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Calcium Dependency and Tetrodotoxin Sensitivity of Neostriatal Dopamine Release in 5‐Day‐Old and Adult Rats as Measured by In Vivo Microdialysis

Abstract: The calcium dependency and tetrodotoxin sensitivity of extracellular dopamine levels were assessed by microdialysis in the neostriatum of 5‐day‐old rat pups and were compared with those obtained in adult rats. The removal of calcium from the dialysate reduced spontaneous levels of extracellular dopamine to 20% of normal in the 5‐day‐old pups and to 10% of normal in the adults. Calcium‐free dialysate also decreased potassium‐evoked dopamine release to ∼20% of baseline in both ages. Furthermore, the addition of tetrodotoxin to the dialysate decreased spontaneous levels of extracellular dopamine to 10% of baseline in both ages. The effects of calcium removal and the addition of tetrodotoxin on extracellular levels of the dopamine metabolite 3,4‐dihydroxyphenylacetic acid were less pronounced. The results of this study demonstrate that extracellular levels of dopamine sampled by microdialysis in rats as young as 5 days of age are both calcium dependent and tetrodotoxin sensitive; thus, they are derived from neuronal activity and not from injury caused by acute implantation of the probe. Other age‐related differences support the hypothesis that dopamine release and turnover is greater In immature rats and may represent a form of compensation for incomplete dopamine nerve terminal ingrowth.