These results show that PAG is an important site not only for the analgesic action of morphine but also for the antagonistic analgesic effect of naloxone.

• 由此可见PAG既是侧脑室注射吗啡镇痛作用的重要中枢部位，又是侧脑室注射纳洛酮拮抗吗啡镇痛的重要中枢部位。