Developing a model of limited-access nicotine consumption in C57Bl/6J mice

The effects of electronic nicotine vapor on voluntary alcohol consumption in female and male C57BL/6 J mice

SIGNIFICANCE

Alcohol drinking and nicotine vaping often co-occur and dependence on both substances is common. However, the impact of nicotine vaping on alcohol consumption is not fully understood.

METHODS

We examined the effects of nicotine vaping on ethanol drinking in female and male C57BL/6 J mice using an electronic nicotine delivery system and intermittent access two-bottle choice (IA-2BC) drinking. Mice were exposed to electronic nicotine vapor (3%) or propylene glycol/vegetable glycerol (PG/VG) control for 3 h sessions daily for 4 weeks and voluntary alcohol consumption was monitored. Nicotine vapor exposure was stopped and voluntary alcohol drinking was measured for a 2 week abstinence period. We also examined the effects of alcohol and nicotine on locomotion, temperature, and nicotine metabolism.

RESULTS

Following acute nicotine vapor exposure, alcohol drinking was increased in males but not in females. Thermoregulation was disrupted following nicotine vapor exposure and voluntary drinking. Male and female mice displayed increased locomotor activity immediately following chronic nicotine vapor exposure, and an anxiolytic effect was seen in males. In nicotine vapor abstinence, female mice displayed increased alcohol consumption. Locomotor activity and anxiolytic effects remained elevated in male but not female mice. Female mice displayed higher levels of serum nicotine and hydroxycotinine, suggesting impaired metabolism following chronic drinking and nicotine vapor exposure.

CONCLUSION

Collectively, these results suggest that while both male and female ethanol-drinking mice experience the stimulatory effects of nicotine vapor, only in males is there a parallel increase in ethanol drinking and only females display impairments in nicotine metabolism after drinking.

Biomedical Research on Substances of Abuse: The Italian Case Study

Substances of abuse have the potential to cause addiction, habituation or altered consciousness. Most of the research on these substances focuses on addiction, and is carried out through observational and clinical studies on humans, or experimental studies on animals. The transposition of the EU Directive 2010/63 into Italian law in 2014 (IT Law 2014/26) includes a ban on the use of animals for research on substances of abuse. Since then, in Italy, public debate has continued on the topic, while the application of the Article prohibiting animal research in this area has been postponed every couple of years. In the light of this debate, we briefly review a range of methodologies - including animal and non-animal, as well as patient or population-based studies - that have been employed to address the biochemical, neurobiological, toxicological, clinical and behavioural effects of substances of abuse and their dependency. We then discuss the implications of the Italian ban on the use of animals for such research, proposing concrete and evidence-based solutions to allow scientists to pursue high-quality basic and translational studies within the boundaries of the regulatory and legislative framework.

Midazolam, methamphetamine, morphine and nicotine intake in high‐drinking‐in‐the‐dark mice

The high-drinking-in-the-dark (HDID) lines of mice were selectively bred for achieving high blood alcohol levels in the drinking-in-the-dark (DID) task and have served as a unique genetic risk model for binge-like alcohol intake. However, little is known about their willingness to consume other addictive drugs. Here, we examined (a) whether the HDID-1 and HDID-2 lines of mice would voluntarily consume midazolam, methamphetamine, morphine and nicotine in a DID test and (b) whether the HDID lines differ from their founders, heterogeneous stock/Northport (HS/NPT), in consumption levels of these drugs at the concentrations tested. Separate groups of HDID-1, HDID-2 and HS/NPT mice were given 4 days of access to each drug, using the single-bottle, limited-access DID paradigm. Male and female mice of both HDID lines consumed all four offered drugs. We observed no genotype differences in 40 μg/ml methamphetamine intake, but significant differences in nicotine, midazolam and morphine intake. Both HDID lines drank significantly more (150 μg/ml) midazolam than their founders, providing strong support for a shared genetic contribution to binge ethanol and midazolam intake. HDID-2 mice, but not HDID-1 mice, consumed more morphine (700 μg/ml) and more nicotine across a range of concentrations than HS/NPT mice. These results demonstrate that the HDID mice can be utilized for tests of voluntary drug consumption other than ethanol and highlight potentially important differences between HDID lines in risk for elevated drug intake.

