Dissecting operant alcohol self-administration using saccharin-fading procedure

BACKGROUND

Although alcohol use disorder is a complex human pathology, the use of animal models represents an opportunity to study some aspects of this pathology. One of the most used paradigms to study the voluntary alcohol consumption in rodents is operant self-administration (OSA).

AIMS

In order to facilitate the performance of this paradigm, we aim to describe some critical steps of OSA under a saccharin-fading procedure.

MATERIAL & METHODS

We used 40 male Wistar rats to study the process of acquiring the operant response through a saccharin-fading procedure under a fixed ratio (FR1) schedule of reinforcement. Next, we analyze the alcohol introduction and concentration increase, the effect of an alcohol deprivation, and the analogy between this paradigm with the Drinking in the Dark-Multiple Scheduled Access paradigm.

RESULTS

During alcohol concentration increase, animals reduced their lever presses in accordance with the increase in alcohol concentration. On the contrary, the consumption measured in g·kg^-1 BW showed a great stability. The lever presses pattern within operant session changes with the introduction of different alcohol concentrations: at higher alcohol concentrations, animals tended to accumulate most of their presses in the initial period of the session.

DISCUSSION

We show the utility of fading with low concentrations of saccharin and the evolution of the operant response through the different concentrations of alcohol.

CONCLUSION

Taken together, our results aimed to dissect the acquisition and maintenance of OSA behavior as well as other related variables, to facilitate the understanding and performance of this paradigm.

The Immune System through the Lens of Alcohol Intake and Gut Microbiota

The human gut is the largest organ with immune function in our body, responsible for regulating the homeostasis of the intestinal barrier. A diverse, complex and dynamic population of microorganisms, called microbiota, which exert a significant impact on the host during homeostasis and disease, supports this role. In fact, intestinal bacteria maintain immune and metabolic homeostasis, protecting our organism against pathogens. The development of numerous inflammatory disorders and infections has been linked to altered gut bacterial composition or dysbiosis. Multiple factors contribute to the establishment of the human gut microbiota. For instance, diet is considered as one of the many drivers in shaping the gut microbiota across the lifetime. By contrast, alcohol is one of the many factors that disrupt the proper functioning of the gut, leading to a disruption of the intestinal barrier integrity that increases the permeability of the mucosa, with the final result of a disrupted mucosal immunity. This damage to the permeability of the intestinal membrane allows bacteria and their components to enter the blood tissue, reaching other organs such as the liver or the brain. Although chronic heavy drinking has harmful effects on the immune system cells at the systemic level, this review focuses on the effect produced on gut, brain and liver, because of their significance in the link between alcohol consumption, gut microbiota and the immune system.

Inhibition of Receptor Protein Tyrosine Phosphatase β/ζ Reduces Alcohol Intake in Rats

BACKGROUND

Pleiotrophin (PTN) and midkine (MK) are cytokines that are up-regulated in the prefrontal cortex (PFC) after alcohol administration and have been shown to reduce alcohol intake and reward. Both cytokines are endogenous inhibitors of receptor protein tyrosine phosphatase (RPTP) β/ζ (a.k.a. PTPRZ1). Recently, a new compound named MY10 was designed with the aim of mimicking the activity of PTN and MK. MY10 has already shown promising results regulating alcohol-related behaviors in mice.

METHODS

We have now tested the effects of MY10 on alcohol operant self-administration and Drinking In the Dark-Multiple Scheduled Access (DID-MSA) paradigms in rats. Gene expression of relevant genes in the PTN/MK signaling pathway in the PFC was analyzed by real-time PCR.

RESULTS

MY10, at the highest dose tested (100 mg/kg), reduced alcohol consumption in the alcohol operant self-administration paradigm (p = 0.040). In the DID-MSA paradigm, rats drank significantly less alcohol (p = 0.019) and showed a significant decrease in alcohol preference (p = 0.002). We observed that the longer the exposure to alcohol, the greater the suppressing effects of MY10 on alcohol consumption. It was demonstrated that the effects of MY10 were specific to alcohol since saccharin intake was not affected by MY10 (p = 0.804). MY10 prevented the alcohol-induced down-regulation of Ptprz1 (p = 0.004) and anaplastic lymphoma kinase (Alk; p = 0.013) expression.

CONCLUSIONS

Our results support and provide further evidence regarding the efficacy of MY10 on alcohol-related behaviors and suggest the consideration of the blockade of RPTPβ/ζ as a target for reducing excessive alcohol consumption.

