FIG. 3.

cAMP causes facilitation but not depression. A: facilitation after ∼40 min of superfused 10⁻³ M 8-Bromo cAMP. β1 and β2 are probably due to roughly synchronized 1st and 2nd firings of the interneurons recruited by the ganglionic root stimulus pulse. B: facilitation is produced by 8-Bromo cAMP at several concentrations. Note that facilitation does not abate during washout (measured in perfusion experiments). C: dose-response curve for various concentrations of superfused 8-Bromo cAMP (individual experiments small circles; averages large open circles with SEs indicated) and fast 5-HT (filled squares). Also shown are points from Teshiba et al. (2001) (filled triangles) and from Yeh et al. (1977) (filled circles), who used gradual applications of 5-HT in a concentration range where slow and fast application would be expected to have similar effects. N′s for higher-dose 5-HT experiments are indicated. Whereas 5-HT produces a maximum facilitation of ∼40% at 5 × 10⁻⁶ M (low) and becomes inhibitory at higher concentrations, cAMP can produce much greater facilitation presumably because it does not recruit competing depression.