Cognitive Impairment and Endoplasmic Reticulum Stress Induced by Repeated Short-Term Sevoflurane Exposure in Early Life of Rats

Abstract

Sevoflurane is one of the most commonly used volatile anaesthetics for children, but the safety of prolonged or repeated clinical use of sevoflurane in infants or children is controversial. Here, we investigated the effects of sevoflurane on rats in early life and the time scale of those effects. Our behavioral results indicated that repeated short-term exposure of new-born rats to sevoflurane caused learning and memory impairment, while a single exposure of rats to sevoflurane was relatively safe. Further mechanistic investigation revealed that repeated sevoflurane exposure impaired long-term potentiation (LTP), downregulated the expression of certain synaptogenesis-related proteins (GluR1, PSD95) and upregulated proteins related to endoplasmic reticulum (ER) stress in the hippocampus. An ER stress inhibitor, tauroursodeoxycholic acid (TUDCA), reversed the changes in the levels of synaptic plasticity proteins. Our results provide new evidence for the clinical concerns regarding repeated sevoflurane anesthesia.

Keywords: cognitive dysfunction; endoplasmic reticulum stress; repeated exposure; sevoflurane; synaptic plasticity.

Figure 1

Schematic timeline of the experimental procedure.

Figure 2

Effects of repeated early-life sevoflurane exposure on behavior. (A) In the open field test, no significant difference was observed between the control group and the sevoflurane group in total distance moved. (B) A typical path during the probe trial for each group. (C) The latency to find the platform during the place navigation training phase of the Morris water maze test. (D) The percentage of time spent in the target quadrant during the probe trial of the Morris water maze test. N = 10 rats for each group. Repeated ANOVA with a post hoc least significant difference (LSD) test and unpaired t-tests were performed for (A,C,D), respectively; ^*p < 0.05. Data are presented as the mean ± SEM.

Figure 3

Repeated sevoflurane exposure abolished LTP in the hippocampus. (A) Schematic representation of bipolar stimulating and recording electrode placement. (B) Tetanic stimulation (one bout of stimulation at 100 Hz) induced LTP in the Schaffer collateral-CA1 pathway of rat hippocampal slices. (C) Representative traces of the fEPSP waves were recorded at baseline (the black line) and after repeated sevoflurane exposure (the gray line); early-life sevoflurane exposure impaired LTP in the rat hippocampus. N = 9 slices, 4 rats for the control group; n = 8 slices, 4 rats for the sevo group.

Figure 4

Repeated sevoflurane exposure decreased the expression of GluR1, PSD95, and CREB. (A) Representative samples showing the hippocampal expression levels of GluR1, PSD95, and CREB in the control group and the sevoflurane group. (B) Densitometric analysis of GluR1, PSD95, and CREB. N = 4–6 times for each protein. Unpaired t-tests; ^*p < 0.05 vs. control. Data are presented as the means ± SEM.

Figure 5

Repeated sevoflurane exposure increased the expression of GRP 78, PERK, and eIF-2α. (A) Representative samples showing the expression levels of GRP 78, PERK, and eIF-2α in the hippocampi of the control group and the sevoflurane group; (B) Densitometric analysis of GRP 78, PERK, and eIF-2α. N = 4–6 times for each protein. Unpaired t-tests; ^*p < 0.05 vs. control. Data are presented as the means ± SEM.

Figure 6

Increased expression of GRP 78, PERK, and eIF-2α and decreased expression of GluR1, PSD95, and CREB were reversed by the ER stress inhibitor TUDCA. (A) Representative samples showing the expression levels of GRP 78, PERK and eIF-2α in the hippocampi of the control group, the sevoflurane group, the TUDCA group and the TUDCA+sevoflurane group; (B) Densitometric analysis of GRP 78, PERK, and eIF-2α. N = 3–6 times for each protein. One-way ANOVA; ^*p < 0.05 vs. control. Data are presented as the means ± SEM. (C) Representative samples showing the expression levels of GluR1, PSD95, and CREB in the hippocampi of the control group, the sevoflurane group, the TUDCA group and the TUDCA+sevoflurane group; (D) Densitometric analysis of GluR1, PSD95, and CREB. One-way ANOVA; ^*p < 0.05 vs. control. Data are presented as the means ± SEM.