FIGURE 6.

[Ca²⁺]_i elevation induced by the peptide neurotensin does not trigger STD DA release. A, 21-day-old DA neuron cultures were pretreated with 10 nm neurotensin (Nt) to activate Ca²⁺ influx and [Ca²⁺]_i mobilization. The release of [³H]DA was measured in the presence of 0.5 mm extracellular Ca²⁺ and 0.5 μm TTX to prevent firing. Neurotensin (10 nm) caused a decrease in STD DA release. The control group was treated only with TTX. B, acute treatment of DA neurons with 10 nm neurotensin induced a fast transient increase in [Ca²⁺]_i in the presence of 0.5 μm TTX. C, summary data presenting the effect of neurotensin on [Ca²⁺]_i in DA neurons (n = 13). D, effect of acute application of neurotensin on STD DA release. The release of [³H]DA upon treatment with 10 nm neurotensin was evaluated in the presence of 0.5 mm extracellular Ca²⁺ and in the presence of 0.5 μm TTX (black circles, STD DA release/TTX/neurotensin) or in the presence of 2 mm extracellular Ca²⁺ (black squares, total/neurotensin) to measure total DA release. A control group without neurotensin (with TTX) is also illustrated. The arrow indicates the time of application of neurotensin (0 min). The numbers inside the bars indicate the number of repetitions in each group. *, p < 0.05 versus control group (A) or basal (C and D). The error bars represent S.D.