HMGB1 increases the excitability of nociceptive dorsal root ganglia (DRG) neurons. Current clamp recordings were performed on small-to-medium (>30 μm - >40 μm) diameter lumbar 4–5 DRG neurons from TNI and naive rats. Firing of 1–2 action potentials (APs) was elicited by a 1 second depolarizing current injection (ranging from 0.1 to 2.0 nA depending on the cell) every 30 seconds. (A) Representative recordings demonstrating that application of HMGB1(0.65 μg/ml) increases the number of elicited action potentials in TNI DRG sensory neurons. Group data showing that HMGB1 caused a significant increase in DRG action potential firing under both naive (B) and TNI conditions, p < 0.05 versus control (C).