Objective      To observe the expression changes of β-amyloid precursor protein (β-APP) and neurofilament light polypeptide (NF-L) in rats with different degrees of diffuse axonal injury (DAI) at different time points

and identify the correlation between the changes and the learning and memory abilities of the rats in the recovery period.       Methods      A total of 100 healthy adult SD rats were randomly divided into control group

and mild

moderate and severe injury groups

with 25 rats in each group. The brain tissue specimens were detected by immunohistochemistry using rabbit antibodies of β-APP at given time points (6

24 and 72 h

1 and 2 weeks after injury)

and at 24 h after injury

the brain tissue specimens were analyzed by HE staining and NF-L immunohistochemical staining. In 2 weeks later

the learning and memory ability of each group was tested by Morris water maze. Callosum and brainstem with cerebral aqueduct were selected as the interest region under a microscope. The correlation between the integral optical density (IOD) of β-APP and NF-L in the interest region at 24 h after injury and the learning and memory abilities of the rats during the recovery period was analyzed.       Results      At 24 h after injury

the bleeding at the brain surface

subarachnoid

and cerebroventricular regions was not observed in all groups. However

typical DAI pathological features such as loosened and disordered nerve bundles

clogged blood vessels

cavitation

swelling and degenerative neurons

vague and unclear nucleus

and fuzzy synaptic structure were observed in the callosum and brainstem under the microscope. The immunohistochemical results showed that the immunoreactivity of β-APP at the callosum of the injury groups was significantly enhanced compared with the control group at the given time points

and semi-quantitative analysis further revealed that the IOD values had significant difference between the control group and the injury groups (P0.05). The IOD values at each time point were changed dynamically in the injury groups

and the immunoreactivity was strongest at 24 h. Compared with the control group

the immunoreactivity of NF-L in the axon and neuron cell body of the brainstem of the injury groups was significantly enhanced at 24 h after injury

and there was statistically significant difference (P0.05). Morris water maze test indicated that the learning and memory abilities had no statistically significant difference between the mild injury group and the control group

but there was statistically significant difference between the control group and the moderate and severe injury groups (P0.05). The correlation analysis showed that the learning and memory ability was negatively correlated with the IOD values of β-APP and NF-L at 24 h after injury (r=-0.937

r=-0.939).       Conclusion      The expression changes of β-APP and NF-L are significantly associated with the injury degree of DAI

and the learning and memory abilities in the recovery period can be predicted based on the expression changes of β-APP and NF-L at early time.