Figure 10. Spontaneous EPSPs in cardiac vagal ganglion principal cells come from a single vagal preganglionic source.

A, with the cell hyperpolarised for 2 min to prevent action potential discharge the EPSPs were discriminated from the first derivative of the voltage trace and plotted as an autocorrelogram (bin width 5 ms). This showed a distinctive central valley feature with an absolute period of synaptic silence of 10 ms and a relative quiescent period (half valley width) of around 150 ms. This pattern of autocorrelogram strongly suggests that the spontaneous EPSPs were originating form a single active preganglionic neurone and the valley is a consequence of the absolute and relative refractory periods of the parasympathetic preganglionic neurone.B, to illustrate the effect of having two active independent preganglionic neurones, the data from the first minute and the second minute of the recording inAwere overlaid on a single time series that was then stretched twofold in the time domain. This was used to represent an equivalent data set but from two independent preganglionic inputs. As can be seen the central valley feature is lost.