Adult-onset hypothyroidism increases ethanol consumption

RATIONALE

Only in Europe it can be estimated that more than 20 million of people would be affected by hypothyroidism in some moment of their life. Given that ethanol consumption is so frequent, it would be reasonable to ask what the consequences of ethanol consumption in those individuals affected by hypothyroidism are.

OBJECTIVES

To study the interaction between hypothyroidism and ethanol consumption.

METHODS

We study ethanol consumption in a rat model of methyl-mercaptoimidazole-induced-adult-onset hypothyroidism and thyroid T4/T3 hormone supplementation. Also, we studied the effects of ethanol on motor activity, memory, and anxiety.

RESULTS

We found that hypothyroidism increased the voluntary ethanol consumption and that this was enhanced by thyroid hormone supplementation. Hypothyroidism was associated with motor hyperactivity which was prevented either by T4/T3 supplementation or ethanol. The relationship between hypothyroidism, ethanol, and anxiety was more complex. In an anxiogenic context, hypothyroidism and T4/T3 supplementation would increase immobility, an anxiety-like behavior, while in a less anxiogenic context would decrease rearing, a behavior related to anxiety. Regarding memory, acute ethanol administration did not alter episodic-like memory in hypothyroid rats. Gene expression of enzymes involved in the metabolism of ethanol, i.e., Adh1 and Aldh2, were altered by hypothyroidism and T4/T3 supplementation.

CONCLUSIONS

Our results suggest that hypothyroid patients would need personalized attention in terms of ethanol consumption. In addition, they point that it would be useful to embrace the thyroid axis in the study of ethanol addiction, including as a possible therapeutic target for the treatment of alcoholism and its comorbid disorders.

Red Bull® energy drink increases consumption of higher concentrations of alcohol

Mixing alcohol with caffeinated energy drinks is a common practice, especially among young people. In humans, the research on this issue has mainly focused on the use of the mass-marketed energy drinks themselves, whereas in animal models, it has focused on the individual effects of their active ingredients (i.e. caffeine). Here, we have characterized how Red Bull®, one of the most consumed caffeinated energy drink worldwide, modulates operant alcohol self-administration in Wistar rats. We found that animals readily and steadily responded for Red Bull (mean: 90 responses, 30 minutes and fixed-ratio 1), which was accompanied by locomotor stimulating effects (26 percent increase). The higher the concentration of alcohol (3-20 percent), the higher the consumption of alcohol (g/kg) and associated blood alcohol levels (91.76 percent) in the mixed Red Bull-alcohol group (60 percent increase). Blood caffeine levels in the Red Bull group were 4.69 μg/ml and 1.31 μg/ml in the Red Bull-alcohol group after the 30-minute session. Because Red Bull also contains 11 percent sucrose, we examined the time course of blood glucose as well as insulin and corticosterone. The correlation between intake of Red Bull and blood glucose levels was higher at 90 minutes than 5 minutes after its consumption, and there was no relationship with blood insulin or blood corticosterone levels. Red Bull did not alter extinction and reacquisition of responding for alcohol nor did it affect relapse-like drinking. Overall, our results suggest that Red Bull might be a vulnerability factor to develop alcoholism given that it intensifies the consumption of higher concentrations of alcohol.

Histone Deacetylase Gene Expression Following Binge Alcohol Consumption in Rats and Humans

BACKGROUND

Alcohol binge drinking is one of the most common patterns of excessive alcohol use and recent data would suggest that histone deacetylases (HDACs) gene expression profiling could be useful as a biomarker for psychiatric disorders.

METHODS

This study aimed to characterize the gene expression patterns of Hdac 1-11 in samples of rat peripheral blood, liver, heart, prefrontal cortex, and amygdala following repeated binge alcohol consumption and to determine the parallelism of Hdac gene expression between rats and humans in peripheral blood. To accomplish this goal, we examined Hdac gene expression following 1, 4, or 8 alcohol binges (3 g/kg, orally) in the rat, in patients who were admitted to the hospital emergency department for acute alcohol intoxication, and in rats trained in daily operant alcohol self-administration.

RESULTS

We primarily found that acute alcohol binging reduced gene expression (Hdac1-10) in the peripheral blood of alcohol-naïve rats and that this effect was attenuated following repeated alcohol binges. There was also a reduction of Hdac gene expression in the liver (Hdac2,4,5), whereas there was increased expression in the heart (Hdac1,7,8) and amygdala (Hdac1,2,5). Additionally, increased blood alcohol concentrations were measured in rat blood at 1 to 4 hours following repeated alcohol binging, and the only group that developed hepatic steotosis (fatty liver) were those animals exposed to 8 alcohol binge events. Finally, both binge consumption of alcohol in humans and daily operant alcohol self-administration in rats increased Hdac gene expression in peripheral blood.

