Objective The Blood-brain barrier (BBB) is a complex structure that protects the central nervous system (CNS) extracellular fluid from peripheral insults. Understanding the molecular basis and functioning of the BBB has a significant potential for future strategies to prevent and treat neurological disorders. The aim of our study was (1) to investigate BBB alterations in an excitotoxic model and (2) to test the protective properties of melatonin.
Methods The glutamate analogue ibotenate was injected intracerebrally in postnatal day 5 (P5) rat pups to mimic excitotoxic injury. Rats were sacrificed at P5+2 h, P5+4 h, P5+18 h. Lesion size and location of tight junction (TJ) proteins were determined by immunohistochemistry and BBB leakage after ibotenate injection by dextran staining. BBB proteins gene expression (TJs efflux transporters and detoxification enzymes) was determined on cortex and plexus. A group of pups was treated with melatonin (5 mg/kg, intraperitoneal).
Results Dextran extravasation was found 2 h after the insult, suggesting a rapid BBB breakdown that resolved at +4 h. A significant reduction in extravasation was observed in melatonin-treated pups. Molecular Biology, immunohistochemistry and electron microscopy showed a dynamic BBB modification during the first 4 h, partially reversed with melatonin. Lesion size evaluation confirmed melatonin white matter neuroprotection.
Interpretation Our study, for the first time, evaluates the BBB at a very early time point, and it demonstrates that excitotoxicity causes early BBB disruption and that at this phase melatonin neuroprotects by preventing TJ proteins modifications, before acting as an anti-inflammatory and antioxidant molecule, and promoting axonal regrowth.