In the present study, cross-tolerance between hypothermia induced by morphi
ne and nicotine in mice has been investigated. Different doses of morphine
or nicotine induced dose-dependent hypothermia. The sub-maximal doses of bo
th drugs were used for interaction studies. Administration of mecamylamine
either intracerebroventricularly (2-6 mug/animal icv) or intraperitoneally
(0.5 and 1 mg/kg ip) decreased both morphine- or nicotine-induced hypotherm
ia. Naloxone either intracerebroventricularly (2-6 mug/animal) or intraperi
toneally (1 and 2 mg/kg) reduced the response to morphine, but not nicotine
's response. Hexamethonium (5 and 10 mg/kg ip) caused a slight decrease in
morphine's hypothermia, but not that of nicotine. Nicotine's response was d
ecreased in the animals which were made tolerant to hypothermic effect of m
orphine, pre-treatment of the animals with low doses of morphine (12.5 or 2
5 mg/kg), once daily for 3 days, did not cause significant tolerance to the
hypothermic response to morphine or nicotine. However, the administration
of low doses of morphine (12.5 or 25 mg/kg) plus nicotine (2 mg/kg), once d
aily for 3 days, increased levels of tolerance to hypothermia induced by ei
ther drug. It is concluded that nicotinic receptor mechanism may play a rol
e in morphine-induced hypothermia and there is cross-tolerance between the
two drugs. (C) 2001 Elsevier Science Inc. All rights reserved.