Postnatal development of rat cerebellum: Glycosaminoglycan changes related to variation in water content, cell formation and organ growth

Changes in the cerebrospinal fluid circulatory system of the developing rat: quantitative volumetric analysis and effect on blood-CSF permeability interpretation

Background

The cerebrospinal fluid (CSF) circulatory system is involved in neuroimmune regulation, cerebral detoxification, and delivery of various endogenous and exogenous substances. In conjunction with the choroid plexuses, which form the main barrier site between blood and CSF, this fluid participates in controlling the environment of the developing brain. The lack of comprehensive data on developmental changes in CSF volume and distribution impairs our understanding of CSF contribution to brain development, and limits the interpretation of blood-CSF permeability data. To address these issues, we describe the evolution of the CSF circulatory system during the perinatal period and have quantified the volume of the different ventricular, cisternal and subarachnoid CSF compartments at three ages in developing rats.

Methods

Immunohistofluorescence was used to visualize tight junctions in parenchymal and meningeal vessels, and in choroid plexus epithelium of 19-day fetal rats. A quantitative method based on serial sectioning of frozen head and surface measurements at the cutting plane was used to determine the volume of twenty different CSF compartments in rat brain on embryonic day 19 (E19), and postnatal days 2 (P2) and 9 (P9). Blood-CSF permeability constants for sucrose were established at P2 and P9, following CSF sampling from the cisterna magna.

Results

Claudin-1 and claudin-5 immunohistofluorescence labeling illustrated the barrier phenotype acquired by all blood–brain and blood-CSF interfaces throughout the entire CNS in E19 rats. This should ensure that brain fluid composition is regulated and independent from plasma composition in developing brain. Analysis of the caudo-rostral profiles of CSF distribution and of the volume of twenty CSF compartments indicated that the CSF-to-cranial cavity volume ratio decreases from 30% at E19 to 10% at P9. CSF compartmentalization within the brain changes during this period, with a major decrease in CSF-to-brain volume ratio in the caudal half of the brain. Integrating CSF volume with the measurement of permeability constants, adds to our understanding of the apparent postnatal decrease in blood-CSF permeability to sucrose.

Conclusion

Reference data on CSF compartment volumes throughout development are provided. Such data can be used to refine blood-CSF permeability constants in developing rats, and should help a better understanding of diffusion, bulk flow, and volume transmission in the developing brain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12987-015-0001-2) contains supplementary material, which is available to authorized users.

Neurotrophic growth factors stimulate glycosaminoglycan synthesis in identified retinal cell populations in vitro

Glycosaminoglycans (GAG) are known to participate in central nervous system processes such as development, cell migration, and neurite outgrowth, but little is known with respect to their regulation through soluble neurotrophic factors. In the present study, we have addressed this issue using cell culture models of three distinct cell populations derived from young rat retinas, namely, purified M uller glia, pigmented epithelium, and neurons respectively. Cultures were maintained in chemically defined media in the presence or absence of either basic fibroblast or epidermal growth factor. In control glial and epithelial cultures, hyaluronic acid dominated the soluble GAG pool, with lesser contributions from dermatan sulfate, chondroitin sulfate, and heparan sulfate (in decreasing order). Retinal neuronal GAG were almost exclusively chondroitin sulfate (approximately 90%). Treatment of glial and epithelial cultures with either factor led to dose-dependent increases in especially hyaluronic acid synthesis (a maximum 6-fold increase relative to control levels), with smaller but consistent changes in chondroitin sulfate. Similar treatment of retinal neurons did not lead to any changes in GAG synthesis. These data indicate that glia and pigment epithelia are the principal sources of GAG components in retina at least in vitro, and that endogenous neurotrophic growth factors can greatly modify GAG synthesis in these two retinal cell populations. Such data suggest that a delicate balance may exist between growth factor availability and glycoconjugate metabolism in vivo, participating in normal or pathological states of the retina.

