Kass L, Pelletier J L, Renninger G H, Barlow R B
Department of Zoology, University of Maine, Orono 04469.
J Comp Physiol A. 1988 Nov;164(1):95-105. doi: 10.1007/BF00612723.
We investigated efferent neurotransmission in the Limulus lateral eye by studying the action of pharmacological agents on responses of photoreceptor cells in vitro. We recorded transmembrane potentials from single cells in slices of retina that were excised during the day and maintained for several days in a culture medium. Potentials recorded in the absence of pharmacological agents resemble those recorded from cells in vivo during the day. Octopamine, a putative efferent neurotransmitter, induced changes in photoreceptor potentials that mimicked in part those generated at night by a circadian clock located in the brain. Specifically, octopamine (100 to 500 microM) decreased the frequency of occurrence of quantum bumps in the dark and increased the amplitude of photoreceptor responses to intermediate and high light intensities. Similar actions were produced by naphazoline (25 to 100 microM, potent agonist of octopamine), forskolin (8 to 400 microM, activator of adenylate cyclase), IBMX (1 mM, inhibitor of phosphodiesterase), and 8-bromo-cAMP (500 microM, analogue of cAMP). 8-bromo-cGMP (500 microM, analogue of cGMP) decreased the rate of spontaneous quantum bumps only. Our results support the hypothesis that (1) octopamine is an efferent neurotransmitter of circadian rhythms in the Limulus eye and that (2) it activates adenylate cyclase to increase levels of the second messenger, cAMP, in photoreceptor cells. Circadian changes in photoreceptor responses to moderate intensities may be a specific action of cAMP, since cGMP has no effect. Circadian changes in the rate of spontaneous quantum bumps may involve a less specific intermediate, since both cAMP and cGMP reduce bump rate. Characteristics of the retinal slice preparation precluded a detailed study of the effects of pharmacological agents on retinal morphology.
我们通过研究药理剂对离体光感受器细胞反应的作用，来探究鲎侧眼的传出神经传递。我们记录了白天切除并在培养基中维持数天的视网膜切片中单个细胞的跨膜电位。在没有药理剂的情况下记录的电位类似于白天在体内细胞记录的电位。章鱼胺，一种假定的传出神经递质，诱导光感受器电位变化，部分模仿了位于大脑中的生物钟在夜间产生的变化。具体而言，章鱼胺（100至500微摩尔）降低了黑暗中量子突增的发生频率，并增加了光感受器对中等和高强度光的反应幅度。萘甲唑啉（25至100微摩尔，章鱼胺的强效激动剂）、福斯可林（8至400微摩尔，腺苷酸环化酶激活剂）、异丁基甲基黄嘌呤（1毫摩尔，磷酸二酯酶抑制剂）和8-溴环磷酸腺苷（500微摩尔，环磷酸腺苷类似物）产生了类似的作用。8-溴环磷酸鸟苷（500微摩尔，环磷酸鸟苷类似物）仅降低了自发量子突增的速率。我们的结果支持以下假设：（1）章鱼胺是鲎眼中昼夜节律的传出神经递质，（2）它激活腺苷酸环化酶以增加光感受器细胞中第二信使环磷酸腺苷的水平。光感受器对中等强度光反应的昼夜变化可能是环磷酸腺苷的一种特定作用，因为环磷酸鸟苷没有作用。自发量子突增速率的昼夜变化可能涉及一种不太特异的中间体，因为环磷酸腺苷和环磷酸鸟苷都降低了突增速率。视网膜切片制备的特性妨碍了对药理剂对视网膜形态影响的详细研究。
