Figure 4. Recruitment of nicotinic EPSPs in the intact superior cervical ganglion using graded presynaptic stimuli.

An example of simultaneous extracellular and intracellular recordings from the acutely isolated intact SCG. A, compound postsynaptic responses were recorded from the ECN. As stronger presynaptic stimuli were applied to the cervical sympathetic trunk, the compound responses grew larger in magnitude. B, simultaneous whole cell recordings from a class 1 SCG neuron. C, the subthreshold responses at the two lower stimulus intensities in panel B are averages comprised of the individual subthreshold secondary EPSPs shown here. In this experiment the postsynaptic responses evoked by 70 μA shocks straddled the action potential threshold. Increasing the stimulus to 80 μA recruited a suprathreshold primary EPSP that distorted the hyperpolarizing spike afterpotential to produce an early depolarizing component. ECN. external carotid nerve.