhibited an increase in CTA magnitude compared to pre-vapor levels. This effect was absent in CIE-exposed rats. These group differences were eliminated upon re-conditioning after vapor exposure. Conclusions: These data suggest that chronic ethanol does not facilitate tolerance to the aversive properties of ethanol but rather, attenuates incubation of ethanol-induced CTA. Loss of CTA incubation suggests that CIE exposure disrupts circuits encoding aversion.

Conserved role for PCBP1 in altered RNA splicing in the hippocampus after chronic alcohol exposure.

We previously discovered using transcriptomics that rats undergoing withdrawal after chronic ethanol exposure had increased expression of several genes encoding RNA splicing factors in the hippocampus. Here, we examined RNA splicing in the rat hippocampus during withdrawal from chronic ethanol exposure and in postmortem hippocampus of human subjects diagnosed with alcohol use disorder (AUD). We found that expression of the gene encoding the splicing factor, poly r(C) binding protein 1 (PCBP1), was elevated in the hippocampus of rats during withdrawal after chronic ethanol exposure and AUD subjects. We next analyzed the rat RNA-Seq data for differentially expressed (DE) exon junctions. One gene, Hapln2, had increased usage of a novel 3' splice site in exon 4 during withdrawal. This splice site was conserved in human HAPLN2 and was used more frequently in the hippocampus of AUD compared to control subjects. To establish a functional role for PCBP1 in HAPLN2 splicing, we performed RNA immunoprecipitation (RIP) with a PCBP1 antibody in rat and human hippocampus, which showed enriched PCBP1 association near the HAPLN2 exon 4 3' splice site in the hippocampus of rats during ethanol withdrawal and AUD subjects. Our results indicate a conserved role for the splicing factor PCBP1 in aberrant splicing of HAPLN2 after chronic ethanol exposure. As the HAPLN2 gene encodes an extracellular matrix protein involved in nerve conduction velocity, use of this alternative splice site is predicted to result in loss of protein function that could negatively impact hippocampal function in AUD.

A translational rodent model of individual differences in sensitivity to the aversive properties of ethanol.

Background: A strong relationship exists between individual sensitivity to the aversive properties of ethanol and risk for alcohol use disorder (AUD). Despite this, our understanding of the neurobiological mechanisms underlying subjective response to ethanol is relatively poor. A major contributor to this is the absence of preclinical models that enable exploration of this individual variability similar to studies performed in humans. Methods: Adult male and female Long-Evans rats were trained to associate a novel tastant (saccharin) with acute exposure to either saline or ethanol (1.5 g/kg or 2.0 g/kg i.p.) over three conditioning days using a standard conditioned taste aversion (CTA) procedure. Variability in sensitivity to ethanol-induced CTA was phenotypically characterized using a median split across the populations studied. Results: When examining group averages, both male and female rats that had saccharin paired with either dose of ethanol exhibited reduced saccharin intake relative to saline controls of ethanol-induced CTA. Examination of individual data revealed a bimodal distribution of responses uncovering two distinct phenotypes present in both sexes. CTA-sensitive rats exhibited a rapid and progressive reduction in saccharin intake with each successive ethanol pairing. In contrast, saccharin intake was unchanged or maintained after an initial decrease from baseline levels in CTA-resistant rats. While CTA magnitude was similar between male and female CTA-sensitive rats, CTA-resistant females were more resistant to the development of ethanol-induced CTA than their male counterparts. Phenotypic differences were not driven by differences in baseline saccharin intake. CTA sensitivity correlated with behavioral signs of intoxication in only a subset of rats. Conclusions: These data parallel work in humans by revealing individual differences in sensitivity to the aversive properties of ethanol that emerge immediately after initial exposure to ethanol in both sexes. This model can be leveraged in future studies to investigate the neurobiological mechanisms that confer risk for AUD.

Involvement of cortical input to the rostromedial tegmental nucleus in aversion to foot shock.

