Figure 2.
Platelet-derived growth factor-BB increases the excitability of nociceptor-like DRG neurons and increases the Rin. (A) Representative traces of typical voltage responses to 500 ms current steps (shown in middle) recorded from the same neuron before (left) and after ∼15 minutes of focal continuous application of 125 ng/mL of PDGF-BB (right, representative of n = 7). (B) Mean frequency–intensity (f-I) curves of DRG neurons recorded before (gray diamonds) and ∼15 minutes after (red inverted triangles) application of PDGF-BB. Note that PDGF-BB induced a significant increase in gain (m, dotted lines; *P < 0.05, paired t test; n = 7, see also Table 1). (C) Superimposed representative traces of a single action potential recorded from the same neuron before (gray) and after (red) the application of PDGF-BB. Arrows indicate the AP threshold, derived from the phase plots shown in (D). (D) Representative phase plots of rate of change of the membrane potential (dV/dt) vs membrane potential (Vm) during an action potential recorded from the same neuron before (gray) and 10 to 20 minutes after the application of PDGF-BB (red). Arrows and dashed lines indicate shift in threshold voltage and quantified in (E). (E) Thresholds for generation of action potentials calculated from the same neurons before and ∼15 minutes after application of PDGF-BB (mean ± SEM, *P < 0.05, paired t test, n = 7). (F) Bar graph depicting Rin before (gray) and after ∼15 minutes exposure to PDGF-BB (red); *P < 0.05, paired t test, n = 8. Inset: representative typical voltage responses to 500 ms, −100 pA current before (gray) and after (red) the treatment with PDGF-BB. All measurements described in this figure were performed at the native resting potential of each cell, adjusted after PDGF-BB application by injecting the appropriate repolarizing DC currents. AP, action potential; DRG, dorsal root ganglion; PDGF, platelet-derived growth factor.