Amphetamine Infusions during Acquisition of Self-Administration. Top Panel: Mean (± SEM) number of infusions earned during the autoshaping phase (sessions 1–7) and after autoshaping was discontinued (sessions 8–10). Middle Panel: Mean (± SEM) number of infusions earned during contingent self-administration sessions during the autoshaping phase (sessions 1–7) and after autoshaping was discontinued (sessions 8–10), collapsed across strain. * indicates a significant difference from EC, p < 0.05; # indicates a significant difference from SC, p < 0.05. Bottom Panel: Mean (± SEM) number of infusions earned for each group during the final day of acquisition (session 10). # indicates a significant difference between LEW and F344 within the SC environment, p < 0.05; * indicates a significant difference from IC within the same strain, p < 0.05.