Sustained nerve growth factor-induced C-nociceptor… : PAIN Reports
ctrical sinusoidal stimuli. Objectives: To explore the temporal profile of nociceptor sensitization to heat and mechanical and electrical stimuli in humans after rhNGF. Methods: Recombinant human nerve growth factor (1 µg) and NaCl (0.9%) was injected into human forearm skin (n = 9, 50 µL/injection). Pain ratings (numeric rating scale) to transcutaneous electrical stimuli (1 ms 20 Hz rectangular pulses, 500-ms half-period sine wave [1 Hz] and 4 Hz sine wave pulses [2.5 and 60 seconds]) were assessed at days 3, 21, and 49 after injection, in addition to heat pain thresholds (HPTs, 9 × 9 mm thermode) and mechanical impact pain (4 and 8 m/second). Results: Suprathreshold sinusoidal stimulation for specific CM (1 Hz) and combined CM and CMi (4 Hz) activation resulted in enhanced pain from day 3 post rhNGF and lasted throughout 7 weeks. These temporal dynamics contrasted minimum HPTs at day 3 (normalized by day 49) or mechanical impact pain (developing slowly until day 21 before declining d