The rostromedial tegmental nucleus (RMTg) encodes negative reward prediction error (RPE) and plays an important role in guiding behavioral responding to aversive stimuli. Previous research has focused on regulation of RMTg activity by the lateral habenula despite studies revealing RMTg afferents from other regions including the frontal cortex. The current study provides a detailed anatomical and functional analysis of cortical input to the RMTg of male rats. Retrograde tracing uncovered dense cortical input to the RMTg spanning the medial prefrontal cortex, the orbitofrontal cortex and anterior insular cortex. Afferents were most dense in the dorsomedial subregion of the PFC (dmPFC), an area that is also implicated in both RPE signaling and aversive responding. RMTg-projecting dmPFC neurons originate in layer V, are glutamatergic, and collateralize to select brain regions. In-situ mRNA hybridization revealed that neurons in this circuit are predominantly D1 receptor-expressing with a high degree of D2 receptor colocalization. Consistent with cFos induction in this neural circuit during exposure to foot shock and shock-predictive cues, optogenetic stimulation of dmPFC terminals in the RMTg drove avoidance. Lastly, acute slice electrophysiology and morphological studies revealed that exposure to repeated foot shock resulted in significant physiological and structural changes consistent with a loss of top-down modulation of RMTg-mediated signaling. Altogether, these data reveal the presence of a prominent cortico-subcortical projection involved in adaptive behavioral responding to aversive stimuli such as foot shock and provide a foundation for future work aimed at exploring alterations in circuit function in diseases characterized by deficits in cognitive control over reward and aversion.

Pi USB Cam: A Simple and Affordable DIY Solution That Enables High-Quality, High-Throughput Video Capture for Behavioral Neuroscience Research.

Video recording is essential for behavioral neuroscience research, but the majority of available systems suffer from poor cost-to-functionality ratio. Commercial options frequently come at high financial cost that prohibits scalability and throughput, whereas DIY solutions often require significant expertise and time investment unaffordable to many researchers. To address this, we combined a low-cost Raspberry Pi microcomputer, DIY electronics peripherals, freely available open-source firmware, and custom 3D-printed casings to create Pi USB Cam, a simple yet powerful and highly versatile video recording solution. Pi USB Cam is constructed using affordable and widely available components and requires no expertise to build and implement. The result is a system that functions as a plug-and-play USB camera that can be easily installed in various animal testing and housing sites and is readily compatible with popular behavioral and neural recording software. Here, we provide a comprehensive parts list and step-by-step instructions for users to build and implement their own Pi USB Cam system. In a series of benchmark comparisons, Pi USB Cam was able to capture ultra-wide fields of view of behaving rats given limited object distance and produced high image quality while maintaining consistent frame rates even under low-light and no-light conditions relative to a standard, commercially available USB camera. Video recordings were easily scaled using free, open-source software. Altogether, Pi USB Cam presents an elegant yet simple solution for behavioral neuroscientists seeking an affordable and highly flexible system to enable quality video recordings.

An operant ethanol self-administration paradigm that discriminates between appetitive and consummatory behaviors reveals distinct behavioral phenotypes in commonly used rat strains.

Alcohol use disorder (AUD) constitutes a major burden to global health. Recently, the translational success of animal models of AUD has come under increased scrutiny. Efforts to refine models to gain a more precise understanding of the neurobiology of addiction are warranted. Appetitive responding for ethanol (seeking) and its consumption (taking) are governed by distinct neurobiological mechanisms. However, consumption is often inferred from appetitive responding in operant ethanol self-administration paradigms, preventing identification of distinct experimental effects on seeking and taking. In the present study, male Long-Evans, Wistar, and Sprague-Dawley rats were trained to lever press for ethanol using a lickometer-equipped system that precisely measures both appetitive and consummatory behavior. Three distinct operant phenotypes emerged during training: 1) Drinkers, who lever press and consume ethanol; 2) Responders, who lever press but consume little to no ethanol; and 3) Non-responders, who do not lever press. While the prevalence of each phenotype differed across strains, appetitive and consummatory behavior was similar across strains within each phenotype. Appetitive and consummatory behaviors were significantly correlated in Drinkers, but not Responders. Analysis of drinking microstructure showed that greater consumption in Drinkers relative to Responders is due to increased incentive for ethanol rather than increased palatability. Importantly, withdrawal from chronic ethanol exposure resulted in a significant increase in appetitive responding in both Drinkers and Responders, but only Drinkers exhibited a concomitant increase in ethanol consumption. Together, these data reveal important strain differences in appetitive and consummatory responding for ethanol and uncover the presence of distinct operant phenotypes.

