van Praag H, Frenk H
Department of Psychology, Tel-Aviv University, Ramat-Aviv, Israel.
Brain Res Dev Brain Res. 1991 Dec 17;64(1-2):71-6. doi: 10.1016/0165-3806(91)90210-a.
The present study studied the development of stimulation produced analgesia (SPA) from the periaqueductal gray (PAG) in rats. A monopolar stimulating electrode was lowered into the dorsal or ventral PAG of animals aged 7, 14, 21, or 90-120 days. Constant current cathodal pulses (100 Hz, 100 microseconds) were delivered, starting 10 s before analgesia was tested by the tail-flick (TF) test and continuing throughout each TF trial or until cut-off (7 s). Current intensity was increased stepwise (3-200 microA). It was found that SPA can be elicited starting at 21 days, but not earlier. However, supraspinal modulation of nociception is still immature at 3 weeks after birth. First, stimulation intensities needed to produce SPA are higher in 21-day-old pups than in adult animals. Second, in 21-day-old pups, but not in adults effective current intensities in the dorsal PAG are higher than in the ventral PAG. Third, naltrexone decreases SPA from the ventral PAG in 21-day-old pups, but not in adult animals. These findings indicate that supraspinal modulation of nociception develops only 3 weeks after birth, with the ventral PAG maturing prior to the dorsal PAG, and that the contribution of endogenous opioids to SPA does not remain constant throughout the ontogeny of rats.
本研究探讨了大鼠中脑导水管周围灰质（PAG）产生的刺激镇痛（SPA）的发育情况。将单极刺激电极插入7、14、21或90 - 120日龄动物的背侧或腹侧PAG。在通过甩尾（TF）试验测试镇痛效果前10秒开始施加恒定电流阴极脉冲（100 Hz，100微秒），并在每个TF试验过程中持续施加，直至截止（7秒）。电流强度逐步增加（3 - 200微安）。结果发现，SPA在21日龄时才可以被诱发，更早则不行。然而，出生后3周时，伤害性感受的脊髓上调制仍未成熟。首先，21日龄幼崽产生SPA所需的刺激强度高于成年动物。其次，在21日龄幼崽中，背侧PAG的有效电流强度高于腹侧PAG，而成年动物中并非如此。第三，纳曲酮可降低21日龄幼崽腹侧PAG产生的SPA，但对成年动物无此作用。这些发现表明，伤害性感受的脊髓上调制在出生后3周才发育，腹侧PAG比背侧PAG先成熟，并且内源性阿片类物质对SPA的作用在大鼠个体发育过程中并非保持恒定。
