The Effect of Injury on Monoamine Concentrations in the Rat Hypothalamus

The monoamine concentrations have been measured in four regions of the brain (hypothalamus, cortex, cerebellum and brain stem) in rats injured by either hind‐limb ischaemia or scald. Both injuries produced a rapid fall in the noradrenaline concentration of the hypothalamus which recovered slowly if the injury was not fatal. This effect of injury was seen after pretreatment with a‐methyl‐p‐tyrosine to inhibit noradrenaline synthesis, indicating an increased rate of utilization of noradrenaline after injury. These injuries did not affect the 5‐hydroxytryptamine concentration in the hypothalamus, but changes were found in the concentration of this monoamine and in that of its metabolite, 5‐hydroxyindole acetic acid, in the brain stem. It is concluded that these forms of injury had specific effects on the brain monoamines. The hypothalamic changes were not secondary to changes in core temperature or to hypotension or hypovolaemia and they are discussed in relation to the impairment of temperature regulation seen in the injured rat.