Microglial cells are the resident macrophages in the central nervous system. These cells of mesodermal/mesenchymal origin migrate into all regions of the central nervous system, disseminate through the brain parenchyma, and acquire a specific ramified morphological phenotype termed "resting microglia." Recent studies indicate that even in the normal brain, microglia have highly motile processes by which they scan their territorial domains. By a large number of signaling pathways they can communicate with macroglial cells and neurons and with cells of the immune system. Likewise, microglial cells express receptors classically described for brain-specific communication such as neurotransmitter receptors and those first discovered as immune cell-specific such as for cytokines. Microglial cells are considered the most susceptible sensors of brain pathology. Upon any detection of signs for brain lesions or nervous system dysfunction, microglial cells undergo a complex, multistage activation process that converts them into the "activated microglial cell." This cell form has the capacity to release a large number of substances that can act detrimental or beneficial for the surrounding cells. Activated microglial cells can migrate to the site of injury, proliferate, and phagocytose cells and cellular compartments.

Physiology of Microglia

Molecular profile of reactive astrocytes—Implications for their role in neurologic disease

Turnbull, Andrew V., and Catherine L. Rivier. Regulation of the Hypothalamic-Pituitary-Adrenal Axis by Cytokines: Actions and Mechanisms of Action. Physiol. Rev. 79: 1–71, 1999. — Glucocorticoids a...

Regulation of the Hypothalamic-Pituitary-Adrenal Axis by Cytokines: Actions and Mechanisms of Action

The present review summarizes recently acquired data in vivo, which support a role of CNS microglia as a source of defense cells in the CNS capable of carrying out certain immune functions autonomously. We have kept the following discussion restricted to microglial cells and have not included work on the immunological functions of astrocytes, which has been recently reviewed elsewhere (Fontana et al.: Immunological Reviews 137:3521-3527, 1987). Resting microglia are scattered uniformly throughout the CNS forming a network of potential immunoeffector cells, which can be activated by stimuli ranging from peripheral nerve injury over viral infections to direct mechanical brain trauma. The term "activated microglia" is used here to describe proliferating cells that demonstrate changes in their immunophenotype but have not undergone transformation into brain macrophages. Such a transformation can be stimulated by neuronal death but not by sublethal neuronal injury. Microglia may function as antigen-presenting cells and may thus represent the effector cell responsible for the recruitment of lymphocytes to the brain resulting in an inflammatory reaction. The recent developments in the understanding of microglial cell function may lead to a redefinition of the often cited "immune privilege" of the brain.

Functional plasticity of microglia: a review.

Myofibroblasts are a unique group of smooth-muscle-like fibroblasts that have a similar appearance and function regardless of their tissue of residence. Through the secretion of inflammatory and an...

Myofibroblasts. I. Paracrine cells important in health and disease.

Neuron theory, the cornerstone of neuroscience, on the centenary of the Nobel Prize award to Santiago Ramón y Cajal.

Co-expression of glial fibrillary acidic protein and vimentin in reactive astrocytes following brain injury in rats.

A lectin-histochemical study on microglial development has been performed on the rat central nervous system. Isolectin B4 from the Griffonia simplicifolia (GSA I-B4) and Ricinus communis agglutinin-120 (RCA-1) were used as labelling lectins. Our results demonstrate the existence of microglial elements in the nervous parenchyma at E18, derived from the meningeal connective tissue layer. Later, another microglial source became evident, namely the cavum septum pellucidum, which serves for entrance of microglia pervading the supraventricular corpus callosum and the subependyma of the lateral ventricles. From P12 onwards, the microglial sources became inactive.

A lectin histochemistry study on the development of rat microglial cells.

Immunoperoxidase methods for the demonstration of three glial antigens, vimentin, glial fibrillary acidic protein, and S-100 protein, were applied to routine-fixed paraffin sections of rat pineal gland. A pre-embedding electron microscope immunoperoxidase method was also used to study the ultrastructural localization of S-100 protein in pineal cells. Light and electron microscopic results showed the presence of these antigenic glial markers in the second pineal cell type. The term glial cell is proposed for the second of parenchymatous cell in rat pineal gland.

/pdf/presence-of-glial-cells-in-the-rat-pineal-gland-a-light-and-2tupkmxygj.pdf

J. Boya

Papers

Neuron theory, the cornerstone of neuroscience, on the centenary of the Nobel Prize award to Santiago Ramón y Cajal.

Co-expression of glial fibrillary acidic protein and vimentin in reactive astrocytes following brain injury in rats.

A lectin histochemistry study on the development of rat microglial cells.

Presence of glial cells in the rat pineal gland: A light and electron microscopic immunohistochemical study

Ultrastructural study on meningeal regeneration and meningo-glial relationships after cerebral stab wound in the adult rat.