The effects of choline on body temperature in conscious rats

Choline (75-300 mu g) produced dose-dependent hypothermia when injected int racerebroventricularly (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-t reatment with the nicotinic receptor antagonist, mecamylamine (20 mu g, i.c .v.). Pirenzepine (25 mu g), a muscarinic M-1 receptor antagonist, or hexah ydro-siladifenidol (HHSD) (100 mu g), a muscarinic M-3 receptor antagonist, also blocked choline-induced hypothermia when injected centrally. Unlike t he other muscarinic receptor antagonists, M-2-selective 11-[[2-[(diethylami no)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodia zepin-6-one (AF-DX116) (10 mu g), did not affect choline-induced hypothermi a. We also found that choline-induced hypothermia was very sensitive to the ambient temperature. Similar to its effect at room temperature, choline pr oduced dose-dependent hypothermia at 4 degrees C, but this effect was aboli shed at 32 degrees C. These data suggest that choline produces hypothermia and this effect is mediated by muscarinic receptors. (C) 1998 Elsevier Scie nce B.V. AU rights reserved.