Fig. 4. Mean ± SEM effect of spinal ondansetron (100 μg) and subsequent systemic administration of pregabalin (10 mg/kg) on mean baseline response profiles of dorsal horn wide dynamic range spinal neurons in morphine-treated animals (n = 8). On postoperative days 7–10, evoked neuronal response to electrical (A ), mechanical (B ), and thermal (C ) stimuli were recorded before and after drug treatment. Ondansetron reduced a subset of electrically evoked responses and the evoked response of spinal neurons to peripherally applied noxious natural stimuli. Pregabalin (10 mg/kg) did not further reduce evoked neuronal response to electrical or natural stimuli. Based on latency measurements, neuronal responses were subdivided into Aβ-, Aδ-, and C-fibers, or postdischarge. *P < 0.05 or **P = 0.01 or ***P < 0.001 versus morphine baseline.