PHYSIOLOGICAL MECHANISM OF 



PRODUCING EXCITATORY TRANSMITTER IN 



THE BRAIN OF DOGS 



Takashi Hayashi 



Department of Physiology, School of Medicine, Keio University, Tokyo 



When metrazol and sodium glutamate were introduced into the ventricle of 

 dogs they produced generahzed seizures as shown in Table 1 with latent 



Table 1. The critical dosage to produce seizure in dogs 



periods of 1 5-30 sec. In contrast, isonicotinic acid hydrazide (INH), oxymethyl 

 pyrimidine (OMP), as well as D-tubocurarine produced seizures with latencies 

 of 600-2400 sec (10-40 min), that is about 30-200 times longer than those of 

 the former substances. To our surprise, vitamin Bi as well as folic acid 

 produced seizure if given in appropriate concentration and the latency belongs 

 to the second group. To our further surprise, all convulsants were found to fall 

 into these two categories. 



The most simple interpretation of this phenomenon would be that con- 

 vulsants of shorter latent periods acted by direct action of their own, while 

 convulsants with longer latent periods acted not directly but by secondary and 

 indirect actions which could be, for example, as follows: 



(1) the substance undergoes some change in its chemical structure to 

 become the real excitatory transmitter; or 



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