Abstract

Certain membrane bound dyes change their optical properties (absorption, fluorescence, birefringence) in response to changes in membrane potential. These signals are thought to arise from electrochromic effects, molecular rotation, and/or changes in aggregation state of the dyes. Several factors make a potentially sensitive optical signal interesting to neuroscientists. First is the possibility of making simultaneous measurements from multiple sites; important because many different neurons in a nervous system may be active during each behavior. In addition, optical measurements can be made with excellent time resolution and they are in some sense noninvasive. Optics was used to obtain an overview of the number and activity of neurons in the Aplysia abdominal ganglion during the gill-withdrawal reflex. Action potential activity in cell bodies was monitored via a 124 element photodiode array using the oxonol dye, NK3041 (nee RH155). In a habituated preparation, activity in 90 neurons was detected during the gill-withdrawal reflex. When this preparation was sensitized, we detected activity in 150 neurons during the reflex. The completeness of these recordings was relatively low; between 250 and 400 of the 700 or 1100 neurons present in the abdominal ganglion were actually active during the reflex. Thus the neuronal substrate of a relatively simple reflex in a relatively simple nervous system may be very complex. These experiments would be easier if the optical signals were larger.

© 1989 Optical Society of America