http://www.smhc.org.cn/uploadfiles/2014/09/20140929090442442.pdf

A Meta-Analysis of Cytokines in Major Depression

Structure and function of the blood–brain barrier

The blood-brain barrier (BBB) is formed by the brain capillary endothelium and excludes from the brain ∼100% of large-molecule neurotherapeutics and more than 98% of all small-molecule drugs. Despite the importance of the BBB to the neurotherapeutics mission, the BBB receives insufficient attention in either academic neuroscience or industry programs. The combination of so little effort in developing solutions to the BBB problem, and the minimal BBB transport of the majority of all potential CNS drugs, leads predictably to the present situation in neurotherapeutics, which is that there are few effective treatments for the majority of CNS disorders. This situation can be reversed by an accelerated effort to develop a knowledge base in the fundamental transport properties of the BBB, and the molecular and cellular biology of the brain capillary endothelium. This provides the platform for CNS drug delivery programs, which should be developed in parallel with traditional CNS drug discovery efforts in the molecular neurosciences.

https://link.springer.com/content/pdf/10.1602%2Fneurorx.2.1.3.pdf

The Blood-Brain Barrier: Bottleneck in Brain Drug Development

Neuronal calcium signaling

The blood-brain barrier: an overview: structure, regulation, and clinical implications.

One mechanism by which blood-borne cytokines might affect the function of the central nervous system (CNS) is by crossing the blood-brain barrier (BBB) for direct interaction with CNS tissue. Saturabl

Passage of Cytokines across the Blood-Brain Barrier

Pathways traversed by peripherally administered protein tracers for entry to the mammalian brain were investigated by light and electron microscopy. Native horseradish peroxidase (HRP) and wheat germ agglutinin (WGA) conjugated to peroxidase were administered intranasally, intravenously, or intraventricularly to mice; native HRP was delivered intranasally or intravenously to rats and squirrel monkeys. Unlike WGA-HRP, native HRP administered intranasally passed freely through intercellular junctions of the olfactory epithelia to reach the olfactory bulbs of the CNS extracellularly within 45-90 minutes in all species. The olfactory epithelium labeled with intravenously delivered HRP, which readily escaped vasculature supplying this epithelium. Blood-borne peroxidase also exited fenestrated vessels of the dura mater and circumventricular organs. This HRP in the mouse, but not in the other species, passed from the dura mater through patent intercellular junctions within the arachnoid mater; in time, peroxidase reaction product in the mouse brain was associated with the pial surface, the Virchow-Robin spaces of vessels penetrating the pial surface, perivascular clefts, and with phagocytic pericytes located on the abluminal surface of superficial and deep cerebral microvasculature. Blood-borne HRP was endocytosed avidly at the luminal face of the cerebral endothelium in all species. WGA-HRP and native HRP delivered intraventricularly to the mouse were not endocytosed appreciably at the abluminal surface of the endothelium; hence, the endocytosis of protein and internalization of cell surface membrane within the cerebral endothelium are vectorial. The low to non-existent endocytic activity and internalization of membrane from the abluminal endothelial surface suggests that vesicular transport through the cerebral endothelium from blood to brain and from brain to blood does not occur. The extracellular pathways through which probe molecules enter the mammalian brain offer potential routes of passage for blood-borne and air-borne toxic, carcinogenic, infectious, and neurotoxic agents and addictive drugs, and for the delivery of chemotherapeutic agents to combat CNS infections and deficiency states. Methodological considerations are discussed for the interpretation of data derived from application of peroxidase to study the blood-brain barrier.

Avenues for entry of peripherally administered protein to the central nervous system in mouse, rat, and squirrel monkey.

Serum proteins bypass the blood-brain fluid barriers for extracellular entry to the central nervous system.

