生物体活动都会受到生物钟的影响，蟑螂也不例外。美国科学家近日研究发现，蟑螂的学习能力在早晚相差巨大。这是首例获得证实的关于昆虫学习能力会受到生物钟影响的研究报告，无疑将对人们深入研究生物钟的作用产生帮助。相关论文9月24日在线发表于《美国国家科学院院刊》（PNAS）上。
领导该项研究的是美国范德比尔特大学的生物学家Terry L. Page。他和研究小组训练蟑螂将它们讨厌的薄荷油味和喜欢的香草味联系起来，并在一天24小时内不同的时间段进行训练，以测试它们能记住这种联系的时间长度。结果发现，在傍晚训练，蟑螂能记住这种联系数天；在夜间训练，效果也不错；而在早晨训练，蟑螂根本就不能形成新的记忆。
Page说，早晨造成的缺陷如此显著，真是让人非常吃惊。那么蟑螂为什么不愿意在这个时间段学习新东西？Page表示目前尚无准确答案。
之前关于生物钟的研究关注的大多都是视觉系统，此次研究则有很大不同。Page表示，此次研究包括了嗅觉系统，这表明生物钟会影响为数众多的感觉器官。
此次实验有助于人们对生物钟和记忆、学习等之间的联系展开更深入的研究。Page说：“此次研究表明，至少从某些情况来说，一天之中特定的时刻具有深远的影响。通过研究生物钟调节学习和记忆的方式，我们能够更深入地了解这些过程发生的机制，以及哪些因素能对它们产生影响。”（科学网 梅进/编译）
原始出处:
Published online before print September 24, 2007
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0702082104
( biological rhythms | cockroach | differential conditioning | memory )
Susan Decker, Shannon McConnaughey, and Terry L. Page *
Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235
Edited by Leslie C. Griffith, Brandeis University, Waltham, MA, and accepted by the Editorial Board August 10, 2007 (received for review March 6, 2007)
Olfactory learning in insects has been used extensively for studies on the neurobiology, genetics, and molecular biology of learning and memory. We show here that the ability of the cockroach Leucophaea maderae to acquire olfactory memories is regulated by the circadian system. We investigated the effect of training and testing at different circadian phases on performance in an odor-discrimination test administered 30 min after training (short-term memory) or 48 h after training (long-term memory). When odor preference was tested by allowing animals to choose between two odors (peppermint and vanilla), untrained cockroaches showed a clear preference for vanilla at all circadian phases, indicating that there was no circadian modulation of initial odor preference or ability to discriminate between odors. After differential conditioning, in which peppermint odor was associated with a positive unconditioned stimulus of sucrose solution and vanilla odor was associated with a negative unconditioned stimulus of saline solution, cockroaches conditioned in the early subjective night showed a strong preference for peppermint and retained the memory for at least 2 days. Animals trained and tested at other circadian phases showed significant deficits in performance for both short- and long-term memory. Performance depended on the circadian time (CT) of training, not the CT of testing, and results indicate that memory acquisition rather than retention or recall is modulated by the circadian system. The data suggest that the circadian system can have profound effects on olfactory learning in insects.
全文下载：Circadian regulation of insect olfactory learning
