Protective effects and mechanisms of L-carnitine on cognitive dysfunction in rats with chronic cerebral hypoperfusion / 中华行为医学与脑科学杂志

ABSTRACT

Objective:To explore the protective effects and mechanisms of L-carnitine (LCAR) on cognitive dysfunction in chronic cerebral hypoperfusion rats.Methods:Totally 90 SD male rats (SPF class) aged 3-4 months were divided into four groups according to random number talbe sham operated control group (SHAM group, n=15), sham operated with L-carnitine treatment group (LCAR group, n=25), 2-vessel occlusion group (2VO group, n=25), and 2-vessel occlusion with L-carnitine treatment group (2VO+ LCAR group, n=25). The chronic cerebral hypoperfusion model was established by bilateral common carotid artery ligation, and the carotid arteries from SHAM group and LCAR group were only separated without ligation.L-carnitine was administered intraperitoneally (300 mg·kg -1·d -1) for 30 days after surgery in the LCAR and 2VO+ LCAR groups.After 30 days of L-carnitine intervention, Morris water maze was performed to test the spatial cognitive function of the rats, the ATP level of hippocampal tissue was detected by chemiluminescence, the mitochondrial structure and synaptic structure of hippocampal neurons were observed by transmission electron microscopy, the degree of mitochondrial damage was scored, the vesicle density was counted and measured, the level of N-methyl-D-aspartate receptor subunit 2A or 2B(NR2A/B) and postsynaptic density 95(PSD95) in hippocampal tissue were detected by Western blot.The expression and distribution levels of transcription factor cAMP response element-binding protein(CREB) in brain tissues were observed by immunofluorescence.SPSS 16.0 software was used for statistical analysis.The escape latency data of repeated learning training in Morris water maze was conducted by repetitive measurement ANOVA, while other data were adopted by one-way ANOVA, and Dunnett's t test was used for further pairwise comparison. Results:(1)Morris water maze results showed that the time and group interaction of escape latency was not significant among the 4 groups of rats ( F=1.4, P>0.05), but the time main effect and group main effect were significant( F=21.6, 15.2, both P<0.05). Morris water maze results showed that platform position learning from 3rd to 7th day, the escape latencies in 2VO group were longer than those in SHAM group and 2VO+ LCAR group (all P<0.05). The results of short-term memory showed that the escape latency in 2VO group was longer than those in SHAM group and 2VO+ LCAR group (all P<0.05). Meanwhile, the retention time and crossing times in the platform area of 2VO group were less than those in SHAM group and 2VO+ LCAR group (all P<0.05). (2) The absolute and relative levels of ATP in hippocampus showed that the difference among the 4 groups were statistically significant ( F=14.6, 13.2, both P<0.05). ATP level of hippocampus in 2VO group was lower than those in SHAM group and 2VO+ LCAR group (both P<0.05). Electron microscopic observation of mitochondrial morphology showed that the Flameng score of mitochondrial damage in the hippocampus of rats in 2VO group (2.82±0.17) was higher than those in SHAM group (0.25±0.07) and 2VO+ LCAR group (1.76±0.09) (both P<0.05). (3) The density of synaptic vesicles in the hippocampus of rats in 2VO group ((289.09±22.41)/μm 2)was lower than those in SHAM group ((497.49±28.89)/μm 2)and 2VO+ LCAR group ((401.23±45.09)/μm 2) (both P<0.01). Western blot results showed that the relative levels of synaptic proteins NR2A/B, PSD95 and CREB in 2VO group were lower than those in SHAM group and 2VO+ LCAR group (all P<0.05). Immunofluorescence results showed that the relative level of CREB expression in hippocampal subregions and cortex in 2VO group was lower than those in SHAM group and 2VO+ LCAR group (both P<0.01). Conclusion:L-carnitine can improve spatial learning and memory dysfunction in rats with chronic cerebral hypoperfusion, which are related with promoting ATP production and protecting mitochondrial morphology, and promoting synaptic vesicle synthesis and synaptic protein expression.