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. Author manuscript; available in PMC: 2010 Sep 1.
Published in final edited form as: Psychopharmacology (Berl). 2009 May 30;205(4):565–575. doi: 10.1007/s00213-009-1563-y

Fig. 2.

Fig. 2

Cocaine self-administration under a fixed-ratio schedule of reinforcement. Data are expressed as the number of injections on the left axis and milligram per kilogram on the right axis. Error bars are SEM values. Open symbols are the data in rats with 1-h access to cocaine (ShA). Filled symbols are the data in rats with 6-h access (LgA). a Data from an entire session for each group, b data from the first hour of a 6-h session in LgA rats and from a 1-h session in ShA rats. *p<0.05, ***p<0.001 compared with session 1