Anoxia-induced dopamine release from rat striatal slices: involvement of reverse transport mechanism

Incubation of rat striatal slices in the absence of oxygen (anoxia), glucose (aglycemia), or oxygen plus glucose (ischemia) caused significant increases in dopamine (DA) release. Whereas anoxia decreased extracellular 3,4-dihydroxyphenylacetic acid levels by 50%, aglycemia doubled it, and ischemia returned this aglycemia-induced enhancement to its control level. Although nomifensine, a DA uptake blocker, completely protected the slices against anoxia-induced DA depletion, aglycemia- and ischemia-induced increases were not altered. Moreover, hypothermia differentially affected DA release stimulated by anoxia, aglycemia, and ischemia. Involvement of glutamate in DA release induced by each experimental condition was tested by using MK-801 and also by comparing the glutamate-induced DA release with that during anoxia, aglycemia, or ischemia. MK-801 decreased the anoxia-induced DA depletion in a dose-dependent manner. This treatment, however, showed a partial protection in aglycemic conditions but failed to improve ischemia-induced DA depletion. Like anoxia, DA release induced by exogenous glutamate was also sensitive to nomifensine and hypothermia. These results indicate that anoxia enhances DA release by a mechanism involving both the reversed DA transporter and endogenous glutamate. Partial or complete lack of effect of nomifensine, hypothermia, or MK-801 in the absence of glucose or oxygen plus glucose also suggests that experimental conditions, such as the degree of anoxia/ischemia, may alter the mechanism(s) involved in DA depletion.