Deafferentation-induced CREB phosphorylation is Ca²⁺ dependent. A, Effects of ionomycin on [Ca²⁺]_i and CREB phosphorylation. a, Fura-2-measured mean [Ca²⁺]_i increase in chick NM neurons in the absence of activity in normal ACSF (▪; 38 neurons;n = 4 slices) and in ACSF containing 5 μm ionomycin (○; 47 neurons; n = 5 slices). Error bars represent the SEM and are <20 nm where not visible. b, Percentage of p-CREB+ NM neurons in the presence (♦) and absence (▵) of 5 μm ionomycin as a function of time in the absence of activity in vitro. Error bars represent the SEM (n = 4 for the 30 min ionomycin data point, 5 for the 60 min data point, and 3 for all others). The NoStimulation data are the same as those presented in Figure 1C. B, Effects of [Ca²⁺]_i on CREB phosphorylation. a, Fura-2-measured mean [Ca²⁺]_i of NM neurons in the absence of activity in normal ACSF (▪; 38 neurons; n = 4 slices; same data shown in Aa), in ACSF containing 1 mm ACPD (▵; 39 neurons; n = 4 slices), in ACSF containing 1 μm nifedipine (○; 37 neurons; n = 4 slices), and in normal ACSF after incubation in 5 μm BAPTA AM (Kd = 160 nm; ⋄; 29 neurons; n = 3 slices). Error bars represent the SEM and are <20 nm where not visible. b, Percentage of p-CREB+ NM neurons after 60 min in the four conditions shown in Ba. Error bars represent the SEM. Control,n = 19; BAPTA, n = 3; ACPD,n = 3; and nifedipine, n = 3. *,p < 0.05