DAMGO antinociception in brain P450-deficient and control mice following icv administration. Control (WT) and Null mice of either sex were tested for nociceptive responses (time zero = baseline, BL), received DAMGO (0.1 nmol) or saline, and were re-tested at the indicated times (abscissa, min). Ordinate shows latencies (sec, mean ± S.E.M.) for the n values in parentheses. Data from both genders were pooled. **P < 0.01 vs. WT Saline at the same time. +, ++P < 0.05, 0.01, respectively vs. WT DAMGO at the same time.