Effect of chronic hypoxia and hypercapnia on learning and memory function in mice and the expression of NT and CGRP in brain

Abstract

The aim of this study is to investigate the effects of chronic hypoxia and hypercapnia on learning and memory function of mice and the expression of neurotensin (NT) and calcitonin gene–related peptide (CGRP) in mice brain. A total of 30 C57BL/6J male mice were randomly divided into normoxia control group (control group, n = 15) and chronic hypoxia and hypercapnia stress group (experimental group, n = 15). The control group was kept under normal temperature and pressure conditions, while the experimental group was kept in a chamber at normal pressure, hypoxia and hypercapnia for 8 h daily and 6 days a week for 4 weeks. On the 28th day, the learning and memory ability of mice was examined by 8-arm maze. The content of 8-hydroxy-deoxyguanosine (8-OHdG) in brain was detected by enzyme-linked immunosorbent assay (ELISA) analysis. Superoxide dismutase (SOD) activity and malondialdehyde (MDA) content were determined by spectrophotometry, and the derangement of hippocampal ultrastructures and numbers of apoptotic neurons were observed by microscope. The expression of NT and CGRP in brain tissue was observed by immunochemistry. Compared to control group, the content of 8-OHdG in hippocampal and serum MDA were significantly increased by 1.3 and 1.78 times, while the activity of SOD in serum was decreased by 27.28% in experimental group. Besides, the cellular structure of the hippocampus was disorderly arranged, the shape is irregular and the quantity is markedly reduced obviously in experimental group. In addition, the content of NT and CGRP in brain tissue was higher in experimental group than in control group ( P < 0.05). The stress of chronic hypoxia and hypercapnia not only can induce learning and memory disorders in mice which may be related to increased neuronal apoptosis and oxidative stress injury but also can increase the expression of NT and CGRP in brain tissue which may have some impact on gastrointestinal motility in mice.