Analyzing the Role of Neuropeptides in the Neurobiology and Physiology of Addiction

Addiction only occurs in a subset of individuals who use drugs of abuse, and understanding the factors contributing to susceptibility is crucial for the prevention and treatment of addiction. Pre-existing biological factors may increase individual susceptibility to behaviors associated with compulsive drug-use. These factors may affect the transition from recreational drug use, to abuse, to addiction. Understanding and identifying biological pathways involved in the likelihood of becoming addicted will provide us with biomarkers to identify individuals with increased susceptibility to drug-abuse and determine therapeutic targets for addiction. In the Carlyle lab we are studying the role of neuropeptides in cognitive impairment; work by us and others have identified neuropeptides such as neurosecretory protein VGF (VGF) and chromogranin A (CHGA) to be consistently dysregulated in the brains and biofluids of patients with dementia. These neuropeptides have also been linked to psychiatric disorders including major depressive and bipolar disorder. We will investigate a putative role for neuropeptides in addiction vulnerability and consequence by combining our strengths in bioinformatics, biomarkers, and neuropeptide analysis with Dr. Stephanie Groman’s expertise in biobehavioral mechanisms of addiction at Yale. Dr. Groman has identified two decision-making parameters: one predictive of future drug-abuse (”vulnerability” Δ1 parameter), and one altered after chronic drug exposure (“consequence” Δ2 parameter). In Dr. Groman’s dataset, there was a trend-level correlation between VGF abundance in the nucleus accumbens and the vulnerability parameter highlighting a potential role of neuropeptides in drug abuse, pathophysiology of addiction and psychiatric disorders, given their established role in dementia and depression.

The functional form of neuropeptides is as secreted, protease-cleaved peptide “proteoforms”. The proteoform composition of processed peptides from VGF and CHGA is currently poorly understood, as are the proteases involved in their cleavage. In Aim 1, we propose to use data-dependent proteomic methods to map size-selected neuropeptide proteoforms in rat cerebrospinal fluid (CSF), to then build a targeted data-independent acquisition method to accurately quantify key proteoforms. In Aim 2a, Dr. Groman will take CSF immediately before sacrifice from drug naïve adult animals exposed to escalating doses of morphine (or water control) during gestation. We will quantify neuropeptide proteoforms using the method built in Aim 1 and relate proteoform levels to decision-making processes. We hypothesize that changes in specific neuropeptide proteoforms will be linked to addiction vulnerability and consequence. In Aim 2b, we will test whether rats exposed to morphine during gestation have altered decision-making processes and altered neuropeptide CSF proteoform profiles after oxycodone self-administration. This proposal will help train the PI on drug abuse and the pathophysiology of addiction, while receiving further training on both data-dependent and data-independent mass spectrometry techniques. VGF and CHGA could represent common targets to enhance cognition after impairment and play a critical role in decision-making. When these neuropeptides are impaired in psychiatric diseases and drug abuse, this could lead to the aberrant decision-making processes that are observed in people diagnosed with psychiatric diseases such as addiction.