Some observations on the localization of hyaluronic acid in adult, newborn and embryonal rat brain

Hyaluronic acid was localized in acetone-fixed cryostat sections of brain and spinal cord obtained from adult, newborn and embryonal rat. The sections were incubated with glial hyaluronate-binding protein (GHAP) of human origin and the protein was visualized by indirect immunofluorescence with monoclonal antibodies raised to human GHAP and not staining rat brain by immunofluorescence. GHAP is a brain extracellular matrix (ECM) glycoprotein, approximately 60,000 molecular weight, which is structurally related to the HA-binding region of cartilage ECM proteins. The distribution of hyaluronate in adult brain white matter and cerebellar cortex was similar to that previously reported for GHAP. In both cases, the reaction product formed a mesh surrounding myelinated axons and granule cells. Hyaluronate was also found in parts of the brain that did not contain GHAP. A finely reticulated mesh was observed in the neuropil between cell bodies in cerebral cortex and basal ganglia. Scattered cortical neurons were surrounded by a rim of reactive material. Perineural staining was the rule rather than the exception in spinal cord anterior horn motoneurons, inferior olivary nucleus, large bulbar reticular neurons and dentate nucleus of cerebellum. The only part of the brain which appeared relatively free of hyaluronate was the molecular layer of the cerebellum. In newborn and embryonal rat, the densely packed cell bodies in cerebral gray matter, periventricular germinal layer and external granular layer of cerebellum were surrounded by hyaluronate. Small droplets of hyaluronate were observed in between the cylindrical epithelial cells lining the neural tube in 11 day embryos. Non-myelinated fiber tracts and the molecular layer of the developing cerebellum were relatively unstained. No hyaluronate was detected in the ependyma lining the cerebral ventricles and the central canal of the spinal cord.

Developing rat cerebellum--II. Effects of abnormal thyroid states and undernutrition on hyaluronic acid

The early postnatal pattern of hyaluronic acid (HA) deposition in rat cerebellum is affected by thyroid deficiency, thyroxine treatment and undernutrition. The modification of HA ontogenesis apparently reflects the smaller number of cells formed in undernourished rats, or alterations of cell maturation (accelerated in thyroxine-treated and slowed down in thyroid-deficient rats). The developmentally regulated loss of tissue water is also affected in the three conditions; this can be correlated with the roughly simultaneous disappearance of extracellular, but not of total, HA.

Developing rat cerebellum--I. Effects of abnormal thyroid states and undernutrition on sulfated glycosaminoglycans

Sulfated glycosaminoglycans deposition during rat postnatal cerebellar developmental is affected by altered thyroid states and undernutrition. These ontogenetic alterations seem not to be specific but to be one aspect of the general acceleration, slowing down and reduction of the cerebellar development occurring in thyroid-deficient, hyperthyroid and undernourished rats, respectively.

Histochemical distribution of acid glycosaminoglycans in rat cerebellum during postnatal development: neuropile

Developmentally regulated modifications of glycosaminoglycans (GAGs) in the central nervous system (CNS) have suggested that also in the CNS, these compounds might participate in morphogenesis and nerve cell differentiation. However very few studies have been reported concerning the regional distribution of these compounds by histochemical techniques. We have used the Alcian Blue staining method also in conjunction with enzymatic digestion and with a technique which allowed the measurement of the degree of GAG sulphatation. The combination of the three techniques showed that during the first week GAGs, presumed to be hyaluronic acid, are localized throughout the neuropile of the entire cerebellum and especially in the medullary region. Sulphated glycans appear later in the medullary region (particularly at the border between the medullary region and the internal granular layer) and in all the layers of cerebellum (in particular around the Purkinje and deep cerebellar nuclei neurons and possibly in the cerebellar glomeruli). Sulphated glycans in the medullary region disappear around the 12th day when myelination starts. The transient presence of glycoproteins in the molecular layer was also detected.