Effect of chronic unpredictable mild stress on brain-pancreas relative protein in rat brain and pancreas

Brain-pancreas relative protein (BPRP) is a novel protein whose biological function remains unknown. Here, we report a possible role of BPRP in male rats exposed to chronic unpredictable mild stress (CUMS) to induce depression for 3 weeks. Compared to unstressed rats, those exposed to CUMS showed significantly less weight gain with age, decreased consumption of (and preference for) sucrose without a change in total fluid consumption. Exposure to CUMS significantly reduced open-field exploration, rearing and grooming indicative of lethargy, apathy and bodily neglect, respectively. Brain MAO-A and MAO-B activity were both significantly increased in the stressed rats. These results verified induction of depressive symptoms by CUMS. The stressed animals showed a significant reduction in pancreatic BPRP, which was accompanied by an increase in levels of blood sugar and a decrease of insulin. But they showed no apparent alteration in levels or distribution of BPRP in the hippocampal formation, which nevertheless displayed a thinner dentate granule cell layer perhaps related to elevated MAO-B activity. These findings suggest that stress-induced reduction of pancreatic BPRP may cause diabetic symptoms. Whether those symptoms in turn contribute to the onset of depression requires further study.