Figure 6.

Comparison of the activation threshold of DRG nociceptive neurons in response to intracellular current injection, between control and cancer rats.

(A) The current threshold is the minimum current required to evoke an AP by intracellular current injection to the soma of DRG neurons. Excitability of the DRG somata was significantly higher in cancer rats relative to control rats, as indicated by lower mean current activation threshold in all types of nociceptive fibres: C-fibre neurons (a), Aδ-fibre neurons (B) and Aβ-fibre neurons (c). (b) A comparison the repetitive discharge characteristics of DRG cells produced by intracellular current injection at the soma. Columns indicate the number of APs evoked by intracellular injection of different magnitudes (Left = 1.5 nA, 100 ms. Middle = 2 nA, 100 ms. Right = 2.5 nA, 100 ms) of depolarizing current in C-fibres (a–c), Aδ-fibres (d–f) and Aβ-fibres (g–i). Most neuron types in cancer rats produced a greater number of APs in response to depolarizing current than control rats. (C) Representative examples of raw recordings to demonstrate the greater number of APs evoked by intracellular current injection in cancer (d–f) than in control rats (a–c) in all neuron fibre types. APs in these examples were evoked by current pulses of 2 nA, 100 ms. *p < 0.05, **p < 0.01. DRG = dorsal root ganglia; AP: action potential;