Stehr Carla M, Linbo Tiffany L, Incardona John P, Scholz Nathaniel L
Ecotoxicology and Environmental Fish Health Program, Northwest Fisheries Science Center, National Oceanic and Atmospheric Administration Fisheries, 2725 Montlake Boulevard East, Seattle, WA 98112, USA.
Toxicol Sci. 2006 Jul;92(1):270-8. doi: 10.1093/toxsci/kfj185. Epub 2006 Apr 12.
Fipronil is a phenylpyrazole insecticide designed to selectively inhibit insect gamma-aminobutyric acid (GABA) receptors. Although fipronil is often used in or near aquatic environments, few studies have assessed the effects of this neurotoxicant on aquatic vertebrates at sensitive life stages. We explored the toxicological effects of fipronil on embryos and larvae using the zebrafish (Danio rerio) experimental model system. Embryos exposed to fipronil at nominal concentrations at or above 0.7 microM (333 mug/l) displayed notochord degeneration, shortening along the rostral-caudal body axis, and ineffective tail flips and uncoordinated muscle contractions along the body axis in response to touch. This phenotype closely resembles zebrafish locomotor mutants of the accordion class and is consistent with loss of reciprocal inhibitory neurotransmission by glycinergic commissural interneurons in the spinal cord. Consistent with the hypothesis that notochord degeneration may be due to abnormal mechanical stress from muscle tetany, the expression patterns of gene and protein markers specific to notochord development were unaffected by fipronil. Moreover, the degenerative effects of fipronil (1.1 microM) were reversed by coexposure to the sodium channel blocker MS-222 (0.6mM). The notochord effects of fipronil were phenocopied by exposure to 70 microM strychnine, a glycinergic receptor antagonist. In contrast, exposure to gabazine, a potent vertebrate GABA(A) antagonist, resulted in a hyperactive touch response but did not cause notochord degeneration. Although specifically developed to target insect GABA receptors with low vertebrate toxicity, our results suggest that fipronil impairs the development of spinal locomotor pathways in fish by inhibiting a structurally related glycine receptor subtype. This represents an unanticipated and potentially novel mechanism for fipronil toxicity in vertebrates.
氟虫腈是一种苯基吡唑类杀虫剂，旨在选择性抑制昆虫的γ-氨基丁酸（GABA）受体。尽管氟虫腈常用于水生环境或其附近，但很少有研究评估这种神经毒素在敏感生命阶段对水生脊椎动物的影响。我们使用斑马鱼（Danio rerio）实验模型系统探究了氟虫腈对胚胎和幼体的毒理学影响。暴露于名义浓度为0.7微摩尔/升（333微克/升）及以上的氟虫腈中的胚胎，出现了脊索退化、沿头-尾身体轴缩短，以及对触摸的尾部翻转无效和沿身体轴的肌肉收缩不协调。这种表型与手风琴类斑马鱼运动突变体非常相似，并且与脊髓中甘氨酸能联合中间神经元的相互抑制性神经传递丧失一致。与脊索退化可能是由于肌肉强直引起的异常机械应力这一假设一致，氟虫腈并未影响脊索发育特异性的基因和蛋白质标志物的表达模式。此外，同时暴露于钠通道阻滞剂MS-222（0.6毫摩尔）可逆转氟虫腈（1.1微摩尔）的退化作用。暴露于70微摩尔的士的宁（一种甘氨酸能受体拮抗剂）可模拟氟虫腈对脊索的影响。相比之下，暴露于强效脊椎动物GABA(A)拮抗剂gabazine会导致触摸反应亢进，但不会引起脊索退化。尽管氟虫腈是专门开发用于靶向具有低脊椎动物毒性的昆虫GABA受体，但我们的结果表明，氟虫腈通过抑制一种结构相关的甘氨酸受体亚型来损害鱼类脊髓运动通路的发育。这代表了氟虫腈在脊椎动物中毒性的一种意外且可能新颖的机制。
