Figure 6. Baroreflex excitation of cardiac vagal ganglion principal cells.

Increasing the perfusion pressure (by increasing perfusate flow) produced a train of EPSPs (revealed by injection of hyperpolarising current) that underlay the spike discharge of principal cells (seen in Fig. 5B). These EPSPs were only triggered once the pressure passed a threshold level of ∼20 mmHg above basal perfusion pressure (dotted lines). The frequency of discharge mirrored the rise in pressure to reach a maximum frequency of 40 Hz at the peak of the pressure response. The EPSPs were seen to temporally summate during the peak of the response although this was counterbalanced by the diminished amplitude of the closely consecutive synaptic events. This suggests the potential for intricate synaptic integration within the principal cells.