Activation and deactivation of periventricular white matter phagocytes during postnatal mouse development.

Brain microglia are related to peripheral macrophages but undergo a highly specific process of regional maturation and differentiation inside the brain. Here, we examined this deactivation and morphological differentiation in cerebral cortex and periventricular subcortical white matter, the main "fountain of microglia" site, during postnatal mouse development, 0-28 days after birth (P0-P28). Only macrophages in subcortical white matter but not cortical microglia exhibited strong expression of typical activation markers alpha5, alpha6, alphaM, alphaX, and beta2 integrin subunits and B7.2 at any postnatal time point studied. White matter phagocyte activation was maximal at P0, decreased linearly over P3 and P7 and disappeared at P10. P7 white matter phagocytes also expressed high levels of IGF1 and MCSF, but not TNFalpha mRNA; this expression disappeared at P14. This process of deactivation followed the presence of ingested phagocytic material but correlated only moderately with ramification, and not with the extent of TUNEL+ death in neighboring cells, their ingestion or microglial proliferation. Intravenous fluosphere labeling revealed postnatal recruitment and transformation of circulating leukocytes into meningeal and perivascular macrophages as well as into ramified cortical microglia, but bypassing the white matter areas. In conclusion, this study describes strong and selective activation of postnatally resident phagocytes in the P0-P7 subcortical white matter, roughly equivalent to mid 3rd trimester human fetal development. This presence of highly active and IGF1- and MCSF-expressing phagocytes in the neighborhood of vulnerable white matter could play an important role in the genesis of or protection against axonal damage in the fetus and premature neonate.

Different patterns of axonal damage after intracerebral injection of malonate or AMPA.

White matter damage occurs following stroke and traumatic brain injury. In preclinical studies of potential therapies to reduce acute brain damage, it is important not only to understand the mechanisms by which this damage occurs, but also to employ techniques that fully quantify the extent of damage. In both respects, neurons have previously received greater attention than axons. The aim of the present study was to compare the extent of axonal damage visualised with different immunohistochemical markers following intracerebral injection of either the excitotoxin AMPA or the mitochondrial inhibitor malonate. Adult mice received intrastriatal injection of toxin and 24 h later the amount of white matter damage visualised with either amyloid precursor protein (APP) or neurofilament 200 (NF200) immunohistochemistry. Malonate induced a dose-dependent increase in the extent of axonal damage with either marker. However, AMPA induced a dose-dependent increase in the extent of axonal damage visualised by NF200 immunoreactivity but not by APP immunoreactivity. Malonate and AMPA also differed in their effects on other assessments of white matter integrity and (14)C-2-deoxyglucose autoradiography revealed the two toxins to differ in their initial effects on cerebral metabolism. These data indicate that the ability of commonly-used axonal damage markers to quantify the full extent of white matter damage differs following initial excitotoxicity or mitochondrial inhibition. We also confirmed that the markers reveal different extents of axonal damage in a rat model of focal cerebral ischaemia. Therefore, in preclinical studies designed to assess brain protecting agents, it is advisable to use more than one marker to quantify the true extent of axonal damage.

Gene expression of connective tissue growth factor in adult mouse.

The connective tissue growth factor (CTGF) is a well-known fibroblast mitogen and angiogenic factor that plays an important role in bone formation during embryogenesis. In the adult, CTGF is involved in wound healing as well as fibrotic and vascular disease. However, little is known about its physiological functions under non-pathological conditions in the adult organism. Here, we describe the cellular site of the CTGF mRNA expression in adult male and female mice as revealed by in situ hybridization histochemistry. Strong and persistent CTGF gene expression was particularly prominent in the mesenchyme of the cardiovascular system (aorta, auricular tissue, renal glomeruli), the mesenchyme surrounding the ovarian follicles or the testicular tubes in the gonadal tissue, and the subcapsular mesenchyme bordering densely innervated parts of whisker hair vibrissae. CTGF hybridization signals were not observed in the mesenchyme of many other organs including gut, muscle, liver or most parts of the lymphatic tissue. Strong expression was also present in the primary (early) ovarian follicles, the epithelium of the deep uterine glands and on myenteric ganglia neurons. These data suggest a selective and continuous mesenchymal function in the gonads and those tissues attracting very strong vascular supply or peripheral innervation. CTGF may also be involved in the cyclical proliferation of the uterine gland epithelium and in the early stages of follicular maturation, as well as in the neuropeptide regulation in the gut, cardiovascular and renal systems.