Engeland Christopher G, Kavaliers Martin, Ossenkopp Klaus Peter
Neuroscience Program, University of Western Ontario, Ontario, N6A 5C2 London, Canada.
Psychoneuroendocrinology. 2003 Nov;28(8):970-91. doi: 10.1016/s0306-4530(02)00118-x.
Lipopolysaccharide (LPS), the minimal immunogenic component of Gram-negative bacteria, is released during infection and causes a variety of sickness behaviors including decreased locomotor activity. This study considered how photoperiod and sex influence the effects of LPS in the meadow vole, Microtus pennsylvanicus. Male and female voles were housed under either reproductively stimulatory (long day: 16 h) or inhibitory (short day: 8 h) photoperiods. On Days 1 and 8, voles were injected with LPS (200 microg/kg, i.p.) or saline vehicle and locomotor activity was assessed 2 h later in an automated open field for 1 h. The first exposure to LPS caused significant decrements in locomotor activity in all LPS-treated groups, regardless of photoperiod or sex. On Day 8, both short day males and females exhibited behavioral tolerance to LPS, no longer displaying significant activity decrements. In contrast, long day females reinjected with LPS on Day 8 still exhibited significant hypoactivity on all locomotor measures. Similarly, long day males also appeared to exhibit a sustained expression of sickness behaviors on Day 8. In long day females, higher circulating progesterone levels were associated with an attenuated rate of tolerance formation to LPS. The present findings support the winter immunoenhancement hypothesis, which states that small mammals which undergo severe seasonal fluctuations undergo compromised immune functioning during the breeding season, and further indicate a potential role for progesterone in modulating these seasonal immune fluctuations in females.
脂多糖（LPS）是革兰氏阴性菌的最小免疫原性成分，在感染过程中释放，可引发多种疾病行为，包括运动活动减少。本研究探讨了光周期和性别如何影响草地田鼠（Microtus pennsylvanicus）对LPS的反应。将雄性和雌性田鼠分别饲养在生殖刺激（长日照：16小时）或抑制（短日照：8小时）的光周期条件下。在第1天和第8天，给田鼠注射LPS（200微克/千克，腹腔注射）或生理盐水，2小时后在自动旷场中评估其运动活动，持续1小时。首次接触LPS后，所有LPS处理组的运动活动均显著下降，与光周期或性别无关。在第8天，短日照的雄性和雌性田鼠对LPS均表现出行为耐受性，运动活动不再显著下降。相比之下，在第8天再次注射LPS的长日照雌性田鼠在所有运动指标上仍表现出显著的活动减少。同样，长日照雄性田鼠在第8天似乎也持续表现出疾病行为。在长日照雌性田鼠中，较高的循环孕酮水平与对LPS耐受性形成速率的减弱有关。本研究结果支持冬季免疫增强假说，该假说认为经历严重季节性波动的小型哺乳动物在繁殖季节免疫功能会受到损害，并进一步表明孕酮在调节雌性这些季节性免疫波动中可能发挥作用。
