Even after periods of abstinence, stress can potently trigger drug cravings and induce relapse. Uncontrollable stress prior to exposure to drug-associated cues (e.g. paraphernalia) can generate enhanced vulnerability to relapse. However, a stressor over which an animal can acquire control produces vastly different behaviors outcomes. These stressors, while still aversive, have been shown to endow animals with resilience against future stressors, even when these stressors occur in different contexts or require unique actions. In an animal model of stressor controllability, rats can turn a wheel to escape tail-shock (escapable stress; ES). However, yoked animals that receives physically identical shock have no such perception of control (inescapable stress; IS). After a single session of repeated trials, ES-experienced animals express reduced neophobia and hypervigilance, similar to stress-nave home-cage controls, while there IS counterparts exhibit heightened states of anxiety. Moreover, cocaine-experienced animals that have learned to control this stressor exhibit accelerated learning to extinguish cocaine-seeking behaviors. This suggests that stressful experiences may produce opposing effects on drug-seeking, dependent upon whether the stressor was controllable or not. It is unknown whether these bi-directional effects reflect distinct changes in the neural circuits responsive to triggers of drug craving, such as drug-associated cues. Notably, cue-reinforced drug-seeking is progressively enhanced over the first 30 days of cocaine abstinence, and this incubation of craving is thought to reflect changes in prelimbic cortex (PL) to nucleus accumbens (NAc) core connectivity. Therefore, the proposed experiments will explore whether controllable (ES) and uncontrollable (IS) stress experiences produce distinct effects on PLNAc core projections over the course of abstinence from either cocaine or sucrose.
In Aim 1, we will use fiber photometry of GCaMP6f transients to record calcium activity from these projections as animals are exposed to cues (i.e. lights) previously associated with administration.
In Aim 2, we will then determine whether these PLNAc core projections are engaged in and necessary for the learning of stressor controllability, such that optogenetic inhibition prevents later expression of trans-situational resilience. The proposed experiments will therefore delineate the role of PLNAc core neurons in the response to stress during abstinence and elucidate how stress-induced changes within these projections modulates drug-seeking behavior.
For addicted individuals, stress can induce drug cravings that trigger relapse episodes, even after long periods of abstinence. In some cases, however, a sense of control can be earned in situations where individuals overcome a stressful event, producing resilience when faced with future stressors, such as drug craving. The proposed experiments will explore the function of neural circuits responsible for this resilience, and investigate whether these changes could provide potential treatments for drug craving and relapse.
