Fig. 1. Intensity and duration of thermal nocifensive blockade using spinal anesthesia. Lower extremity blockade, assessed by withdrawal latency to a modified hotplate test in rats at baseline and at times shown postblock, for postnatal day/ages P7 (A ), P14 (B ), and P21 (C ), using low-dose bupivacaine (3.75 mg/kg), high-dose bupivacaine (7.5 mg/kg), or saline. Sample sizes of P7/P14/P21: n = 9/8/9 (total, n = 26) for low-dose bupivacaine, n = 8/8/7 (total, n = 23) for high-dose bupivacaine, and n = 9/9/9 (total, n = 27) for spinal saline. *P < 0.05 compared with spinal saline. †P < 0.05 compared with low-dose bupivacaine.