Glial cells central nervous system

Category of glial cells in the vertebrate central nervous system with long radial processes. Astrocytes provide structural support to neive cells and help to control their chemical and ionic extracellular environment. 

The blood-brain barrier (BBB) forms a physiological barrier between the central nervous system and the blood circulation. It consists of glial cells and a special species of endothelial cells, which form tight junctions between each other thereby inhibiting paracellular transport. In addition, the endothelial cells of the BBB express a variety of ABC-transporters to protect the brain tissue against toxic metabolites and xenobiotics. The BBB is permeable to water, glucose, sodium chloride and non-ionised lipid-soluble molecules but large molecules such as peptides as well as many polar substances do not readily permeate the battier. 

In the central nervous system (CNS) the concept that localized microdomains of calcium are responsible for triggering vesicle fusion generally refers to neurons (Rizzuto and Pozzan 2006). Concerning glial cells although the existence of structural... 

Ahn SY, Cho CH, Park KG, Lee HI, Lee S, Park SK, Lee IK, Koh GY (2004) Tumor necrosis factor-alpha induces fractaUdne expression preferentially in arterial endothelial cells and mithramycin A suppresses TNF-alpha-induced fractaUdne expression. Am J Pathol 164 1663-1672 Alfano M, Schmidtmayerova H, Amelia CA, Pushkarsky T, Bukrinsky M (1999) The B-oligomer of pertussis toxin deactivates CC chemokine receptor 5 and blocks entry of M-tropic HIV-1 strains, [see comments]. J Exp Med 190 597-605 Ambrosini E, Alois F (2004) Chemokines and glial cells a complex network in the central nervous system. [Review] [239 refs]. Neurochem Res 29 1017-1038 Azuma Y, Ohura K (2002) Endomorphins 1 and 2 inhibit IL-10 and IL-12 production and innate immune functions, and potentiate NE-kappaB DNA binding in THP-1 differentiated to macrophagelike cells. Scand J Immunol 56 260-269... 

The central nervous system, CNS, includes both neurons and glial cells. The peripheral nervous system, PNS, has no glial cells. 

Figure 14.4 Different types of glial cells. Astrocytes connect capillaries and neurones. Fibrous astrocytes, with less branching and more filamentous processes, occur mainly in white matter while protoplasmic astrocytes are located principally in the grey matter. Oligodendrocytes form the myelin sheath by wrapping themselves around axons. The connection between the myelin sheath and the oligodendrocyte is permanent and provides material for the myelin sheath. Microgliocytes (microglia) are the phagocytes of the nervous system. The ciliated ependymal cells line the cavities of the central nervous system.

The entry of toxins into the brain and central nervous system (CNS) is frequently more difficnlt than into other tissues. The function of this blood-brain barrier is related to impaired permeability of the blood capillaries in brain tissne, the necessity for toxins to penetrate glial cells, and the low protein content of the CNS interstitial flnid (Klaassen, 1986). Lipid solnbihty of a toxin is an important factor in the penetration of the blood-brain barrier. 

Wei, L.C., Shi, M., Chen, L.W., Cao, R, Zhang, P., Chan, Y.S. (2002). Nestin-containing cells express glial fibrillaiy acidic protein in the proliferative regions of central nervous system of postnatal developing and adult mice. Brain Res Dev Brain Res, 139, 9-17. 

Morshead, C.M., Garcia, A.D., Sofroniew, M.V., van Der Kooy, D. (2003). The ablation of glial fibrillary acidic protein-positive cells from the adult central nervous system results in the loss of forebrain neural stem cells but not retinal stem cells. Eur J Neurosci, 18, 76-84. 

The A3AR is expressed in relatively high densities in lung, liver, neutrophils, macrophages, and glial cells. In the heart and brain, there are distinct effects on cell survival, but the A3AR is expressed at a much lower level. Its presence on neurons in the central nervous system was controversial, but now well established (Lopes et al. 2003 Yaar et al. 2002). 

Activated macrophages and microglia are likely cellular sources of IL-1 in the central nervous system. IL-la and p, both 17-kDa proteins, are the products of two distinct genes and produce many of the same effects that TNF has on glial cells. IL-1 upregulates cytokine production, includes cell surface molecules, activates nitric oxide, and stimulates proliferation. When used alone, IL-1 and TNFa both stimulate nitric oxide production in C6 cells. However, in human fetal astrocyte cultures, IL-1 is a better nitric oxide inducer when used in combination with IFNy. 

Besides the well-established role of cytokines in the immune system, several recent reports demonstrated that chemokines also play a role in the central nervous system (CNS) (B2, Ml3). In the CNS, chemokines are constitutively expressed by microglial cells, astrocytes, and neurons, and their expression can be increased after induction with inflammatory mediators (M13). Chemokines are involved in brain development and in the maintenance of normal brain homeostasis, and play a role in the migration, differentiation, and proliferation of glial and neuronal... 

Glial cells play an important role in the control of pain in fact, it is known that neuronal plasticity is triggered by many inflammatory mediators and these are mainly produced by glial cells in the central nervous system. Indeed, in the past... 

Since the first description of glial cells, Camillo Golgi (1843-1926) and Santiago Ramon y Cajal (1852-1934) recognized that astrocytes are located in strategic positions between neurons and capillaries to act as a conduit for signals between different cells types in the central nervous system (CNS Ramon y Cajal, 1899). Later on, examination of the nervous system at the ultrastructural level has shown that astrocytes can be intimately associated with synapses, literally enwrapping many pre- and postsynaptic terminals. For instance, in the hippocampus, 57% of the axon-spine interfaces are associated with astrocytes (Ventura and Harris, 1999). It is likely that this close physical relationship provides an opportunity for many functional interactions between astrocytes and neurons. 

---