Simultaneous electrophysiological and behavioral studies were performed on 21–32 day old juvenile medaka (Oryzias latipes) exposed at sublethal concentrations to organic chemicals representing various modes of action. Non-invasive recordings were made of the electrical impulses generated within giant neuronal Mauthner cells, associated interneurons and motoneurons, and axial musculature, all of which initiate the startle or ‘escape’ response in fish. Timing in ms between these electrical sequelae was measured for each fish before and after 24 and 48 h exposure to a chemical. Carbaryl and phenol affected Mauthner cell to motoneuron transmission while chlorpyrifos, carbaryl, phenol and 2,4-dinitrophenol (DNP) showed neuromuscular effects. The variety of neurological effects detected at various concentrations of chemicals tested here suggest that different mechanisms may be responsible. Also noted was the number of startle responses to number of stimuli ratio (R:S); this ratio was affected by most chemicals. Medaka generally appeared to be more susceptible to predation after exposure to chlorpyrifos, carbaryl, fenvalerate, endosulfan, phenol, 1-octanol and DNP. The effects threshold for many of the test compounds was found to be consistent for both the neurophysiological and behavioral endpoints. Consequently, electrophysiological responses of Mauthner cell-initiated startle responses provided a measure of neurological injury that is also directly correlated to a definitive and ecologically relevant behavioral endpoint.
- Mauthner cell,
- Startle response,
Available at: http://works.bepress.com/steven_bradbury/21/