School of Medicine Professor Receives Nearly $500K NIH Grant to Study Neural Mechanisms Related to Drug Addiction

Dr. Kristen Ashley Horner

MACON – Kristen Ashley Horner, Ph.D., professor of pharmacology in Mercer University School of Medicine, recently received a National Institutes of Health (NIH) Academic Research Enhancement Award (AREA) grant in the amount of $462,660 to further investigate the neural pathways that contribute to the development of habitual drug use.

AREA (also known as R15) grants support research projects in the biomedical and behavioral sciences conducted by faculty and students in health professional schools and other academic components that have not been major recipients of NIH research grant funds.

Dr. Horner’s project, titled “The Role of Patch Compartment Neurons in Reward and Habitual Behavior,” received an R15 grant through the NIH’s National Institute on Drug Abuse.

“I am absolutely thrilled and humbled that I am able to secure this funding from the National Institute on Drug Abuse and NIH to continue my research on the mechanisms of methamphetamine addiction,” said Dr. Horner. “I believe that understanding the neural pathways that contribute to addiction will allow us to approach the reversal of habitual drug use from an informed and precise standpoint. Furthermore, a knowledge of how habits are formed has a broad-based appeal, in that this information could be used to inform the neural underpinnings of a number of behaviors that are habitual in nature, from smoking to alcohol abuse to compulsive gambling.”

The primary focus of her project is to delineate whether a region of the brain called the patch compartment, which has been implicated in repetitive behaviors, contributes to the progression of goal-directed drug use to habitual and inflexible drug-seeking behaviors.

Habitual behavior is defined as behavior that is insensitive to outcome devaluation, meaning when habitual behavior is paired with a negative stimulus there is no effect on that behavior.

In a laboratory, rats can be trained to self-administer a sucrose solution, which results in a high level of sucrose self-administration. Once a high level of responding has been established, the rats can be given sucrose, followed by a large dose of lithium chloride, which results in gastrointestinal discomfort. Eventually the rat learns that sucrose is no longer rewarding, and develops an aversion to sucrose. However, after the rat has developed an aversion to sucrose, and is given the opportunity to once again self-administer sucrose, the rat will do so, and will respond at a level on par with what was seen prior to the pairing of sucrose with lithium chloride.

Another example of how outcome devaluation does very little to correct or reverse habitual behaviors can be found in a person who suffers from addiction to methamphetamine. The individual may be threatened with incarceration, losing their jobs, their families or even their lives; however, none of these things will deter an addict from seeking and using drugs.

Previous work in Dr. Horner’s laboratory has shown that destruction of the neurons of the patch compartment results in a reduction in habitual sucrose self-administration, and she hypothesizes that these neurons also participate in the development of habitual methamphetamine use.

Preliminary work on this project was funded by a Navicent Health Foundation research grant that was awarded to Dr. Horner’s lab in 2016, allowing her to gather data that she used in her NIH application.

“Support from the NIH will give us the opportunity to further investigate the factors that contribute to addiction,” added Dr. Horner. “I would like to thank Navicent Health and the School of Medicine for their support, without which this NIH grant would not have been possible.”

About Mercer University School of Medicine (Macon, Savannah and Columbus)

Mercer University’s School of Medicine was established in 1982 to educate physicians and health professionals to meet the primary care and health care needs of rural and medically underserved areas of Georgia. Today, more than 60 percent of graduates currently practice in the state of Georgia, and of those, more than 80 percent are practicing in rural or medically underserved areas of Georgia. Mercer medical students benefit from a problem-based medical education program that provides early patient care experiences. Such an academic environment fosters the early development of clinical problem-solving and instills in each student an awareness of the place of the basic medical sciences in medical practice. The School opened a full four-year campus in Savannah in 2008 at Memorial University Medical Center. In 2012, the School began offering clinical education for third- and fourth-year medical students in Columbus. Following their second year, students participate in core clinical clerkships at the School’s primary teaching hospitals: Medical Center, Navicent Health in Macon; Memorial University Medical Center in Savannah; and The Medical Center and St. Francis Hospital in Columbus. The School also offers master’s degrees in family therapy, preclinical sciences and biomedical sciences.