Reliable ultrastructural techniques are applied for cytochemical identification of glycogen and localization of glucose-6-phosphatase (G6Pase) activity within neurons and glia of the adult mammalian CNS. Modulations in the cerebral localizations of glycogen and G6Pase activity are identified during various experimental conditions (i.e., salt-stress, fasting, and trauma). The cytochemical reaction for demonstration of G6Pase activity implies that the enzyme acts as a phosphohydrolase to convert glucose-6-phosphate to glucose. The degradation of glycogen in vivo is one source of glucose-6-phosphate as a substrate for G6Pase. Glycogen is preserved by perfusion-fixation of the brain with 2% glutaraldehyde-2% formaldehyde. Chopper sections of this material are postfixed in buffered 1% osmium tetroxide-1.5% potassium ferrocyanide, which serves as a contrast stain for glycogen, or in buffered 1% osmium tetroxide. Plastic-embedded ultrathin sections of CNS tissue postfixed in 1% osmium tetroxide are stained for glycogen with periodic acid–thiocarbohydrazide-silver protein. Intracellular glycogen appears as electron-dense isodiametric particles and, under normal and experimental conditions, is most abundant within astrocytes. Neuronal glycogen is sparse to negligible normally but appears increased within specific neuronal populations during stressful states.



Optimal preservation of G6Pase activity in the brain is obtained by brief perfusion-fixation with 2% glutaraldehyde. Tissue sections are incubated in a modified Leskes medium containing glucose-6-phosphate or mannose-6-phosphate as substrate and lead nitrate. Utilizing the Gomori lead capture technique, G6Pase reaction product is localized within the lumen of the endoplasmic reticulum (ER) and related organelles (i.e., nuclear envelope, Golgi complex) of perikarya, dendrites, and glia. The ER in axons and axon terminals fails to express G6Pase activity under normal conditions but does so in some neurons exhibiting a degenerating appearance. A transient, cytochemical decrease in G6Pase activity may occur within some perikarya during stressed conditions.



The results indicate that within neurons and glia of the adult CNS cytochemical stains are well suited for ultrastructural identification of glycogen and localization of G6Pase activity. Modulations in glycogen particle concentration and in localization of G6Pase activity in the neuron can occur in response to conditions that influence the energy metabolism of the cell. These modulations may reflect differences in the regional utilization of glucose as an energy-producing substrate and as a derivative of glycogenolysis within the CNS.

Cytochemical identification of cerebral glycogen and glucose‐6‐phosphatase activity under normal and experimental conditions: I. Neurons and glia

Intracellular glycogen and glucose-6-phosphatase (G6Pase) activity were identified cytochemically within epithelia of the choroid plexus and ependyma of the cerebral ventricles including the median eminence and area postrema, the cerebral endothelium and pericytes from control, salt-stressed and fasted adult mice. Identification of glycogen was obtained by employing osmium tetroxide-potassium ferrocyanide and the periodic acid-thiocarbohydrazide-silver protein technique as ultrastructural contrast stains. A lead-capture method was used to localize G6Pase activity with glucose-6-phosphate or mannose-6-phosphate as substrate. Cerebral G6Pase functions predominantly as a phosphohydrolase to convert glucose-6-phosphate to glucose. Some glucose-6-phosphate in vivo may be derived from the breakdown of glycogen stores. Within the sampled cell types, presumptive glycogen appeared as electron-dense, isodiametric particles scattered throughout the cytoplasm. Reaction product for G6Pase activity was localized consistently within the lumen of the nuclear envelope and endoplasmic reticulum and frequently within an outer saccule of the Golgi complex under normal conditions. Choroid plexus epithelia from stressed mice exhibited a qualitative increase in cytoplasmic glycogen and a decrease in G6Pase activity; the other cell types did not express demonstrable alterations in glycogen concentration and G6Pase activity. The results indicate that glycogen and G6Pase activity are prevalent within non-neural cells of the adult mammalian CNS. Glucose utilization in the choroid plexus epithelium may be altered by stressful conditions that influence the functional activity of this cell.

Cytochemical identification of cerebral glycogen and glucose-6-phosphatase activity under normal and experimental conditions. II. Choroid plexus and ependymal epithelia, endothelia and pericytes.

Richard D. Broadwell

Papers

Passage of Cytokines across the Blood-Brain Barrier

Avenues for entry of peripherally administered protein to the central nervous system in mouse, rat, and squirrel monkey.

Serum proteins bypass the blood-brain fluid barriers for extracellular entry to the central nervous system.

Cytochemical identification of cerebral glycogen and glucose‐6‐phosphatase activity under normal and experimental conditions: I. Neurons and glia

Cytochemical identification of cerebral glycogen and glucose-6-phosphatase activity under normal and experimental conditions. II. Choroid plexus and ependymal epithelia, endothelia and pericytes.