Systemic administration of racemic baclofen reduces both acquisition and maintenance of alcohol consumption in male and female mice

Baclofen is a GABAB receptor agonist with proposed use as a treatment for alcohol use disorder (AUD). In preclinical studies, racemic baclofen decreases alcohol consumption in both mice and rats; however, there is a significant disparity in the efficacy of the drug across species. We previously demonstrated that baclofen is enantioselective, with the racemic enantiomer successfully reducing binge-like alcohol consumption during Drinking-in-the-Dark (DID) in C57BL/6J (B6) mice, as well as 24-h consumption during two-bottle choice (2BC) preference drinking in replicate 1 High Alcohol Preferring (HAP) mice. Here we extend these findings by investigating the effects of racemic baclofen on the acquisition and maintenance of alcohol consumption, locomotor activity, and saccharin drinking in two different mouse genotypes and drinking paradigms. Adult male and female B6 mice were allowed free access to 20% (v/v) alcohol for 2 h daily in a 14-day DID procedure. Adult male and female replicate 2 HAP (HAP2) mice were allowed 24-h access to 10% (v/v) alcohol versus tap water in a 2BC procedure for 14 days. Systemic injections of baclofen (0.0 or 3.0 mg/kg) were given 3 h into the dark cycle on days 1-5 in alcohol acquisition experiments and days 6-10 in alcohol maintenance experiments. We found that racemic baclofen significantly reduces acquisition of DID and 2BC alcohol drinking in male and female B6 and HAP2 mice, whereas it only significantly reduces the maintenance of DID alcohol intake in B6 mice. Racemic baclofen did not alter home cage locomotor activity but did alter saccharin intake, suggesting it may have nonspecific effects. The current data add to literature suggesting that smaller doses of racemic baclofen may be an effective treatment of AUD. Future work should focus on the longitudinal efficacy of racemic baclofen in high-drinking mouse genotypes to further investigate whether it is effective for those with a genetic predisposition to AUD.

Reducing effect of the novel positive allosteric modulator of the GABAB receptor, COR659, on binge-like alcohol drinking in male mice and rats

RATIONALE

Binge drinking (BD) is a widespread drinkingpattern that may contribute to promote the development of alcohol use disorder (AUD). The comprehension of its neurobiological basis and the identification of molecules that may prevent BD are critical. Preclinical studies demonstrated that positive allosteric modulators (PAMs) of the GABA_B receptor effectively reduced, and occasionally suppressed, the reinforcing and motivational properties of alcohol in rodents, suggesting their potential use as pharmacotherapy for AUD, including BD. Recently, we demonstrated that COR659, a novel GABA_B PAM, effectively reduced (i) alcohol drinking under the 2-bottle choice regimen, (ii) alcohol self-administration under both fixed and progressive ratio schedules of reinforcement, and (iii) cue-induced reinstatement of alcohol-seeking behavior in Sardinian alcohol-preferring (sP) rats.

OBJECTIVES

The present study investigated whether the "anti-alcohol" properties of COR659 extend to binge-like drinking in rodents.

METHODS

COR659 was tested on the "drinking in the dark" (DID) paradigm in C57BL/6J mice and the 4-bottle "alcohol [10%, 20%, 30% (v/v)] versus water" choice regimen with limited and unpredictable access to alcohol in sP rats.

RESULTS

Acute administration of non-sedative doses of COR659 (10, 20, and 40 mg/kg; i.p.) effectively and selectively suppressed the intake of intoxicating amounts of alcohol (> 2 g/kg) consumed by C57BL/6J mice and sP rats exposed to these binge-like drinking experimental procedures.

CONCLUSIONS

The present data demonstrate the ability of COR659 to suppress binge-like drinking in rodents and strengthen the hypothesis that GABA_B PAMs may represent a potentially effective pharmacotherapy for alcohol misuse.

Rewarding Effects of Nicotine Self-administration Increase Over Time in Male and Female Rats

INTRODUCTION

Smoking and the use of other nicotine-containing products is rewarding in humans. The self-administration of nicotine is also rewarding in male rats. However, it is unknown if there are sex differences in the reward-enhancing effects of nicotine self-administration and if the rewarding effects of nicotine change over time.

