[Role of brain biogenic amines in the central thermoregulatory mechanism of the rat (author's transl)]

Abstract

Changes in rectal and skin temperatures following intraventricular injection of biogenic amines and related substances were investigated in rats. Intraventricular injection of norepinephrine in a small dose (6 mug) produced a slight elevation of rectal temperature, but in larger amounts (25-50 mug) resulted in a dose-dependent hypothermia which was associated with a marked rise of skin temperature. No change was observed in plasma free fatty acid and glucose levels and oxygen consumption after intraventricular injection of norepinephrine (25 mug). Intraventricular injection of imipramine and safrazine produced a slight fall in the rectal temperature. Norepinephrine-induced hypothermia was more pronounced in rats pretreated with safrazine and less in rats pretreated with alpha-methyl-p-tyrosine, as compared with that in controls. Intraventricular injection of 6-hydroxydopamine (0.75-250 mug) brought about a marked dose-dependent hypothermia. The second injection of 6-hydroxydopamine 5 days after the first injection had no effect on the body temperature. Norepinephrine injection 2 days after the second injection of 6-hydroxydopamine produced a more pronounced hypothermia than the change in control rats without pretreatments. Haloperidol did not affect the hypothermia induced by 6-hydroxydopamine. Intraventricular injection of dopamine and L-DOPA showed less effect that norepinephrine had. Intraventricular injection of phenoxybenzamine prior to norepinephrine blocked the hypothermia and skin temperature elevation which are normally observed following norepinephrine injection, while propranolol given in the same way showed less or no effect. Intraventricular injection of phenylephrine produced a dose-dependent hypothermia, whereas no dose-response relationship was obtained by isoproterenol. These results suggest that in the rat the hypothermic effect of norepinephrine injected intraventricularly is mediated by an action of central alpha-receptor. At high and low ambient temperatures hypothermia was similarly observed following intraventricular injection of 5-hydroxytryptamine (25 mug) as at normal room temperature. On the other hand, norepinephrine (25 mug) produced a rise in rectal temperature at high ambient temperature and a marked fall at low ambient temperature. The hypothermic effect of norepinephrine was not different between cold-adapted ones at room temperature. From the results the role of norepinephrine and other biogenic amines in the brain in thermoregulatory processes was discussed.