574 C. S. BACHOFER 



Methods 



The ventral caudal nerve of the white rat was selected for studies involv- 

 ing the effects of x-rays on mammalian nerve trunk. This is a long, clean 

 nerve with minimal branching and a uniform fiber spectrum, giving com- 

 pact, sharp action potentials on oscillographic traces. Mature white rats of 

 the Sprague-Dawley strain, descendants of a single pair bred in this 

 laboratory in 1954, were used. Two types of experiment were undertaken. 

 Excised nerves were irradiated m vitro in a nerve chamber which permitted 

 remote recording of activity during irradiation (Bachofer, 1957; Bachofer 

 and Gautereaux, 1960b). Recordings were also made from nerves in situ, 

 with the nerve trunk disturbed only at limited regions where electrodes 

 made contact with the nerve (Bachofer and Gautereaux, 1960a). Details of 

 the preparation and shielding of the animal are shown in Fig. 1. 



Studies involving radiation effects on giant nerve fibers were carried out 

 on the nerves of the earthworm, Lumhricus terrestris, and of the lobster, 

 Homarus americanus. Recordings were made of the bioelectric activity of the 

 median giant fiber and of the lateral giant fibers of the earthworm. Com- 

 plete details of the experimental procedure have been presented (Bachofer 

 and Gautereaux, 1959). 



The results presented here are based on the responses of the giant fibers of 

 the earthworm, although the basic phenomena have been confirmed in 

 experiments involving the median giant axons of the lobster in the circum- 

 esophageal, thoracic, and abdominal regions. 



Standard electrophysiologic procedures were followed in recording re- 

 sponses, the quantitative parameters of which were subsecjuently obtained 

 from photographic reproductions of oscillographic traces, projected for 

 accuracy of measurement and analysis. 



A Picker Vanguard deep-therapy x-ray generator, operated at 280 kv and 

 20 ma, was the source of x-rays, given at 6 kr per min. This gave a reason- 



FiG. 1. Arrangement used in recording bioelectric responses of rat caudal nerves 

 in situ. A. Electrode board with Plexiglas tail holder, to which macromanipulators are 

 attached. Perpendicular copper shield isolates electrostatic fields produced by stimu- 

 lating electrode connections. B. Superior view of electrode board, showing rat in 

 place for beginning of recording. Body and legs of rat were restrained as needed. 

 C. Sectional view of Plexiglas tail holder. The macromanipulator with special plati- 

 num electrode is shown in contact with nei-ve. Confining rods along tail and plastic 

 clips over tail reduce movement. D. Box constructed of lead 1 in. thick with opening 

 in top for x-irradiation of tail and opening in side for cables, thermocouple leads, etc. 

 When grounded, lead box shields the preparation and connections against electro- 

 static fields. 



