Fig. 4.
Modeled intra-accumbens cocaine levels fluctuate widely and are reduced to low levels at breakpoint. A, Strip chart histogram of the firing of an LPE cell (filled bars) during a PR session; bin width is 30 sec. Dotted line reflects modeled cocaine levels during this experiment; inputs to the model were the times at which cocaine rewards were received during this session. Vertical dashesabove the plot indicate lever presses;R indicates reward. Note decrease in cocaine level with increased PR and cell firing. B, Comparison of modeled cocaine levels for PR (dotted line) and FR (black line) sessions. Inputs to the model depicted by these lines were the mean inter-reward intervals obtained from rats during PR and FR sessions. Load up rewards were spaced 30 sec apart.