Conway C M, Martinez J, Lytle L D
Department of Psychology, University of California, Santa Barbara 93106-9660, USA.
Dev Psychobiol. 1998 Jul;33(1):47-60.
Some find developmental differences in rodent thermal nociceptive responses and others do not. To address these inconsistencies, the escape latencies of immature (5-to 25-day-old) and adult (3-to 4-month-old) albino rats were recorded following tail exposure to different intensities of radiant heat (650-W halogen lamp placed 10-30 mm from the tail) or conductive heat 35-50 degrees C water). Developmental differences in tail flick latencies were not observed in immature rats when the lamp was closest to the tail (although adult latencies were longer than 5-and 15-day-old responses) When radiant heat intensity was reduced, 5-day-old rats had shorter escape latencies than 15-, 25-, and 90-day-old animals. Age differences persisted in the latencies of immature animals even when the test aperture was varied to compensate for maturational changes in tail width (whereas adult responses no longer differed from those of 5-and 15-day-old rats). Developmental differences were eliminated when the tail skin was blackened so as to normalize the absorption of radiant heat across age. Similar age-and intensity-dependent differences were observed in rats exposed to conductive heat: Five-and 10-day-old pups had shorter escape responses than older rats when tails were immersed in intermediate (40 or 45 degrees C) but not lower (35 degree C) or higher (50 degrees C) temperature water. Blackening the tails did not change conductive heat escape latencies. No sex differences were found at any age or stimulus intensity with either type of heat. Higher intensities of thermal stimuli applied to the tail are required to elicit escape responses in older rats compared to younger ones, but the use of relatively intense thermal test stimuli can mask age-dependent differences in nociception. Some of the inconsistent results reported previously about maturational changes in thermal nociception may be due to intensity differences in the noxious test stimuli used. Maturational differences in the radiant absorption properties of the tail seem to account for most of the age-related changes in rodent responses to radiant heat, but the mechanism(s) which subserve developmental differences in conductive heat nociception need to be elucidated.
一些研究发现啮齿动物的热痛觉反应存在发育差异，而另一些研究则未发现。为了解决这些不一致的情况，记录了未成熟（5至25日龄）和成年（3至4月龄）白化大鼠在尾巴暴露于不同强度的辐射热（距离尾巴10 - 30毫米处放置650瓦卤素灯）或传导热（35 - 50摄氏度的水）后的逃避潜伏期。当灯离尾巴最近时，未成熟大鼠未观察到甩尾潜伏期的发育差异（尽管成年大鼠的潜伏期比5日龄和15日龄大鼠的反应长）。当辐射热强度降低时，5日龄大鼠的逃避潜伏期比15日龄、25日龄和90日龄的动物短。即使改变测试孔径以补偿尾巴宽度的成熟变化，未成熟动物的潜伏期仍存在年龄差异（而成年大鼠的反应与5日龄和15日龄大鼠的反应不再有差异）。当尾巴皮肤变黑以使各年龄组的辐射热吸收标准化时，发育差异消失。在暴露于传导热的大鼠中也观察到了类似的年龄和强度依赖性差异：当尾巴浸入中等温度（40或45摄氏度）而非较低温度（35摄氏度）或较高温度（50摄氏度）的水中时，5日龄和10日龄的幼崽比年长的大鼠逃避反应短。尾巴变黑并未改变传导热逃避潜伏期。在任何年龄或刺激强度下，两种热刺激类型均未发现性别差异。与年幼大鼠相比，年长大鼠需要更高强度的热刺激作用于尾巴才能引发逃避反应，但使用相对强烈的热测试刺激可能会掩盖痛觉感受中与年龄相关的差异。先前报道的关于热痛觉成熟变化的一些不一致结果可能是由于所用有害测试刺激的强度差异所致。尾巴辐射吸收特性的成熟差异似乎是啮齿动物对辐射热反应中大多数与年龄相关变化的原因，但传导热痛觉发育差异的潜在机制仍有待阐明。
