The purpose of this study is to investigate the mechanism of alternative responses to low dose irradiation for neuronal cell proliferation in the dentate gyrus of rats. To determine the effect of a single exposure to radiation, rats were irradiated with a single dose of 0.1, 1, 10 or 20 Gy. To determine the effect of the cumulative dose, the animals were irradiated daily with 0.01 Gy or 0.1 Gy from 1 to 4 days. The neuronal cell proliferation was evaluated using immunohistochemistry for 5-bromo-2'-deoxyuridine (BrdU), Ki-67 and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. Four consecutive daily irradiations with a 0.01 Gy/fraction increased the number of BrdU-positive and Ki-67-positive cells in a dose dependent manner, but this did not affect the number of TUNEL-positive cells. However, there was not a dose dependent relationship for the 0.1 Gy/fraction irradiation with the number of BrdU, Ki-67 and TUNEL positive cells. Our data support the explanation that the adaptive response, induced by low-dose radiation, in the hippocampus of rats is more likely a reflection of the perturbations of cell cycle progression.
Rats, Sprague-Dawley ; Rats ; Radiation Dosage ; Neurons/*cytology/*radiation effects ; Neuronal Plasticity/*radiation effects ; Male ; Dose-Response Relationship, Radiation ; Dentate Gyrus/*cytology/*radiation effects ; Cell Survival/radiation effects ; Cell Proliferation/*drug effects ; Animals ; Adaptation, Physiological/radiation effects

We investigated the effect of low dose radiation on diabetes induced suppression of neurogenesis in the hippocampal dentate gyrus of rat. After 0.01 Gy, 0.1 Gy, 1 Gy and 10 Gy radiation was delivered, the dentate gyrus of hippocampus of streptozotocin (STZ)-induced diabetic rats were evaluated using immunohistochemistry for 5-bromo-2-deoxyuridine (BrdU), caspase-3, and terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL) staining. The number of BrdU positive cells in the non-diabetic rats, diabetic rats without radiation, diabetic rats with 0.01 Gy radiation, diabetic rats with 0.1 Gy radiation, diabetic rats with 1 Gy radiation and diabetic rats with 10 Gy radiation were 55.4+/-8.5/mm2, 33.3+/-6.4/mm2, 67.7+/-10.5/mm2, 66.6+/-10.0/mm2, 23.5+/-6.3/mm2 and 14.3+/-7.2/mm2, respectively. The number of caspase-3 positive cells was 132.6+/-37.4/mm2, 378.6+/-99.1/mm2, 15.0+/-2.8/mm2, 57.1+/-16.9/mm2, 191.8+/-44.8/mm2 and 450.4+/-58.3/mm2, respectively. The number of TUNEL-positive cells was 24.5+/-2.0/mm2, 21.7+/-4.0/mm2, 20.4+/-2.0/mm2, 18.96+/-2.1/mm2, 58.3+/-7.9/mm2, and 106.0+/-9.8/mm2, respectively. These results suggest low doses of radiation paradoxically improved diabetes induced neuronal cell suppression in the hippocampal dentate gyrus of rat.
Rats, Sprague-Dawley ; Rats ; Radiotherapy/methods ; Neurons/*metabolism ; Male ; In Situ Nick-End Labeling ; Hippocampus/*cytology/metabolism/radiation effects ; Diabetes Mellitus, Experimental/radiotherapy ; Dentate Gyrus/drug effects/*radiation effects ; Cell Proliferation ; Caspase 3/metabolism ; Bromodeoxyuridine/pharmacology ; Apoptosis ; Animals