gms | German Medical Science

Objective: Neuroprotective treatment strategies aiming at interfering with either inflammation or cell death indicate the importance of these mechanisms in the development of brain injury after SAH. Our previous study showed microglia accumulation in the injured brain, releasing pro-inflammatory cytokines and causing neuronal cell death after experimental SAH. Herein, we aimed to determine the influence of minocycline, a semi-synthetic tetracycline, known for its neuroprotective properties, on inflammation following SAH and evaluate the underlying mechanisms.

Method: The endovascular filament perforation was used to induce SAH in mice. Sham-operated mice were used as controls for SAH vehicle-treated and SAH minocycline-treated mice. Animals were sacrificed after 7 or 14 days. Minocycline (45 mg/kg i.p.) was applied in the 7 days-group daily and in the 14 days-group the first 7 days every day and until day 14 every second day. Brain cryosections were immunolabeled for Iba-1 to detect microglia and NeuN to visualize neurons. By co-localizing these markers with Ki67 we were able to detect proliferating cells, whereas apoptotic cells were stained using a commercially available TUNEL-kit. The number of microglia and neurons was counted in regions of interest in all experimental groups. Additionally, the activity status was determined by morphological quantification.

Results: The number of microglia increased from the baseline level of sham-operated mice up to 15.8 ± 2.6-fold on day 7 and up to 19.7 ± 5.1-fold on day 14. The morphology of these cells was changed from ramified to round, reflecting their activated, phagocytic status. At both time points the number of microglia was reduced in response to minocycline treatment to 3.1 ± 0.9-fold and to 3.6 ± 1.7-fold of the sham control, respectively. The number of apoptotic neurons was increased by 59.1 ± 18.4-fold on day 7 and by 21.6 ± 9.3-fold on day 14 after SAH. Minocycline injections reduced neuronal cell death to 4.1 ± 2.0-fold on day 7 and to 1.9 ± 1.4-fold on day 14 of the control, respectively.

Conclusions: Our study reveals that minocycline exerts neuroprotective effects by diminishing neuronal cell death after SAH. We hypothesize that this effect might be mediated by lowering the number of microglial cells. Thus, minocycline may exhibit important clinical potentials in the management of SAH. However, further functional studies will be conducted to find out the impact of minocycline on microglial activity and neuronal function.