An increase in [ 3H]QNB binding by proton-beam irradiation in intact rat brain: an apparent positive cooperativity of binding

After focal irradiation of rat brains with a beam of proton (dose, 30 Gy), [ 3H]quinuclidinyl benzilate (QNB) binding, both in vitro and in vivo, was measured, using either autoradiographic or tissue-dissection methods. No changes in in vitro [ 3H]QNB binding were seen in autoradiograms of brain slices from irradiated rat. The irradiated side of the brain showed a significant increase in [ 3H]QNB binding in vivo in the striatum and cerebral cortex 24 h after irradiation. This increase in binding was transient, and had almost disappeared 2 weeks after irradiation. These results indicate that early changes in receptor function as a results of radiation damage are only detected in in-vivo conditions. In the striatum of the intact rat brain, an apparent positive cooperativity of binding was observed, which was more pronounced on the irradiated side.