Neural oscillations in the ventral striatum reveal differences between the encoding of palatable food and ethanol consumption.

BACKGROUND: Across multiple levels of investigation, there appear to be convergent neuronal processes underlying substance use and other motivated behaviors (i.e., the pursuit and consumption of rewarding substances). The consumption of alcohol and sweet, high-fat food engages many of the same brain regions, especially, the ventral striatum. In the current study, we hypothesized that ventral striatal local field potentials (LFPs) recorded during self-administration sessions could be used to detect when the consumption of 10% ethanol or sweet-fat food (SF) was occurring compared to all other behaviors, including naturalistic controls (i.e., water or house-chow). METHODS: We used an intermittent limited access approach to condition Sprague-Dawley rats to consume either ethanol or SF while we recorded LFPs. We used machine learning and simple logistic regressions to determine whether LFP features could classify when consumption of each substance was occurring, and whether a general model could predict consumption of both substances. We report performance as the average area under the receiver operator characteristic curve (AUROC). RESULTS: Consumption of a single substance was differentiable from all other behaviors, as evidenced by the AUROC (ethanol = 0.84 and SF = 0.83, p < 0.01). Models built from the combined dataset (general) did modestly overall (general → general = 0.68, p < 0.05), and did not detect the consumption of the two substances similarly (general → SF = 0.5 and general → ethanol = 0.63, p > 0.05). CONCLUSIONS: Models successfully classified ethanol and SF consumption versus all other behavior/naturalistic controls. However, the findings highlight differences in how the ventral striatum represents the consumption of ethanol and SF and show that, although there is potential for finding biomarkers related to substance use, it may be difficult to build a model that performs well detecting multiple substances.

Maternal immune activation and adolescent alcohol exposure increase alcohol drinking and disrupt cortical-striatal-hippocampal oscillations in adult offspring.

Maternal immune activation (MIA) is strongly associated with an increased risk of developing mental illness in adulthood, which often co-occurs with alcohol misuse. The current study aimed to begin to determine whether MIA, combined with adolescent alcohol exposure (AE), could be used as a model with which we could study the neurobiological mechanisms behind such co-occurring disorders. Pregnant Sprague-Dawley rats were treated with polyI:C or saline on gestational day 15. Half of the offspring were given continuous access to alcohol during adolescence, leading to four experimental groups: controls, MIA, AE, and Dual (MIA + AE). We then evaluated whether MIA and/or AE alter: (1) alcohol consumption; (2) locomotor behavior; and (3) cortical-striatal-hippocampal local field potentials (LFPs) in adult offspring. Dual rats, particularly females, drank significantly more alcohol in adulthood compared to all other groups. MIA led to reduced locomotor behavior in males only. Using machine learning to build predictive models from LFPs, we were able to differentiate Dual rats from control rats and AE rats in both sexes, and Dual rats from MIA rats in females. These data suggest that Dual "hits" (MIA + AE) increases substance use behavior and disrupts activity in reward-related circuits, and that this may be a valuable heuristic model we can use to study the neurobiological underpinnings of co-occurring disorders. Our future work aims to extend these findings to other addictive substances to enhance the translational relevance of this model, as well as determine whether amelioration of these circuit disruptions can reduce substance use behavior.

The Impact of Adolescent Alcohol Exposure on Nicotine Behavioral Sensitization in the Adult Male Neonatal Ventral Hippocampal Lesion Rat.

