Figure 1. GABA-induced and spontaneous [Ca²⁺]_i increases in immature cultured midbrain neurons at DIV 12.

A, somatic Ca²⁺ transients from 33 cells with decreasing and constant amplitudes were elicited by repetitive applications of GABA (G, 50 μm, 15 s pulse) and KCl (K20, 20 mm, 15 s pulse), respectively, in the presence of 0.3 μm TTX and 20 μm DNQX. Washout of TTX and DNQX (*) resulted in small spontaneous rises in [Ca²⁺]_i in a few cells. After blockade of GABA_A receptor-mediated inhibition (Bic, 20 μm), cells displayed spontaneous synchronized Ca²⁺ oscillations that were reversibly blocked by DNQX (20 μm). Synchronous activity ceased after washout of bicuculline. B, average of the 33 traces shown in A. Ca²⁺ transients were recorded in solutions buffered with HCO₃⁻. Inset shows fluorescence image of Fura-2-AM-loaded neurons from this experiment excited at 357 nm; scale bar, 50 μm. The change in [Ca²⁺]_i is presented as the change (Δ) in the fluorescence ratio obtained at the two excitation wavelengths (F₃₅₇/F₃₈₀). Δ is given in arbitrary units in this and all other figures.