The Effects Of Mulsified Isoflurane On Learning And Memory In Adult Rats

Objective:To observe ethology of rats through the Morris water maze test and determine the content of the plasma corticosterone, brain hippocampal BNDF and NGF after a single injection of emulsified isoflurane (EI) intravenous anesthesia. Providing assistance to explore the effect of EI on learning and memory function and the mechanism of postoperative cognitive dysfunction, further to provide experimental basis for the El clinical application security.Methods:Seventy-two healthy male SD rats weighing 267.7±11.8g were randomly divided into control group (groupC n=12),30% intralipid group (group E n=12), and emulsified isoflurane group (group EI n=48). The EI group is divided into 4 subgroups (i.e.2h, 1d,7d, 14d after EI anesthesia, respectively, each group n=12). All rats were trained consecutively to place navigation in Morris water maze for 5 days before anesthesia to form some learning and memory. The escape latency and the total swimming distance were recorded. Memory consolidation of rats were observed through the spatial probe test on the sixth day. Platform was removed and the swimming time within 120s in platform quadrant, the percentage of swimming distance in target quadrant, the average swimming speed and the platform passing times within 120s were recorded. After the test, group C was without drug intervention, group E were injected 30% intralipid (1.5ml/kg) through tail intravenous. Two hours later, group E were tested Morris water maze again together with group C; each subgroup of group EI were given 8% emulsified isoflurane (1.5ml/kg) and tested water maze again in 2h, Id,7d,14d after anesthesia awaking, respectively, observing the same things as pre-anesthesia. After water maze test, rats were anesthetized with 1% sodium pentobarbital (4mg/100g) by intraperitoneal injection,2-4ml blood was drawn from every rat's orbits and collected into a heparin tube, centrifugated at 3000r for 15min under 6℃then aspirated the plasma for plasma corticosterone content detection by enzyme linked immunosorbent assay (ELISA).6 rats in each group were randomly selected, both sides of hippocampus of which were removed after decapitation and then homogenized, the homogenates were centrifugated at 9000r (0-4℃) for 15min, aspirated supernatant for hippocampal BDNF, NGF content detection by ELISA. The other 6 rats in each group were opened chest and perfused cerebral with 4% paraformaldehyde through aorta before decapitation at each time point, then removed the whole brain. The expression of hippocampal BDNF and NGF were determined by immunohistochemistry after the cerebrals were embedded in paraffin, and sliced.Results:1. The results of the water maze test showed that the escape latency (15.5±15.3s) and the total distance (386.8±227.2s)cm of the group 2h after El anesthesia was significantly longer than the group C, E (8.8±6.1s and 234.8±118.4cm,9.3±2.8s and 291.6±89.3cm, respectively) (P<0.01), but compared with the group C and E, the group 1d, 7d,14d after El anesthesia had no statistically significant (P>0.05). Compared with the group C (45.4±12.7s), the swimming time of platform quadrant in the group 2h after El anesthesia (35.0±9.8s) was significantly shorter (P<0.01), but the percentage of the distance of platform quadrant, swimimg speed and platform passing times showed no significant difference between each group (P>0.05).2. The results of ELISA showed that there was no significant difference of corticosterone level between the groups (P>0.05). The content of BDNF in the hippocampus was significantly lower in the group 2h, 1d after El than group C (P<0.05). Compared with the group 2h, 1d after El, the BDNF content of group 7d,14d after El increased, but it had no statistically significant (P>0.05). After El injection, the NGF content began to increase from Id, in group Id,7d,14d after EI, it was significantly higher than the group C, E and group 2h after El (P<0.01).3. The results of immunohistochemistry showed that in rats hippocampal DG area and CA3 area, the average BDNF positive optical density value of group 2h after El decreased compared with group C and E, the staining intensity also reduced (P<0.05). The content of BDNF in other areas of hippocampus was no significant difference between groups (P>0.05). The differences of hippocampal NGF content between each group were not statistically significant (P>0.05).Conclusion:The single tail intravenous injection of El in 2h has an impact on learning and memory ability in adult rats, This may be related to the inhibition of hippocampus BDNF expression by EI. The spatial learning and memory ability of rats can be recovery to the level before anesthesia on the next day after withdrawal. The study has suggested that a single injection of El did not cause lasting learning and memory impairment.