CONCLUSIONS

Our results suggest that increases in HDAC gene expression within the peripheral blood are associated with chronic alcohol consumption, whereas HDAC gene expression is reduced following initial exposure to alcohol.

Common single nucleotide variants underlying drug addiction: more than a decade of research

Drug-related phenotypes are common complex and highly heritable traits. In the last few years, candidate gene (CGAS) and genome-wide association studies (GWAS) have identified a huge number of single nucleotide polymorphisms (SNPs) associated with drug use, abuse or dependence, mainly related to alcohol or nicotine. Nevertheless, few of these associations have been replicated in independent studies. The aim of this study was to provide a review of the SNPs that have been most significantly associated with alcohol-, nicotine-, cannabis- and cocaine-related phenotypes in humans between the years of 2000 and 2012. To this end, we selected CGAS, GWAS, family-based association and case-only studies published in peer-reviewed international scientific journals (using the PubMed/MEDLINE and Addiction GWAS Resource databases) in which a significant association was reported. A total of 371 studies fit the search criteria. We then filtered SNPs with at least one replication study and performed meta-analysis of the significance of the associations. SNPs in the alcohol metabolizing genes, in the cholinergic gene cluster CHRNA5-CHRNA3-CHRNB4, and in the DRD2 and ANNK1 genes, are, to date, the most replicated and significant gene variants associated with alcohol- and nicotine-related phenotypes. In the case of cannabis and cocaine, a far fewer number of studies and replications have been reported, indicating either a need for further investigation or that the genetics of cannabis/cocaine addiction are more elusive. This review brings a global state-of-the-art vision of the behavioral genetics of addiction and collaborates on formulation of new hypothesis to guide future work.

Effects of topiramate on ethanol-cocaine interactions and DNA methyltransferase gene expression in the rat prefrontal cortex

BACKGROUND AND PURPOSE

Recent and ongoing clinical studies have indicated that topiramate (Topamax®) could be effective in treating ethanol or cocaine abuse. However, the effects of topiramate on the co-administration of ethanol and cocaine remain largely unknown.

EXPERIMENTAL APPROACH

We studied the effects of topiramate, in Wistar rats, on operant ethanol self-administration with the co-administration of cocaine (i.p.). The psychomotor effects of topiramate were examined before ethanol self-administration and cocaine exposure. Blood samples were collected to analyse ethanol and cocaine metabolism (blood ethanol levels and benzoylecgonine). Quantitative real-time PCR was used to characterize the gene expression in the prefrontal cortex.

KEY RESULTS

Topiramate prevented the cocaine-induced increased response to ethanol in a dose-dependent manner without causing any motor impairment by itself. This effect was observed when topiramate was administered before ethanol access, but not when topiramate was administered before the cocaine injection. Topiramate did not block cocaine-induced psychomotor stimulation. Topiramate reduced blood ethanol levels but did not affect cocaine metabolism. Ethanol increased the gene expression of DNA methyltransferases (Dnmt1 and Dnmt3a), the corepressor Dnmt1-associated protein 1 (Dmap1), and the RNA methyltransferase Trdmt1. These effects were prevented by topiramate or cocaine. Gene expression of histone deacetylase-2 and glutamate receptor kainate-1 were only increased by cocaine treatment. Topiramate and cocaine co-administration caused an up-regulation of dopamine (Drd1, Th) and opioid (Oprm1) receptor genes. Topiramate showed a tendency to alter episodic-like memory.

CONCLUSIONS AND IMPLICATIONS

Topiramate is an effective inhibitor of the cocaine-induced increase in operant ethanol self-administration.

A spontaneous deletion of α-synuclein is associated with an increase in CB1 mRNA transcript and receptor expression in the hippocampus and amygdala: effects on alcohol consumption

