Monitoring of extracellular dopamine levels in the dorsal striatum and the nucleus accumbens with 5-minute on-line microdialysis in freely moving rats.

Abstract

We report a reliable 5-min on-line monitoring of dopamine released from the dorsal striatum and the nucleus accumbens of rats using in vivo brain microdialysis. The detection limit for dopamine was approximately 20 fg in a 10-microl injection sample using high-performance liquid chromatography with electrochemical detection set-up. Basal levels of dopamine in the dorsal striatum and the nucleus accumbens 4 h after probe insertion were 2.65 +/- 0.30 pg/5 min and 1.57 +/- 0.31 pg/5 min, respectively, whereas those of 20 h after probe insertion were lower: 0.97 +/- 0.21 pg/5 min and 0.51 +/- 0.09 pg/5 min, respectively. Infusion of the sodium channel blocker, tetrodotoxin (TTX; 2 microM), essentially suppressed levels of dopamine in both brain areas. At 4 h after probe insertion, TTX perfused for 4 h via dialysis probe reduced levels of dopamine to 0.47 +/- 0.08 pg/5 min (80% reduction) in the dorsal striatum and to 0.56 +/- 0.19 pg/5 min (65% reduction) in the nucleus accumbens. At 20 h after probe insertion, a similar TTX perfusion more rapidly reduced levels of dopamine to 0.05 +/- 0.01 pg/5 min (95% reduction) in the dorsal striatum and to 0.08 +/- 0.01 pg/5 min (85 % reduction) in the nucleus accumbens. These results suggest that relatively fast changes in extracellular dopamine levels in these two brain areas can reliably be followed by this in vivo microdialysis technique.