OBJECTIVE

The blood-brain barrier (BBB) is often perceived as a passive membrane. However, evidence has demonstrated that the BBB plays an active role in normal homeostasis and in certain disease processes.

METHODS

Approximately 300 peer-reviewed publications that discussed normal or abnormal BBB function were reviewed.

RESULTS

The role of the BBB and how it contributes to disorders of the central nervous system vary, depending on the specific disease process.

CONCLUSION

In health and disease and extending to old age, endothelial cells, neurons, and glia constitute a neurovascular unit that regulates the BBB. Advances toward penetrating the BBB must account for both normal and abnormal functions of the neurovascular unit.