Conditioned stress prevents cue-primed cocaine reinstatement only in stress-responsive rats

Neurobiological mechanisms underlying comorbid posttraumatic stress disorder (PTSD) and cocaine use disorder (CUD) are unknown. We aimed to develop an animal model of PTSD+CUD to examine the neurobiology underlying cocaine-seeking in the presence of PTSD comorbidity. Rats were exposed to cat urine once for 10-minutes and tested for anxiety-like behaviors one week later. Subsequently, rats underwent long-access (LgA) cocaine self-administration and extinction training. Rats were re-exposed to the trauma context and then immediately tested for cue-primed reinstatement of cocaine-seeking. Plasma and brains were collected afterwards for corticosterone assays and real-time qPCR analysis. Urine-exposed (UE; n=23) and controls not exposed to urine (Ctrl; n=11) did not differ in elevated plus maze behavior, but UE rats displayed significantly reduced habituation of the acoustic startle response (ASR) relative to Ctrl rats. A median split of ASR habituation scores was used to classify stress-responsive rats. UE rats (n=10) self-administered more cocaine on Day 1 of LgA than control rats (Ctrl+Coc; n=8). Re-exposure to the trauma context prevented cocaine reinstatement only in stress-responsive rats. Ctrl+Coc rats had lower plasma corticosterone concentrations than Ctrls, and decreased gene expression of corticotropin releasing hormone (CRH) and Glcci1 in the hippocampus. Rats that self-administered cocaine displayed greater CRH expression in the amygdala that was independent of urine exposure. While we did not find that cat urine exposure induced a PTSD-like phenotype in our rats, the present study underscores the need to separate stressed rats into cohorts based on anxiety-like behavior in order to study individual vulnerability to PTSD+CUD.