Sublethal Effects of Environmental Toxicants on Oligochaete Escape Reflexes

Abstract

SYNOPSIS. Soft-bodied oligochaetes that reside in soil and benthic environments are frequently exposed to pesticides and other environmental toxicants. Using noninvasive electrical recording techniques, some of the sublethal neurophysiological effects of these toxicants have been assessed in selected terrestrial and freshwater oligochaetes: Lumbricus terrestris, Eisenia foetida, and Lumbriculus variegatus. Under laboratory conditions, short-term cutaneous exposure to a wide variety of toxicants produces sublethal and reversible disruptions of giant nerve fiber spike activity and other bioelectric events that mediate rapid escape reflexes. Generally, electrophysiological effects include one or more of the following: (a) hypo- or hyper-excitability of giant fibers to mechanosensory stimulation, (b) reduction in giant fiber conduction velocity, (c) induction of abnormal giant fiber activity (i.e., spontaneous, rebound, or ectopic spiking), (d) increased delay or block of central transmission between the medial giant interneuron (MGF) and its associated pool of motorneurons, and (e) attenuation of MGF-mediated electrical potentials in longitudinal muscle. These efforts to describe the systemic impact and time course of neurotoxicant effects in vivo are necessary steps in ultimately predicting the ecological consequences of neurotoxicant exposure in situ.