Impact of sex, strain, and age on blood ethanol concentration and behavioral signs of intoxication during ethanol vapor exposure.

Animal models of alcohol drinking and dependence are a critical resource for understanding the neurobiological mechanisms and development of more effective treatments for alcohol use disorder (AUD). Because most rat strains do not voluntarily consume large enough quantities of alcohol to adequately model heavy drinking, dependence, and withdrawal-related symptoms, researchers frequently turn to experimenter administered methods to investigate how prolonged and repeated exposure to large quantities of alcohol impacts brain and behavior. Vaporized ethanol is a common method used for chronically subjecting rodents to alcohol and has been widely used to model both binge and dependence-inducing heavy drinking patterns observed in humans. Rodent strain, sex, and age during exposure are all well-known to influence outcomes in experiments utilizing intraperitoneal or intragastric methods of repeated ethanol exposure. Yet, despite its frequent use, the impact of these variables on outcomes associated with ethanol vapor exposure has not been widely investigated. The present study analyzed data generated from over 700 rats across an eight-year period to provide a population-level assessment of variables influencing level of intoxication using vapor exposure. Our findings reveal important differences with respect to strain, sex, and age during ethanol exposure in the relationship between blood ethanol concentration and behavioral signs of intoxication. These data provide valuable scientific and practical insight for laboratories utilizing ethanol vapor exposure paradigms to model AUD in rats.

The Next 50 Years of Neuroscience.

On the 50th anniversary of the Society for Neuroscience, we reflect on the remarkable progress that the field has made in understanding the nervous system, and look forward to the contributions of the next 50 years. We predict a substantial acceleration of our understanding of the nervous system that will drive the development of new therapeutic strategies to treat diseases over the course of the next five decades. We also see neuroscience at the nexus of many societal topics beyond medicine, including education, consumerism, and the justice system. In combination, advances made by basic, translational, and clinical neuroscience research in the next 50 years have great potential for lasting improvements in human health, the economy, and society.

Inhibition of the rostromedial tegmental nucleus reverses alcohol withdrawal-induced anxiety-like behavior.

Acute withdrawal from alcohol is associated with a number of unpleasant symptoms that play an important role in preventing recovery and long-term abstinence. Considerable research has focused on the role that neuropeptide systems and the amygdala play in mediating affective symptoms of acute withdrawal, but promising preclinical findings have not translated successfully into the clinic. The rostromedial tegmental nucleus (RMTg) has been implicated in both fear and anxiety. In addition, RMTg neurons exert inhibitory control over midbrain dopamine neurons, the activity of which are suppressed during acute withdrawal. Thus, we hypothesized that the RMTg may play a role in mediating symptoms of acute withdrawal. Using a chronic ethanol vapor exposure paradigm that renders rats physically dependent on ethanol, we observed significant withdrawal-induced enhancement of cFos expression in the RMTg. This was accompanied by a significant increase in somatic symptoms and a decrease in reward sensitivity as measured by intracranial self-stimulation (ICSS). Both measures followed a similar time course to RMTg cFos expression with peak symptom severity occurring 12 h following cessation of ethanol exposure. Heightened anxiety-like behavior was also observed in withdrawn rats at this same time point. RMTg inhibition had no effect on somatic signs of withdrawal or withdrawal-induced changes in reward sensitivity, but significantly attenuated withdrawal-induced anxiety-like behavior. Together, these data demonstrate that the RMTg plays a distinct role in the negative affective state associated with acute withdrawal and may therefore be critically involved in the neurobiological mechanisms that promote relapse during early stages of recovery.

The histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) alleviates depression-like behavior and normalizes epigenetic changes in the hippocampus during ethanol withdrawal.

