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CHRONIC DIETARY EXPOSURE WITH INTERMITTENT SPIKE DOSES OF CHLORPYRIFOS FAILS TO ALTER FLASH OR PATTERN REVERSAL EVOKED POTENTIALS IN RATS.
Citation:
Herr, D W., J. E. Graff, R. Marshall, AND D. Hunter. CHRONIC DIETARY EXPOSURE WITH INTERMITTENT SPIKE DOSES OF CHLORPYRIFOS FAILS TO ALTER FLASH OR PATTERN REVERSAL EVOKED POTENTIALS IN RATS. Presented at Society of Toxicology, Nashville, TN, March 17-21, 2002.
Description:
Human exposure to pesticides is often characterized by chronic low level exposure with intermittent spiked higher exposures. Visual disturbances are often reported following exposure to xenobiotics, and cholinesterase-inhibiting compounds have been reported to alter visual function. This study examined the effects of chronic (1 year) dietary exposure (0, 1, or 5 mg/kg/day) to chlorpyrifos in male Long Evans rats (100-110 days old at study initiation). These doses were chosen to produce minimal and approximately 50% inhibition of brain cholinesterase activity, respectively. In addition to dietary exposure, half of the animals received an oral bolus of 45 mg/kg chlorpyrifos (in corn oil) every other month (n = 16-18 rats/treatment). Subjects were weight maintained at 350g throughout the study. After the final spiked exposure, the animals were allowed to recover for about 2.5 months, so only irreversible effects would be examined. Subjects were surgically implanted with screw electrodes over the visual cortex and allowed to recover for one week. Unanesthetized animals were placed in a restrainer and presented with vertical bar stimuli (square wave spatial and temporal modulation) of 0.06, 0.13, and 0.26 cpd visual angle, at contrast levels of 15, 30, and 60 percent contrast. Reversal rate was 0.49 Hz, and a mean illuminance of 50 lux was maintained between stimuli. After pattern testing, the animals were presented with a 10 s flash stimulus at 11, 39, and 148 lux-s, with an ambient illumination of 15 lux. Dietary exposure to chlorpyrifos (alone or in combination with oral spike doses) did not produce changes in either flash- or pattern reversal-evoked potentials. The evoked potentials did show the expected intensity and spatial frequency dependent changes, showing that the animal's responses were under stimulus control. Thus, chronic exposure to chlorpyrifos did not appear to alter visual responses at the level of the cortex in adult animals. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.