Changes in resting membrane potentials (RMP) and action potential threshold (TP) of small-sized DRG neurons in rats with intra-tibial injections of MRMT-1 cells. (A) - (C): Summary of the absolute values of RMP in low-, medium-, and high-firing threshold neurons in naïve, PBS-, HK-, and MRMT-1-rats. (D) - (F): Summary of the absolute values of TP in naïve, PBS-, HK-, and MRMT-1-rats. *p < 0.05, **p < 0.01,***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 action potentials evoked by 100-ms, 25-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. Note that implantation of MRMT-1 tumor cells into the tibial canal in rats caused a depolarizing shift of RMP and a reduction of TP in small-sized DRG neurons.