The effects of continuous and single-dose radiation on choline uptake in organotypic tissue slice cultures of rabbit hippocampus

The objective of the present study was to determine the time-dependent cour se of choline uptake in mature organotypic slice cultures of rabbit hippoca mpal formation and to assess the effects of continuous and single high-dose irradiation on choline uptake in cultivated slices in vitro. Transverse sl ices of hippocampus were dynamically incubated in a cerebrospinal fluid-lik e culture medium for 72 h. To study the changes in choline uptake longitudi nally, the slice cultures were processed with 0.1 muM [H-3]-choline, and tr itium accumulation was counted. Two different gamma irradiation sources (I- 125 seeds and a clinical Co-60 source) were used as representative models o f interstitial radiosurgery and other radiosurgical techniques. A total dos e of approximately 6000 cGy was delivered to the brain slices in one sessio n or in a continuous, relatively low-close rate fashion, and their effects on high-affinity choline uptake were examined, in another set of experiment s with I-125, 5 muM hemicholinium-3 was used in choline uptake procedures a s a competitive high-affinity choline uptake inhibitor. The results can be summarized as follows: (1) in the control group of the hippocampal tissue c ulture, there was a significant increase in tritium accumulation values fro m 0 to 48 h and a decrease thereafter; (2) continuous I-125 irradiation. ca used a highly significant depression of the accumulation of tritium compare d to that observed in the control group throughout its application for 72 h ; (3) there was no significant change in the accumulation of tritium in the slices after single high-close rate irradiation with a Co-60 source; and ( 4) 5 muM hemicholinium significantly depressed the accumulation of tritium in both the control and the I-125-irradiated groups, and there was no longe r a difference between I-125-irradiated and control groups when both groups were treated with hemicholinium. These results demonstrate that the delive ry of continuous but relatively low-dose rate gamma irradiation is more eff icacious than single high-dose external irradiation on high-affinity cholin e uptake in hippocampal nervous tissue. The results also,indicate that cont inuous irradiation specifically affected the high-affinity energy-dependent choline uptake mechanism, whereas nonspecific choline uptake did not seem to be disturbed.