Improvement of cognitive deficients by selegiline on isoflurane-induced post-operative cognitive disorder model

다국어 초록 (Multilingual Abstract)

Abstract

Improvement of cognitive deficients
by selegiline on isoflurane-induced
post-operative cognitive disorder model


by Choi Geun-wook
Department of East-West medicine, Graduate School of East-West Medical Science, Kyung Hee University, Yong-in, 17104, Republic of Korea

(Advised by Professor.
Jae-hwan Lew K.M.D / Sungho Maeng M.D / Chang Shik Yin K.M.D)

The pathophysiology of post-operative cognitive dysfunction (POCD) is not fully understood in detail, but its association with anxiety and local inflammation during general anesthesia is suspected. In addition, the elderly and children are more vulnerable to POCD, which is problematic because general anesthesia or major surgery is more often required due to congenital anomaly and malignancy. Currently, no reagents consistently benefit the improvement of POCD symptoms yet. It was known that enhanced synaptic release of gamma-aminobutyric acid (GABA) by inflammatory astrocytes might inhibit synaptic activity. Therefore, monoamine oxidase b (MAO-B) inhibition may reduce GABA production from putrescine in reactive astrocytes.
This study was conducted to determine whether midazolam, an anxiolytic reagent, and selegiline, a MAO-B inhibitor, can improve cognitive symptoms in isoflurane-induced POCD model mice. In order to test POCD induction, 2-week, 8-week and 24-month over old C57BL / 6N mice have exposed to 1.5-2% isoflurane 1 session for 3 hours or 5 sessions every other day for 3 hours each, and behavioral experiments were performed. Then the pharmacological effect of midazolam and selegiline was tested. Changes of glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (Iba-1) were measured biochemically in POCD model mice and field excitatory postsynaptic potential (fEPSP) was measured on organotypic hippocampal slices to determine the effect of selegiline and midazolam during the isoflurane progress on long-term potentiation (LTP).
After isoflurane anesthesia, working memory, object recognition memory, and spatial memory declined compared to the control group, but avoidance memory was unaltered. As such cognitive changes were much clearer in 5 repetitive anesthetic sessions for 3 hours than a single session for 3 hours, and subsequently, all repeated anesthesia was performed 5 times in drug trial as a POCD model. In POCD model mice, selegiline improved the anesthesia-induced working memory and spatial memory but did not improve object recognition memory and midazolam did not improve cognitive symptoms in these animals. There were astrocytosis but not microgliosis in the prefrontal cortical and hippocampal regions which supported by immunoblotting. As a result of the measurement of local synaptic potentials, it was found that selegiline can unblock the LTP blocking effect by isoflurane.
In summary, MAO-B inhibition improved cognitive symptoms in POCD model animals while midazolam did not affect. These findings implicate that enhanced MAO-B activity is related to the pathophysiology of POCD and MAO-B inhibitors such as selegiline can be used for POCD treatment.
Keywords: POCD, Repeated Anesthesia, Reactive Astrocyte, MAO-B Inhibitor, Selegiline, Midazolam, Behavior test.

목차 (Table of Contents)

• Ⅰ. Introduction 01
• Ⅱ. Materials and methods 06
• 1 Reagents 06
• 2 Experimental animals 06
• 3 Isoflurane treatment 08
• 4 Y-maze test 09
• 5 Novel Object Recognition test 10
• 6 Passive Avoidance test 10
• 7 Morris Water Maze test 11
• 8 Western blotting analyses 12
• 9 Electrophysiological measurement of focal synaptic activity 13
• 10 Statistical Analyses 17
• Ⅲ Results 18
• 1 POCD model mice were made with repeated isoflurane anesthesia 5 sessions for 3 hours every other day 18
• 1. Y-maze test 18
• 2. Novel Object Recognition test 21
• 3. Passive avoidance test 24
• 4. Morris Water Maze test 26
• 2. Selegiline but not midazolam improved isoflurane-induced cognitive disorder in POCD model mice 28
• 1. Y-maze test 28
• 2. Novel Object Recognition test 31
• 3. Morris Water Maze test 34
• 3. Anesthesia-induced change of GFAP and Iba-1 expression in the Prefrontal cortex and the Hippocampus 37
• 4. Electrophysiological properties of isoflurane on ex vivo cultured hippocampal slices 40
• 1. Isoflurane inhibited fEPSPs in HFS-induced potentiation in ex vivo cultured hippocampal slices 40
• 2. Isoflurane reversibly inhibits excitatory synaptic transmission 42
• 3. Block of HFS-induced LTP by isoflurane 44
• 4. In the presence of picrotoxin, selegiline, isoflurane does not block LTP but not midazolam 56
• Ⅳ. Discussion 48
• Ⅴ. Summary 58
• Ⅵ. Reference 59
• Abstract in Korean 81