No abstract

Use of exogenous cannabinoids disrupts the fine-tuned endocannabinoid receptor system, possibly leading to alterations in cognition, memory, and emotional processes that endure long after cannabinoid use has stopped. Long-term adolescent use may uniquely disrupt these behaviors when compared to adult use. The current study explored the acute and long-term behavioral effects of six 10 mg/kg Δ9-tetrahydrocannabinol (THC) injections across the adolescent or early adult period in male inbred C57Bl/6J and DBA/2J mice. The acute and prolonged effects of THC on object memory using the novel object recognition task, unconditioned anxiety in the elevated plus maze and open field, and sedative effects in the open field were examined. Acute THC treatment resulted in anxiogenic activity in both strains, but only caused sedation in B6 mice. Repeated THC treatment resulted in a protracted effect on object recognition, but not unconditioned anxiety, assessed 4 weeks later. In both strains, an adolescent history of THC treatment disrupted later object recognition. Interestingly, in B6 mice an adult history of THC exposure appeared to rescue a deficit in object recognition observed in vehicle-treated adults. Repeated THC administration also produced a protracted effected on CB1R protein expression. Animals treated with THC in adolescence maintained increased levels of CB1R protein expression compared to their adult THC-treated counterparts at five weeks following the last injection. These results indicate that THC use may have long-lasting effects with adolescence being a unique period of susceptibility.

The rise in cannabinoid legalization and decriminalization in the US has been paired with an increase in adolescents that perceive marijuana as a “no risk” drug. However, a comprehensive review of human literature indicates that cannabinoid usage may have both beneficial and detrimental effects, with adolescent exposure being a critical window for harming cognitive development. Although the cannabinoids Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) are often used together for recreational and medical purposes, no study has previously observed the acute and long-lasting effects of THC+CBD in a battery of behavioral assays analogous to subjective human reports. The current study observed the acute and long-term effects of THC, CBD, and THC+CBD on object recognition memory, anxiety-like behavior, and activity levels in adolescent and adult mice of both sexes. Acute THC alone and in combination with CBD resulted in robust effects on anxiety-like and locomotor behavior. A history of repeated cannabinoid treatment followed by a period without drug administration resulted in minimal effects in these behavioral assays. Most notably, the strongest effects of repeated cannabinoid treatment were seen in adult females administered THC+CBD, which significantly impaired their object recognition. No effects of repeated cannabinoid history were present on hippocampal protein expression. These studies represent a detailed examination of age- and sex-effects of acute and repeated cannabinoid administration. However, the acute and long-term effects of THC with and without CBD on additional behaviors in adolescents and adults will need to be examined for a more complete picture of these drug effects.

The GABAB agonist baclofen has been widely researched clinically and preclinically as a treatment of alcohol use disorders (AUDs). However, the efficacy of baclofen remains uncertain. The clinically used racemic compound can be separated into separate enantiomers. These enantiomers have produced different profiles in behavioral assays, with the S- compound often being ineffective compared to the R- compound, or the S- compound antagonizing the effects of the R- compound. We have previously demonstrated that the R(+)-baclofen enantiomer decreases binge-like ethanol intake in the Drinking-in-the-Dark (DID) paradigm, whereas the S(-)-baclofen enantiomer increases ethanol intake. One area implicated in drug abuse is the nucleus accumbens shell (NACsh).The current study sought to define the role of the NACsh in the enantioselective effects of baclofen on binge-like ethanol consumption by directly microinjecting each enantiomer into the structure. Following bilateral cannulation of the NACsh, C57Bl/6J mice were given 5 days of access to ethanol or saccharin for 2 hours, 3 hours into the dark cycle. On Day 5 mice were given an injection of aCSF, 0.02 R(+)-, 0.04R(+)-, 0.08 S(-)-, or 0.16 S(-)-baclofen (μg/side dissolved in 200nl of aCSF). It was found that the R(+)-baclofen dose-dependently decreased ethanol consumption, whereas the high S(-)-baclofen dose increased ethanol consumption, compared to the aCSF group. Saccharin consumption was not affected. These results further confirm that GABAB receptors and the NACsh shell are integral in mediating ethanol intake. They also demonstrate that baclofen displays bidirectional, enantioselective effects which are important when considering therapeutic uses of the drug.

The GABAB receptor agonist baclofen has been studied extensively in preclinical models of alcohol use disorders, yet results on its efficacy have been uncertain. Racemic baclofen, which is used clinically, can be broken down into separate enantiomers of the drug. Baclofen has been shown to produce enantioselective effects in behavioral assays including those modeling reflexive and sexual behavior. The current studies sought to characterize the enantioselective effects of baclofen in two separate models of ethanol consumption. The first was a Drinking-in-the-Dark procedure that provides “binge-like” ethanol access to mice by restricting access to a two hour period, three hours into the dark cycle. The second was a two-bottle choice procedure that utilized selectively bred High Alcohol Preferring 1 (HAP1) mice to model chronic ethanol access. HAP1 mice are selectively bred to consume pharmacologically relevant amounts of ethanol in a 24-hour two-bottle choice paradigm. The results showed that baclofen yields enantioselective effects on ethanol intake in both models, and that these effects are bidirectional. Total ethanol intake was decreased by R(+)- baclofen, while total intake was increased by S(-)-baclofen in the binge-like and chronic drinking models. Whereas overall binge-like saccharin intake was significantly reduced by R(+)- baclofen, chronic intake was not significantly altered. S(-)- baclofen did not significantly alter saccharin intake. Neither enantiomer significantly affected locomotion during binge-like reinforcer consumption. Collectively, these results demonstrate that baclofen produces enantioselective effects on ethanol consumption. More importantly, the modulation of consumption is bidirectional. The opposing enantioselective effects may explain some of the variance seen in published baclofen literature.

