Figure 1.
Spontaneous activity increases with development culminating in the generation of Up states. A, Spontaneous activity was recorded in cortical organotypic slices during the first through fourth weeks in vitro. The bottom of each panel (A1–A4) depicts 10 30 s sweeps from a cell at the indicated age. Voltage is represented in color (see color bar in A1; color range is −70 mV in blue to −40 mV in red). The trace in the top of each panel corresponds to the first sweep and is shown for comparison. A developmental change is observed in the quantity and mode of spontaneous events. During the first week in vitro, few spontaneous correlated events are observed. In the second week in vitro, PSPs and, in some cells, a few short duration Up states are observed. By the third and fourth weeks, slices exhibit longer-duration PSPs and Up states, which sometimes occur with spontaneous spiking. B, C, With development, there is a significant increase in spontaneous event frequency (B) (ANOVA, F(3,64) = 6.96; p < 0.001) and event time (C), which is the percentage of time spent above threshold (ANOVA, F(3,63) = 4.07; p < 0.05). D, Event area, a combined measure of event time and amplitude (reported as area during a 30 s sweep calculated from an average of 10 sweeps), also significantly increases with time in culture (ANOVA, F(3,64) = 8.22; p < 0.0001). E, Example of the bimodal voltage distribution of a neuron displaying Up states. The histogram represents the time spent at each observed membrane potential (in 0.5 mV by 1 ms bins) for a sample neuron recorded at 27 DIV. Because of the small percentage of time spent in Up states, the second peak tends to be much smaller than the peak at resting potential. To visualize the second peak on the same scale, we used segments of 10 s, which began at spontaneous event onset. B–D, 4–7 DIV, n = 16 (6); 8–14 DIV, n = 26 (11); 15–21 DIV, n = 11 (5); >21 DIV, n = 12 (4); for all figures, n represents the number of neurons, and the number in parentheses represents the number of slices.