Regulation by interleukin-1beta of formation of a line of delimiting astrocytes following prenatal trauma to the brain of the mouse.

The regulation of perinatal glia limitans (GL) reformation by interleukin-1beta (IL-1beta) following prenatal neural trauma in the mouse was studied in lesioned fetal mice by immunocytochemistry and computer-assisted image analysis for presence and distribution of astrocytes and IL-1beta immunoreactivity (ir). Astrocytes stained with anti-glial fibrillary acidic protein (GFAP) were observed as a line of delimiting astrocytes (LDA) near the lesion edge on Postnatal Day 0 (P0, 2 days postlesion). At P6, a new and complete GL composed of GFAP-positive astrocytes was continuous with that of adjacent undamaged tissue. The new GL was located in the same area at P6 as was the LDA at P0, suggesting that the LDA is the precursor structure to a reformed GL. Astrocytes comprising the new GL were positive for anti-IL-1beta. The IL-1 receptor antagonist (IL-1ra), administered acutely into the lesion, produced a significantly decreased optical density of IL-1beta-ir at the LDA at P0 compared to animals that received injections of vehicle, human recombinant IL-1beta, or a combination injection of IL-1ra + IL-1beta. Furthermore, although GFAP-stained cells appeared at the lesion site, an organized LDA was not visible at P0 in IL-1ra-treated animals. Vehicle-, IL-1beta-, and combination-injected animals showed a robust LDA at the lesion site at P0. These data suggest that upregulation of IL-1beta in astrocytes and interaction of IL-1beta with the neural IL-1 receptor are important for reconstruction of the GL following prenatal lesion in the murine brain.

Cellular and molecular correlates to plasticity during recovery from injury in the developing mammalian brain.

In summary, our studies indicate that the perinatal mammalian brain shows considerable plasticity in response to trauma. Studies carried out both in vivo in the perinatal mouse brain and in vitro in cell line culture and organotypic slice cultures of developing brain tissue, indicate that the cytokine, interleukin-1 beta (IL-1 beta) regulates early healing responses that restore the integrity of the damaged structure and create conditions conducive to the sprouting of new connections involved in plasticity. In response to a lesion placed in the cerebral cortex in a late third trimester embryo, astrocytes form a line that delimits damaged tissue being removed by phagocytic macrophages from tissue that will remain part of the neural parenchyma. By six days after birth, this line of delimiting astrocytes (LDA) appears to become the new glial limiting membrane or glial limitans at the lesion site. A gliotic scar covers the new glial limitans, but no gliosis appears within the neural parenchyma itself. The expression of IL-1 beta is upregulated in astrocytes that form the LDA and is also upregulated in the parenchyma internal to the LDA. Experiments done in vivo where the type 1 interleukin-1 receptor was blocked via injection of interleukin-receptor antagonist protein (IL-ra) indicated that both LDA formation and wound closure were dependent upon interleukin type 1 receptor activation. To test the idea that IL-1 beta could directly influence astrocyte shape and orientation, in vitro studies were carried out on astrocytic C6 glioma cells in culture. IL-1 beta induced changes in cell shape and orientation similar to those seen in in vivo formation of the LDA. Addition of IL-1ra blocked IL-1 beta induced changes in C6 cells. IL-1 beta, then, acting upon its type 1 receptor, regulates astrocytic activities that, in vivo, produce successful healing in the perinatal brain. Studies in organotypic slice cultures of early postnatal mouse hippocampus parallel in vivo studies. Phagocytic cells, in this case, "reactive/activated" microglia, reach peak numbers immediately after injury induced by culture preparation. The round microglia were replaced over 10 days in culture by "resting/ramified" microglia. Over the first 2 days of culture, astrocytes appeared thin and elongated, resembling cells that form the LDA in vivo. Over the next 8 days in cultures, astrocytes underwent hypertrophy to form a gliotic scar over the surface of the culture. The scar resembled that seen external to the LDA after healing in in vivo experiments. IL-1 beta was abundantly expressed throughout the culture period by cells showing a variety of morphologies. Finally, neurite sprouting, an indicator of circuit reorganization and plasticity, occurred rapidly in the hippocampal dentate gyrus in both in vivo and in vitro paradigms. A prenatally placed lesion in the entorhinal cortex that partially deafferents the developing dentate gyrus, induced novel sprouting of the axons of dentate granule cells, the mossy fibers, into the dentate molecular layer. Similar sprouting occurred in vitro in organotypic slice culture of deafferented hippocampus. In culture, sprouting was first observed at the time of onset of astrocyte hypertrophy, indicating that astrocyte derived factors may play a role in regulating circuit reorganization. Viewed together, in vivo and in vitro studies indicate that IL-1 beta upregulation in neural tissue correlates with glial activities that underlie rapid healing and repair in the perinatal brain, and that glial activities associated with deafferentation may play a role in inducing compensatory neurite sprouting and cicuit reorganization.

Chemoarchitectonic subdivisions of the visual pulvinar in monkeys and their connectional relations with the middle temporal and rostral dorsolateral visual areas, MT and DLr.

The organization of the inferior pulvinar complex (PI) in squirrel monkeys was studied with histochemical localization of the calcium binding proteins calbindin-D28k and parvalbumin, and of cytochrome oxidase. With each of these markers, the inferior pulvinar complex can be subdivided into four distinct regions. Calbindin-D28k immunoreactivity is densely distributed in cells and neuropil within PI, except for a distinct centromedially located gap. This calbindin-poor zone, termed the medial division of the inferior pulvinar (PIM), corresponds precisely to a region that contains elevated cytochrome oxidase activity and parvalbumin immunostaining. The PIM extends slightly above and behind the classically defined limit of the inferior pulvinar, the corticotectal tract. Regions of inferior pulvinar with intense immunostaining for calbindin-D28k were the posterior division of the inferior pulvinar (PIP, medial to PIM) and the central division (PIC, lateral to PIM). A newly recognized lateral region, PIL, adjoins the lateral geniculate nucleus and stains more lightly for calbindin and parvalbumin immunoreactivity and for cytochrome oxidase. Staining patterns for calbindin, parvalbumin, and cytochrome oxidase in the pulvinar of rhesus monkeys closely resemble those shown in squirrel monkey inferior pulvinar, suggesting that a common organization exists in all primates. In order to examine cortical connection patterns of the histochemically defined compartments in the inferior pulvinar, injections of up to five neuroanatomical tracers (wheat germ agglutinin conjugated to horseradish peroxidase and fluorescent retrograde tracers) were placed in the same cerebral hemisphere. Single injection sites were in the middle temporal area (MT), and several separate injections were placed in a strip corresponding to the rostral subdivision of the dorsolateral area (DLr). Injections that involved only DLr and not MT labeled principally the PIC, and more sparsely PIP and PIL. DLr connections occupied a "shell" region dorsal to PIM that extended from PIC into the lateral and medial divisions of the pulvinar, PL and PM. Injection sites that included MT or were largely restricted to MT produced dense label in PIM and moderate label in PIC and PIL. The retinotopic organization within the inferior pulvinar was inferred from patterns of connections. Connections with cortex related most closely to central vision were found posteriorly in PIM and in adjacent portions of PIC as it wraps around the caudal pole of PIM. Cortex related to more peripheral locations in the lower visual field connected with more rostral PIM and PIC. Patterns of label within the portions of PL and PM that were immediately adjacent to PIM roughly paralleled those in PIM and PIC.(ABSTRACT TRUNCATED AT 400 WORDS)