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CHRONIC DIETARY EXPOSURE WITH INTERMITTENT SPIKE DOSES OF CHLORPYRIFOS FAILS TO ALTER BRAINSTEM AUDITORY EVOKED RESPONSE (BAERS) IN RATS.
Citation:
Graff, J. E., D W. Herr, R. Marshall, AND D. Hunter. CHRONIC DIETARY EXPOSURE WITH INTERMITTENT SPIKE DOSES OF CHLORPYRIFOS FAILS TO ALTER BRAINSTEM AUDITORY EVOKED RESPONSE (BAERS) IN RATS. Presented at Society of Toxicology, Salt Lake City, UT, 3/9-13/2002.
Description:
Human exposure to pesticides is often characterized by chronic low level exposure with intermittent spiked higher exposures. Cholinergic transmission is involved in auditory structures in the periphery and the brainstem and is altered following chlorpyrifos exposure. 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) on BAERs. The chlorpyrifos 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 cerebellum and allowed to recover for one week. Unanesthetized animals were placed in a restrainer and presented with the following auditory stimuli (presented at 5.6 hz): rarefaction click, 4 and 16 kHz pure tone pips presented at 50, 65, and 80 dB SPL, and 64 kHz pure tone pip presented at 65, 70 and 80 dB SPL. Dietary exposure to chlorpyrifos (alone or in combination with oral spike doses) did not produce changes in brainstem auditory evoked responses. The evoked responses showed the expected intensity and frequency-dependent changes, indicating that the animals' responses were under stimulus control. Thus, chronic exposure to chlorpyrifos did not appear to alter auditory responses at the level of the brainstem in adult animals. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.