The effects on body temperature of noradrenaline, adrenaline and 5-hydroxytryptamine (5-HT), when injected into the cerebral ventricles vary in different species. For instance, the two catecholamines lower body temperature in cats, dogs and monkeys, raise it in rabbits and sheep, and have no effect on goats and oxen. On the other hand, 5-HT raises temperature in cats, dogs and monkeys, has a weak and inconsistent hypothermic effect in rabbits and sheep, and produces pronounced hypothermia in goats and oxen (von Euler, Linder & Myrin, 1943;Feldberg & Myers, 1964;Cooper, Cranston & Honour, 1965;Andersson, Jobin & Olsson, 1966;Bligh, 1966; Feldberg, Hellon & Lotti, 1967; Feldberg & Lotti, 1967;Findlay & Robertshaw, 1967).As shown in the present experiments, rats respond differently again to the monoamines injected into the cerebral ventricles. As in goats and oxen, 5-HT produces a fall in rectal temperature, but the catecholamines are not inactive-according to dosage they produce hyper-or hypothermic effects.Up to now, the effect of intraventricular injections of the MAO inhibitor tranylcypromine on body temperature has been examined in three species (El Hawary, Feldberg & Lotti, 1967; Feldberg & Lotti, 1967). In cats and dogs in which 5-HT produces hyperthermia, tranylcypromine also raises body temperature, but in rabbits in which 5-HT has a weak and inconsistent hypothermic effect, tranylcypromine did not affect temperature. The question thus arose of how it would affect temperature in a species like the rat in which intraventricular 5-HT lowers rectal temperature.
METHODSSprague-Dawley rats of either sex weighing 250-280 g were used. Rectal temperature was measured with a thermistor probe inserted about 6 cm into the rectum and taped to the base of the tail. Temperature was monitored continuously by a Kent multichannel recorder. The figures in this paper are plotted directly from the tracings obtained in this way. The rats were placed in a 19-cm long tunnel-shaped wire mesh container, with a flat bottom and front made of cork. The back was a removable rubber bung of 6 cm diameter with a hole for the tail and thermistor probe. For the injections, the rats were removed from the container and returned immediately afterwards.Room temperature was between 21 and 230 C.