PET Imaging of neurochemical transmission in cocaine use disorders

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Cocaine use disorder (CUD) is a chronic disorder associated with numerous relapses and periods of abstinence. Studies in CUD suggest that ~ 60 to 75% of abstinent addicts relapse over twelve months (Aharonovich et al., 2003; Simpson et al., 1999). Documenting specific neurochemical abnormalities that lead to relapse in individuals with CUD has the potential to accelerate the development of medications to prevent relapse. Basic investigations postulate an imbalance between brain stress and anti-stress/resilience systems as the underlying mechanism that drives negative reinforcement, craving, and relapse in addiction (Koob, 2008). Nociceptin (N/OFQ), which binds to the nociceptive opioid peptide receptors (NOP) is a critical component of the brain’s anti-stress system. N/OFQ exerts its anti-stress effect by counteracting the functional effects of the primary stress-promoting neuropeptide corticotrophin releasing factor (CRF) in the brain (Ciccocioppo et al., 2001). Studies have also shown that acute increases in CRF and stress are countered by increased NOP receptor expression (~ 10% ) in brain regions that regulate stress such as the bed nucleus of the stria terminalis (Rodi et al., 2008). PET studies with the NOP radiotracer [11C]NOP-1A show increased binding to NOP in CUD compared to healthy controls (HC) (Narendran et al., 2019). PET studies also show NOP receptors to upregulate (~ 15%) in response to an acute intravenous hydrocortisone challenge (1 mg/Kg). NOP upregulation may represent an adaptive mechanism in the brain to counteract stress-induced increases in cortisol and CRF. Here, we postulate a failure in this adaptive mechanism as a reason that leads to relapse in CUD. CUD subjects and HC will be studied with [11C]NOP- 1A before and after an intravenous hydrocortisone challenge (aim 1). Hydrocortisone is used as a challenge because it increases cortisol and CRF in brain regions that regulate stress. We hypothesize that hydrocortisone-induced increases in [11C]NOP-1A binding (DVT) will be smaller in CUD relative to HC, and this will be associated with less time to relapse in a 12-week follow up. Mechanistic studies have also shown N/OFQ to act on ventral tegmental area/midbrain NOP receptors to inhibit the firing of dopamine neurons and limit reward to cocaine (Murphy and Maidment, 1999; Parker et al., 2019). Imaging amphetamine-induced dopamine release in a subset of CUD subjects who participate in aim 1 will allow us to link midbrain NOP receptor expression with ventral striatum (VST) dopamine release and examine its role in reinforcement (aim 2). The aims proposed in this study have the potential to clarify the role of N/OFQ and NOP in stress, reward, and relapse in CUD.