Optical indications of early appearance of postsynaptic potentials in the embryonic chick brain stem.

A basic problem in neurophysiology is concerned with the functional organization/architecture of the central nervous system (CNS). This problem has been studied through a variety of experiments and theoretical approaches. The ontogenetic approach is potentially a very useful strategy for analyzing the complex and subtle functional organization/architecture of the central nervous system. However, for investigations of the early embryonic CNS, conventional electrophysiological recording techniques, including microelectrodes, are extremely difficult or impossible to employ, owing to the small size, fragility and topology of the immature or newly matured neurons. For this reason, investigations of electrophysiology in the vertebrate CNS during the early phases of development have been hampered. Optical techniques using voltage-sensitive dyes have made it possible to monitor electrophysiological events in living systems that are inaccessible to microelectrodes [1, 2]. Furthermore, optical recording methods have been developed into a powerful tool for recording electrical activity simultaneously from many sites in one living preparation [3-5]. Applying these optical techniques, we have overcome traditional obstacles to functional approaches to embryonic heart and CNS during early development [6-8]. We describe here some results obtained with optical techniques in the early embryonic chick brain stem.