Nicotine and alcohol use is highly prevalent among patients with serious mental illness, including those with schizophrenia (SCZ), and this co-occurrence can lead to a worsening of medical and psychiatric morbidity. While the mechanistic drivers of co-occurring SCZ, nicotine use and alcohol use are unknown, emerging evidence suggests that the use of drugs during adolescence may increase the probability of developing psychiatric disorders. The current study used the neonatal ventral hippocampal lesion (NVHL) rat model of SCZ, which has previously been shown to have enhanced nicotine behavioral sensitization and, following adolescent alcohol, increased alcohol consumption. Given how commonly alcohol is used by adolescents that develop SCZ, we used the NVHL rat to determine how exposure to adolescent alcohol impacts the development of nicotine behavioral sensitization in adulthood. Male Sprague-Dawley rats underwent the NVHL surgery or a sham (control) surgery and subsequently, half of each group was allowed to drink alcohol during adolescence. Nicotine behavioral sensitization was assessed in adulthood with rats receiving subcutaneous injections of nicotine (0.5 mg/kg) each day for 3 weeks followed by a nicotine challenge session 2 weeks later. We demonstrate that all groups of rats became sensitized to nicotine and there were no NVHL-specific increases in nicotine behavioral sensitization. We also found that NVHL rats appeared to develop sensitization to the nicotine paired context and that adolescent alcohol exposure blocked this context sensitization. The current findings suggest that exposure to alcohol during adolescence can influence behaviors that manifest in the adult NVHL rat (i.e., context sensitization). Interestingly, nicotine behavioral sensitization levels were not altered in the NVHL groups regardless of adolescent alcohol exposure in contrast to prior reports.

Sex differences in the ability of corticostriatal oscillations to predict rodent alcohol consumption.

BACKGROUND: Although male and female rats differ in their patterns of alcohol use, little is known regarding the neural circuit activity that underlies these differences in behavior. The current study used a machine learning approach to characterize sex differences in local field potential (LFP) oscillations that may relate to sex differences in alcohol-drinking behavior. METHODS: LFP oscillations were recorded from the nucleus accumbens shell and the rodent medial prefrontal cortex of adult male and female Sprague-Dawley rats. Recordings occurred before rats were exposed to alcohol (n = 10/sex × 2 recordings/rat) and during sessions of limited access to alcohol (n = 5/sex × 5 recordings/rat). Oscillations were also recorded from each female rat in each phase of estrous prior to alcohol exposure. Using machine learning, we built predictive models with oscillation data to classify rats based on: (1) biological sex, (2) phase of estrous, and (3) alcohol intake levels. We evaluated model performance from real data by comparing it to the performance of models built and tested on permutations of the data. RESULTS: Our data demonstrate that corticostriatal oscillations were able to predict alcohol intake levels in males (p < 0.01), but not in females (p = 0.45). The accuracies of models predicting biological sex and phase of estrous were related to fluctuations observed in alcohol drinking levels; females in diestrus drank more alcohol than males (p = 0.052), and the male vs. diestrus female model had the highest accuracy (71.01%) compared to chance estimates. Conversely, females in estrus drank very similar amounts of alcohol to males (p = 0.702), and the male vs. estrus female model had the lowest accuracy (56.14%) compared to chance estimates. CONCLUSIONS: The current data demonstrate that oscillations recorded from corticostriatal circuits contain significant information regarding alcohol drinking in males, but not alcohol drinking in females. Future work will focus on identifying where to record LFP oscillations in order to predict alcohol drinking in females, which may help elucidate sex-specific neural targets for future therapeutic development.

Corticostriatal Oscillations Predict High vs. Low Drinkers in a Rat Model of Limited Access Alcohol Consumption.

Individuals differ in their vulnerability to develop alcohol dependence, which is determined by innate and environmental factors. The corticostriatal circuit is heavily involved in the development of alcohol dependence and may contain neural information regarding vulnerability to drink excessively. In the current experiment, we hypothesized that we could characterize high and low alcohol-drinking rats (HD and LD, respectively) based on corticostriatal oscillations and that these subgroups would differentially respond to corticostriatal brain stimulation. Male Sprague-Dawley rats (n = 13) were trained to drink 10% alcohol in a limited access paradigm. In separate sessions, local field potentials (LFPs) were recorded from the nucleus accumbens shell (NAcSh) and medial prefrontal cortex (mPFC). Based on training alcohol consumption levels, we classified rats using a median split as HD or LD. Then, using machine-learning, we built predictive models to classify rats as HD or LD by corticostriatal LFPs and compared the model performance from real data to the performance of models built on data permutations. Additionally, we explored the impact of NAcSh or mPFC stimulation on alcohol consumption in HD vs. LD. Corticostriatal LFPs were able to predict HD vs. LD group classification with greater accuracy than expected by chance (>80% accuracy). Moreover, NAcSh stimulation significantly reduced alcohol consumption in HD, but not LD (p < 0.05), while mPFC stimulation did not alter drinking behavior in either HD or LD (p > 0.05). These data collectively show that the corticostriatal circuit is differentially involved in regulating alcohol intake in HD vs. LD rats, and suggests that corticostriatal activity may have the potential to predict a vulnerability to develop alcohol dependence in a clinical population.

