ACUTE EFFECTS OF RADIATION ON SPINAL NEURONS 565 



5080 r 



Control — ^-— — — — 



22min 



'270^ ^1^ 6350r 



4min 31 min 



2540r p^_^ 7620r 



9min 45min 



_.^.. 



38l0r /V_ 



65 min 



I7min 



Fig. 3. Extracellular response from afferent fibers at the dorsal horn, during and 

 after successive irradiation. Vertical and horizontal bars represent 1 mv and 1 msec, 

 respectively. The total doses of irradiation and the time from the initial irradiation 

 are shown. 



Extracellular Response from Motor Neurons Evoked by 

 Orthodromic and Antidromic Stimulation 



As the tip of the microelectrode approaches the motor neuron, the 

 amplitude of the extracellular response increases gradually. However, the 

 maximum amplitude that can be recorded just at the surface of the cell 

 membrane is approximately the same for every cell under the same condi- 

 tions. This extracellular response is satisfactorily stable, so it can be recorded 

 for more than 2 hours without showing any distortion in the shape of the 

 response. Figure 4 shows the maximum amplitude response from a motor- 

 neuron during and after successive irradiation, with observation continued 

 for about 3 hours after initial irradiation. The response did not show any 

 significant change in shape within the first 2 hours, despite high doses of 

 successive irradiation. Thereafter, however, it showed an unexpected in- 

 crease in amplitude for both antidromic and orthodromic stimulations. 



Intracellular Response from Motor Neurons Evoked By 

 Orthodromic and Antidromic Stimulations 



To investigate the acute effect of irradiation on the intracellular response 

 from the motor neurons, an intracellular recordins; was made on the same 



