Buck Leslie T, Bond Hilary C, Malik Aqsa
Department of Cell and Systems Biology, University of British Columbia, Vancouver, BC, Canada; Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada.
Department of Cell and Systems Biology, University of British Columbia, Vancouver, BC, Canada.
Comp Biochem Physiol A Mol Integr Physiol. 2017 Jan;203:193-200. doi: 10.1016/j.cbpa.2016.09.016. Epub 2016 Sep 21.
The pond snail Lymnaea stagnalis is reported to be anoxia-tolerant and if the tolerance mechanism is similar to that of the anoxia-tolerant painted turtle, GABA should play an important role. A potentially confounding factor investigating the role of GABA in anoxia tolerance are reports that GABA has both inhibitory and excitatory effects within L. stagnalis central ganglion. We therefore set out to determine if seasonality or photoperiod has an impact on: 1) the anoxia-tolerance of the intact pond snail, and 2) the response of isolated neuroganglia cluster F neurons to exogenous GABA application. L. stagnalis maintained on a natural summer light cycle were unable to survive any period of anoxic exposure, while those maintained on a natural winter light cycle survived a maximum of 4h. Using intracellular sharp electrode recordings from pedal ganglia cluster F neurons we show that there is a photoperiod dependent shift in the response to GABA. Snails exposed to a 16h:8h light:dark cycle in an environmental chamber (induced summer phenotype) exhibited hyperpolarizing inhibitory responses and those exposed to a 8h:16h light:dark cycle (induced winter phenotype) exhibited depolarizing excitatory responses to GABA application. Using gramicidin-perforated patch recordings we also found a photoperiod dependent shift in the reversal potential for GABA. We conclude that the opposing responses of L. stagnalis central neurons to GABA results from a shift in intracellular chloride concentration that is photoperiod dependent and is likely mediated through the relative efficacy of cation chloride co-transporters. Although the physiological ramifications of the photoperiod dependent shift are unknown this work potentially has important implications for the impact of artificial light pollution on animal health.
据报道，静水椎实螺对缺氧具有耐受性，如果其耐受机制与耐缺氧的锦龟相似，那么γ-氨基丁酸（GABA）应该发挥重要作用。研究GABA在缺氧耐受性中作用的一个潜在混杂因素是，有报道称GABA在静水椎实螺中枢神经节内具有抑制和兴奋作用。因此，我们着手确定季节性或光周期是否对以下方面有影响：1）完整静水椎实螺的耐缺氧能力，以及2）分离的神经节簇F神经元对外源性GABA应用的反应。维持在自然夏季光照周期的静水椎实螺无法在任何缺氧暴露时间段内存活，而维持在自然冬季光照周期的螺最多存活4小时。通过对足神经节簇F神经元进行细胞内尖锐电极记录，我们发现对GABA的反应存在光周期依赖性变化。在环境箱中暴露于16小时光照：8小时黑暗周期（诱导夏季表型）的螺对GABA应用表现出超极化抑制反应，而暴露于8小时光照：16小时黑暗周期（诱导冬季表型）的螺则表现出去极化兴奋反应。使用短杆菌肽穿孔膜片钳记录，我们还发现GABA的反转电位存在光周期依赖性变化。我们得出结论，静水椎实螺中枢神经元对GABA的相反反应是由细胞内氯离子浓度的变化引起的，这种变化依赖于光周期，并且可能是通过阳离子-氯离子共转运体的相对效能介导的。尽管光周期依赖性变化的生理后果尚不清楚，但这项工作可能对人工光污染对动物健康的影响具有重要意义。
