Fig. 2.  Intensity and duration of mechanical nocifensive blockade using spinal anesthesia. Withdrawal thresholds (g) to von Frey filaments are shown for postnatal day P7 rats (A ), P14 rats (B ), and P21 rats (C ), respectively using low-dose bupivacaine (3.75 mg/kg), high-dose bupivacaine (7.5 mg/kg), or spinal saline. Sample sizes of P7/P14/P21: n = 7/7/7 (total, n = 21) for low-dose bupivacaine, n = 6/7/6 (total, n = 19) for high-dose bupivacaine, and n = 6/6/6 (total, n = 18) for spinal saline. *P < 0.05 compared with spinal saline. †P < 0.05 compared with low-dose bupivacaine.