EFFECT OF SOME METABOLIC AGENTS ON NERVOUS ACTIVITIES

Abstract

The threshold and the resting potential of a node of a single motor nerve fiber under the action of various agents were compared in a toad with those of a neighbouring node immersed in Ringer solution.
The following are the results of the experiment:
1) The decrease of threshold and the positive resting potential is produced in the test node when one of such compounds of the Krebs cycle as succinate, fumarate, malate, α-ketoglutarate and citrate (0.02M) are introduced to the test node; the contrast node being also somewhat affected with a decrease of the threshold in the case of succinate, fumarate and malate. Of these compounds, α-ketoglutarate was also examined as to its effects on the oxygen consumption of nerve fibers. The oxygen consumption is found to be enhanced and the results obtained seem to indicate that nervous activities are closely related to oxidative metabolism.
2) Besides the compounds of the Krebs cycle, such amino acids as glutamic and aspartic acid, have also effects as accelerators on nervous activities.
3) All metabolic inhibitors used, except malonate, have the reverse action compared with that of accelerators, viz., increase of the threshold and a negative potential is produced in the test node by the action of the inhibitors, and the contrast node immersed in Ringer solution is not affected.
4) It is conceivable that the resting potential measured under various metabolic conditions may be taken as the results of oxidoreduction of nerve fibers when the resting potential represents the balance of potentials between the two neighbouring nodes.
The results of the present experiments constitute strong evidence that the Krebs cycle plays a major rôle in the intermediary energy metabolism of nerve fibers.