Release of dopamine from coaggregate cultures of mesencephalic tegmentum and corpus striatum

Dissociated dopamine (DA) neurons from 14-day fetal mice were dissected from the rostral mesencephalic tegmentum (RMT) and were allowed to reaggregate in vitro with cells from the corpus striatum (CS). As previously demonstrated under these conditions, DA neurons develop punctate fluorescent varicosities and the capacity to synthesize, accumulate, and retain DA (Kotake, C., P. C. Hoffmann, and A. Heller (1982) J. Neurosci. 2: 1307-1315). After 17 to 22 days in culture, the RMT-CS coaggregates were assessed for their ability to release DA. Coaggregates were incubated in 5.6 x 10(-6) M [3H]DA, washed, and then superfused at 100 microliters/min for 2 hr. Fractions were collected every 2 min. Basal efflux of [3H]DA/2 min was 1% of tissue stores of 3H. K+, 70 mM infused for 8 min induced a peak release of 5.87% of tissue stores of 3H, and 50 mM K+ induced a peak release of 2.13%. The potassium-induced release of [3H]DA was calcium dependent. When d-amphetamine was infused for 12 min, 100 microM solutions induced a peak release of 8.91%, 10 microM induced a peak release of 4.36%, and 1 microM induced a peak release of 1.85% of tissue stores of 3H. Substance P at 100 microM induced a peak release of 2.19% of tissue stores of 3H. Tetrodotoxin (0.5 and 2.5 microM) decreased basal efflux by 40%, blocked substance P-induced release, but did not affect either potassium- or d-amphetamine-induced release of [3H]dopamine.