Studies on the mechanism of shock. The importance of central catecholaminergic neurons in the response to injury.

Destruction of central catecholaminergic nerve terminals and axons by the injection of 6-hydroxydopamine (6-OHDA) into a lateral cerebral ventricle lowered the resistance of rats to 4-h bilateral hindlimb ischaemia. Although treatment with 6-OHDA alters food intake and growth rate its effect on the resistance of rats to this injury could not be attributed to differences in the size of the limbs which were made ischaemic or in nutritional state. It was not seen after peripheral chemical sympathectomy produced by the intravenous injection of 6-OHDA. Pretreatment with intraventricular 6-OHDA affected the core temperature changes during and after the limb ischaemia and impaired the blood pressure response after removal of the tourniquets. The lesions in the hypothalamus associated with these changes were examined with fluorescence histochemistry and found to be severe and widespread. It was concluded that the catecholaminergic fibres innervating the hypothalamus and other parts of the brain concerned in homoeostasis play a beneficial role in the defence against injury.