The effect of trauma on the formaldehyde-induced fluorescence of noradrenaline in the hypothalamus and brain stem of the rat.

Noradrenaline (NA) fluorescence in the hypothalamus and brain stem of the rat has been examined during and up to 1.5 h after a 4-h period of bilateral hind-limb ischaemia. A decrease in the fluorescence of the NA terminals in the n. supraopticus and n. paraventricularis was seen during the second half of the period of limb ischaemia and became more marked 1.5 h after removal of the tourniquets. Changes in the preoptic-anterior hypothalamic (POAH) area and n. dorsomedialis occurred more slowly and depletion was best seen after the limb ischaemia. Measurements of the fluorescence with a microphotometer confirmed the changes seen in the POAH area, the n. supraopticus and the n. dorsomedialis 1.5 h after 4 h bilateral hind-limb ischaemia but suggested that the visual gradings of changes in the n. paraventricularis, which normally has a high NA content, could be unreliable. No changes were seen at any of the times studied in the ventral part of n. striae terminalis. The cells of origin of the affected terminals could not be identified since no changes were detected in the fluorescence of the cells in the NA nuclei of the brain stem. alpha-Methyl-p-typrosine, given at the start of the experiment to inhibit tyrosine hydroxylase, reduced the fluorescence of these cells but still no difference could be discerned between those in the control and injured rats. These results confirm the previous chemical findings of a fall in the NA concentration in the hypothalamus after injury with little change in that of brain stem. The results are discussed in relation to the effects of the injury on the homoeostatic functions of the hypothalamus.