Influence of transient ischemia on monoamine metabolism in the rat brain during nitrous oxide and phenobarbitone anaesthesia.

Cerebral ischemia was induced in normothermic, artificially ventilated rats, anesthetized with 70% N2O or 150 mg/kg of phenobarbitone, by bilateral occlusion of the common carotid arteries and by simultaneous depression of the mean arterial blood pressure to 50 mm Hg. The levels of tyrosine, dopamine (DA), noradrenaline (NA), tryptophan, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were measured after 15 min of ischemia as well as after 30 min of recirculation. In separate experiments (70% N2O) the rate of accumulation of DOPA and 5-hydroxytryptophan (5-HTP) was determined in three different brain regions (striatum, limbic forebrain and hemispheres) during recirculation. During ischemia, the monoamine pattern was unaffected. Following recirculation, increases in DA, 5-HIAA, tyrosine and tryptophan were found irrespective of the type of anesthesia used. Pronounced postischemic decreases in NA and 5-HT were observed in animals anesthetized with nitrous oxide but not in those given phenobarbitone. During recirculation the rate of tyrosine hydroxylation increased in all three brain regions while tryptophan hydroxylation was reduced. It is tentatively concluded that following transient, global cerebral ischemia, neuronal activity is low or eliminated in dopaminergic and serotoninergic neurons and high in noradrenergic neurons.