International Journal of Neuroscience, 2015; 125(1): 66–69 Copyright © 2015 Informa Healthcare USA, Inc. ISSN: 0020-7454 print / 1543-5245 online DOI: 10.3109/00207454.2014.901968

RESEARCH ARTICLE

Different effects of etomidate and propofol on memory in immature rats Yi-hong Jiang,1 Xu-qing Ni,2 Wei-wei Xiong,1 Hua Wang,1 Yi Tan,1 Zhi-hua Huang,1 and Xin-yu Yao2 Department of Anesthesiology, Affiliated Hospital of Guilin Medical University, Guilin, Guangxi, China; 2 Guilin Medical University, Guilin, Guangxi, China

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This study is to investigate the effects of etomidate and propofol on memory and possible involved mechanisms using immature rats. Forty-eight rats randomly received intraperitoneal injection of 5 mg/kg etomidate ( n = 16), 50 mg/kg propofol ( n = 16) or normal saline (control, n = 16). Three hours after awakening, memory was assessed by Y-maze test using 10 rats in each drug group. Gamma-aminobutyric acid (GABA) content in hippocampal tissue was measured using six rats in each group. Etomidate group had more total reaction time (TRT) compared with the control group in Y-maze test ( p < 0.05). No other difference between these two groups was observed. Propofol group had less number of correct response ( p < 0.01) and more TRT ( p < 0.05) in Y-maze test, as well as more GABA concentration detected in hippocampal tissue ( p < 0.01) than the control group. Propofol group also showed less number of correct response ( p < 0.05) and more hippocampal GABA concentration ( p < 0.01) compared with etomidate group. Etomidate does not show significant effects on memory in rat and further investigation is required. Propofol can affect memory in rat possibly via increasing the synthesis and/or secretion of GABA as one of the factors. KEYWORDS: etomidate, propofol, memory, Y-maze, GABA

Introduction Concerns have been arisen about anesthetic safety recently as evidence shows neurocognitive decline can be induced by anesthetics [1]. Anesthesia has been proposed as one of the factors causing postoperative cognitive dysfunction [2, 3], which is a cognitive decline after surgery lasting for weeks or months. For children and infants, anesthesia exposure are neurotoxic to the developing brain [4], leading to consequent memory, learning and cognitive problems. A retrospective study shows early childhood exposure to anesthesia will increase the risk of developmental and behavioral disorders by 1.1–4.0 times depending on operation times [5]. General anesthesia is usually implemented for children and infants, and etomidate and propofol are commonly used intravenously. Etomidate and propofol tar-

get different sites of gamma-aminobutyric acid type A (GABAA ) receptors, the principal inhibitory neurotransmitter receptors in the central nervous system, to implement anesthetic actions [6–8]. Meanwhile, anesthetic agents may trigger histopathologic central nervous system changes [9]. Propofol can increase neurodegeneration and induce acute neurotrophic imbalance and neuroapoptosis in newborn rats [10, 11]. Etomidate has been known to inhibit adrenal steroidogenesis [12], and it can also regulate memory blockade via alpha5 GABAA receptors [13]. This study investigated the effects of etomidate and propofol on memory as well as on GABA content in hippocampal tissue, and discussed the possible mechanisms involved, which could provide further understanding of anesthetic-induced cognitive problems and data to guide clinicians when choosing anesthetic regimens.

Materials and Methods Received 7 October 2013; revised 6 February 2014; accepted 4 March 2014 Correspondence: Yi-hong Jiang, Department of Anesthesiology, Affiliated Hospital of Guilin Medical University, Guilin, Guangxi 541001, China. Tel: +86-0773-2823244. Fax: +86-0773-2833802. E-mail: [email protected]

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Drugs Etomidate (Lot No. 20120401) was purchased from Jiangsu Nhwa Pharmaceutical Corporation. Propofol

Etomidate, propofol and cogitation

(Lot No. 16EK0078) was purchased from Fresenius Kabi.

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Animals Clean grade Sprague-Dawley (SD) rats (either sexes, aged 17 to 18 days, weighing 31–40 g) were provided by the Laboratory Animal Center of Guilin Medical University. Forty-eight rats fitting the following criteria were selected. First, the rats were active, sensitive and rapidly responsive to electric shock in a preliminary Ymaze screening. Second, the rats reacted correctly twice out of no more than three times training in the screening. Third, the rats met a 90% success rate (≥18/20) in a standard Y-maze test before anesthesia. Animal experiments were approved by the Committee of the Ethics on Animal Experiments of Affiliated Hospital of Guilin Medical University.

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ultrapure water followed by vortex and 20-min sonication. Then, 1 ml of 4% salicylsulfonic acid was added. The mixture was settled to a volume of 5 ml and centrifuged for 5 min at 5000 rpm. Supernatant was filtered by a 0.45-μm membrane. Finally, 100-μl filtrate was injected into a Hitachi L-8800 Amino Acid Analyzer to quantify the concentration of GABA. Reference GABA was purchased from Sigma.

Statistics Statistical analyses were performed by SAS 9.1 (SAS Institute, Cary, NC). Data were expressed as mean ± SD. Difference between groups were compared by oneway ANOVA using Fisher’s Least Significant Difference (LSD) test. A p-value < 0.05 was considered significant.

Results Study design The rats were randomly and evenly divided into three groups, the etomidate group, propofol group and control group (n = 16 in each group). For the etomidate group, 5 mg/kg etomidate was intraperitoneally injected, so was 50 mg/kg propofol for the propofol group and 0.90% (w/v) NaCl solution for the control group. Ten and six rats were randomly selected from each group for Y-maze test and GABA measurement, respectively, 3 h after recovery from anesthesia.