The Lateral Habenula Directs Coping Styles Under Conditions of Stress via Recruitment of the Endocannabinoid System.

BACKGROUND: The ability to effectively cope with stress is a critical determinant of disease susceptibility. The lateral habenula (LHb) and the endocannabinoid (ECB) system have independently been shown to be involved in the selection of stress coping strategies, yet the role of ECB signaling in the LHb remains unknown. METHODS: Using a battery of complementary techniques in rats, we examined the localization of type-1 cannabinoid receptors (CB1Rs) and assessed the behavioral and neuroendocrine effects of intra-LHb CB1R manipulations. We further tested the extent to which the ECB system in the LHb is impacted following chronic unpredictable stress or social defeat stress, and whether manipulation of LHb CB1Rs can bias coping strategies in rats with a history of chronic stress. RESULTS: Electron microscopy studies revealed CB1R expression on presynaptic axon terminals, postsynaptic membranes, mitochondria, and glial processes in the rat LHb. In vivo microdialysis experiments indicated that acute stress increased the amount of 2-arachidonoylglycerol in the LHb, while intra-LHb CB1R blockade increased basal corticosterone, augmented proactive coping strategies, and reduced anxiety-like behavior. Basal LHb 2-arachidonoylglycerol content was similarly elevated in rats that were subjected to chronic unpredictable stress or social defeat stress and positively correlated with adrenal weight. Finally, intra-LHb CB1R blockade increased proactive behaviors in response to a novel conspecific, increasing approach behaviors irrespective of stress history and decreasing the latency to be attacked during an agonistic encounter. CONCLUSIONS: Alterations in LHb ECB signaling may be relevant for development of stress-related pathologies in which LHb dysfunction and stress-coping impairments are hallmark symptoms.

Unique Effects of Clozapine: A Pharmacological Perspective.

Schizophrenia is a heterogenous and severe neuropsychiatric disorder that affects nearly 1% of the population worldwide. Antipsychotic drugs are the mainstay of treatment, but not all patients with schizophrenia respond to treatment with these agents. Clozapine, the first atypical antipsychotic, is a highly effective medication for patients with schizophrenia who do not respond to other antipsychotics. Although clozapine tends not to produce extrapyramidal symptoms, other side effects of the drug (e.g., agranulocytosis, myocarditis, seizures) limit its widespread use. This chapter reviews clozapine's unique clinical effects and unusual pharmacological profile. In addition to its effects in treatment-resistant schizophrenia, clozapine has been shown to decrease suicidality, which occurs at an increased rate in patients with schizophrenia. Still preliminary, but consistent data, also suggest that clozapine limits substance use in these patients, an important effect since substance use disorders are common in patients with schizophrenia and are associated with a poor outcome, including an increased risk for suicide and poor response to treatment. We have suggested, from animal studies, that clozapine's apparent ability to limit substance use may occur through its actions as a weak dopamine D2 receptor antagonist, a potent norepinephrine α-2 receptor antagonist and a norepinephrine reuptake inhibitor. Using animal models, we have built combinations of agents toward creation of safer clozapine-like drugs to reduce substance use in these patients. Future research into the mechanisms of action of clozapine toward the development of safe clozapine-like agents is of great public health importance.

The link between schizophrenia and substance use disorder: A unifying hypothesis.

