The effects of choline on body temperature in conscious rats

Abstract

Choline (75-300 mu g) produced dose-dependent hypothermia when injected intracerebroventricularly (i.c.v.). Pre-treatment with the muscarinic receptor antagonist, atropine (10 mu g, i.c.v.), blocked the hypothermic effect of choline (150 mu g), but the response was only partially attenuated by pre-treatment with the nicotinic receptor antagonist, mecamylamine (20 mu g, i.c.v.). Pirenzepine (25 mu g), a muscarinic M-1 receptor antagonist, or hexahydro-siladifenidol (HHSD) (100 mu g), a muscarinic M-3 receptor antagonist, also blocked choline-induced hypothermia when injected centrally. Unlike the other muscarinic receptor antagonists, M-2-selective 11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one (AF-DX116) (10 mu g), did not affect choline-induced hypothermia. We also found that choline-induced hypothermia was very sensitive to the ambient temperature. Similar to its effect at room temperature, choline produced dose-dependent hypothermia at 4 degrees C, but this effect was abolished at 32 degrees C. These data suggest that choline produces hypothermia and this effect is mediated by muscarinic receptors.