Chemical Excitation of Spinal Neurones

Abstract

THE presence of comparatively large quantities of glutamic acid in brain together with the conflicting evidence of the effects of glutamic acid administration¹ have led to an investigation of the effects of this and related monoamino-dicarboxylic acids upon spinal cells. When applied ionophoretically, both glutamic and aspartic acids were very effective in evoking repetitive discharges from all types of inter-neurones located in the dorsal horn and intermediate nucleus of the spinal cord of the cat. For example, Fig. 1A illustrates the spike potentials of a dorsal horn cell activated orthodromically and recorded by means of one barrel of a double-barrelled electrode. The background discharge-rate of this cell was zero (Fig. 1B). Several seconds after a current of 120 mμ, amp. was employed to pass anion from a saturated solution of the sodium salt of L-glutamic acid (pH 8.5) in the other barrel of the electrode, the cell fired with a frequency of 100 per sec. (Fig. 1C), and 5 sec. later this had risen to 440 per sec. (Fig. 1D). 1 sec. after the current was stopped, the cell ceased firing. Control experiments indicated that this excitatory action was due specifically to the amino-acids and not to other effects arising from the passage of the ionophoretic currents.