Fig. 8. ( A ) The sag ratio is an indication of the influence of IH(H current) on transmembrane potential during hyperpolarization. Voltage trace ( top panel ) of an Aα/β control neuron is shown during injection of hyperpolarizing current through the recording electrode (current trace in lower panel ). Sag ratio is quantified as the degree of voltage relaxation (sag) toward resting membrane potential during hyperpolarization as a fraction of total hyperpolarization. ( B ) After spinal nerve ligation, sag is decreased in directly injured L5 neurons but is increased in adjacent L4 neurons. Mean ± SEM. Symbols are described in the legend to figure 3 . ( C ) Anode break action potential (AP) may follow depolarization after a period of hyperpolarization. A voltage trace of an Aα/β control neuron is shown during membrane hyperpolarization by current injection through the recording electrode (current trace in lower panel ). In a small subset of neurons, termination of the hyperpolarizing current pulse is followed by an anode break AP ( arrow ). The relatively high level of noise in the voltage traces here and in A is due to use of discontinuous current clamp mode.