ABSTRACT
There is increasing interest in the behavior of peptides at the mammalian blood-brain barrier (BBB). It is becoming clear that in addition to the presence of receptors for peptides there are mechanisms operating at the BBB for the transport of peptides into and out of brain. The BBB helps to maintain a constant internal environment for brain and spinal cord by acting as a selective filter, regulating the passage of substances between the general circulation and brain tissue. It has been established by electron microscopy that principal site of barrier or filter is the endothelial cell layer of blood capillaries supplying the brain. The role of pericytes, which are even closely associated with the endothelial cells, is unknown, but they have been implicated in blood vessel contractility and may have phagocytic properties. Endothelial cells of the cerebral circulation are exposed to peptides at luminal side from the blood and at the abluminal side from the extracellular fluid or from neurons.
