Investigating the Interaction Between Nicotine and GPR3: Gene expression, cell activity and withdrawal

PROJECT SUMMARY Nicotine products are a major public health problem worldwide, causing millions of deaths per year. The US government spends billions of dollars annually in healthcare costs due to nicotine-related illnesses. Further, electronic cigarette usage has skyrocketed, conferring additional addiction liability among the population. Most people using nicotine products report wanting to quit, but the vast majority are not successful in the long term. Cessation aids available, including nicotine replacement therapy, varenicline and bupropion, have limited long term efficacy. Recent research in our lab has focused on alternative targets for cessation aids, such as targeting the G-protein coupled receptor 3 (GPR3), an orphan receptor with promising results in mitigating nicotine intake. GPR3 is an orphan, Gas coupled receptor that exhibits constitutive activity. GPR3 is expressed in brain regions that mitigate nicotine intake and preliminary data shows that a GPR3 agonist decreases nicotine self- administration in male and female mice. It is unknown, however, if drug exposure regulates GPR3 expression in brain regions related to nicotine intake and withdrawal. It is also unknown how the GPR3 agonist alters the actions of nicotine on a cellular level. Further, we do not know the effects of GPR3 activity on nicotine withdrawal. To address these gaps in the field, this proposal aims to investigate environmental factors that influence GPR3 gene expression, effects of the GPR3 agonist on cell excitability and the effects of the GPR3 agonist on nicotine withdrawal. Because of the high GPR3 expression and known involvement in nicotine intake and withdrawal, the medial habenula will be the focus of the expression and electrophysiological experiments in this proposal. Aim 1 will test the effects of nicotine exposure on GPR3 expression in the medial habenula. For these studies, the effect of repeated nicotine exposure will be tested on their effects on GPR3 mRNA expression in the medial habenula. Aim 2 will test the effects of the GPR3 agonist on cell excitability in the medial habenula. For these studies, patch clamp electrophysiology will be used to determine the effects of the GPR3 agonist on cell firing frequency. The GPR3 agonist will be given in combination with nicotine to reveal the effects of GPR3 activity on nicotine-induced cell excitability. Lastly, aim 3 will test the effects of the GPR3 agonist on nicotine withdrawal symptoms in mice. Mice will be exposed to a nicotine vapor protocol that has been validated to increase nicotine withdrawal symptoms. For withdrawal testing, mice will be treated with the GPR3 agonist directly prior to testing in order to determine its effects on mitigating nicotine withdrawal symptoms. All studies in this proposal will be powered to detect sex differences, if any exist. Overall, these studies will provide insight into biological and environmental factors which may influence GPR3 expression, reveal the effects of a GPR3 agonist at a cellular level, and determine effects of GPR3 agonism on nicotine withdrawal symptoms.