Role of prelimbic cortical endocannabinoid signaling in enhanced cocaine-seeking behavior following combined repeated stress and cocaine use in rats

Project summary/Abstract Addiction remains a vast problem in the United States and complicating the issue is the lack of FDA-approved medications for the treatment of cocaine use disorder (CUD) making it a critical unmet need. A difficulty in identifying treatment options is that CUD is multi-faceted involving interactions among several external factors, including stress, which is unavoidable in daily life. Despite the prevalence of stress in human populations of CUD, most pre-clinical addiction research does not incorporate stress as a factor during periods of drug use. To examine the importance of stress-cocaine interactions on cocaine use and seeking behavior we use a model where, in rats demonstrating otherwise stable cocaine self-administration (SA), a stressor delivered daily at the time of cocaine SA, escalates cocaine intake and enhances cocaine-seeking behavior. This likely involves neurobiological mediators that connect stress-responsive and reward systems in the brain, such as endocannabinoid signaling (eCB). In support of this, systemic administration of a cannabinoid receptor 1 antagonist attenuates cocaine-induced reinstatement only in rats with a history of stress. Furthermore, we have localized this effect to the prelimbic cortex (PrL), a key site for regulation of stress and drug-seeking behavior. Importantly, eCB signaling, through attenuation of inhibitory neurotransmission, is well positioned to regulate PrL pyramidal neuron activity and output which ultimately results in expression of enhanced cocaine-seeking behavior. This proposal tests the novel hypothesis that repeated stress at the time of cocaine SA produces long-lasting upregulation of eCB signaling in the PrL leading to increased pyramidal neuron activity and drug- seeking behavior through dysregulated GABAergic signaling. To test this hypothesis, we will use behavioral, molecular, and neurophysiological techniques to assess the involvement of PrL eCB signaling in the long-term consequences of repeated stress-cocaine interactions. First, we will assess the role of PrL eCB signaling, via pharmacological manipulation, in enhanced cocaine-induced reinstatement in stress-escalated rats. We will then identify how combined repeated stress and cocaine SA regulates PrL eCB signaling by quantifying cell type-specific changes in molecular components of the eCB system using fluorescent in situ hybridization, and measure changes in PrL eCB content with mass spectrometry following cocaine-induced reinstatement. Lastly, we will examine changes in eCB-mediated inhibitory synaptic plasticity that are associated with enhanced cocaine-induced reinstatement, using whole-cell patch clamp recordings in the PrL. We will also use in vivo fiber photometry measurement of Ca2+signaling to identify the contribution of eCB signaling to changes in PrL pyramidal neuron activity associated with enhanced cocaine-induced reinstatement. These studies will provide much needed information about how stress-drug interactions regulate prefrontal cortical circuits and has treatment implications for those with CUD, especially for those for whom stress is a predominant contributing factor by identifying unique neurobiological mechanisms that may provide therapeutic targets.