Changes in the amplitude and duration of afterhyperpolarization (AHP) of action potentials recorded from small-sized DRG neurons in rats with intra-tibial injections of MRMT-1 cells. (A) - (C): Summary of the AHP amplitude of action potentials in LT, MT, and HT neurons in naïve, PBS-, HK-, and MRMT-1-rats. (D) - (F): Summary of the AHP duration at 80% repolarization (AHP80%) in naïve, PBS-, HK-, and MRMT-1-rats. *p < 0.05,***p < 0.001, as compared with HK groups, two-tailed Student's t-test. LT, MT, and HT mean low-, medium-, and high-firing threshold neurons, respectively. (G): Representative of the AHP amplitude and duration of action potentials evoked by 100-ms, 40-pA depolarizing current pulse, recorded from low-firing threshold DRG neurons. The red trace represents the discharges recorded from a representative small DRG neuron in a MRMT-1-implanted rat. The vertical dot line to trough shows the AHP amplitude, and the horizontal dot line shows the AHP80%. Action potentials have been amputated due to high gain. Note that implantation of MRMT-1 tumor cells into the tibial canal in rats decreased the amplitude and duration of afterhyperpolarization (AHP) in small-sized DRG neurons.