ACUTE EFFECTS OF RADIATION ON SPINAL NEURONS 567 



Control 



3200 r 



15 mm 



Fig. 5. Increased intracellular response from the motor neuron after irradiation. 

 Vertical and horizontal bars show 20 mv and 2 msec, respectively. Left and right 

 columns are antidromic and orthodromic responses, respectively. 



cell for more than 20 minutes, including the periods of irradiation. In this 

 experiment, 3 out of 10 showed a slight increase in amplitude of both the 

 antidromic and orthodromic responses and in threshold strength of the 

 stimulation (Fig. 5) . The remainder showed no significant change in ampli- 

 tude of responses although they showed a slight increase in threshold (Fig. 

 6). When the cell seems to have deteriorated, the amplitude becomes 

 lower and the duration becomes longer, even without irradiation. As we 

 often experienced such an increase in amplitude of the intracellular response, 

 even in the control experiments, we interpreted this increase as possibly due 

 to an incidental change in resting membrane potential caused by a slight 

 change in contact between the microelectrode tip and the cell membrane. 



fL 



.L 



Control 



I270r 

 4min 



JJ V__ 



2540r 

 9min 



n .i:o'4ur 



-I ^ Qmin 



JL 



5080r 

 22min 



Fig. 6. Intracellular recordings from a motor neuron during successive irradiation. 

 Vertical and horizontal bars show 20 mv and 2 msec, respectively. Left and right 

 columns are antidromic and orthodromic responses, respectively. Total dose and time 

 from the initial radiation are shown. 



