The effects of the concentration of cocaine (0, 100, 200, 400 and 800 pmol/100 nl) infused into the nucleus accumbens shell on the average (± SEM) number of infusions received during sessions 4 (acquisition) and 7 (reinstatement) by P (left panel) and Wistar (right panel) rats. * indicates significantly greater infusions during session 7 by P rats (left panel) for the 100, 200, 400 and 800 pmol/100 nl groups compared to session 4, and greater infusions during session 7 by Wistar rats (right panel) for the 400 and 800 pmol/100 nl groups compared to session 4.