[Blood brain barrier: development of a structure which supports the functional heterogeneity of the central nervous...

To analyze the functional reasons justifying the existence of the blood brain barrier with an emphasis on its fundamental role supporting neuroglial coupling.

We review in an integrated manner the contributions of different research areas in physiology and metabolism of the central nervous system which allow to understand the functional need for the existence of the blood brain barrier. In particular, we describe the physiological basis of the metabolic functional coupling and the metabolic interactions between neurons and glial cells, two properties directly derived from the presence of the blood brain barrier. Likewise the blood brain barrier is presented as an important determinant of the heterogeneous activation of cerebral tissue as detected by neuroimaging technologies as positron emission tomography and functional magnetic resonance imaging.

The main function of the blood brain barrier is to maintain a stable composition of the extracellular milieu in nervous tissue. This allows the changes in ionic composition and neurotransmitter concentration in the extracellular milieu, to reflect indirectly the generation of action potentials and the state of neurotransmission of neuronal circuits. Glial cells induce the development of the blood brain barrier and are the main sensors of neuronal function, due to their important take up capacity for extracellular potassium and neurotransmitters. Glial homeostasis of the extracellular milieu is circuit specific, limiting the functional metabolic coupling to discrete regions of the brain and generating the classical pattern of heterogeneous activity in the different modules of the nervous tissue.