During the early part of this fiscal year, we began to investigate the process of heat production associated with impulse conduction in the myelinated nerve fibers. Because of the rapidity and the smallness of the amount of thermal energy liberated by these rapidly conducting nerve fibers, the classical thermal detector, namely, a thermopile-galvanometer system, is known to be inadequate to determine the time-course of heat production in these fibers (see Keynes and Ritchie; J. Physiol., Vol. 210, 29P, 1970) Using thin film of poly(vinylidene fluoride) we have constructed a sensitive thermal detector with a time-resolution of about one millisecond. [Note that the time-resolution achieved by the classical detector was 50-100 milliseconds.] We have succeeded in determining the time-course of the heat generated by the amphibian sciatic nerve at 5 degrees C. The results obtained have been interpreted based on the divalent-univalent cation-exchange theory developed previously in this laboratory. In December of 1991, we started investigating the origin of the rapid structural changes in the garfish olfactory nerve associated with the excitation process. By combining our devices for detecting changes in the optical properties of extrinsic dye molecules with the piezo-electric device, we have recorded several types of non-electrical manifestations of the excitation process in the olfactory nerve. We have found that, at the site of electric stimulation, the lateral expansion of the nerve fibers (i.e. swelling) starts simultaneously with, or precedes, the onset of many optical changes. The results of these measurements strongly suggest that a rise of the water-content in the superficial layer of the nerve fiber is at the base of the observed optical signals.
