FIGURE 9.

Baclofen enhances PPF of fEPSP_slope. (A) Cumulative data of the effects of various baclofen concentrations on PPF are shown for the dorsal and the ventral hippocampus; example traces obtained before (traces in black) and during application of 10 μM baclofen (traces in violet) in a dorsal and a ventral slice are shown on the top of the graph. In the example of the dorsal hippocampus, similar unconditioned fEPSP_slope under control and drug conditions were selected for comparison reasons. Drug concentrations are segregated into three groups: 0.5−1, 5−10, and 20–100 μM. PPF is expressed as the percent change of the ratio fEPSP2/fEPSP1 observed under baclofen with respect to control conditions. The number of slices used in each condition is indicated into parenthesis on the top of each bar. Baclofen significantly increased PPF in both hippocampal segments (ANOVA, F = 4.8, p < 0.005 in dorsal and F = 5.6, p < 0.001 in ventral hippocampus). (B) The antagonist of GABA_BR CGP52432 (10 μM) reversed the increase of PPF induced by 20 μM baclofen in four dorsal and four ventral slices (asterisks indicate statistically significant difference with respect to control values, at p < 0.05, paired t-test). Blockade of GABA_BRs under basal conditions did not significantly affect PPF in either dorsal (n = 8) or ventral (n = 4) hippocampal slices. In all cases PPF was induced at 50 ms. Respective examples are shown on the top of the graph. (C) PPF plotted as a function of IPI in dorsal (left) and ventral (right) under control conditions, application of CGP52432, and application of baclofen with or without adjustment of fEPSP_slope to control levels. Horizontal bars denote statistically significant differences between control and baclofen-corrected conditions (paired t-test, p < 0.05). Also, asterisks in the left graph indicate that application CGP52432 significantly increased PPF in dorsal slices.