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.