Figure 5. Reacquisition of Cocaine Self-administration in Vaccinated Monkeys.

Number of cocaine (●) and candy (○) reinforcers earned each session (maximum = 10) during the reacquisition phase when cocaine was available again in the 4 vaccinated monkeys (V1–V4). B = baseline and refers to the number of cocaine and candy reinforcers earned during week 20 of the cocaine self-administration phase (see Figure 2 C–F; week −1 was used for V2, the one monkey who shifted preference from cocaine to candy). Gray arrows indicate when dAd5GNE or vehicle was administered. The x-axis corresponds to weeks post-vaccination and indicates the number of sessions to reacquire cocaine self-administration for each monkey. Gray circles indicate when the candy lever was locked and only cocaine was available (V2, V3 and V4). The first set of dashed arrows indicate when the response cost was reduced (FR dec) to FR5 for cocaine and FR1 for candy (V2, V3 and V4) and the second set of dashed arrows indicate when the cocaine dose available for self-administration was doubled (Dose inc) to 0.2 mg/kg/injection under the lower response requirements (V3 and V4). Vaccinated monkey V2 did not reliably reacquire cocaine self-administration after 61 sessions despite reducing the response requirement and occasionally locking the candy lever. Further testing could not be conducted due to a failed VAP near study completion (indicated by the break on the x-axis). For vaccinated monkey V3, experimental testing was interrupted due to blockage of the VAP (indicated by the break on the x-axis). Typically there were 4–5 sessions per week; each data point (other than B) represents a single session.