Withdrawal from chronic alcohol drinking can cause depression, leading to an inability to function in daily life and an increased risk for relapse to harmful drinking. Understanding the causes of alcohol withdrawal-related depression may lead to new therapeutic targets for treatment. Epigenetic factors have recently emerged as important contributors to both depression and alcohol use disorder (AUD). Specifically, acetylation of the N-terminal tails of histone proteins that package DNA into nucleosomes is altered in stress-induced models of depression and during alcohol withdrawal. The goal of this study was to examine depression-like behavior during alcohol withdrawal and associated changes in histone acetylation and expression of histone deacetylase 2 (HDAC2) in the hippocampus, a brain region critical for mood regulation and depression. Male Sprague-Dawley rats were treated with the Lieber-DeCarli ethanol liquid diet for 15 days and then underwent withdrawal. Rats were treated with the HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA), during withdrawal and were tested for depression-like behavior. In a separate group of rats, the hippocampus was analyzed for mRNA and protein expression of HDAC2 and levels of histone H3 lysine 9 acetylation (H3K9ac) during chronic ethanol exposure and withdrawal. Rats undergoing ethanol withdrawal exhibited depression-like behavior and had increased HDAC2 and decreased H3K9ac levels in specific structures of the hippocampus. Treatment with SAHA during withdrawal ameliorated depression-like behavior and normalized changes in hippocampal HDAC2 and H3K9ac levels. These results demonstrate that ethanol withdrawal causes an altered epigenetic state in the hippocampus. Treatment with an HDAC inhibitor can correct this state and alleviate depression-like symptoms developed during withdrawal. Targeting histone acetylation may be a novel strategy to reduce ethanol withdrawal-induced depression.

Absence of compulsive drinking phenotype in adult male rats exposed to ethanol in a binge-like pattern during adolescence.

The abuse of alcohol during adolescence is widespread and represents a particular concern, given that earlier age of drinking onset is associated with increased risk for the development of alcohol use disorders (AUDs). Despite this risk, it remains unclear whether binge-like adolescent alcohol exposure facilitates drinking despite aversive consequences, a characteristic common among individuals with AUDs. The present study examined voluntary alcohol consumption and aversion-resistant drinking in adult male Long-Evans rats that had undergone adolescent intermittent ethanol (AIE) exposure by vapor inhalation between postnatal days (PD) 28-44. Ethanol consumption during adulthood was examined using a two-bottle choice (2BC) intermittent access procedure. Rats were tested for aversion-resistant drinking using ethanol adulterated with quinine (10, 30, 100 mg/L) after two 7-week periods of 2BC drinking. After completion of the second test of aversion-resistant drinking, rats were trained to operantly self-administer ethanol. The results revealed that both air control (AIR) and AIE-exposed rats exhibited similar ethanol intake and preference in the 2BC paradigm. After 7 weeks of 2BC drinking, quinine adulteration significantly suppressed ethanol intake, but only at the highest concentration examined (100 mg/L). However, upon retesting after a total of 17 weeks of 2BC drinking, 30-mg/L quinine suppressed ethanol intake. Notably, AIR- and AIE-exposed rats were equally sensitive to quinine-adulterated ethanol at both time points. In addition, AIR- and AIE-exposed rats responded similarly during operant ethanol self-administration on both fixed and progressive ratio schedules of reinforcement. Finally, both AIR- and AIE-exposed rats exhibited similar preference for sucrose. The results of this study show that binge-like ethanol vapor exposure during adolescence does not alter voluntary ethanol consumption, motivation to operantly respond for ethanol, or promote aversion-resistant ethanol consumption in adulthood. These data, together with previous work reporting conflicting results across various rodent models of adolescent alcohol exposure, underscore the need to further explore the role that exposure to alcohol during adolescence has on the development of heavy and compulsive drinking phenotypes in adulthood.

Binge-Like Alcohol Exposure During Adolescence Disrupts Dopaminergic Neurotransmission in the Adult Prelimbic Cortex.

