Figure 1

Persistent inflammation of the hindpaw results in an increase in the excitability of cutaneous neurons that is associated with an increase in action potential duration. Excitability was assessed in acutely dissociated DRG neurons retrogradely labeled from the glabrous skin of the hindpaw harvested from naïve and inflamed (CFA) rats. Depolarizing current injection was used to determine action potential (AP) threshold (A), rheobase (B) and the response to suprethreshold current injection (C, D), which was injected at intensities 1, 2, and 3 times rheobase. The voltage traces in C, are typical of the pooled data plotted in D. As indicated in D, pooled data for all panels are from 10 neurons from naïve and 23 neurons from inflamed rats. The number of action potentials evoked at 2 and 3x rheobase in neurons from inflamed rats is significantly greater than that in neurons from naïve rats. Error bars for data from naïve neurons are smaller than the symbol. Inset: The slope of the stimulus response function (SRF) is significantly greater for neurons from inflamed rats than that for neurons from naïve rats. E. Typical action potentials from naïve (black trace) and inflamed (gray trace) rats evoked in response to a 4 ms current injection are overlayed with the average action potential duration indicated for each. These values are significantly different (p < 0.05). F. The afterhyperpolarization (AHP) following the action potentials shown in E are plotted to illustrate the trend toward a decrease in the AHP duration in neurons from inflamed rats. The full amplitude of the action potential is clipped in these traces to facilitate visualization of the AHP. Average values are indicated next to each trace, and these differences are significantly different. * is p < 0.05 and ** is p < 0.01