Objective To investigate the protective effect of mitochondrial division inhibitor 1(Mdivi-1),a mitophagy inhibitor,on cognitive dysfunction in immature SD rats induced by hypoxia combined with propofol.Methods A total of 72 neonatal SD rats(half male and half female,aged 7 d,weighing 16.14±3.08 g)were randomly divided into 4 groups(n=18):blank control group(CON),Mdivi-1+blank control group(MCON),propofol+hypoxia group(PH),and Mdivi-1+propofol+hypoxia group(MPH).The MCON group and MPH group were pretreated with 2.4 mg/kg Mdivi-1 in 30 min in advance,and subsequently,50 mg/kg propofol was respectively given to the PH group and the MPH group.Immediately after the intraperitoneal injections were completed,the corresponding rats were transferred into a constant temperature chamber containing 18%O2.Then the rats were continuously monitored until resuming the reversing reflex and then transferred to a normoxic environment.The hypoxic treatment was carried out once per day for 7 consecutive days.Transcriptome sequencing was used to screen for differential expressed genes(DEGs),and Kyoto encyclopedia of genes and genomes(KEGG)enrichment analysis was employed to conduct functional analysis.Morris water maze test was applied to exam spatial learning and memory abilities.HE staining was used to observe the morphological changes of neurons in the hippocampal CA1 region.Morphological changes of mitochondria in hippocampal neurons were observed by transmission electron microscopy(TEM).Western blotting was utilized to detect the expression of Parkin Rbr E3 ubiquitin protein ligase(Parkin)and PTEN-induced putative kinase 1(PINK1)in the hippocampal tissues.Results KEGG analysis results indicated that the mitophagy pathway was more significantly enriched in the PH group when compared with the CON group.Morris water maze test revealed that the PH group exhibited obviously prolonged escape latency(P<0.05),reduced frequency of crossing the platform(P<0.05),and shortened residence time in the target quadrant(P<0.01)when compared with the CON group and the MPH group.HE staining demonstrated that the cells in the PH group were in disordered arrangement,with great loss in cell count in some areas,and widened intercellular spaces.Although the cell arrangement in the MPH group also showed a sparse state,but the condition was milder than that in the PH group,with slightly widened intercellular space.In the CON group and the MCON group,the cells exhibited round in shape,good morphological structure,relatively clear contours,and uniform cell nuclei.TEM revealed that in the hippocampal neurons of the PH group,the mitochondria were swollen and deformed,and mitochondrial cristae were disordered,dissolved and disappeared.In the MPH group,only some mitochondria were swollen and the cristae were reduced.However,the mitochondrial morphology of the CON and MCON groups was relatively complete,and the matrix was uniform.Western blot analysis showed that the expression levels of Parkin and PINK1 in the hippocampus were up-regulated in the PH group than the CON group(P<0.05),and reduced in the MPH group than the PH group(P<0.05).Conclusion Mdivi-1 may reduce hippocampal neuron damage by inhibiting excessive mitophagy and then improve cognitive dysfunction in immature SD rats induced by hypoxia combined with propofol.