Hoholm Fredrik, Zhu Xiaodong, Ashton Francis T, Freeman Andrea S, Veklich Yuri, Castelletto Anthony, Lamont Stephan, Schad Gerhard A
Department of Pathobiology/Parasitology, School of Veterinary Medicine, University of Pennsylvania, 3800 Spruce Street, Philadelphia, Pennsylvania 19104, USA.
J Parasitol. 2005 Feb;91(1):61-8. doi: 10.1645/GE-3398.
The infective larvae (L3i) of the nematode parasite of swine, Oesophagostomum dentatum, are passively ingested by their hosts. The L3i exhibit certain behaviors that are probably selected to increase the likelihood of ingestion, by strategic positioning in the environment. The larvae show positive geotactic behavior and respond to temperature variations in their environment, as shown by their behavior on a thermal gradient. To investigate neuronal control of this behavior, we initiated a study of the structure of the amphidial neurons of this parasite. The same number and types of neuronal dendritic processes are found in the amphids of the O. dentatum L3i as in those of its close relatives Haemonchus contortus and Ancylostoma caninum. Well-developed dendritic processes of wing cells are located in the amphidial sheath cells, these being similar to wing cells AWA in the free-living nematode Caenorhabditis elegans but actually more extensive. Similar to its close relatives just mentioned, and C. elegans as well, O. dentatum L3i has prominent finger cell processes, the finger cell neurons being the thermoreceptors in all 3 of the preceding species. However, unlike the arrangement seen in H. contortus and A. caninum, where the microvilli-like "fingers" of these neurons lie dorsal to the amphidial channel and occupy a very large portion (>50%) of the anterior end of the larva, the dendritic process of the finger cells in O. dentatum extends into unusual linguiform projections that, in turn, extend into the lumen of the mouth tube, a complex structural arrangement that has not been described for any other nematode.
猪的线虫寄生虫齿状食道口线虫的感染性幼虫(L3i)被其宿主被动摄取。L3i表现出某些行为,这些行为可能是通过在环境中的策略性定位来增加被摄取的可能性而被选择的。幼虫表现出正向地性行为,并对其环境中的温度变化做出反应,如它们在热梯度上的行为所示。为了研究这种行为的神经控制,我们开始了对这种寄生虫两性感觉器神经元结构的研究。在齿状食道口线虫L3i的两性感觉器中发现的神经元树突状突起的数量和类型,与它的近亲捻转血矛线虫和犬钩口线虫中的相同。翼细胞发育良好的树突状突起位于两性感觉器鞘细胞中,这些类似于自由生活线虫秀丽隐杆线虫中的翼细胞AWA,但实际上更广泛。与上述近亲以及秀丽隐杆线虫一样,齿状食道口线虫L3i有突出的指状细胞突起,指状细胞神经元是前三个物种中所有的温度感受器。然而,与在捻转血矛线虫和犬钩口线虫中看到的排列不同,在那里这些神经元的微绒毛状“手指”位于两性感觉器通道的背侧,并占据幼虫前端的很大一部分(>50%),齿状食道口线虫中手指细胞的树突状突起延伸成不寻常的舌状突起,这些舌状突起又延伸到口管的管腔中,这种复杂的结构排列在任何其他线虫中都没有描述过。