ASSESSING SUBLETHAL NEUROTOXICITY EFFECTS IN THE FRESH-WATER OLIGOCHAETE, LUMBRICULUS-VARIEGATUS

The sublethal neurotoxic and behavioral effects of five chemicals (4-aminopyridine, cadmium chloride, carbofuran, chloroform and diazinon) were examined in the freshwater oligochaete, Lumbriculus variegatus (Family Lumbriculidae), following short-term exposure by immersion. Noninvasive electrophysiological recordings of touch-evoked medial giant nerve fiber (MGF) spikes were obtained, before and after exposure, using printed circuit board recording grids. Neurotoxic effects included substantial, and reversible, decreases in MGF conduction velocity following exposure to all chemicals, except CdCl2. Reversible losses of MGF touch sensitivity occurred with exposure to chloroform and CdCl2. Hypersensitivity of the MGF to touch, accompanied by high-frequency spike trains and rebound spikes, occurred with exposure to 4-aminopyridine. Our approach provides a rapid and sensitive means of detecting and differentiating sublethal neurotoxic effects, in vivo, in this cosmopolitan benthic oligochaete.