Original recordings. Original recordings of three different single motor units previous to and after the administration of iv. cumulative doses of gabapentin in normal (A), arthritic (B) and neuropathic animals (C). The units were activated in three minute cycles by 10 s of noxious mechanical stimulation and 16 electrical pulses (2 ms pulse width, 1 Hz and twice the threshold intensity for the recruitment of C-fibers). Gabapentin was administered iv. in log2 cumulative doses every three cycles of stimulation (9 minutes) from 40 to 1,280 μmol/kg (7 to 224 mg/kg). The administration of gabapentin dose-dependently reduced the nociceptive responses in arthritic and neuropathic animals but not in normal rats.