Astrocytes: Blood Brain Barrier

Astrocytes help form the blood brain barrier. The blood brain barrier prevents harmful materials from moving out of the bloodstream and into the brain. It helps maintain an ion gradient and is important in the transport of materials into and out of the brain. Its endothelial cells contain many tight and adherens junctions, which make the endothelial cells of these capillaries tighter than in other places in the body. Astrocyte feet are in physical contact with the capillary endothelial cells. In order to regulate the blood brain barrier, the astrocyte feet secrete molecules that regulate the tight junctions.
Astrocytes play a role in the reuptake of neurotransmitters. They also have a role in providing activity dependent metabolic support to neurons. This is done via the lactate shuttle. When an action potential is fired, some presynaptic neurons release glutamate into the synapse. The glutamate response is eventually terminated by the reuptake of glutamate in astrocytes. Within the astrocyte, the glutamate is converted to glutamine. Then, the glutamine is transported from the astrocyte to the presynaptic cell. In the presynaptic cell, the glutamine is converted back to glutamate,
During the reuptake of glutamate (from the synapse to the astrocyte), glutamate was cotransported into the astrocyte with Na+. This resulted in an increased concentration of Na+ inside the astrocyte. The increased Na+ concentration activated the sodium potassium pumps. This, in turn, activated glycolysis to produce glucose. Glucose was converted into lactate. The lactate was shuttled from the astrocyte to the presynaptic neuron. Within the presynaptic neuron, the lactate was converted back to glucose and glucose was used to produce ATP though the Krebbs cycle and oxidative phosphorylation. In other words, astrocytes provide the metabolic support neurons need via lactate