Changes in 40 cps EEG activity in the olfactory bulb following gamma irradiation of the cat

The initial electrical, chemical, and behavioral changes following gamma irradiation were investigated with five total dose groups of 17 mongrel, male cats that received either sham irradiation, 500 r. whole body (WB), 800 r. head only (HO), 1000 r. HO, or 2000-3000 r. HO irradiation. During preliminary investigation, 800 r. and 1000 r. K0 irradiated animals were trained to perform 30 min. daily sessions on a FR-5 schedule for milk reinforcement and EEG recordings were taken during performance. For the major investigation, four 500 r. WB, six 2000-3000 r. HO, and two sham irradiated animals were trained to perform a visual discrimination task which required the animals to press a bar for milk reinforcement during the presence of a 10 sec. 7 cps. flashing light. Fifty dally trials were continued until the animals were making less than one intertrial response for every reinforced response as determined by a criterion ratio during three consecutive sessions. Total number of responses, intertrial responses, and reinforced responses were recorded following each daily session. Following criterion performance, EEG recordings were taken on the unrestrained animals during five performance sessions on the task. The animals were exposed to Co60 sources at Texas A. & M. University. The dose rates for these exposures were 60 and 90 r./min. Total doses were determined by exposure time. Subsequently 3, 24, 48 hour and 7-8 day EEG recordings were taken while the animals were performing the behavioral task. Six chronically implanted and three nonelectrode animals receiving 2000-3000 r. HO or sham irradiation were sacrificed at 3, 24 hours and 8 days for serotonin and norepinephrine assays of olfactory tissue. The EEG recordings and computerized frequency analysis of the 2000-3000 r. HO animals showed a loss of the 40 cps. activity in the olfactory bulb 3 and 24 hours after irradiation during 10 sec. nonstimulation and stimulation periods of a trial. The loss of the 40 cps. activity appeared in the EEG recordings and computerized frequency analysis of the WB animals 7 days after irradiation during 10 sec. nonstimulation and stimulation periods of a trial. No 40 cps. changes were observed up to 7 days after 800 and 1000 r. HO irradiation. Serotonin content of the olfactory tissue tended to increase and norepinephrine content tended to decrease slightly at the 3 hour period following irradiation. No impairments in behavioral performance were detected until radiation sickness appeared. The 40 cps. loss was attributed to increased serotonin content in the olfactory structures. Behavior as measured by performance on a visual discrimination task was unrelated to the initial electrical and chemical changes.