α-Synuclein (α-syn) protein and endocannabinoid CB1 receptors are primarily located in presynaptic terminals. An association between α-syn and CB1 receptors has recently been established in Parkinson's disease, but it is completely unknown whether there is an association between these two proteins in alcohol addiction. Therefore, we aimed to examine the α-syn mRNA transcript and protein expression levels in the prefrontal cortex, striatum, amygdala and hippocampus. These brain regions are the most frequently implicated in alcohol and other drug addiction. In these studies, we used C57BL/6 mice carrying a spontaneous deletion of the α-syn gene (C57BL/6(Snca-/-) ) and their respective controls (C57BL/6(Snca) (+/) (+) ). These animals were monitored for spontaneous alcohol consumption (3-10%) and their response to a hypnotic-sedative dose of alcohol (3 g kg(-1) ) was also assessed. Compared with the C57BL/6(Snca+/+) mice, we found that the C57BL/6(Snca-/-) mice exhibited a higher expression level of the CB1 mRNA transcript and CB1 receptor in the hippocampus and amygdala. Furthermore, C57BL/6(Snca-/-) mice showed an increase in alcohol consumption when offered a 10% alcohol solution. There was no significant difference in sleep time after the injection of 3 g/kg alcohol. These results are the first to reveal an association between α-syn and the CB1 receptor in the brain regions that are most frequently implicated in alcohol and other drug addictions.

Developmentally-induced hypothyroidism alters the expression of Egr-1 and Arc genes and the sensitivity to cannabinoid agonists in the hippocampus. Possible implications for memory and learning

We analyzed the role of the cannabinoid system in the cognitive deficits caused by developmentally-induced hypothyroidism. We studied in control and hypothyroid rats the effect of a cannabinoid agonist on spatial memory, hippocampal phosphorylation of CREB and expression of early genes. Our results show that, 1-basal hippocampal expression of early genes and spatial learning are decreased in hypothyroid rats; 2-hypothyroid rats are very sensitive to cannabinoid agonists. Low dose of cannabinoid agonist ineffective in controls altered spatial memory, CREB's phosphorylation and early gene expression in hypothyroids. These effects are not due a change in CB1 receptor (CB1R) content. 3-Treatment of hypothyroid rats with thyroid hormones normalized the biochemical and behavioral responses to cannabinoid agonists but did not correct the low basal levels of early gene transcripts and the deficits in spatial learning. All these data suggest that the hippocampal deregulation of early genes expression could play an important role in the basal cognitive deficits of hypothyroid rats.

C957T polymorphism of the dopamine D2 receptor gene is associated with motor learning and heart rate

Genetic variants that are related to the dopaminergic system have been frequently found to be associated with various neurological and mental disorders. Here, we studied the relationships between some of these genetic variants and some cognitive and psychophysiological processes that are implicated in such disorders. Two single nucleotide polymorphisms were chosen: one in the dopamine D2 receptor gene (rs6277-C957T) and one in the catechol-O-methyltransferase gene (rs4680-Val158Met), which is involved in the metabolic degradation of dopamine. The performance of participants on two long-term memory tasks was assessed: free recall (declarative memory) and mirror drawing (procedural motor learning). Heart rate (HR) was also monitored during the initial trials of the mirror-drawing task, which is considered to be a laboratory middle-stress generator (moderate stress), and during a rest period (low stress). Data were collected from 213 healthy Caucasian university students. The C957T C homozygous participants showed more rapid learning than the T allele carriers in the procedural motor learning task and smaller differences in HR between the moderate- and the low-stress conditions. These results provide useful information regarding phenotypic variance in both healthy individuals and patients.

The genetic basis of the endocannabinoid system and drug addiction in humans

The cannabinoid receptor (CNR1) and the fatty acid amide hydrolase (FAAH) genes are located on chromosomes 6 and 1 in the 6q15 and 1p33 cytogenetic bands, respectively. CNR1 encodes a seven-transmembrane domain protein of 472 amino acids, whereas FAAH encodes one transmembrane domain of 579 amino acids. Several mutations found in these genes lead to altered mRNA stability and transcription rate or a reduction of the activity of the encoded protein. Increasing evidence shows that these functional mutations are related to dependence upon cocaine, alcohol, marijuana, heroin, nicotine and other drugs. One of the most compelling associations is with the C385A single nucleotide polymorphism (SNP), which is found in the FAAH gene. For all of the genetic polymorphisms reviewed here, it is difficult to form overall conclusions due to the high diversity of population samples being studied, ethnicity, the use of volunteers, heterogeneity of the recruitment criteria and the drug addiction phenotype studied. Care should be taken when generalizing the results from different studies. However, many works have repeatedly associated polymorphisms in the CNR1 and FAAH genes with drug-related behaviours; this suggests that these genes should be examined in further genetic studies focusing on drug addiction and other psychiatric disorders.

