Cortical Spreading Depression induced Preconditioning in Mouse Neocortex

19 Cortical spreading depression (CSD) is able to confer neuroprotection when 20 delivered at least one day in advance of an ischemic event. However, its 21 ability to confer neuroprotection on a more immediate time frame has not 22 previously been investigated. Here we have used mouse neocortical brain 23 slices to study the effects of repeated episodes of CSD in layer V and layer 24 II/III pyramidal neurons. In layer V, CSD evoked at 15 minute intervals caused 25 successively smaller membrane depolarisations and increases in intracellular 26 calcium compared with the response to the first CSD. With an inter-CSD 27 interval of 30 minutes this preconditioning effect was much less marked, 28 indicating that preconditioning lasts between 15 and 30 minutes. A single 29 episode of CSD also provided a degree of protection in oxygen glucose 30 deprivation (OGD) by significantly lengthening the time a cell could withstand 31 OGD before anoxic depolarisation occurred. In layer II/III pyramidal neurons 32 no preconditioning by CSD on subsequent episodes of CSD was observed, 33 demonstrating that the response of pyramidal neurons to repeated CSD is 34 laminar specific. The A1 receptor antagonist 8-CPT reduced the layer V 35 preconditioning in a concentration-related manner. Inhibition of extracellular 36 formation of adenosine by blocking ecto-5’-nucleotidase with α,β37 methyleneadenosine 5'-diphosphate prevented preconditioning in most but 38 not all cells. Block of equilibrative nucleoside transporters 1 and 2 with 39 dipyramidole alone or in combination with 6-[(4-Nitrobenzyl)thio]-9-β-D40 ribofuranosylpurine also prevented preconditioning in some but not all cells. 41 These data provide evidence that rapid preconditioning of one CSD by 42 another is primarily mediated by adenosine. 43 44