| Abstract No.: | B-B2029 |
| Country: | Canada |
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| Title: | THE EFFECTS OF MITOCHONDRIAL RESCUE STRATEGIES ON ISCHEMIA-INDUCED SYNAPTIC FAILURE
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| Authors/Affiliations: | 1 Borna Kavousi*; 1 Chris Feeney; 1 Peter Carlen;
1 Toronto Western Hospital, Department of Physiology, ON, Canada
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| Content: | Ischemia-induced synaptic dysfunction may be due to many factors, including the decreased ability of mitochondria to buffer Ca2+ loads. Ischemia-induced mitochondrial Ca2+ efflux can occur through the mitochondrial Na+/Ca2+ exchanger (mNCX) or the mitochondrial permeability transition pore (mPTP). Raised intracellular Ca2+ from ischemia induced mitochondrial dysfunction may contribute to the immediate and delayed synaptic dysfunction characterized by decreased evoked and increased spontaneous neurotransmitter release. Since blocked synaptic transmission due to mitochondrial dysfunction is an early event in ischemia which precedes cell death, it may be a target for neuroprotective strategies.
OBJECTIVES: To identify the relative time courses of oxygen-glucose deprivation (OGD) necessary to cause irreversible changes in synaptic transmission loss. Since the effects of ischemia vary with age, acute hippocampal slices from young and mature mice were used. Next, we investigated whether specific mitochondrial rescue strategies can ameliorate OGD-induced alteration in synaptic transmission. Specifically, mPTP inhibition using Cyclosporin A (CsA: 4 µM) and mNCX inhibition using CGP-37157 (10 µM) were investigated. We hypothesized that mPTP and mNCX inhibition may ameliorate OGD-induced synaptic dysfunction.
Methods and Materials: B6C3F1 mice (young: 3 – 6 weeks; mature: 13 – 16 weeks) were used to obtain 400 µM thick hippocampal slices. ACSF used during perfusion of slices while in the recording chamber, contained (in mM): 125 NaCl, 26 NaHCO3, 5 KCl, 1.8 CaCl2, 1.72 MgSO4, 1.25 NaH2PO4, and 10 glucose, and was continuously aerated with 95% O2/5% CO2. OGD was induced by changing the ACSF aerated with 95% O2/5% CO2 to zero glucose solution aerated with 95% N2/5% CO2. Electrophysiological recordings were obtained by stimulating Schaffer collaterals using a bipolar electrode (125 µm diameter) placed in the stratum radiatum. Orthodromic extracellular responses were recorded from CA1 pyramidal neuron dendritic layer. Analysis of the amplitude of the fEPSPs was performed using Clampfit 9.2 (Axon Instruments); significance determined using Tukey test.
Results: We found that 8 minutes of OGD in young control slices and 6 minutes of OGD in mature control slices were critical time points, where the decline in fEPSPs was irreversible upon oxygen and glucose reintroduction. Next, CsA was administered during 8 minutes of OGD in young slices and 6 minutes of OGD in mature slices. As well, CsA was also present during reintroduction of glucose and oxygen. Our results showed that the addition of CsA during OGD and during reperfusion, allowed for significant recovery in fEPSPs in young and mature slices. In young slices, CsA administered 30 minutes before, during and after 8 minutes of OGD conferred the greatest amount of fEPSP recovery. CGP-37157 administered in the same manner resulted in a significant amount of fEPSP recovery in young slices.
Conclusions: Susceptibility to ischemia varies in terms of age, likely reflecting differing Ca2+ buffering capabilities. Mitochondrial dysfunction, specifically its inability to buffer Ca2+ loads, contributes to the OGD-induced impairments in synaptic transmission. Inhibition of mPTP and mNCX significantly ameliorated the OGD-induced impairments in synaptic transmission.
Supported by: CIHR
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