Low oxygen post conditioning prevents thalamic secondary neuronal loss caused by excitotoxicity after cortical stroke

Giovanni Pietrogrande,Katarzyna Zalewska,Frederick R Walker,Sarah J Johnson,Mahmoud Abdolhoseini,Michael Nilsson,Sonia Sanchez-Bezanilla,Zidan Zhao,Lin Kooi Ong,Wei Zhen Chow

doi:10.1038/s41598-019-39493-8

Abstract

In the current study, we were interested in investigating whether Low oxygen post-conditioning (LOPC) was capable of limiting the severity of stroke-induced secondary neurodegeneration (SND). To investigate the effect of LOPC we exposed adult male C57/BL6 mice to photothrombotic occlusion (PTO) of the motor and somatosensory cortex. This is known to induce progressive neurodegeneration in the thalamus within two weeks of infarction. Two days after PTO induction mice were randomly assigned to one of four groups: (i) LOPC-15 day exposure group; (ii) a LOPC 15 day exposure followed by a 15 day exposure to normal atmosphere; (iii) normal atmosphere for 15 days and (iv) normal atmosphere for 30 days (n = 20/group). We observed that LOPC reduced the extent of neuronal loss, as indicated by assessment of both area of loss and NeuN+ cell counts, within the thalamus. Additionally, we identified that LOPC reduced microglial activity and decreased activity within the excitotoxic signalling pathway of the NMDAR axis. Together, these findings suggest that LOPC limits neuronal death caused by excitotoxicity in sites of secondary damage and promotes neuronal survival. In conclusion, this work supports the potential of utilising LOPC to intervene in the sub-acute phase post-stroke to restrict the severity of SND.

Highlights

Ischemic stroke is caused by the sudden interruption of the blood supply to the CNS
In order to investigate the neuroprotective activity of low oxygen post conditioning (LOPC), we estimated the number of neurons by counting NeuN+ cells in thalamic posterior (PO) and ventral posterolateral nuclei (VPL) (Fig. 2A)
Data show that LOPC group at 30 days have significantly more NeuN+ cells in thalamus (p < 0.01) and inside the regions ventral posterolateral nucleus (VPL) (p < 0.01) and posterior complex (PO) (p < 0.05), and that the area of PO affected by secondary neurodegeneration (SND) was smaller after LOPC both at 15 and 30 days (p < 0.05 and p < 0.01 respectively)

Summary

Introduction

Ischemic stroke is caused by the sudden interruption of the blood supply to the CNS In most instances this interruption leads to neuronal loss and impaired brain function[1]. While inhibiting NMDAR activity has been of interest because of its potential to limit excitotoxicity, modulation has been difficult because of the central role that this receptor plays in normal CNS function[9]. To overcome this challenge, it has been demonstrated that suppressing PSD-95 binding to NMDAR acutely post-stroke can restrict excitotoxicity without markedly influencing NMDA activity[10], such effects, have not been demonstrated over longer time frames. More pertinent to the context of SND, a recent study showed that exposure to 8% oxygen for 5 days post-stroke reduces thalamic atrophy in a model of MCAO17

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