The chemical events of excitation have received considerably less attention than their physical counterparts. This comparative neglect can probably be explained by the remarkable suitability of physical methods for the study of short lasting phenomena, contrasting with the lack of chemical methods capable of detecting rapidly reversible changes.However, the importance of the chemical aspects of the excitation problem is more and more widely recognized, as witnessed by the increasing amount of work devoted to the ionic shift, the energy-yielding reactions, and other chemical changes associated with excitation.The present paper deals with alterations of proteins induced by stimulation of nerves and nerve centers. The over-all problem of the chemistry of cellular excitation will be surveyed in a review to be published (Ungar, 1957).A number of observations indicate a high rate of protein breakdown in nerve structures submitted to prolonged and intense stimulation (Soula, 1912(Soula, , 1913Soula and Faure, 1913; Hydra, 1943 Hydra, , 1955Geiger et al., 1953). More subtle and possibly reversible changes in protein structure have been postulated by Meyer (1937), McElroy (1947), Nassonov (1948), and Segal (1956) without, however, the support of direct experimental evidence. It is believed that the experiments reported in this paper have produced some evidence in favor of reversible molecular rearrangements taking place in the proteins of stimulated structures.
MethodsElectrical stimulation was used in all experiments by means of a 60 cycle, 40 volt alternating current from a Harvard stimulator connected to platinum electrodes. Frog and rat sciatic nerves were excised, placed in the appropriate Ringer solution, and stimulated for the specified interval. Stimulation of the cerebral cortex in cats and dogs was produced with the technique described by Geiger, Dobkin, and Magnes (1953) through electrodes placed on the brachial plexus. The unstimulated side was * Some of the results reported in this paper were presented at the International Physiological Congress in Brussels (Ungar et al., 1956). 635