Figure 7.

Effect of membrane-permeant cAMP analog (8-cpt-cAMP) on spikes elicited by fluctuating current injection. Recording mode, conditions, and figure format are as in Figure 5. A, Current injected (left) and histogram of current amplitude (right). The left and right parts of A superimpose two traces recorded at B and D in E, and their corresponding amplitude histograms, respectively. The inset superimposes current recorded between 8.0 and 8.1 s of each 10 s trace. The histograms fit to a Gaussian distribution with mean and SD of ∼5 pA (arrow) and 8 pA, respectively. B–D, Spiking and subthreshold membrane voltage changes induced by current in A, ∼5 min before (B), ∼5 min after (C), and ∼13 min after (D) application of 8-cpt-cAMP began (here, 2 μl of 50 mm stock solution was added to 0.9 ml recording bath). Histograms of voltages traversed during each fluctuating current injection are plotted to right. Mean voltages between and during fluctuating current injections were set to −72 mV (dashed horizontal line through voltage traces) and −58 mV (at arrow next to each histogram), respectively. E, Time course of 8-cpt-cAMP effect on total spike number. Each point plots total number of spikes elicited by 10 s injection of fluctuating current (e.g., those in B–D are plotted at correspondingly labeled times in E). F, G, Membrane voltage on expanded timescale. Three traces recorded at times bracketed before and during 8-cpt-cAMP in E are superimposed in F and G, respectively.