Enhanced excitability of primary sensory neurons and altered gene expression of neuronal ion channels in dorsal root ganglion in paclitaxel-induced peripheral neuropathy

Abstract

Background: The mechanism of chemotherapy-induced peripheral neuropathy after paclitaxel treatment is not well understood. Given the poor penetration of paclitaxel into central nervous system, peripheral nervous system is most at risk.

Methods: Intrinsic membrane properties of dorsal root ganglion neurons were studied by intracellular recordings. Multiple-gene real-time polymerase chain reaction array was used to investigate gene expression of dorsal root ganglion neuronal ion channels.

Results: Paclitaxel increased the incidence of spontaneous activity from 4.8 to 27.1% in large-sized and from 0 to 33.3% in medium-sized neurons. Paclitaxel decreased the rheobase (nA) from 1.6 ± 0.1 to 0.8 ± 0.1 in large-sized, from 1.5 ± 0.2 to 0.6 ± 0.1 in medium-sized, and from 1.6 ± 0.2 to 1.0 ± 0.1 in small-sized neurons. After paclitaxel treatment, other characteristics of membrane properties in each group remained the same except that Aδ neurons showed shorter action potential fall time (ms) (1.0 ± 0.2, n = 10 vs. 1.8 ± 0.3, n = 9, paclitaxel vs. vehicle). Meanwhile, real-time polymerase chain reaction array revealed an alteration in expression of some neuronal ion channel genes including up-regulation of hyperpolarization-activated cyclic nucleotide-gated channel 1 (fold change 1.76 ± 0.06) and Nav1.7 (1.26 ± 0.02) and down-regulation of Kir channels (Kir1.1, 0.73 ± 0.05, Kir3.4, 0.66 ± 0.06) in paclitaxel-treated animals.

Conclusion: The increased neuronal excitability and the changes in gene expression of some neuronal ion channels in dorsal root ganglion may provide insight into the molecular and cellular basis of paclitaxel-induced neuropathy, which may lead to novel therapeutic strategies.

Fig. 1

Increased incidence of spontaneous activity (SA) in dorsal root ganglion (DRG) neurons from animals with paclitaxel neuropathy. (A) Paclitaxel chemotherapy induced a significant increase of SA from DRG myelinated neurons including large (P = 0.003) and medium-sized (P = 0.027) neurons. * P < 0.05, ** P < 0.01, Chi-square test. (B) An example of irregular SA recorded from a medium-sized neuron, noticing the subthreshold membrane potential oscillations between each discharge. (C) Continuous discharges were recorded from a spontaneously active large neuron. (D) Spontaneous bursting discharges were recorded from a large neuron after paclitaxel chemotherapy. Subthreshold oscillations (arrows) were obvious between each episode of bursting discharges (arrow).

Fig. 2

Dorsal root ganglion (DRG) neurons showed increased excitability after paclitaxel chemotherapy. (A) Sample recordings of large neurons from paclitaxel- and vehicle-treated animals. The input resistance of each cell was measured based on the steady-state voltage changes at the end of the application of a series of hyperpolarizing/depolarizing currents as indicated by arrowhead. Comparison of electrophysiological properties of DRG neurons with different size, including resting membrane potential (RMP) (B), current threshold (C), number of action potentials (AP) induced by a 1-sec 2 X current threshold intracellular depolarizing current (D) and input resistance (E). * P < 0.001, ** P < 0.0001, One-way ANOVA.

Fig. 3

Dorsal root ganglion (DRG) neurons showed similar conduction velocity (CV) and action potential (AP) properties after paclitaxel chemotherapy. (A) AP was recorded intracellularly from soma of a C-neuron evoked by peripheral nerve stimulation. AP properties were measured as illustrated: (1) AP amplitude, (2) AP rise time, (3) AP fall time, (4) AP duration at base, (5) afterhyperpolarization (AHP) amplitude, (6) AHP 50% duration. Comparisons of CV (B), AP amplitude (C), AP duration (D), AP rise time (E), AP fall time (F), AHP amplitude (G) and AHP 50% duration (H) were made after paclitaxel chemotherapy. * P < 0.05, One-way ANOVA.