Reduction in open field-induced hyperthermia in the rat exposed to chlorpyrifos, an anticholinesterase pesticide
2001
Gordon, C.J. | Yang, Y.L.
Rodents develop a marked elevation in core temperature (T(c)) when they are placed in an open field environment (OFE). Open field-induced hyperthermia (OFH) involves activation of thermoregulatory systems that are quiescent under baseline conditions. Cholinergic stimulation arising from exposure to organophosphates (OP) is expected to modulate OFH; subtle effects of OPs may be observed during OFH that would not occur in the absence of stress. We have found that methyl scopolamine (MS), a peripheral muscarinic antagonist, attenuates stress-induced hyperthermia. To this end, we assessed if a low dose of the OP pesticide chlorpyrifos (CHP) would alter OFH with and without administration of MS. T(c) and motor activity (MA) of male, Sprague-Dawley rats were monitored by telemetry while housed in their home cage at an ambient temperature of 22 degrees C. At 9 AM the rats were gavaged with corn oil or 10 mg/kg CHP that resulted in a approximately 40% inhibition in plasma cholinesterase activity. T(c) and MA were the same in the control and CHP groups prior to OFE. The rats were then dosed IP with saline or 1.0 mg/kg MS at 12 noon and subjected to OFE (61 x 61 x 61 cm box) for 1 h while T(c) and MA were monitored every 2 min. T(c) of the corn oil/saline group increased by 1.2 degrees C during OFE, whereas T(c) of the CHP/saline group was significantly attenuated. Administration of MS attenuated the OFH in rats treated with corn oil and CHP. Overall, exposure to OFE exacerbated the effects of a relatively low dose of CHP that had no effect in the unstressed animal. In addition, the OFH response to MS suggests a peripheral (i.e., outside of CNS) cholinergic pathway is operative in the control of OFH.
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