Neuroplasticity after hypoxic-ischemic brain injury in neonatal pigs based on time-dependent behavior of 1H-MRS-Tau protein and synaptic associated proteins and synaptic structure analysis
Authors: Zheng Yang , Wang Xiaoming 
Published: September 2022

Abstract
Introduction:
Neonatal brain has strong plasticity, which can adapt to pathological remission through changes in protein expression and neural structure.
Objective
To reflect changes in Tau protein expression, synaptophysin (SYP), neurocan (Neu), and synaptic structure at different time points with 1H-MRS after hypoxic ischemia (HI), and to investigate neuroplasticity after HI injury.
Methods
A total of 59 healthy neonatal pigs (body weight 1–1.5 Kg) from 3–5 days after birth were used. Six pigs were excluded from analysis, due to intermediate death, modeling failure, and movement artifacts. There were 10 pigs in the control group and 43 in the HIBI model group. At different time points, 0–2, 2–6, 6–12, 12–24, 24–48, and 48–72 h after HI, Tau protein content was reflected by 1H-MRS imaging; SYP and Neu changes in the control and HI model groups were detected by immunofluorescence and the changes to the synaptic structure of nerve cells were observed by transmission electron microscope. Data were statistically analyzed by independent sample T test, ANOVA, and Spearman rank correlation analysis. P < 0.05 was considered statistically significant.
Results
1H-MRS and immunofluorescence showed an increasing trend followed by a decrease in Tau protein levels after HI. Immunofluorescence showed the highest Tau protein levels at 24–48 h after HI; there were significant differences among all time HI groups except between 2–6 and 48–72 h (P = 0.087) and 6–12 and 48–72 h (P = 0.105). After HI, Neu expression decreased, then increased, finally decreasing. Compared with the control group, there were significant differences among all time HI groups (control group vs 48–72 h, P = 0.007, P = 0.000 for the rest). There were significant differences between the 6–12 h group at valley, control group, and other model groups (P = 0.000). SYP expression after HI first increased, reaching a maximum at 6–12 h, and decreasing. There was no significant difference between the control group and other model groups at 24–48 h (P = 0.112), but there was a significant difference between the control group and other model groups (P < 0.05). The peak of the 6–12 h group significantly differed from the control and other model groups (P < 0.05). SYP was negatively correlated with Neu, with a correlation coefficient of -0.877 (P = 0.000). SYP was not correlated with Tau (P = 0.229), neither was Neu with Tau (P = 0.342). Compared with the control group, the number of synaptic vesicles decreased and PSD thickness increased 6–12 h after HI. In the 12–24 h group, the number of synaptic vesicles increased and PSD thickness slightly decreased. At 24–48 h, the vesicle number decreased, PSD became thinner, interrupting continuity, mitochondria swelled, and mitochondrial cristae blurred and disappeared.
Conclusion
After HI injury, Tau and SYP protein expression followed an increasing followed by decreasing trend, while Neu did the opposite. SYP, Neu, and Tau protein expression are associated with changes to synaptic and myelin structures, which may reflect different changes to neural plasticity.