Fig. 4. Effects of activation of GABABreceptors by reverse dialysis of baclofen on nucleus accumbens levels of GABA, dopamine, and glutamate in chronic saline- and cocaine-treated rats. Increasing concentrations of baclofen were added to the dialysis buffer, and, in some experiments, 300 μm 2-OH-saclofen was added to the final concentration of baclofen to block the stimulation of GABAB receptors (B+S). A, Baclofen produced parallel effects on GABA in both treatment groups. A two-way ANOVA with repeated measures showed a significant difference between treatment (chronic saline vs cocaine;F(1,13) = 15.45; p= 0.0017) and over dose (F(16,208) = 2.03; p = 0.0128) but no time × treatment interaction (F(16,208) = 0.373;p = 0.987). B, Baclofen significantly decreased extracellular dopamine levels in both groups of rats. A two-way ANOVA with repeated measurement shows a significant difference over dose (F(17,204) = 8.05;p = 0.0001) but no difference between treatments (F(1,12) = 0.48; p= 0.51) or a time × treatment interaction (F(17,204) = 0.654;p = 0.845). C, Baclofen similarly decreased extracellular glutamate levels in both the saline- and cocaine-treated groups. A two-way ANOVA with repeated measurements shows a significant difference over dose (F(19,247) = 5.42;p = 0.0001) but no effect of treatment (F(1,13) = 0.1; p = 0.98) or the time × treatment interaction (F(19,247) = 1.09;p = 0.366). *p < 0.05 compared with the average of the last three of the five baseline samples.