Figure 1
FIG. 1. Intravenous self-injection of caffeine in each of three male baboons with histories of self-injection of various stimulant and sedative drugs. Using methods similar to those described previously (52), injections were dependent on a lever-press response under fixed-ratio 2 (FR 2) schedule of reinforcement; daily sessions were terminated after 50 injections or after 2 hr, whichever came first. Data points show number of injections self-administered each day; numerals above points indicate number of injections when that number exceeded 32. Dashed line indicates the point at which saline (caffeine vehicle) was substituted for caffeine (Griffiths, Sannerud, and Kaminski, unpublished data; see Table 2).

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published 2000