The following drugs were kept at −20°C as stock solutions and dissolved in aCSF to their final concentrations on the day of experiments: L-(−)-norepinephrine (+)-bitartrate salt monohydrate (NE, 10-100 μM, Sigma-Aldrich, shielded from light exposure during preparation, storage and application), picrotoxin (PTX, 50 μM, Tocris), prazosin hydrochloride (10 μM, Sigma-Aldrich), (R)-(−)-phenylephrine hydrochloride (100 μM, Sigma-Aldrich), yohimbine hydrochloride (20 μM, Tocris), tetrodotoxin (TTX, 1 μM, Tocris), TNP-ATP triethylammonium salt (10 μM, Tocris), pyridoxalphosphate-6-azophenyl-2′,4’-disulfonic acid tetrasodium salt (PPADS, 100 μM, Tocris).
Fluorocitric acid (FCA, Sigma-Aldrich) was prepared on the day of experiments with DL-fluorocitric acid barium salt (Paulsen et al., 1987 (link)) dissolved in 1 mL of 0.1 M HCl. Two-to-three drops of 0.1 M Na2SO4 was added to precipitate the Ba2+, after which 2 mL of 0.1 M Na2HPO4 was added and the suspension was centrifuged at 1000 g for 5 min. The supernatant was added to the aCSF to achieve a concentration of 100 μM.
Fluorocitric acid (FCA, Sigma-Aldrich) was prepared on the day of experiments with DL-fluorocitric acid barium salt (Paulsen et al., 1987 (link)) dissolved in 1 mL of 0.1 M HCl. Two-to-three drops of 0.1 M Na2SO4 was added to precipitate the Ba2+, after which 2 mL of 0.1 M Na2HPO4 was added and the suspension was centrifuged at 1000 g for 5 min. The supernatant was added to the aCSF to achieve a concentration of 100 μM.