On the Use of Heterogeneous Stock Mice to Map Transcriptomes Associated With Excessive Ethanol Consumption

We and many others have noted the advantages of using heterogeneous (HS) animals to map genes and gene networks associated with both behavioral and non-behavioral phenotypes. Importantly, genetically complex Mus musculus crosses provide substantially increased resolution to examine old and new relationships between gene expression and behavior. Here we report on data obtained from two HS populations: the HS/NPT derived from eight inbred laboratory mouse strains and the HS-CC derived from the eight collaborative cross inbred mouse strains that includes three wild-derived strains. Our work has focused on the genes and gene networks associated with risk for excessive ethanol consumption, individual variation in ethanol consumption and the consequences, including escalation, of long-term ethanol consumption. Background data on the development of HS mice is provided, including advantages for the detection of expression quantitative trait loci. Examples are also provided of using HS animals to probe the genes associated with ethanol preference and binge ethanol consumption.

Neuropeptidergic regulation of Compulsive Ethanol Seeking in C. elegans

An improved understanding of the molecular basis of alcohol seeking despite the catastrophic consequences of alcohol abuse is likely to enrich our treatments for Alcohol Use Disorders (AUD) and comorbidities. The compulsive seeking is characterized by an imbalance between the superior drive to substance and disruption in control of substance use. To model the development of compulsive engagement of alcohol seeking, we exploit two distinct behavioral programs of C. elegans in conflict, ethanol preference and avoidance of aversive stimulus, simultaneously. We demonstrate that C. elegans exhibited the recapitulation of the pivotal features of compulsive alcohol seeking in mammals, which are repeated attempts, endurance, and finally aversion-resistant ethanol seeking. We find that the neuropeptide signaling via SEB-3, CRF receptor-like GPCR, facilitates the development of ethanol preference and compels animals to seek ethanol compulsively. Furthermore, our functional genomic approach and behavioral elucidation suggest the interaction between neuropeptidergic signaling, SEB-3 and TKR-1, Neurokinin receptor orthologue, to progress compulsive ethanol seeking behavior.

Cannabinoids differentially modulate behavioral and developmental responses to ethanol in Drosophila

Prolonged prenatal or adult exposure to ethanol is detrimental to mental and physical well-being, resulting in developmental abnormalities, progressive addiction and ultimate death. A growing number of studies have shown the therapeutic potential of cannabinoids in ethanol-related behaviors in mammals. However, the potential pharmacological actions of cannabinoids in ethanol responses have not been examined in the model organism Drosophila melanogaster. Here, we systematically investigated the effects of various cannabinoids on ethanol preference, ethanol sensitivity and tolerance, and ethanol-induced developmental defect in Drosophila. We showed that treatment with the phytocannabinoid cannabidiol (CBD) displayed a significant decrease in preference for consuming ethanol in adult flies. Interestingly, cannabinoids exhibited differential roles in short- and long- term ethanol tolerance in flies. Although cannabinoids had no detectable effects on short-term ethanol tolerance, CBD and the endocannabinoid anandamide (AEA) suppressed long-term tolerance to ethanol. Moreover, ethanol exposure delayed larval-to-pupal development and increased larval/pupal size. Unexpectedly, treatment with CBD or endocannabinoids did not attenuate ethanol-induced developmental delay, instead, exacerbated its detrimental effect. Thus, our systematical study reveals, for the first time, a differential role of the cannabinoids in the modulation of ethanol-related responses in Drosophila.

Social Housing Leads to Increased Ethanol Intake in Male Mice Housed in Environmentally Enriched Cages

An individual's social environment affects alcohol intake. However, the complex interactions between social context and alcohol intake remain understudied in preclinical models. In the present study, we sought to characterize the effects of social housing on voluntary ethanol intake in male C567BL/6J mice using a continuous access two-bottle choice model. This was accomplished using HM2 cages, which allow for the continuous monitoring of individuals' fluid intake through radiofrequency tracking while they remain undisturbed in a group setting. These cages are moderately environmentally enriched compared to standard shoebox cages. By analyzing the levels of voluntary ethanol intake between socially- and individually-housed mice in HM2 cages, we were able to parse apart the effects of environmental enrichment vs. social enrichment. We found that while intake levels were overall lower than those observed when animals are singly housed in standard shoebox cages, socially-housed males consumed significantly more ethanol compared to individually-housed mice, suggesting that while environmental enrichment attenuates ethanol intake, social enrichment may, in fact, potentiate it. This effect was not specific for alcohol, however, in that ethanol preference did not differ as a product of social context. We also found that the total number of non-consummatory channel entries were consistently higher in individually-housed mice. Additionally, a single corticotropin releasing factor receptor 1 antagonist treatment significantly decreased both water and ethanol intake in socially- and individually-housed mice up to 3 h post-treatment, though the effect on water intake was longer lasting. This treatment also significantly decreased the number of non-consummatory channel entries in individually-housed mice, but not in socially-housed mice, suggesting that increased channel visits may be a stress-related behavior. Lastly, we examined blood ethanol concentrations and FosB immunoreactivity to characterize the physiological responses to ethanol intake in socially- and individually-housed mice. The number of FosB-positive cells in the centrally-projecting Edinger-Westphal nucleus and nucleus accumbens shell positively correlated with average baseline ethanol intake in individually-housed mice, but not in socially-housed mice. Overall, we found that social, but not environmental, enrichment can increase ethanol intake in male C57BL/6J mice. Future studies need to test this phenomenon in female mice and assess the generalizability of this finding.

Voluntary intake of psychoactive substances is regulated by the dopamine receptor Dop1R1 in Drosophila

Dysregulated motivation to consume psychoactive substances leads to addictive behaviors that often result in serious health consequences. Understanding the neuronal mechanisms that drive drug consumption is crucial for developing new therapeutic strategies. The fruit fly Drosophila melanogaster offers a unique opportunity to approach this problem with a battery of sophisticated neurogenetic tools available, but how they consume these drugs remains largely unknown. Here, we examined drug self-administration behavior of Drosophila and the underlying neuronal mechanisms. We measured the preference of flies for five different psychoactive substances using a two-choice feeding assay and monitored its long-term changes. We found that flies show acute preference for ethanol and methamphetamine, but not for cocaine, caffeine or morphine. Repeated intake of ethanol, but not methamphetamine, increased over time. Preference for methamphetamine and the long-term escalation of ethanol preference required the dopamine receptor Dop1R1 in the mushroom body. The protein level of Dop1R1 increased after repeated intake of ethanol, but not methamphetamine, which correlates with the acquired preference. Genetic overexpression of Dop1R1 enhanced ethanol preference. These results reveal a striking diversity of response to individual drugs in the fly and the role of dopamine signaling and its plastic changes in controlling voluntary intake of drugs.