Immobilization of albino rats for 2 h showed ambient temperature-dependent changes in rectal temperature,
hypothermia at temperatures below 30 degrees C, and
hyperthermia at 35 degrees C and above. Adrenalectomized (Adre) rats showed more
hypothermia compared to
sham operated controls at 25 +/- 2 degrees C. The increased
hypothermia in adrenalectomized rats was reversed by 10 mg/kg IP or 100 microgram/rat ICV of
hydrocortisone. Groups of rats pretreated with
desmethylimipramine (DMI, 25 mg/kg IP) and
6-hydroxydopamine (6-HD, 100 microgram/rat ICV) or methyl
ester of parachlorophenylalanine (ME-PCPA, 100 microgram/rat ICV for 3 days) or
5,6-dihydroxytryptamine (DHT, 75 microgram/rat ICV) showed significantly less
hypothermia at the end of 2 h of immobilization. Applying analysis of variance test, the
hypothermia in Adre, ME-PCPA and DHT groups, was found to be not significantly different from their respective control groups between 0 and 45 min of immobilization but was significantly different between 45 to 120 min of immobilization. DMI-6-HD group however, showed significant difference between 0--45 min only and not between 45--120 min of immobilization. The results suggest that the early phase of immobilization
induced hypothermia between 0--45 min is
dopamine and the late phase of
hypothermia between 45--120 min is
5-hydroxytryptamine mediated.