The effect of trauma on the activity of central noradrenergic neurones.

Changes in the concentration of the main noradrenaline metabolite in rat brain, 4-hydroxy-3-methoxy-phenylethyleneglycol sulphate (MOPEG-SO4) have been studied during and after injury by limb ischaemia. In the hypothalamus the MOPEG-SO4 concentration rose in about 30 min to a new plateau level which was maintained during a 4 h period of bilateral hind-limb ischaemia and then rose further when the circulation to the limbs was restored. After about 2 h hind-limb ischaemia the concentration in the hind-brain, particularly in the caudal half, rose progressively and this rise continued when the tourniquets were removed after 4 h. Limb ischaemia did not affect the MOPEG-SO4 concentration in the cerebellum but the concentration rose in the cerebrospinal fluid. Attempts to study the production of MOPEG-SO4 in more detail by inhibiting its transport from the brain with probenecid were not helpful and reasons are given for thinking that probenecid is not a useful tool for this type of investigation. The results are considered to provide further evidence that trauma activates ascending and descending pathways which arise from the noradrenergic nerve cells in the hind-brain.