564 



MAKOTO SATO, GEORGE AUSTIN, AND WALTER STAHL 



05Kr IKr 5Kr lOKr 20Kr 



<^ 3 



o-^Mono 

 *— IMS 



Time 30' 60' 90' 120' 150' 180' 210' 



Fig. 2. Amplitude versus the time course (in minutes) of successive irradiation. 

 Key for curves is the same as in Fig. 1. 



Extracellular Response from the Afferent Fibers at the 

 Dorsal Horn 



The maximum amplitude of the extracellular response from the dorsal 

 horn at 10 /a in depth from the surface of the cord was taken as a criterion 

 for the effect of the irradiation on the afferent fibers. Usually a stimulating 

 voltage twice the height of threshold was enough to elicit the maximum 

 amplitude response. Figure 3 shows the responses recorded during and after 

 the successive irradiations. The amplitudes showed a gradual decrease with 

 successive irradiations. This corresponded to the decrease in amplitude of 

 the intramedullary spike of the cord potential. 



Intracellular Response from Afferent Fibers 



Although we did not systematically investigate the intracellular response 

 from the afferent fibers, we could often record normal responses intracellu- 

 larly even after irradiation with 10 kr. 



Intracellular Response from Interneurons 



Because the amplitudes of the intracellular responses from the inter- 

 neurons varies greatly, depending on the cells, it was difficult to estimate the 

 effect of irradiation on the amplitude. However, no significant change in 

 time course of the response or in repetitive activity could be seen even after 

 irradiation with 10 kr. 



