Optical recording of voltage changes in nerve terminals and in fine neuronal processes.

Optical techniques for the measurement and analysis of transmembrane elec­ trical events have found a wide range of applications over the past decade and a half because, while they usually provide less detailed information than the voltage clamp, they offer certain advantagef; over the voltage clamp and other conventional measurement techniques. Because the membranes of interest are not mechanically violated, optical methods are comparatively noninvasive. Spatial resolution is limited only by microscope optics and noise con­ siderations. Already changes in membrane potential from regions of an isolated cell with linear dimensions of approximately one micron can be measured. Also, optical sectioning, with near elimination of scattering by means of confocal imaging, may soon permit optical recording from compar­ ably small regions of cells in intact ganglia or brains. Temporal resolution is limited by the physical response of the probes « 2 JLs; B. M. Salzberg, A. L. Obaid, & F. Bezanilla, unpublished observations) and by the bandwidth imposed upon the measurement, again usually by noise considerations; re­ sponse times faster than typical membrane time constants are readily achieved. Because mechanical access is not required, unusual latitude is possible in the choice of preparation, and voltage changes may be monitored in membranes that are otherwise inaccessible. Also, since no recording electrodes are employed and the measurements are made at a distance from