Variations in the level of noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT), and homovanillic acid (HVA) in brain tissue were measured for 2 days in conscious rabbits in which a circumscribed traumatic injury had been produced by the insertion of a small pressure cannula into the brain. The implanted cannula, occupying 0.0093 cm3 volume in the brain, has previously been shown to cause intracranial hypertension mainly by means of a local brain edema. The brain concentration of both DA and HVA were lowered during the entire period of intracranial hypertension, indicating an impaired formation of DA in damaged neurons located close to the ventricular system. On the other hand, the NA level was found to be significantly increased on the day following the injury, after which it normalized during the next day. This may indicate a less pronounced pressure-induced involvment of the NA neurons, known to be present more diffusely in the brain, away from the ventricular system. Accordingly, the amount of 5-HT in the brain stem appeared to remain unaffected by the traumatic injury.
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Edvinsson et al. (1971) studied this question.
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