Substance use disorders occur commonly in patients with schizophrenia and dramatically worsen their overall clinical course. While the exact mechanisms contributing to substance use in schizophrenia are not known, a number of theories have been put forward to explain the basis of the co-occurrence of these disorders. We propose here a unifying hypothesis that combines recent evidence from epidemiological and genetic association studies with brain imaging and pre-clinical studies to provide an updated formulation regarding the basis of substance use in patients with schizophrenia. We suggest that the genetic determinants of risk for schizophrenia (especially within neural systems that contribute to the risk for both psychosis and addiction) make patients vulnerable to substance use. Since this vulnerability may arise prior to the appearance of psychotic symptoms, an increased use of substances in adolescence may both enhance the risk for developing a later substance use disorder, and also serve as an additional risk factor for the appearance of psychotic symptoms. Future studies that assess brain circuitry in a prospective longitudinal manner during adolescence prior to the appearance of psychotic symptoms could shed further light on the mechanistic underpinnings of these co-occurring disorders while identifying potential points of intervention for these difficult-to-treat co-occurring disorders.

Understanding marijuana's effects on functional connectivity of the default mode network in patients with schizophrenia and co-occurring cannabis use disorder: A pilot investigation.

Nearly half of patients with schizophrenia (SCZ) have co-occurring cannabis use disorder (CUD), which has been associated with decreased treatment efficacy, increased risk of psychotic relapse, and poor global functioning. While reports on the effects of cannabis on cognitive performance in patients with SCZ have been mixed, study of brain networks related to executive function may clarify the relationship between cannabis use and cognition in these dual-diagnosis patients. In the present pilot study, patients with SCZ and CUD (n=12) and healthy controls (n=12) completed two functional magnetic resonance imaging (fMRI) resting scans. Prior to the second scan, patients smoked a 3.6% tetrahydrocannabinol (THC) cannabis cigarette or ingested a 15mg delta-9-tetrahydrocannabinol (THC) pill. We used resting-state functional connectivity to examine the default mode network (DMN) during both scans, as connectivity/activity within this network is negatively correlated with connectivity of the network involved in executive control and shows reduced activity during task performance in normal individuals. At baseline, relative to controls, patients exhibited DMN hyperconnectivity that correlated with positive symptom severity, and reduced anticorrelation between the DMN and the executive control network (ECN). Cannabinoid administration reduced DMN hyperconnectivity and increased DMN-ECN anticorrelation. Moreover, the magnitude of anticorrelation in the controls, and in the patients after cannabinoid administration, positively correlated with WM performance. The finding that DMN brain connectivity is plastic may have implications for future pharmacotherapeutic development, as treatment efficacy could be assessed through the ability of therapies to normalize underlying circuit-level dysfunction.

Sex- and hormone-dependent alterations in alcohol withdrawal-induced anxiety and corticolimbic endocannabinoid signaling.

Alcohol dependence is associated with anxiety during withdrawal. The endocannabinoid (ECB) system participates in the neuroendocrine and behavioral response to stress and changes in corticolimbic ECB signaling may contribute to alcohol withdrawal-induced anxiety. Moreover, symptoms of alcohol withdrawal differ between sexes and sexual dimorphism in withdrawal-induced ECB recruitment may be a contributing factor. Herein, we exposed intact male and female rats and ovariectomized (OVX) female rats with or without estradiol (E2) replacement to 6 weeks of chronic intermittent alcohol vapor and measured anxiety-like behavior, ECB content, and ECB-related mRNA in the basolateral amygdala (BLA) and ventromedial prefrontal cortex (vmPFC). Acute alcohol withdrawal increased anxiety-like behavior, produced widespread disturbances in ECB-related mRNA, and reduced anandamide (AEA) content in the BLA and 2-arachidonoylglycerol (2-AG) content in the vmPFC of male, but not female rats. Similar to males, alcohol-exposed OVX females showed reductions in Napepld mRNA in the BLA, decreased AEA content in the BLA and vmPFC, and reductions in all ECB-related genes measured in the vmPFC. Importantly, E2 replacement prevented withdrawal-induced alterations in ECB content (but not mRNA) in OVX females, and although alcohol-exposed OVX females failed to exhibit more anxiety compared to their respective control, chronic alcohol exposure abolished the anxiolytic properties of E2 in OVX rats. These data indicate that ovarian sex hormones (but not E2 alone) protect against withdrawal-induced alterations in corticolimbic ECB signaling but do not impart resilience to withdrawal-induced anxiety. Thus, the mechanisms implicated in the manifestation of alcohol withdrawal-induced anxiety are most likely sex-specific. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Alcohol vapor exposure differentially impacts mesocorticolimbic cytokine expression in a sex-, region-, and duration-specific manner.