Functional interactions between endogenous cannabinoid and opioid systems: focus on alcohol, genetics and drug-addicted behaviors

Although the first studies regarding the endogenous opioid system and addiction were published during the 1940s, addiction and cannabinoids were not addressed until the 1970s. Currently, the number of opioid addiction studies indexed in PubMed-Medline is 16 times greater than the number of cannabinoid addiction reports. More recently, functional interactions have been demonstrated between the endogenous cannabinoid and opioid systems. For example, the cannabinoid brain receptor type 1 (CB1) and mu opioid receptor type 1 (MOR1) co-localize in the same presynaptic nerve terminals and signal through a common receptor-mediated G-protein pathway. Here, we review a great variety of behavioral models of drug addiction and alcohol-related behaviors. We also include data providing clear evidence that activation of the cannabinoid and opioid endogenous systems via WIN 55,512-2 (0.4-10 mg/kg) and morphine (1.0-10 mg/kg), respectively, produces similar levels of relapse to alcohol in operant alcohol self-administration tasks. Finally, we discuss genetic studies that reveal significant associations between polymorphisms in MOR1 and CB1 receptors and drug addiction. For example, the SNP A118G, which changes the amino acid aspartate to asparagine in the MOR1 gene, is highly associated with altered opioid system function. The presence of a microsatellite polymorphism of an (AAT)n triplet near the CB1 gene is associated with drug addiction phenotypes. But, studies exploring haplotypes with regard to both systems, however, are lacking.

Cannabinoid-induced increase in relapse-like drinking is prevented by the blockade of the glycine-binding site of N-methyl-D-aspartate receptors

The endocannabinoid system is a neuromodulatory system which controls the release of multiple neurotransmitters, including glutamate and both, the endocannabinoid and glutamatergic systems, have been implicated in alcohol relapse. Cannabinoid agonists induce an increase in relapse-like drinking whereas glutamate receptor antagonists could prevent it. Here we hypothesize that cannabinoid-induced increases in relapse-like alcohol drinking could be mediated by glutamatergic N-methyl-d-aspartate (NMDA) receptors. To test this hypothesis, Wistar rats with a background of alcohol operant self-administration were treated with the cannabinoid receptor agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl), pyrrolo [1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate (WIN 55.212-2, WIN) (2.0 mg/kg) during periods of alcohol deprivation. For five consecutive days, 30 min before the reintroduction of alcohol, rats were injected with the NMDA/glycine receptor antagonist 7-chloro-4-hydroxy-3-(3-phenoxy)phenylquinolin-2-[1H]-one (L-701) (1.25-5.0 mg/kg) and alcohol reinforcement was evaluated. Our results clearly show that L-701 prevented the cannabinoid-induced increase in relapse-like drinking in a dose-dependent manner, whereas L-701 alone, in the absence of WIN treatment, did not significantly alter alcohol intake. The potentiation of relapse-like drinking induced by WIN is not caused by nonspecific anxiogenic effects, since no effect was observed in the elevated-plus maze test. These alcohol-related behaviors are linked to differential changes in CNR1 and NR1 subunit mRNA transcripts. In WIN-treated rats, an increase in CNR1 transcript levels was observed in the hypothalamus and striatum, whereas in the amygdala and anterior cingulate cortex, brain regions involved in emotional processing, a decrease was observed. Interestingly, such changes were blocked after L-701 treatment. Finally, WIN treatment also caused a reduction in NR1 mRNA levels in the amygdala. In conclusion, pharmacological inactivation of the glycine-binding site of NMDA receptors may control cannabinoid-induced relapse-like drinking, which is associated with altered expression of CNR1 and NR1 gene expression as observed after WIN treatment.

Nicotine in alcohol deprivation increases alcohol operant self-administration during reinstatement

Tobacco and alcohol are highly co-abused by humans. Most experimental studies have evaluated ethanol consumption in animals exposed concomitantly to nicotine. However, little is known regarding the effects of nicotine administered during periods of alcohol deprivation. In the present study, adult male Wistar rats with an extended background of operant self-administration of ethanol were alcohol-deprived and treated with nicotine (0.1, 0.2, 0.4 and 0.8 mg/kg) or saline during five consecutive days in one chamber of a place conditioning apparatus. Nicotine-induced changes in locomotion were monitored daily, whereas the expression of place conditioning was studied the day after the last nicotine injection. Forty-eight hours after testing for conditioning, the animals resumed operant self-administration of ethanol and their alcohol intake was evaluated during the next 14 days. We observed that alcohol consumption was increased in animals treated with nicotine at doses of 0.2, 0.4 and 0.8 mg/kg but not in animals treated with the dose of 0.1 mg/kg or saline. Additionally, the dose of 0.8 mg/kg of nicotine not only induced persistent changes in alcohol self-administration but also produced conditioned place aversion and depressed locomotor activity. These results indicate that nicotine administration during the ethanol deprivation period can exacerbate the maintenance of alcohol consumption.