Minocycline, a tetracycline derivative, is neuroprotective against excitotoxicity by inhibiting activation and proliferation of microglia

Minocycline, a semisynthetic tetracycline derivative, protects brain agains t global and focal ischemia in rodents. We examined whether minocycline red uces excitotoxicity in primary neuronal cultures. Minocycline (0.02 muM) si gnificantly increased neuronal survival in mixed spinal cord (SC) cultures treated with 500 muM glutamate or 100 muM kainate for 24 hr. Treatment with these excitotoxins induced a dose-dependent proliferation of microglia tha t was associated with increased release of interleukin-1 beta (IL-1 beta) a nd was followed by increased lactate dehydrogenase (LDH) release. The excit otoxicity was enhanced when microglial cells were cultured on top of SG cul tures. Minocycline prevented excitotoxin-induced microglial proliferation a nd the increased release of nitric oxide (NO) metabolites and IL-1 beta. Ex citotoxins induced microglial proliferation and increased the release of NO metabolites and IL-1 beta also in pure microglia cultures, and these respo nses were inhibited by minocycline. In both SG and pure microglia cultures, excitotoxins activated p38 mitogen-activated protein kinase (p38 MAPK) exc lusively in microglia. Minocycline inhibited p38 MAPK activation in SC cult ures, and treatment with SB203580, a p38 MAPK inhibitor, but not with PD980 59, a p44/42 MAPK inhibitor, increased neuronal survival. In pure microglia cultures, glutamate induced transient activation of p38 MAPK, and this was inhibited by minocycline. These findings indicate that the proliferation a nd activation of microglia contributes to excitotoxicity, which is inhibite d by minocycline, an antibiotic used in severe human infections.