Optical monitoring of activity from many areas of the in vitro and in vivo salamander olfactory bulb: a new method for studying functional organization in the vertebrate central nervous system.

We have investigated the use of voltage-sensitive dyes to monitor neuronal activity in the intact salamander olfactory bulb. After a 10- to 20-min staining period, a magnified image of an in vitro or an in vivo preparation was formed on a 124-element photodiode array. The array was used to simultaneously record absorption or fluorescence changes from 124 adjacent areas of the bulb. At the magnifications used, each detector received light from 100 to 1000 neurons. Relatively large absorption and fluorescence signals were found in response to olfactory nerve stimulation; all of the results presented were from single trials. Because of the large signal size, measurements on in vivo preparations using epi-illumination also had good signal-to-noise ratios. There were significant differences in signal time course between adjacent detectors which suggested a spatial resolution on the order of 200 microns. Tentative assignments of the cellular origins of some signals could be made from the results of paired volley experiments. The results suggest that optical monitoring of membrane potential could provide a useful method for studying neuronal organization in the intact vertebrate central nervous system.