Simultaneous monitoring of activity of many neurons from invertebrate ganglia using a multielement detecting system.

The optical monitoring system has reached a level of sophistication where activity from a network of cells can be recorded in a minimally dissected behaving animal. We monitored activity in the buccal ganglion of the mollusk, Navanax inermis, during spontaneous expansions and during feeding. Deleterious pharmacological effects and photodynamic damage appear to be negligible in this preparation. The S/N is large enough to detect individual cell's activity without signal averaging, provided the cell soma is of sufficient size (greater than 20 microns). Indeed, if the S/N is large enough, it is possible to see graded or subthreshold potentials without the use of signal averaging. The activity of adjacent cells in the same focal plane could be detected as different cells by a single detector. In addition, cells that were out of focus but whose projected images fell on a detector also have their activity recorded as a significant signal by that detector. This finding suggested that recording from all the cells in a ganglion was possible. Preliminary evidence suggests that our recordings from Navanax buccal ganglia are at least 70% complete. It appears that the assumption that most of the cells' activity is being recorded is reasonable. A problem that could prevent correct identification of activity was the effect of light scattering on the signal. A signal dispersed owing to light scattering could give an erroneous estimate as to the cell size. However, the effect of light scattering on Navanax signals is small, and we feel that our estimates of cell size are accurate.