Rowsey_2002_J.Appl.Physiol_92_789

Exposure to an open field is psychologically stressful and leads to an elevation in core temperature T(c Methyl scopolamine MS a muscarinic antagonist and pyridostigmine PYR a carbamate that inhibits acetylcholinesterase do not cross the blood-brain barrier and have little effect on T(c in resting nonstressed animals However we have found that MS has an antipyretic effect on T(c that is caused by handling and cage-switch stress PYR should act pharmacologically to reverse the effects of MS To this end we assessed the effects of MS and PYR on stress-induced hyperthermia Male Sprague-Dawley rats at 90 days of age were housed individually at an ambient temperature of 22 degrees C T(c and motor activity were monitored by radiotelemetry in an open-field chamber Rats were dosed intraperitoneally at 1200 with 1.0 mg/kg MS 0.1 mg/kg PYR a combination of MS and PYR or saline and placed immediately inside the open-field chamber for 60 min Stress-induced hyperthermia was suppressed immediately by MS and enhanced by PYR T(c only increased by 0.3 degrees C in the MS-treated animals The hyperthermic response in the PYR group was nearly 0.6 degrees C above that of rats dosed with saline Coadministration of PYR and MS led to a stress-induced hyperthermia response nearly identical to that of rats injected with saline Overall open-field stress exacerbated the effects of MS and PYR on body T(c and provides support for a peripheral cholinergic mechanism that mediates stress-induced hyperthermia