Simultaneous recording from several neurones in an invertebrate central nervous system

Abstract

THE ability to monitor activity in many neurones simultaneously might provide a powerful tool for solving certain problems in neurobiology. There are several changes in the optical properties of a neurone that occur during an action potential^1–3 that might be used in an apparatus that could monitor spike activity in many neurones simultaneously. Although the changes in intrinsic (native) optical properties have been useful in other instances where an optical measurement of membrane potential was desired, larger signals were needed for this application. Therefore, a search was begun for extrinsic probe molecules which could serve as sensitive molecular transducers in stained membranes, transforming changes in membrane potential into changes in light intensity^4,5. In earlier experiments we demonstrated changes in fluorescence⁶ and absorption⁷ during action potentials in individual neurones of a segmental ganglion from the leech, Hirudo medicinalis. In those experiments the ganglion was stained with a merocyanine dye8. In the experiments described here, carried out on the supraoesophageal ganglion of the barnacle, Balanus nubilus, the absorption change of a new merocyanine-oxazolone dye^9,10 was used. In measurements on squid giant axons, the signal obtained with the new dye was five times larger. In addition, the photodynamic damage^5,11 associated with photochemical effects of intense illumination in the presence of dye and oxygen was 100 times smaller with the new dye.