TNF-α knockout and minocycline treatment attenuates blood–brain barrier leakage in MPTP-treated mice

Following intraparenchymal injection of the dopamine (DA) neurotoxin 6-hydroxydopamine, we previously demonstrated passage of fluoresceinisothiocyanate-labeled albumin (FITC-LA) from blood into the substantia nigra (SN) and striatum suggesting damage to the blood–brain barrier (BBB). The factors contributing to the BBB leakage could have included neuroinflammation, loss of DA neuron control of barrier function, or a combination of both. In order to determine which factor(s) was responsible, we assessed BBB integrity using the FITC-LA technique in wild-type (WT), tumor necrosis factor alpha (TNF-α) knockout (KO), and minocycline (an inhibitor of microglia activation) treated mice 72 h following treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Compared with WT mice, TNF-α KO mice treated with MPTP showed reduced FITC-LA leakage, decreased numbers of activated microglia, and reduced proinflammatory cytokines (TNF-α and interleukin 1β) associated with significant MPTP-induced DA neuron loss. In contrast, minocycline treated animals did not exhibit significant MPTP-induced DA neuron loss although their FITC-LA leakage, numbers of activated microglia, and MPTP-induced cytokines were markedly attenuated. Since both TNF-α KO and minocycline treatment attenuated MPTP-induced BBB dysfunction, microglial activation, and cytokine increases, but had differential effects on DA neuron loss, it appears that neuroinflammation and not DA neuron loss was responsible for disrupting the blood–brain barrier integrity.