METHODS

Rats were prepared with catheters and intracranial self-stimulation (ICSS) electrodes to investigate the effects of nicotine and saline self-administration on reward function. A decrease in thresholds in the ICSS procedure reflects an enhancement of reward function. The ICSS parameters were determined before and after the self-administration sessions from days 1 to 10, and after the self-administration sessions from days 11 to 15.

RESULTS

During the first 10 days, there was no sex difference in nicotine intake, but during the last 5 days, the females took more nicotine than the males. During the first 10 days, nicotine self-administration did not lower the brain reward thresholds but decreased the response latencies. During the last 5 days, nicotine lowered the reward thresholds and decreased the response latencies. An analysis with the 5-day averages (days 1-5, 6-10, and 11-15) showed that the reward enhancing and stimulatory effects of nicotine increased over time. There were no sex differences in the reward-enhancing and stimulatory effects of nicotine. The nicotinic receptor antagonist mecamylamine diminished the reward-enhancing and stimulatory effects of nicotine.

CONCLUSION

These findings indicate that the rewarding effects of nicotine self-administration increase over time, and there are no sex differences in the reward-enhancing effects of nicotine self-administration in rats.

IMPLICATIONS

This study investigated the rewarding effect of nicotine and saline self-administration in male and female rats. The self-administration of nicotine, but not saline, enhanced brain reward function and had stimulatory effects. The rewarding effects of nicotine increased over time in the males and the females. Despite that the females had a higher level of nicotine intake than the males, the reward-enhancing effects of nicotine self-administration were the same. These findings suggest that in new tobacco and e-cigarette users, nicotine's rewarding effects might increase quickly, and a higher level of nicotine use in females might not translate into greater rewarding effects.

Electronic Nicotine Vapor Exposure Produces Differential Changes in Central Amygdala Neuronal Activity, Thermoregulation and Locomotor Behavior in Male Mice

Nicotine is an addictive substance historically consumed through smoking and more recently through the use of electronic vapor devices. The increasing prevalence and popularity of vaping prompts the need for preclinical rodent models of nicotine vapor exposure and an improved understanding of the impact of vaping on specific brain regions, bodily functions, and behaviors. We used a rodent model of electronic nicotine vapor exposure to examine the cellular and behavioral consequences of acute and repeated vapor exposure. Adult male C57BL/6J mice were exposed to a single 3-h session (acute exposure) or five daily sessions (repeated exposure) of intermittent vapes of 120 mg/ml nicotine in propylene glycol:vegetable glycerol (PG/VG) or PG/VG control. Acute and repeated nicotine vapor exposure did not alter body weight, and both exposure paradigms produced pharmacologically significant serum nicotine and cotinine levels in the 120 mg/ml nicotine group compared with PG/VG controls. Acute exposure to electronic nicotine vapor increased central amygdala (CeA) activity in individual neuronal firing and in expression of the molecular activity marker, cFos. The changes in neuronal activity following acute exposure were not observed following repeated exposure. Acute and repeated nicotine vapor exposure decreased core body temperature, however acute exposure decreased locomotion while repeated exposure increased locomotion. Collectively, these studies provide validation of a mouse model of nicotine vapor exposure and important evidence for how exposure to electronic nicotine vapor produces differential effects on CeA neuronal activity and on specific body functions and behaviors like thermoregulation and locomotion.

Differential patterns of alcohol and nicotine intake: Combined alcohol and nicotine binge consumption behaviors in mice