Y-maze test Memory was evaluated by Y-maze test. The test was performed at 2–5 pm in a quiet, soundproofing room with controlled room temperature of 24 ± 1◦ C. Single blind test was employed to minimize any human influences. Ten rats were randomly selected from each group. Each rat was placed in a Y-maze. After 5-min adaption, a fixed 20-time and stochastic restless testing method (FSR) was applied to train the rat s. Briefly, a safe arm was randomly chosen; light would be last for 10–15 s when the rats escaped to the safe arm after electric shock (50–70 V, 5-s latency). Then, the safe arm would be the starting location for the next training. Correct response was that the rat made it to the safe arm. The number of correct response and total reaction time (TRT) was recorded.

GABA measurement Six rats were randomly selected from each group, sacrificed by decapitation and placed on ice. Rats were not anesthetized before decapitation. Hippocampal tissue was immediately taken, weighed and immersed in 2 ml  C

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Y-maze test after anesthesia The number of correct response showed no significant between etomidate (12.40 ± 2.07) and control (13.30 ± 2.00) group, while less number of correct response (9.80 ± 2.39) was observed in propofol group compared with either etomidate (p < 0.05) or control (p < 0.01) group (Figure 1A). On the other hand, both the etomidate (79.10 ± 11.64 s) and propofol (82.30 ± 10.20 s) group needed more TRT than control (67.70 ± 12.18 s) group, but TRT had no significant difference between etomidate and propofol group (Figure 1B).

GABA concentration in hippocampal tissue after anesthesia Meanwhile, the GABA concentration in hippocampal tissue was measured. There was no significant difference between etomidate (47.88 ± 10.86 mg/100 g) and control (39.08 ± 10.56 mg/100 g) group, while more GABA (73.14 ± 11.79 mg/100 g) was detected in the propofol group than either etomidate (p < 0.01) or control (p < 0.01) group (Figure 2).

Discussion We assessed the effects of two commonly used intravenous anesthetics, etomidate and propofol on memory in rats. Results showed propofol could affect the memory possibly via a GABA-mediated mechanism, while etomidate offers better performance. The 17- to 18-day-old rats are in the brain developmental period and the brains are very vulnerable to anesthetics-induced neurodegeneration [14]. Y-maze

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Y.-h. Jiang et al.

The number of correct response (A) and total reaction time (B) of each group in the Y-maze test after anesthesia. Error bars indicate standard deviation. Significant difference where observed was indicated by p < 0.01 or < 0.05. s, second.

Figure 1.

has been widely used and well established in memory studies. Here, we employed Y-maze test to evaluate the memory of immature rats after anesthetics exposure. Propofol anesthesia dramatically reduced the number of correct response and meanwhile increased the TRT, suggesting memory was negatively affected. By contrast, etomidate anesthesia had no effect on the number of correct response and only prolonged the TRT. We hypothesize the reason may be that due to a long elimination half-life (2–5 h) [15], etomidate might not be completely metabolized after recovery of anesthesia and the

The GABA concentration in hippocampal tissue of each group. Error bars indicate standard deviation. Significant difference where observed was indicated by p < 0.01.

Figure 2.

remaining would lead to hypersomnia, tranquilization or apathy. Y-maze can also assess learning to some extent. The results thus suggest propofol anesthesia may affect learning as well. Etomidate and propofol anesthesia is mediated via GABAA receptor-mediated mechanisms by targeting different sites on GABAA receptors [6–8, 16, 17]. The GABAA receptors also play an important role in memory, learning and cognition [18, 19]. Therefore, activation of GABAA receptors by propofol and etomidate may cause cognitive problems as well, while the different effects suggest the process may be binding targetdependent. On the other hand, general anesthetics can facilitate GABA release from cortical nerve terminal [20]. As an important inhibitory neurotransmitter in the central nervous system, GABA has been hypothesized as a critical factor involved in neuropathological process [21–23]. The glutamic acid (Glu)/GBGA system in the central nervous system is essential to learning and memory. Glu has a positive regulating function, while GABA acts as a negative regulator. Normal learning and memory relies on an appropriate level of GABA. Either increased or decreased GABA concentration will impair learning and memory [24, 25]. Elevated prefrontal cortex GABA level in schizophrenia has also been reported [22]. Here, we observed higher level of GABA in hippocampal tissue in propofol group, suggesting propofol might upregulate GABA release and acts as one of the factors leading to the memory-learning decline. But how propofol can increase the GABA level and why etomidate lead to limited GABA alteration awaits further investigation. It should also be noticed propofol affects memory and learning at different levels via neurotoxic International Journal of Neuroscience

Etomidate, propofol and cogitation

effects that are mostly associated with GABAergic transmission [26–28]. Propofol interacting GABA receptors has been widely studied, and here we showed propofol that can alert GABA levels as well, which could be one the factors affecting memory and learning.

Conclusion

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Etomidate can increase TRT in rat, but does not show strong effects on memory, which means further studies are needed; propofol can affect memory in rat probably via increasing the synthesis and/or secretion of GABA.

Declaration of Interest The authors report no conflicts of interest The authors alone are responsible for the content and writing of this paper. This study was supported by Department of Education (Grant No. 201204LX243) and Department of Health (Grant No. Z2012397) of Guangxi Zhuang Autonomous Region.

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Different effects of etomidate and propofol on memory in immature rats.

This study is to investigate the effects of etomidate and propofol on memory and possible involved mechanisms using immature rats. Forty-eight rats ra...
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