568 



MAKOTO SATO, GEORGE AUSTIN, AND WALTER STAHL 



To exclude this effect, we recorded intracellularly from several cells imme- 

 diately after irradiation in order to take an average value of the amplitudes. 

 As a result, no significant change in amplitude or time course could be found 

 during or following irradiation with 12 kr or even 2 hours after the initial 

 irradiation (Fig. 7). The membrane potential showed no significant change 

 in amplitude throughout the experiment. 



Discussion 



Site Affected by Irradiation in the Spinal Cord 



Since the amplitude of the response from the cell is attributable to the 

 magnitude of the ion shift across the membrane and is closely related to the 

 ionic permeability of the membrane, we may expect some change in the 

 excitatory process of a single neural element. Rothenberg (1950) has re- 

 ported an increase in the uptake of Na^* by irradiated squid axon. Bachofer 

 and Gautereaux (1959) have reported an initial increase in amplitude of the 

 response from the dissected giant axon of the earthworm immediately after 

 irradiation with 30 kr. The doses used in our experiments were smaller than 

 theirs and possibly were not large enough to cause the change in excitability. 



Fig. 7. Intracellular responses from different motor neurons evoked by antidromic 

 stimulation, during and after successive irradiation. Vertical bar shows 20 mv and 

 horizontal bar shows 2 msec and 1 msec in left and right columns, respectively. Re- 

 cordings 1, 2, and 3 were made after irradiation at 3,850, 8,970 and 14,090 r, re- 

 spectively; recording 4, 1 hour after the last irradiation. 



