Chunk #19 — Results — Differential dopamine release dynamics in the core versus shell relative to cocaine-reinforced responding during self-administration
in the core had two distinct components; an initial increase in dopamine within seconds before the response followed by a larger more sustained increase following response completion. As in prior studies, the pre-response increase began approximately 1 s before the response and reached a maximum of 80 nM. This was followed by a larger post-response increase in dopamine that peaked within 1 s following the operant response (maximum [DA] was 200 nM) and declined thereafter. Increases in [DA] were also observed before and following the response in the shell (representative example in Figure 1B). However, these included a larger pre-response increase, and a post-response that was less synchronized to the operant response than observed in the core. Specifically, the increase in dopamine signal in the shell began approximately 6 seconds preceding the response with a peak maximum concentration of 165 nM, exhibited a delayed post-response that peaked approximately 4 s after the press (250 nM) and remained elevated for approximately 9 s following response completion. Thus, dopamine signaling relative to the reinforced response for cocaine occurred in the shell, but appeared to be of longer duration and was not so tightly time-locked to the response as that observed in the