Late adolescence and young adulthood, corresponding to the high school and college years, are vulnerable periods for increased alcohol and nicotine use. The dramatic increase in the prevalence of electronic cigarette use is particularly concerning in these age groups. Late adolescents and young adults are more likely to engage in cycles of binge drug consumption, and alcohol and nicotine are frequently used together. However, there are few data examining the combination of alcohol and nicotine in binge models in animal models. In this study, our objectives were to determine how voluntary nicotine consumption beginning in late adolescence influenced subsequent binge alcohol consumption in young adulthood, how a combination of alcohol and nicotine binge consumption differed from alcohol-only binge consumption, and whether nicotine would be consumed when presented in a binge procedure. Male C57BL/6J mice voluntarily consumed unsweetened alcohol and nicotine in continuous-access bottle-choice procedures in combination with cycles of drinking-in-the-dark. Our results show that experience with voluntary nicotine consumption in late adolescence did not affect subsequent binge alcohol consumption in early adulthood. However, mice that consumed nicotine in adolescence showed an initial decrease in alcohol preference, and consequently increase in nicotine preference, on the first session of combined ethanol and nicotine binge consumption in adulthood compared with mice that drank only water during late adolescence. Lastly, we found that mice readily consumed unsweetened nicotine when presented in a binge procedure, and the level of consumption exceeded the nicotine consumption observed in the combination alcohol and nicotine binge. Our data show that expansion of the patterns of alcohol and nicotine co-consumption in a mouse models is possible, which will enable us to dissect relevant molecular targets underlying these consumption patterns and better inform drug development efforts.

Therapeutic challenges for concurrent ethanol and nicotine consumption: naltrexone and varenicline fail to alter simultaneous ethanol and nicotine intake by female alcohol-preferring (P) rats

RATIONALE AND OBJECTIVES

Simultaneous alcohol and nicotine consumption occurs in the majority of individuals with alcohol use disorder (AUD) and nicotine dependence. Varenicline (Var) is used to assist in the cessation of nicotine use, while naltrexone (Nal) is the standard treatment for AUD. Despite evidence that ethanol (EtOH) and nicotine (NIC) co-use produces unique neuroadaptations, preclinical research has focused on the effects of pharmacotherapeutics on a single reinforcer. The current experiments examined the effects of Var and Nal on EtOH, NIC, or EtOH+NIC intake.

METHODS

Animals were randomly assigned to one of four drinking conditions of 24-h access to a three-bottle choice paradigm, one of which always contained water. Drinking conditions were water only, 0.07 and 0.14 mg/mL NIC (NIC only), 15% and 30% EtOH (EtOH only), or 15% and 30% EtOH with 0.14 mg/mL NIC (EtOH+NIC). The effects of Var (0, 1, or 2 mg/kg) or Nal (0, 1, or 10 mg/kg) injections on maintenance and relapse consumption were determined during four consecutive days.

RESULTS

Var reduced maintenance and relapse NIC intake but had no effect on EtOH or EtOH+NIC drinking. Conversely, Nal reduced EtOH maintenance and relapse drinking, but had no effect on NIC or EtOH+NIC drinking.

DISCUSSION

The results indicate the standard pharmacological treatments for nicotine dependence and AUD were effective at reducing consumption of the targeted reinforcer but neither reduced EtOH+NIC co-use/abuse. These findings suggest that co-abuse may promote unique neuroadaptations that require models of polysubstance abuse to develop pharmacotherapeutics to treat AUD and nicotine dependence.

Suppressing Effect of Baclofen on Multiple Alcohol-Related Behaviors in Laboratory Animals

This paper summarizes the several lines of experimental evidence demonstrating the ability of the prototypic GABA_B receptor agonist, baclofen, to suppress multiple alcohol-related behaviors in laboratory rodents and non-human primates exposed to validated experimental models of alcohol use disorder (AUD). Specifically, treatment with baclofen has repeatedly been reported to suppress alcohol-induced locomotor stimulation, alcohol drinking (including binge- and relapse-like drinking), operant oral alcohol self-administration, alcohol seeking, and reinstatement of alcohol seeking in rats and mice. Treatment with baclofen also reduced operant oral alcohol self-administration in baboons. Several of these effects appear to be mediated by GABA_B receptors located in the ventral tegmental area. The often observed co-occurrence of "desired" pharmacological effects and "unwanted" sedative effects represents the major drawback of the preclinical, anti-alcohol profile of baclofen. Collectively, these data underline the role of the GABA_B receptor in the mediation of several alcohol-related behaviors. These data possess remarkable translational value, as most of the above effects of baclofen have ultimately been reproduced in AUD patients.