FIG. 9.

Visualization of the spread of optical activity during evoked and spontaneous bursts viewed through the lateral aspect of the cord. A—C: imaging of an electroporated cord during VR-evoked (A), spontaneous (B), and DR-evoked (C) bursting in the presence of bicuculline (40 μM) and strychnine (4 μM). Each image is a median filtered, 4 frame average of the difference image obtained by subtracting the active frames from a preburst average. The time over the images indicates the frames used in the average. The panels to the left of each series of video-micrographs show the optical signals normalized to the peak activity from the ventral (blue), medial (orange), and dorsal (green) areas of the cord (T₁₃–L₁ area, left side) over a 55-frame period (30-Hz acquisition) aligned with the VR activity (black traces under optical signals; left L₆ ventral root in B and C, and the left L₃ in A). The time of the last stimulus in the ventral root train applied to the left T₁₃ ventral root (5 pulses, 20 Hz, 55 μA) is shown by the arrow beneath the electrical trace. The arrow in C indicates the time of a single stimulus applied to the left T₁₃ and L₁ dorsal roots (30 μA). The dots under the electrical traces indicate the timing of the last frame of the 4 frame average for each of the 4 sequential video-micrograph averages shown on the right. The frames shown below the images in A and marked 0–3 show individual, sequential frames at the onset of the earliest optical activity in response to a ventral root train of stimuli. Each frame has been averaged from video sequences obtained in 4 different ventral-root evoked bursts and shows the ventral origin of the optical activity. D: graph summarizing the timing (in frames and in ms) of the fluorescent transients recorded from the regions of interest shown in E. The 50% rise time of the optical transient is expressed with respect to the 50% rise time of the most ventral transient. Data are averaged from 5 experiments and expressed as means ± SE.