Reactive microgliosis.

Damage to the central nervous system (CNS) elicits the activation of both astrocytes and microglia. This review is focused on the principal features that characterize the activation of microglia after CNS injury. It provides a critical discussion of concepts regarding microglial biology that include the relationship between microglia and macrophages, as well as the role of microglia as immunocompetent cells of the CNS. Mechanistic and functional aspects of microgliosis are discussed primarily in the context of microglial neuronal interactions. The controversial issue of whether reactive microgliosis is a beneficial or a harmful process is addressed, and a resolution of this dilemma is offered by suggesting different interpretations of the term 'activated microglia' depending on its usage during in vivo or in vitro experimentation.

Chemokine receptor expression in cultured glia and rat experimental allergic encephalomyelitis.

Chemokines are a group of pro-inflammatory peptides that mediate leukocyte migration and activation. Several members of the chemokine family have been shown to be synthesized by cells of the central nervous system (CNS). To begin to address the role of chemokine receptors in CNS physiology, we identified, by molecular cloning techniques, the rat orthologs of the chemokine receptors, CCR2, CCR3, CCR5, and CXCR4. CCR2 and CCR5 expression was detected in rat spleen, lung, kidney, thymus and macrophages; CCR5 mRNA was also detected in rat brain. Primary cultures of rat microglia expressed CCR5 mRNA that was regulated by IFN-gamma, while both cultured astrocytes and microglia were found to contain mRNA for CXCR4 and CX3CR1. Induction of experimental allergic encephalomyelitis (EAE) in the rat was accompanied by increased levels of CCR2, CCR5, CXCR4, and CX3CR1 mRNAs in the lumbar spinal cords of animals displaying clinical signs of the disease. These data identify the rat orthologs of chemokine receptors and demonstrate that brain, spinal cord, and cultured glial cells express chemokine receptors that can be regulated both in vitro and in vivo.

Tracing of fluoro-gold prelabeled microglia injected into the adult rat brain.

In light of a recent interest in the transplantation of cultured microglial cells, we have examined the use of the fluorescent dye Fluoro-Gold (FG) as a tracer for these cells. Following injection into the adult rat brain, FG prelabeled microglial cells were readily traceable for up to 2 weeks with minimal labeling of endogenous cell populations. Some of the injected cells differentiated into ramified microglial cells as a result of exposure to the adult CNS environment. Injection of free FG into the adult rat brain resulted in the widespread labeling of neurons and perivascular cells, but not endogenous microglial cells, indicating that perivascular cells, but not resting microglia, are actively pinocytotic cells of the CNS. Our results show that FG is an effective label for the tracing of transplanted microglial cells.

Colonization of neural allografts by host microglial cells: relationship to graft neovascularization.

In order to illuminate functional roles of microglial cells within neural allografts, we have transplanted both whole and microglial and endothelial cell-depleted E14 neural cell suspensions into the intact striatum of Sprague-Dawley rats. Following posttransplantation times of up to 30 days, the intrastrial allografts were analyzed histochemically using the Griffonia simplicifolia B4 isolectin, a marker for both microglia and blood vessels. Our results indicate that both whole and depleted suspension grafts develop identically in terms of neovascularization and microglial colonization. In both types of transplants microglial cells appeared before any blood vessels were apparent. The main phase of graft vascularization occurred between days 7 and 10 posttransplantation and neovascularization was complete by day 21, as revealed by quantitative image analysis. Microglial cells, which were present as ameboid cells during early posttransplantation times, underwent continuing cell differentiation with time that paralleled graft vascular development. By 30 days posttransplantation microglia within the grafts had assumed the fully ramified phenotype characteristic of resting adult microglia. During graft development and vascularization, microglia were often seen in close proximity to ingrowing blood vessels and vascular sprouts. In conclusion, our study has shown that microglial colonization of grafts and graft vascularization occurs independent of donor-derived microglial and endothelial cells, and suggests that the great majority of microglia and vessels within the graft are host derived. We hypothesize that the host microglia invading the allografts play an active role in promoting graft neovascularization.

Characterization of myomodulin-related peptides from the pulmonate snail Helix aspersa.

Three myomodulin-related peptides--pQLSMLRLamide, PMSMLRLamide, and SLGMLRLamide--have been purified and sequenced from extracts of whole snails. The level of immunoreactive myomodulin was shown by HPLC and RIA to be widely distributed among 26 different snail tissues, with the highest levels (higher even than those in the central ganglia) occurring in certain male reproductive organs. Synthetic pQLSMLRLamide modified either the spontaneous rhythmic activity or the resting tone of several isolated muscular organs: the aorta, ventricle, upper gut, epiphallus, flagellum, and spermatheca; but the retractor muscles of the pharynx, penis, and tentacle were unaffected.

Lectin staining of sheep microglia.

The B4-isolectin from Griffonia simplicifolia is known to stain microglial cells in a variety of species. The present report describes a lectin staining method that has been modified to facilitate staining of resting microglia, as well as perivascular cells, in vibratome sections of normal sheep brain. This modified method employs tissue fixed in formaldehyde or paraformaldehyde and requires incubating sections with Triton X-100 prior to staining.