Release of a proposed activator of spreading depolarization by abrupt hyperthermia
Spreading depolarization (SD) is a wave of lost membrane potential moving across the gray matter within 1-2 minutes of metabolic compromise as during stroke, post-injury fever or migraine aura. Research is ongoing to protect the brain from the potentially damaging effects of SD on neurons, but progress has been slow because the molecular events initiating and sustaining SD are poorly understood. Therefore, we searched for evidence of an SD activating molecule (SDa) which is released from metabolically stressed gray matter and triggers SD, essentially acting like an endogenous palytoxin (PLTX). First, we tested if SD could be routinely evoked in a naïve, healthy brain slice by elevating the temperature quickly from 35 to 40oC. This “hyperthermic SD” (htSD) was confirmed using light transmittance (LT) imaging. Then, SD induction was attempted in a naïve slice by superfusing the artificial cerebral spinal fluid (aCSF) which previously bathed several slices undergoing htSD. This solution was termed “aCSFPost-SD” and was suspected of containing a released SDa. In support, SD could be evoked by aCSFPost-SD in ~62% of naïve slices at a normal temperature of 35oC. Moreover, SD onset evoked by the aCSFPost-SD was unaffected by slight elevations in [K+]O (5 mM) or by the inhibition of glutamate receptors by kynurenic acid (2 mM). SD induced by O2/glucose deprivation (OGD) was also not hindered by rostafuroxin, which blocks the inhibitory effect of a potential endogenous ouabain (EO). Chemical analysis of the aCSFPost-SD using size-exclusion high pressure liquid chromatography (HPLC) and matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS) detected compounds with MW of ~300-400 and ~500-600 Da associated with SD. Analysis of HPLC traces of substances released from brain slices evoked by brief hyperthermia, by OGD or by high [K+] revealed the same elevated peaks, implicating biomolecules common to SD in general. Further characterization of SD-related molecules will help us identify an SDa as part of a continuing effort to identify therapeutic targets/biomarkers involved in SD-associated acute brain injury.
URI for this recordhttp://hdl.handle.net/1974/28184
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