Background & Aims: Therapeutic X-irradiation of brain possibly causes cognitive impairment associated with synaptic dysfunction. Drebrin is a postsynaptic actin-binding protein and plays an important role for learning and memory. We have recently reported that drebrin decreases transiently in the molecular layer of dentate gyrus (MLDG) of hippocampus after X-irradiation in parallel with fear memory impairment. However, the mechanism regulating the drebrin decrease is not clarified. Our previous study has shown that activation of N-methyl-D-aspartate (NMDA) receptors induces transient drebrin exodus from dendritic spines. In the present study, we examined whether NMDA receptor relates to X-irradiation-induced drebrin decrease. Methods: Ten-week-old male mice, pretreated with an NMDA receptor antagonist MK801, were exposed to 10 Gy of whole brain X-irradiation and fixed after 8 hours. Immunostaining intensity of drebrin and PSD-95 in MLDG and number of doublecortin (DCX) positive neurons in dentate gyrus (DG) were analyzed. Results: X-irradiation decreased the intensity of drebrin and doublecortin-positive neurons. MK801 inhibited the decrease of drebrin intensity, but not the decrease of DCX-positive neurons. PSD-95 intensity did not change after irradiation. Conclusion: Our results indicate that NMDA receptor mediates the X-irradiation-induced decrease of drebrin, and suggest that NMDAR-mediated drebrin decrease underlies X-irradiation-induced acute transient cognitive impairment.

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A 50-year-old man was transported to our emergency outpatient clinic presenting with lower abdominal pain and vomiting. Abdominal CT revealed a cystic tumor approximately 8cm in diameter in the left peritoneal cavity, and the “whirl sign” was seen in the small intestine loops and branches of the superior mesenteric artery. The diagnosis of cystic small intestine tumor with small intestine volvulus necessitated urgent laparotomy on the same day. Upon laparotomy, the small intestine was found to be twistwed 360°clockwise around the superior mesenteric artery. The intestine was not necrosed when strangulation was released. A cystic tumor, about 8 cm in diameter, was found in the jejunum 140 cm from the Treitz'ligament. He underwent partial resection of the jejunum, including the tumor. A solid tumor was found inside the cyst. The histopathological diagnosis was low-grade malignancy gastrointestinal stromal tumor (GIST) of the small intestine. Immunostaining showed the tumor was positive for c-kit and CD34. We report this rare case of cyst-forming GIST causing small-bowel volvulus, with a brief review of the literature.

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