Alcohol exposure elicits the production of cytokines that regulate the host response to infection, immunity, inflammation, and trauma. Although increased production of pro-inflammatory cytokines has been linked to symptoms of alcoholism, few studies have evaluated whether cytokine expression changes across the development of alcohol dependence, or whether these changes are region and/or sex specific. In the present study, we subjected adult male and female rats to different regimens of alcohol vapor exposure (acute, subchronic, or chronic) and measured relative mRNA expression for tumor necrosis factor alpha (TNFα), interleukin-6 (IL-6), and chemokine (C-C motif) ligand 2 (CCL2) in reward-related brain regions. Results indicated that acute alcohol exposure increased TNFα mRNA expression in the basolateral amygdala (BLA), nucleus accumbens (NAc), and ventral tegmental area (VTA), whereas IL-6 expression was increased in the VTA, NAc, and ventromedial prefrontal cortex (vmPFC) only in males. After subchronic exposure (1week daily intermittent exposure, 14h on:10h off), TNFα expression remained elevated in the BLA, NAc, and VTA, while IL-6 expression was reduced in the male vmPFC. Chronic alcohol exposure (6week daily intermittent exposure, 14 h on: 10 h off) increased TNFα mRNA expression in the NAc and increased IL-6 mRNA in the vmPFC and NAc. Interestingly, chronic alcohol exposure also robustly increased CCL2 mRNA expression in the BLA and VTA in males but not females. Thus, alcohol vapor exposure elicits sex-, region-, and duration-specific cytokine alterations that may contribute to differences in the manifestation and progression of symptoms of alcohol dependence in male and female populations.

Sex differences in alcohol consumption and alterations in nucleus accumbens endocannabinoid mRNA in alcohol-dependent rats.

Chronic intermittent alcohol (CIA) exposure produces altered motivational states characterized by anxiety and escalated alcohol consumption during withdrawal. The endocannabinoid (ECB) system contributes to these symptoms, and sex differences in alcohol dependence, as well as bidirectional interactions between ECBs and gonadal hormones have been documented. Thus, we evaluated sex differences in alcohol consumption, anxiety-like behavior, and ECB mRNA expression in the nucleus accumbens (NAc) of alcohol-dependent rats during acute withdrawal. Male rats exposed to six weeks of CIA showed escalated alcohol consumption during acute withdrawal and reductions in NAc N-acyl phosphatidylethanolamine phospholipase D (NAPEPLD), DAG lipase alpha (DAGLα), and monoacylglycerol lipase (MAGL) mRNA. Intact alcohol-dependent female rats also escalated their consumption, but notably, this effect was also present in non-dependent females. No differences in NAc ECB mRNA were observed between CIA- and air-exposed females during acute withdrawal. However, when these data were analyzed according to estrous stage, significant differences in NAPEPLD and MAGL mRNA expression emerged in the NAc of air-exposed control rats, which were absent in alcohol-dependent females. We subsequently measured alcohol consumption and NAc ECB mRNA in ovariectomized (OVX) females with or without estradiol (E2) replacement during withdrawal. Neither E2 nor CIA altered alcohol consumption in OVX females. However, E2 reduced both DAGLα and MAGL mRNA, suggesting that E2 may influence the biosynthesis and degradation of 2-arachidonoylglycerol (2-AG) in the NAc. Collectively, these studies indicate sexual dimorphism in alcohol consumption in non-dependent rats and suggest that E2-mediated alterations in NAc ECB mRNA expression during withdrawal may be a mechanism by which sex differences in alcohol dependence emerge.