Facilitation of ischemia-induced release of dopamine and neuronal damage by dexamethasone in the rat striatum

Abstract

Glucocorticoids have been reported to aggravate ischemia-induced neuronal damage in both humans and experimental animals. Because an excess release of neurotransmitters is closely related to the outcome of ischemic neuronal damage, we evaluated the effects of dexamethasone on monoaminergic release and histological outcome. Changes in the extracellular concentrations of monoamines and their metabolites in the striatum produced by occlusion of the middle cerebral artery for 20 min were measured using a microdialysis high-performance liquid chromatography procedure, and the effects of intracerebroventricular administration of dexamethasone (10 μg) were evaluated in halothane-anesthesized rats. The histological outcome was evaluated by light microscopy 7 days after ischemia. Additionally, the effects of lesioning of the substantia nigra were estimated. The extracellular concentrations of neither dopamine nor serotonin were affected by the administration of dexamethasone in the nonischemic state. The occlusion of the middle cerebral artery produced a marked increase in the extracellular concentration of dopamine in the striatum, the peak value being 240 times that before ischemia. The preischemic administration of dexamethasone enhanced the increase in dopamine level during ischemia, and the peak value in the dexamethasone group was 640% of that in the vehicle group. After 7 days, ischemic neuronal damage in the dexamethasone group was severe compared with that in the vehicle group. In rats receiving the substantia nigra lesion, the ischemic release of dopamine was abolished, and the aggravation of ischemic neuronal damage by dexamethasone was completely alleviated. Changes in the release of monoamines may be a contributing factor in the development of the ischemic neuronal damage induced by glucocorticoids.