Kavaliers M, Colwell D D
Division of Oral Biology, Faculty of Dentistry, University of Western Ontario, London, Canada.
Physiol Behav. 1994 Mar;55(3):505-10. doi: 10.1016/0031-9384(94)90108-2.
Parasites have been shown to have a broad range of effects on host behavior, including alterations of host responses to predators. Response to the threat of predation consist of a number of defensive behaviors, including a reduction in pain sensitivity and the induction of analgesia. The present study examined the relationships between subclinical (i.e., nonpathological) infection with the naturally occurring, enteric, sporozoan (coccidian) parasite, Eimeria vermiformis, predator exposure, and nociceptive responses in male mice. Brief (30 s) exposure of nonparasitized mice to a predator (a cat) induced marked, relatively short-lived analgesia that was insensitive to naloxone and blocked by the serotonin-1A (5-HT1A) agonist, 8-OH-DPAT. In contrast, mice acutely infected for 6 days with E. vermiformis, failed to show a predator-induced analgesia. The parasitized mice did display a naloxone-sensitive hypoalgesia or analgesia. However, restraint-stressed mice, which displayed a naloxone-sensitive hypoalgesia similar in amplitude to that of the infected mice, still exhibited a nonopioid mediated, predator-induced analgesia. These observations indicate that parasite infection attenuates 5-HT1A-sensitive predator-induced analgesia and likely reduces the accompanying fear and anxiety related anticipatory defense reactions of the host to the predator.
寄生虫已被证明对宿主行为有广泛影响，包括改变宿主对捕食者的反应。对捕食威胁的反应包括一系列防御行为，包括疼痛敏感性降低和镇痛作用的诱导。本研究考察了雄性小鼠自然发生的肠道孢子虫（球虫）寄生虫微小艾美耳球虫的亚临床（即非病理性）感染、捕食者暴露与伤害感受反应之间的关系。将未感染寄生虫的小鼠短暂（30秒）暴露于捕食者（猫）会诱导显著的、持续时间相对较短的镇痛作用，该作用对纳洛酮不敏感，并被5-羟色胺-1A（5-HT1A）激动剂8-羟基二丙胺四乙酸（8-OH-DPAT）阻断。相比之下，急性感染微小艾美耳球虫6天的小鼠未表现出捕食者诱导的镇痛作用，但感染寄生虫的小鼠确实表现出对纳洛酮敏感的痛觉减退或镇痛作用。然而，表现出与感染小鼠幅度相似的对纳洛酮敏感的痛觉减退的束缚应激小鼠，仍表现出非阿片类药物介导的捕食者诱导的镇痛作用。这些观察结果表明，寄生虫感染减弱了5-HTlA敏感的捕食者诱导的镇痛作用，并可能降低宿主对捕食者伴随的恐惧和焦虑相关的预期防御反应。
