Evidences showing that under certain circumstances, inflammatory response could be neuroprotective and could also promote adult neurogenesis are growing. In this context, the objective of this work was to investigate the impact of microglial cells in the neuroplastic events. Rats were subjected to photothrombotic ischemia and microglial cells activation was blocked by the mean of poly(ADP-ribose)polymérase-1 (PARP-1) inhibition using 3- aminobenzamide (3-AB) since this protein has been shown to play a major role in this activation. Our results show that PARP-1 activity reduction was associated with a strong repression of the acute microglial activation. Beside, 3-AB treated animals exhibited a decrease in synaptophysin (synaptogenesis) and GAP-43 (axonal growth) expressions. Taken together, our data argue for a supportive role of microglial in adaptive brain plasticity events. According to the preponderant contribution of BDNF in these events, assessment of its cellular localization was performed, and confirmed that these cells represent a significant source. Beside, BDNF immunoreactivity (IR) in microglial cells and BDNF levels in the lesioned and surrounding lesioned areas were found decreased in 3-AB treated animals. However, since this neurotrophin can exert ambivalent biological actions through pro- versus mature forms, we investigate the proper effect of cerebral ischemia on total (Elisa), pro- and mature (Western blotting) expressions. Our results show that total, pro- and mature BDNF expressions are augmented in the early times (4-24h) of ischemia within the lesioned, the surrounding non lesioned and the contralateral cortical areas. At longer time points, total BDNF was still increased at 8d in regions distant from the lesion (hippocampi and contralateral cortex) while pro- and mature forms rise between 8d to 30d in hippocampic territories only. In term of cellular distribution, BDNF-IR was found in neurons but also in non neuronal cells ipsilaterally whereas in the opposite side BDNF staining was restricted to neurons. Our data while raising the question of the pertinence of total BDNF expression in a context of studying its supportive potential action indicate that such assessment has to be coupled with the discrimination of both forms. In addition, our data confirm the important role of BDNF in post-stroke adaptive mechanisms and argue in favour of an important contribution of the hippocampal territory and of the contralateral hemisphere in BDNF related post-stroke neuronal circuit remodelling suggesting that strategies targeting this hemisphere are likely to mediate functional compensation.
