Farr S A, Flood J F, Scherrer J F, Kaiser F E, Taylor G T, Morley J E
Geriatric Research Education and Clinical Center (GRECC), VA Medical Center, St. Louis University School of Medicine, MO 63106, USA.
Physiol Behav. 1995 Oct;58(4):715-23. doi: 10.1016/0031-9384(95)00124-2.
Mice were trained to avoid footshock in a T-maze, with retention tested one week later. Adult male CD-1 mice made their first avoidance during acquisition after fewer trials than random cycling females and with less variability. Female mice in diestrus, when plasma levels of progesterone are low, learned to avoid footshock faster than females in estrus. Ovariectomized (OVX) mice learned in fewer trials than intact random cycling mice. Similar differences, though of a smaller magnitude, were found on the retention tests (i.e. males had better retention than females, mice in diestrus showed better retention 8 days later when in the same part of the estrous cycle than those in estrus, and OVX mice had better retention than cycling females). OVX mice with estrogen implants learned faster than those with progesterone implants or progesterone plus estrogen implants. Hormonal status did not affect sensitivity to acoustic or footshock stimuli as measured by a startle reflex, nor did it affect activity. Pretraining administration of amphetamine, picrotoxin and strychnine attenuated the impairing effect of progesterone on acquisition. The possibility that progesterone may impair learning and to some extent, retention by facilitating the GABAergic activity and thereby reducing arousal level is discussed.
将小鼠置于T型迷宫中训练以避免足部电击，并在一周后进行记忆保持测试。成年雄性CD-1小鼠在习得过程中首次成功避免电击所需的试验次数比随机周期的雌性小鼠少，且变异性更小。处于动情间期（此时血浆孕酮水平较低）的雌性小鼠比处于发情期的雌性小鼠更快学会避免足部电击。卵巢切除（OVX）小鼠比完整的随机周期小鼠在更少的试验次数中学会。在记忆保持测试中也发现了类似的差异，只是程度较小（即雄性比雌性有更好的记忆保持，处于动情间期的小鼠在发情周期的同一阶段8天后比处于发情期的小鼠有更好的记忆保持，并且OVX小鼠比周期循环的雌性小鼠有更好的记忆保持）。植入雌激素的OVX小鼠比植入孕酮或孕酮加雌激素的小鼠学得更快。激素状态并不影响通过惊吓反射测量的对听觉或足部电击刺激的敏感性，也不影响活动。训练前给予苯丙胺、印防己毒素和士的宁可减弱孕酮对习得的损害作用。文中讨论了孕酮可能通过促进GABA能活性从而降低唤醒水平来损害学习并在一定程度上损害记忆保持的可能性。
