Hypoxic-ischemic injury includes number of neuropathological changes seen in the light microscope examination. Within 1 h of the insult microvacuolization with normal or shrunken nucleus, cell shrinkage, normal or slightly basophilic cytoplasm, and perineuronal spaces around some neurons may be observed. These changes cannot be distinguished from postmortem autolysis [
27]. For this reason we proposed BYSL as a new marker of early ongoing neuronal changes after hypoxic-ischemic episodes.
Typical neuropathological hypoxic-ischemic changes include: ischemic cell change - seen in the first 6 h of survival, with further neuronal nucleus and cytoplasm shrinkage and pink cytoplasm staining; homogenizing cell change typically seen around 24 h after survival; and a final stage termed “ghost cell” with reduced or absent cytoplasm around a dark and shrunken nucleus and eventual cell loss [
27]. In our HI group ischemic neurons were present despite the fact that death occurred immediately after the ischemic episode. This further emphasizes a need for a validated early marker of hypoxic-ischemic changes.
In our study we documented that acute and fatal hypoxic-ischemic brain injury results in increased BYSL expression in cortical neurons, especially in layers 3–5. Similar findings were documented previously
in vitro [
25] and in animal studies [
24]. BYSL expression seems to be more prominent in ischemic episodes (e.g. fatal bleeding) and moderate in hypoxic ones (e.g. CO poisoning), but it is possible that the length of the episode plays an important role here. Minimal BYSL expression in control group shows, that ischemic brain injury in cardiac arrest may also be distinguished and recognized with this technique. Previous studies describe minimal BYSL expression in astrocytes of cerebral cortex in a physiologically “normal” CNS [
24]. Similarly, previous studies showed that BYSL expression is a more sensitive marker for reactive astrocytes and can be considered one of the common characteristics of astrogliosis [
25]. Here we documented BYSL as a potential marker of hypoxic-ischemic brain injury with a short survival time after the episode, which could be useful for future forensic examinations. In spite of GFAP expression not revealing differences between hypoxic-ischemic and hypoxic-ischemic-reperfusion groups, BYSL expression was increased and detectable (within ≤48 h) after the hypoxic-ischemic episode, which could be potentially useful for dating of hypoxic-ischemic episodes. Further studies including animal ones are needed to establish the precise dynamics of BYSL expression. Previous studies prompted a hypothesis that cell death results in decrease of BYSL expression [
25]. This hypothesis, however, requires further studies. In
in vitro models 0.5 and 3 h ischemia induced significant BYSL astrocyte expression while no differences between the control group and 24 h ischemia and 24 h ischemia/reperfusion were observed. Similarly mild chemical hypoxia induced significant BYSL expression
in vitro. These increases were not accompanied by increased GFAP expression [
25]. In experimental animal models of brain injury elevated BYSL level was observed more than 5 weeks after the injury [
24] and it was suggested that BYSL may be involved in glia activation and differentiation as its increased expression was observed
in vitro during astrocyte IL-β transformation [
24]. Studies
in vitro showed increased BYSL expression was observed positively correlated with IL-1β, IFN-γ, NGF action [
24].