Human brain makes new neurons after stroke
MedWire News: The human brain generates new neurons within days of a stroke, shows research published in the journal Neurology.
Animal models show that new cells arise in the subventricular zone following stroke and migrate to the infarcted area.
Joan Martí-Fàbregas (Hospital de la Santa Creu i Sant Pau, Barcelona, Spain) and colleagues studied this process in humans by obtaining brain tissue samples from seven people who had died an average of 10 days after a stroke. The patients were an average of 82 years old and four were men.
The team found structural changes in the ipsilateral subventricular zone, including increased thickness of the ribbon layer, relative to that in the contralateral subventricular zone. The astrocytes that largely comprised the ipsilateral ribbon layer were nearly two-thirds larger than those in the contralateral ribbon layer.
The researchers also observed a more than two-fold increase in cells bearing proliferation markers (Ki-67 and PCNA) in the patients’ ipsilateral compared with the contralateral subventricular zones.
A marker of neural cells (GFAP) was present on 86% of these cells, whereas just 8% bore an inflammatory cell marker (CD-68). The cells were located in the gap and ribbon layers of the ipsilateral subventricular zone.
There was also a six-fold increase in neuroblasts in the ipsilateral subventricular zone. Some of these cells bore markers indicative of migrating neuroblasts and immature neurons, “indicating that there is not only proliferation but also migration of neuroblasts,” say Martí-Fàbregas et al.
These cells were mostly present in the gap layer (52%) of the ipsilateral subventricular zone, whereas those in the contralateral zone were mostly seen in the ribbon layer (65%), implying a role for the gap layer in neuroblast migration.
Migrating neuroblasts were not found adjacent to the subventricular zone, however.
“This could be due to the short survival time,” suggest the researchers. “Probably, if the patients lived longer, migrating neuroblasts would exit the subventricular zone and start to migrate to the ischemic area.”
In an accompanying editorial, Gail Pyne-Geithman (University of Cincinnati, Ohio, USA) commented that the time course of neurogenesis after brain damage has been much studied in animals, but is still unclear in humans.
She said that studies such as the current one “may lead to development of new therapeutic approaches in the essential early hours following ischemic stroke (after all, time is brain), perhaps extending the window for use of lytic and interventional therapies, as well as enhancing effectiveness of long-term rehabilitation efforts.”
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By Eleanor McDermid