Mackie G O, Marx R M, Meech R W
Biology Department, University of Victoria, Victoria, British Columbia, V8W 3N5, Canada.
J Exp Biol. 2003 Jul;206(Pt 14):2487-505. doi: 10.1242/jeb.00450.
The hydromedusan jellyfish Aglantha digitale feeds on small planktonic organisms carried to the margin by tentacle flexions. During feeding, the manubrium bends across ("points") and seizes the prey with flared lips. In immobilized preparations, pointing to a source of electrical stimulation was accurate, 70% of the time, to within 15 degrees. Cutting experiments showed that the conduction pathways concerned with pointing and lip flaring are located in eight radial strands consisting of a radial canal, a giant nerve axon and a bundle of small axons with FMRFamide-like immunoreactivity. Application of food juices to sites on the margin and tentacles evoked trains of impulses in the axon bundles (F events; conduction velocity 15.5+/-3.7 cm s(-1)) and in the epithelium lining the radial canals (E events; conduction velocity 28.5+/-3.5 cm s(-1)). Impulses were conducted circularly in the outer nerve ring (F events) or in the ring canal (E events). Unilateral flexions of the manubrium during pointing arise from preferential excitation of one or more of eight longitudinal "muscle bands" in the wall of the manubrium and peduncle. Lip flaring represents symmetrical contraction of all eight bands. Cutting experiments revealed that F events mediate pointing; E events mediate lip flaring. Thus the endodermal radial canals, which in other hydromedusae mediate protective 'crumpling', provide the conduction pathway for manubrial lip flaring. Aglantha's alternative protective response--escape swimming--makes crumpling unnecessary, releasing the pathway for use in feeding. Trains of E events, generated in the manubrium during ingestion, propagate to the margin and inhibit rhythmic (slow) swimming with a duration that depended on their number and frequency. Inhibition of swimming appeared to facilitate transfer of food from the margin to the mouth, but how it comes about is unclear.
水螅水母类的指状艾氏水母以触手弯曲带到边缘的小型浮游生物为食。进食时，垂管会弯折（“指向”）并用张开的唇抓住猎物。在固定标本中，指向电刺激源的准确率为70%，误差在15度以内。切断实验表明，与指向和唇张开相关的传导通路位于八条放射状束中，这些束由一条放射管、一条巨大神经轴突和一束具有FMRF酰胺样免疫反应性的小轴突组成。将果汁施加到边缘和触手的部位会在轴突束（F事件；传导速度15.5±3.7厘米/秒）和放射管内衬的上皮组织（E事件；传导速度28.5±3.5厘米/秒）中诱发一连串冲动。冲动在外围神经环（F事件）或环管（E事件）中循环传导。指向时垂管的单侧弯曲源于垂管和柄壁中八条纵向“肌带”中一条或多条的优先兴奋。唇张开代表所有八条肌带的对称收缩。切断实验表明，F事件介导指向；E事件介导唇张开。因此，在其他水螅水母中介导保护性“皱缩”的内胚层放射管，为垂管唇张开提供了传导通路。艾氏水母的另一种保护反应——逃避游泳——使皱缩变得不必要，从而释放出该传导通路用于进食。在摄食过程中垂管产生的一连串E事件传播到边缘并抑制节律性（缓慢）游泳，其持续时间取决于它们的数量和频率。游泳的抑制似乎有助于食物从边缘转移到口部，但具体机制尚不清楚。
