Localization of the brain regions concerned in the inhibition of shivering by trauma.

The effect on the inhibition of shivering by limb ischaemia of small 6-hydroxydopamine (6-OHDA) lesions in the hypothalamus has been studied in rats. The injection of 6-OHDA into the posterior part of the hypothalamus in the neighbourhood of the N. dorsomedialis or into the ventral ascending catecholaminergic bundle caudal to that nucleus prevented the depression of the ambient temperature threshold for the onset of shivering which usually occurs during hind-limb ischaemia and lowered the slope of the regression line relating the intensity of shivering to ambient temperature. In rats not treated with 6-OHDA this slope is unaffected by limb ischaemia. These lesions reproduced the changes seen when 6-OHDA was injected into the lateral cerebral ventricle. Lesions in other parts of the hypothalamus were without effect. It is concluded that the inhibitory catecholaminergic synapses are situated in the posterior part of the hypothalamus and that the impulses reach them from nerve cells in the hind-brain via the ventral bundle. The lesions produced in these experiments had little effect on thermoregulation in non-injured rats.