Background Crossed High Alcohol Preferring (cHAP) mice were selectively bred from a cross of the HAP1xHAP2 replicate lines, and demonstrate blood ethanol concentrations (BECs) during free-choice drinking reminiscent of those observed in alcohol-dependent humans. In this report, we investigated the relationship between free-choice drinking, intoxication, tolerance, and sensitization in cHAP mice. We hypothesized that initially mice would become ataxic after drinking alcohol, but that increased drinking over days would be accompanied by increasing tolerance to the ataxic effects of ethanol. Methods Male and female cHAP mice had free-choice access to 10% ethanol and water (E), while Water mice (W) had access to water alone. In experiment 1, the first drinking experience was monitored during the dark portion of the cycle. Once E mice reached an average intake rate of ≥1.5 g/kg/h, they, along with W mice, were tested for footslips on a balance beam, and BECs were assessed. In experiments 2, 3, and 4, after varying durations of free-choice 10% ethanol access (0, 3, 14 or 21 days), mice were challenged with 20% ethanol and tested for number of footslips on a balance beam or locomotor stimulant response. Blood was sampled for BEC determination. Results We found that cHAP mice rapidly acquire alcohol intakes that lead to ataxia. Over time, cHAP mice developed behavioral tolerance to the ataxic effects of alcohol, paralleled by escalating alcohol consumption. However, locomotor sensitization did not develop following 14 days of free-choice ethanol access. Conclusions Overall, we observed increases in free-choice drinking with extended alcohol access paralleled by increases in functional tolerance, but not locomotor sensitization. These data support our hypothesis that escalating free-choice drinking over days in cHAP mice is driven by tolerance to alcohol’s behavioral effects. These data are the first to demonstrate that escalating free-choice consumption is accompanied by increasing alcohol tolerance. In addition to buttressing the hypothesized importance of tolerance in drinking, our findings suggest that cHAP mice may be a unique, translational resource for studying tolerance as a contributor to and consequence of chronic, excessive ethanol consumption.

Background Binge co-consumption of highly caffeinated energy drinks with alcohol (ethanol) has become a common practice among adolescents/young adults and has been associated with an increased incidence of hazardous behaviors. Animal models are critical in advancing our understanding the neurobehavioral consequences of this form of binge drinking. Surprisingly, virtually no work has explored caffeine and ethanol co-consumption or its long-term consequences in adolescent animals. The primary objective of the current study was to extend a previously established mouse model of voluntary binge caffeine and ethanol co-consumption to explore adolescent consumption and responses compared to adults. Methods Adolescent and adult male C57BL/6J mice had daily limited access to caffeine (0.03% w/v), ethanol (20% (v/v), a combined ethanol/caffeine solution, or water for 14 days via the binge-like drinking paradigm, Drinking-in-the-Dark. Home cage locomotor activity was measured during DID in a subset of mice. Following DID, all mice rested for 18 days so that adolescents reached adulthood, whereupon all mice underwent 7 days of continuous access two-bottle choice drinking for 10% (v/v) ethanol or water. Results Co-consumption with caffeine significantly increased ethanol intake and resultant blood ethanol concentrations in both adolescent and adult mice. In addition, adolescent mice exhibited a uniquely robust locomotor stimulant response to caffeine and ethanol co-consumption. Later ethanol intake and preference was not influenced, however, by prior fluid consumption history via DID. Conclusion Together with findings from the human literature, our results suggest that caffeine co-consumption may positively influence binge alcohol consumption in adolescents/young adults. Importantly, this age group may be particularly sensitive to the additive stimulant effects of caffeinated alcohol consumption, an effect which may be related to the high incidence of associated negative outcomes in this population. These observations are particularly concerning considering the heightened plasticity of the adolescent brain.

Allosteric modulators of metabotropic glutamate 5 receptors (mGlu5 receptors) have been identified as a promising treatment to independently alleviate both negative affective states and ethanol-seeking and intake. However, these conditions are often comorbid and might precipitate one another. Acute and protracted ethanol withdrawal can lead to negative affective states. In turn, these states are primary drivers of alcohol relapse, particularly among women. The current review synthesizes preclinical studies that have observed the role of mGlu5 receptor modulation in negative affective states following ethanol exposure. The primary behavioral assays discussed are ethanol-seeking and intake, development and extinction of ethanol-associated cues and contexts, behavioral despair, and anxiety-like activity. The work done to-date supports mGlu5 receptor modulation as a promising target for mediating negative affective states to reduce ethanol intake or prevent relapse. Limitations in interpreting these data include the lack of models that use alcohol-dependent animals, limited use of adolescent and female subjects, and a lack of comprehensive evaluations of negative affective-like behavior.