Badre Nicolas H, Martin M Elisabeth, Cooper Robin L
Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA.
Comp Biochem Physiol A Mol Integr Physiol. 2005 Mar;140(3):363-76. doi: 10.1016/j.cbpb.2005.01.019.
Adult and larval insects are rapidly anesthetized by carbon dioxide (CO2); however, the mechanisms have not been addressed. In this study, we use larval Drosophila to investigate the actions of CO2 to explain the behavioral effects of rapid immobilization and cardiac arrest with acute exposure to CO2. To determine if the central nervous system (CNS) is required, studies were performed with and without the CNS. The effects of low pH induced by exposure to CO2 were also examined. An acidic saline increases the heart rate in contrast to saline containing CO2. Synaptic transmission at the skeletal neuromuscular junction (NMJ) is blocked by CO2 but not by low pH. The site of action is postsynaptic by a decreased sensitivity to glutamate, the neurotransmitter at Drosophila NMJs. The CNS remains active in synaptic transmission when exposed to CO2 which is in contrast to the synapses at the NMJ. In summary, the effects of CO2 are directly mediated on the heart to stop it and at skeletal NMJs by a reduced sensitivity to glutamate, the released neurotransmitter, from the motor nerve terminals. The rapid behavioral and physiological effects cannot be accounted for by action on the CNS within the larvae nor by a pH effect indirectly induced by CO2. The glutamate receptors in the D. melanogaster preparation are similar in function to ionotropic glutamate receptors in vertebrates which could account for the observational phenomena of CO2 not yet explained mechanistically in vertebrates.
成年和幼虫昆虫会被二氧化碳（CO₂）迅速麻醉；然而，其作用机制尚未得到研究。在本研究中，我们利用果蝇幼虫来探究CO₂的作用，以解释急性暴露于CO₂时快速固定和心脏骤停的行为效应。为了确定是否需要中枢神经系统（CNS），我们进行了有或没有CNS的研究。我们还研究了暴露于CO₂所诱导的低pH的影响。与含CO₂的生理盐水相比，酸性生理盐水会增加心率。CO₂可阻断果蝇幼虫骨骼肌神经肌肉接头（NMJ）处的突触传递，但低pH不会。作用位点是突触后，原因是对果蝇NMJ处的神经递质谷氨酸的敏感性降低。与NMJ处的突触不同，暴露于CO₂时，CNS在突触传递中仍保持活跃。总之，CO₂的作用是直接作用于心脏使其停止跳动，并在骨骼肌NMJ处通过降低对运动神经末梢释放的神经递质谷氨酸的敏感性来实现。CO₂对幼虫CNS的作用以及由CO₂间接诱导的pH效应都无法解释其快速的行为和生理效应。黑腹果蝇制剂中的谷氨酸受体在功能上与脊椎动物中的离子型谷氨酸受体相似，这可以解释在脊椎动物中尚未从机制上得到解释的CO₂的观察现象。