Repeated binge-like exposure to alcohol during adolescence has been reported to perturb prefrontal cortical development, yet the mechanisms underlying these effects are unknown. Here we report that adolescent intermittent ethanol exposure induces cellular and dopaminergic abnormalities in the adult prelimbic cortex (PrL-C). Exposing rats to alcohol during early-mid adolescence (PD28-42) increased the density of long/thin dendritic spines of layer 5 pyramidal neurons in the adult PrL-C. Interestingly, although AIE exposure did not alter the expression of glutamatergic proteins in the adult PrL-C, there was a pronounced reduction in dopamine (DA) D1 receptor modulation of both intrinsic firing and evoked NMDA currents in pyramidal cells, whereas D2 receptor function was unaltered. Recordings from fast-spiking interneurons also revealed that AIE reduced intrinsic excitability, glutamatergic signaling, and D1 receptor modulation of these cells. Analysis of PrL-C tissue of AIE-exposed rats further revealed persistent changes in the expression of DA-related proteins, including reductions in the expression of tyrosine hydroxylase and catechol-O-methyltransferase (COMT). AIE exposure was associated with hypermethylation of the COMT promoter at a conserved CpG site in exon II. Taken together, these findings demonstrate that AIE exposure disrupts DA and GABAergic transmission in the adult medial prefrontal cortex (mPFC). As DA and GABA work in concert to shape and synchronize neuronal ensembles in the PFC, these alterations could contribute to deficits in behavioral control and decision-making in adults who abused alcohol during adolescence.

Role for the Rostromedial Tegmental Nucleus in Signaling the Aversive Properties of Alcohol.

BACKGROUND: While the rewarding effects of alcohol contribute significantly to its addictive potential, it is becoming increasingly appreciated that alcohol's aversive properties also play an important role in the propensity to drink. Despite this, the neurobiological mechanism for alcohol's aversive actions is not well understood. The rostromedial tegmental nucleus (RMTg) was recently characterized for its involvement in aversive signaling and has been shown to encode the aversive properties of cocaine, yet its involvement in alcohol's aversive actions have not been elucidated. METHODS: Adult male and female Long-Evans rats underwent conditioned taste aversion (CTA) procedures where exposure to a novel saccharin solution was paired with intraperitoneal administration of saline, lithium chloride (LiCl), or ethanol (EtOH). Control rats underwent the same paradigm except that drug and saccharin exposure were explicitly unpaired. Saccharin consumption was measured on test day in the absence of drug administration, and rats were sacrificed 90 to 105 minutes following access to saccharin. Brains were subsequently harvested and processed for cFos immunohistochemistry. The number of cFos-labeled neurons was counted in the RMTg and the lateral habenula (LHb)-a region that sends prominent glutamatergic input to the RMTg. RESULTS: In rats that received paired drug and saccharin exposure, EtOH and LiCl induced significant CTA compared to saline to a similar degree in males and females. Both EtOH- and LiCl-induced CTA significantly enhanced cFos expression in the RMTg and LHb but not the hippocampus. Similar to behavioral measures, no significant effect of sex on CTA-induced cFos expression was observed. cFos expression in both the RMTg and LHb was significantly correlated with CTA magnitude with greater cFos being associated with more pronounced CTA. In addition, cFos expression in the RMTg was positively correlated with LHb cFos. CONCLUSIONS: These data suggest that the RMTg and LHb are involved in the expression of CTA and are consistent with previous work implicating the RMTg in aversive signaling. Furthermore, increased cFos expression in the RMTg following EtOH-induced CTA suggests that this region plays a role in signaling alcohol's aversive properties.

Development of a system for individual feeding of baboons maintained in an outdoor group social environment.

We developed a system that allows individual feeding of adult baboons, 8-15 years of age, maintained in an outdoor group social environment. The purpose of the system is to allow careful monitoring and control of individual diet. Baboons were housed in two group cages, 16 females and a single male in one and 12 females and a single male in the other. Baboons exited the group cage once daily and passed along a chute and over a scale into individual cages where they received their individual diets. Food intake was monitored during their 2-hour stay in the individual cages. Baboons rapidly learned to use this system. Food intake and weight were stable within 20 days. Food consumed decreased during the period of sexual receptivity. The maintenance of the group social environment allowed observations on the group's dominance structure and the relationship of dominance to food consumption. Speed of food access in the group cage was related to dominance. Dominance was not related to food consumed in individual cages. The system permits study of many variables related to behavior and food intake while still retaining critical social interactions.