关键词：
hypoxia
O-2 sensing
serotonin (5-HT)
sensory
motor
cilia
gastropod
Helisoma trivolvis
摘要：
Oxygen (O-2) is one of the most important environmental factors that affects both physiological processes and development of aerobic animals, yet little is known about the neural mechanism of O-2 sensing and adaptive responses to low O-2 (hypoxia) during development. In the pond snail, Helisoma trivolvis, the first embryonic neurons (ENC1s) to develop are a pair of serotonergic sensory-motor cells that regulate a cilia-driven rotational behavior. Here, we report that the ENC1-ciliary cell circuit mediates an adaptive behavioral response to hypoxia. Exposure of egg masses to hypoxia elicited a dose-dependent and reversible acceleration of embryonic rotation that mixed capsular fluid, thereby facilitating O-2 diffusion to the embryo. The O-2 partial pressures (Po-2) for threshold, half-maximal, and maximal rotational response were 60,28, and 13 mm Hg, respectively. During hypoxia, embryos relocated to the periphery of the egg masses where higher Po-2 levels occurred. Furthermore, intermittent hypoxia treatments induced a sensitization of the rotational response. In isolated ciliary cells, ciliary beating was unaffected by hypoxia, suggesting that in the embryo, O-2 sensing occurs upstream of the motile cilia. The rotational response of embryos to hypoxia was attenuated by application of the serotonin receptor antagonist, mianserin, correlated to the development of ENC1-ciliary cell circuit, and abolished by laser-ablation of ENC1s. Together, these data suggest that ENC1s are unique oxygen sensors that may provide a good single cell model for the examination of mechanistic, developmental, and evolutionary aspects of O-2 sensing. (C) 2002 Wiley Periodicals, Inc.
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中文科技期刊
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