Fig. 2.

Effects of baclofen, SKF97541, GHB, and GBL, administered intramuscularly immediately before the session, on fixed ratio 20 responding in a one-key, food-reinforced procedure in pigeons (n = 4–9). The potency to decrease the rate of key peck responding is plotted as a function of time from the beginning of the session. Circles represent ED₅₀ and 95% confidence limits. For each drug, open circles indicate ED₅₀ values that differed significantly from the lowest observed value, and closed circles indicate ED₅₀ values that did not. Squares represent interval estimates of ED₅₀ values.