Figure 1.

Cumulative records showing the behavioral (lever press) response pattern for a single animal during acquisition of self-administration in a water-cocaine multiple schedule. During the first session of cocaine exposure (initial), the animal completed 28 responses for water with a mean INT of 22.19 sec. During the self-administration phase, water was placed on the cocaine lever three times (indicated by open arrowheads), and the animal was primed several times (indicated by closed arrowheads). During the first session of reliable responding, lever pressing for water remained stable (16 presses; INT, 22.08), and responding for intravenous cocaine was present but erratic. During the stable component (day 7), behavioral responding was stable for both water (21 responses; mean INT, 42.85 sec) and cocaine (22 responses; mean INT, 6.13 min).