Lethal and sublethal effects of ivermectin in a freshwater oligochaete, Lumbriculus variegatus

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2000-01-01
Authors
Ding, Jing
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Veterinary Pathology
Abstract

Ivermectin inhibited swimming, reversal, crawling frequency, and crawling speed in a time- and concentration- dependent manner with an IC₅₀ at 3 h of 1.1, 16, 91 and 5lnM, respectively. Ivermectin at 0.3 nM, or higher, also significantly decreased the frequency of helical swimming waves after 3h treatment. Picrotoxin (Cl ̄channel blocker) antagonized the ivermectin-induced decrease in swimming frequency, crawling frequency and crawling speed. The worms retained escape reflex function 3 h after treatment with 300 nM ivermectin. Electrophysiological recordings showed that ivermectin had no effects on the conduction velocity of medial or lateral giant fiber systems (MGF or LGF), or on muscle potentials evoked by MGF action potentials. The results indicate that locomotor behaviors controlled by non-giant interneuron pathways are more sensitive to ivermectin than are those controlled by giant interneurons, and suggest that C1 ̄channels are involved in mediating ivermectin's inhibitory effects.Ivermectin is a potent antiparasitic drug against nematode and arthropod parasites. Although lethal levels have been determined in some non-target species, the effects of sublethal doses have seldom been examined. In this study, we examined the lethal and sublethal effects of ivermectin in a freshwater oligochaete, Lumbriculus variegatus (order Lumbriculida). LC₅₀ at 72 h after ivermectin treatment was 560 nM. The endpoints for sublethal effects of ivermectin focused on several stimulus-evoked locomotor behaviors: (1) escape reflex controlled by giant interneuron pathways; (2) swimming and reversal in open water; and (3) crawling on wet surface or in confined spaces under water. Swimming, reversal and crawling are controlled by non-giant interneuron pathways.

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Sat Jan 01 00:00:00 UTC 2000