Bolbecker Amanda R, Lim-Kessler Corrinne C M, Li Jia, Swan Alicia, Lewis Adrienne, Fleets Jennifer, Wasserman Gerald S
Department of Psychological and Brain Sciences, Indiana University, Indiana, USA.
J Neurophysiol. 2009 Aug;102(2):1132-8. doi: 10.1152/jn.91167.2008. Epub 2009 Jun 17.
Efferent nerves coursing from the brain to the lateral eye of the horseshoe crab, Limulus polyphemus, increase its nighttime sensitivity to light. They release octopamine, which produces a categorical increase of photoreceptor response duration in vitro. Analogous in vivo timing effects on the electroretinogram (ERG) were demonstrated when octopamine was infiltrated into the eye of an otherwise intact animal; nighttime ERGs were longer than daytime ERGs. Related effects on the ERG were produced by daytime electrical stimulation of efferent fibers. Surprisingly, in a departure from effects predicted solely from in vitro octopamine data, nighttime ERG onsets were also accelerated relative to daytime ERG onsets. Drawing on earlier reports, these remarkable accelerations led to an examination of substance P as another candidate neuromodulator. It demonstrated that infiltrations of either modulator into the lateral eyes of otherwise intact crabs increased the amplitude of ERG responses but that each candidate modulator induced daytime responses that specifically mimicked one of the two particular aspects of the timing differences between day- and nighttime ERGs: octopamine increased the duration of daytime ERGs and substance P infiltrated during the day accelerated response onset. These results indicate that, in addition to octopamine's known role as an efferent neuromodulator that increases nighttime ERG amplitudes, octopamine clearly also affects the timing of photoreceptor responses. But these infiltration data go further and strongly suggest that substance P may also be released into the lateral eye at night, thereby accelerating the ERG's onset in addition to increasing its amplitude.
从大脑延伸至鲎（美洲鲎）侧眼的传出神经增强了其在夜间对光的敏感度。这些神经释放章鱼胺，在体外可使光感受器的反应持续时间显著增加。当将章鱼胺注入原本完整的动物眼中时，在体内也证实了其对视网膜电图（ERG）有类似的时间效应；夜间的ERG比白天的更长。对传出纤维进行白天的电刺激也会产生与ERG相关的效应。令人惊讶的是，与仅从体外章鱼胺数据预测的效应不同，相对于白天的ERG起始，夜间ERG的起始也加快了。借鉴早期的报告，这些显著的加速现象促使人们研究P物质作为另一种候选神经调节剂。结果表明，将这两种调节剂中的任何一种注入原本完整的螃蟹侧眼，都会增加ERG反应的幅度，但每种候选调节剂诱导的白天反应都具体模仿了白天和夜间ERG时间差异的两个特定方面之一：章鱼胺增加了白天ERG的持续时间，而在白天注入的P物质加速了反应起始。这些结果表明，除了章鱼胺作为一种能增加夜间ERG幅度的传出神经调节剂的已知作用外，章鱼胺显然还会影响光感受器反应的时间。但这些注入数据进一步有力地表明，P物质可能在夜间也释放到侧眼中，从而除了增加ERG幅度外还加速其起始。
