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Briana Hempel

Briana Hempel in Asbury courtyard.

bg0767a@student.american.edu

Curriculum Vitae

I am a fifth year doctoral student in the behavior, cognition and neuroscience program at American University. My research interests center around the motivational properties of marijuana and their neurobiological mediation, including how a number of environmental and experiential factors influence marijuana use and abuse. Our lab investigates the affective properties of abused drugs using animal models. Although the rewarding properties of a given compound are typically described as driving its abuse, we posit that both the rewarding and aversive effects of a drug impact drug-taking behavior and that assessing these stimulus properties can enable better predictions of abuse liability.

Marijuana abuse is particularly difficult to study in animals, as there is currently no reliable pre-clinical rodent model. The majority of my research has focused on developing a viable model by assessing factors that are known to enhance the rewarding properties of abused drugs, and more recently, attempting to bridge the gap between human recreational marijuana use (typically inhalation of the plant material) versus drug administration in animal research (intraperitoneal injections of Δ9-tetrahydrocannabinol or THC, the main psychoactive component of marijuana).

In my master’s thesis, I sought to optimize the conditions under which THC’s rewarding properties might be demonstrated by giving rats a history of THC prior to an assessment of its subjective effects (i.e. place and taste conditioning). My data showed that although a drug history of THC clearly weakened its aversive effects, there was no corresponding rise in reward. These findings indicate that even when the negative subjective effects of THC (likely anxiety, paranoia, etc.) are eliminated, rats do not find THC rewarding. However, the marijuana plant includes over 80 other phytocannabinoids besides THC that likely modulate its overall subjective effect. As such, I investigated whether cannabidiol (CBD), a prominent phytocannabinoid known for its therapeutic properties, is able to impact THC’s affective profile. Overall, CBD had a transient and weak effect on THC induced place aversions, such that at one dose ratio (1:1 CBD:THC) the aversive properties of THC were attenuated. Based on these findings, it’s likely that CBD alone is not shifting the abuse liability of marijuana. However, a full analysis of different phytocannabinoid combinations and their relative abuse potentials is much needed. 

For my dissertation studies, I shifted my focus from THC’s rewarding effects to how THC modified the affective profile of other drugs. I became interested in the field of transgenerational inheritance, whereby ancestral experience with an environmental stimulus (e.g., a drug of abuse) prior to conception produces altered phenotypes in the next generation likely via epigenetic changes to germ cells. Specifically, I explored how parental exposure to THC impacted the self-administration of cocaine, heroin and nicotine in adult male and female offspring. Interestingly, we found that male, but not female, subjects with a parental THC history exhibited decreased motivation to self-administer heroin, but not cocaine or nicotine. This work suggests that cross-generational THC experience may impact abuse vulnerability in progeny in a drug and sex specific manner.