Patrizia Aimar

Chain formation and glial tube assembly in the shift from neonatal to adult subventricular zone of the rodent forebrain.

The subventricular zone (SVZ) is regarded as an embryonic germinal layer persisting at the end of cerebral cortex neurogenesis and capable of generating neuronal precursors throughout life. The two distinct compartments of the adult rodent forebrain SVZ, astrocytic glial tubes and chains of migrating cells, are not distinguishable in the embryonic and early postnatal counterpart. In this study we analyzed the SVZ of mice and rats around birth and throughout different postnatal stages, describing molecular and morphological changes which lead to the typical structural arrangement of adult SVZ. In both species studied, most changes occurred during the first month of life, the transition being slightly delayed in mice, in spite of their earlier development. Important modifications affected the glial cells, eventually leading to glial tube assembly. These changes involved an overall reorganization of glial processes and their mutual relationships, as well as gliogenesis occurring within the SVZ which gives rise to glial cell subpopulations. The neuroblast cell population remained qualitatively quite homogeneous throughout all the stages investigated, changes being restricted to the relationships among cells and consequent formation of chains at about the third postnatal week. Electron microscopy showed that chain formation is not directly linked to glial tube assembly, generally preceding the occurrence of complete glial ensheathment. Moreover, chain and glial tube formation is asymmetric in the medial/lateral aspect of the SVZ, being inversely related. The attainment of an adult SVZ compartmentalization, on the other hand, seems linked to the pattern of expression of adhesion and extracellular matrix molecules. J. Comp. Neurol. 487:407–427, 2005.

Cellular composition and cytoarchitecture of the rabbit subventricular zone and its extensions in the forebrain

Persistent neurogenic sites, harboring neurogenic progenitor cells, which give rise to neuronal precursors throughout life, occur in different mammals, including humans. The telencephalic subventricular zone (SVZ) is the most active adult neurogenic site. Despite remarkable knowledge of its anatomical and cellular composition in rodents, detailed arrangement of SVZ in other mammals is poorly understood, yet comparative studies suggest that differences might exist. Here, by analyzing the cellular composition/arrangement in the SVZ of postnatal, young, and adult rabbits, we found a remarkably heterogeneous distribution of its chain and glia compartments. Starting from postnatal stages, this heterogeneity leads to a distinction between a ventricular SVZ and an abventricular SVZ, whereby the former contains small chains and isolated neuroblasts and the latter is characterized by large chains and a loose astrocytic meshwork. In addition to analysis of the SVZ proper, attention has been focused on its extensions, called parenchymal chains. Anterior parenchymal chains are compact chains surrounded by axon bundles and frequently establish direct contact with blood vessels. Posterior parenchymal chains are less compact, being squeezed between gray and white matter. In the shift from neonatal to adult rabbit SVZ, chains occur very early, both in the SVZ and within the brain parenchyma. Comparison of these results with the pattern in rodents reveals different types of chains, displaying a variety of relationships with glia or other substrates in vivo, an issue that might be important in understanding differences in the adaptation of persistent germinative layers to different mammalian brain anatomies. J. Comp. Neurol. 498:491–507, 2006.

The galactocerebrosidase enzyme contributes to maintain a functional neurogenic niche during early post-natal CNS development

We report a novel role for the lysosomal galactosylceramidase (GALC), which is defective in globoid cell leukodystrophy (GLD), in maintaining a functional post-natal subventricular zone (SVZ) neurogenic niche. We show that proliferation/self-renewal of neural stem cells (NSCs) and survival of their neuronal and oligodendroglial progeny are impaired in GALC-deficient mice. Using drugs to modulate inflammation and gene transfer to rescue GALC expression and activity, we show that lipid accumulation resulting from GALC deficiency acts as a cell-autonomous pathogenic stimulus in enzyme-deficient NSCs and progeny before upregulation of inflammatory markers, which later sustain a non-cell-autonomous dysfunction. Importantly, we provide evidence that supply of functional GALC provided by neonatal intracerebral transplantation of NSCs ameliorates the functional impairment in endogenous SVZ cells. Insights into the mechanism/s underlying GALC-mediated regulation of early post-natal neurogenic niches improve our understanding of the multi-component pathology of GLD. The occurrence of a restricted period of SVZ neurogenesis in infancy supports the implications of our study for the development of therapeutic strategies to treat this severe pediatric neurodegenerative disorder.

Post-natal development of the Reeler mouse cerebellum: An ultrastructural study

Reelin, an extracellular protein promoting neuronal migration in brain areas with a laminar architecture, is missing in the Reeler mouse (reelin(-/-)). Several studies indicate that the protein is also necessary for correct dendritic outgrowth and synapse formation in the adult forebrain. By transmission electron microscopy, we characterize the development and synaptic organization of the cerebellar cortex in Reeler mice and wild type control littermates at birth, postnatal day (P) 5, 7, 10 and 15. Ultrastructural analysis shows deep alterations in cortical architecture and mispositioning of the Purkinje neurons (Pns), which remain deeply embedded in a central cellular mass within the white matter, with highly immature features. Quantitative examination shows that Reeler mice display: (i) a lower density of granule cells and a higher density of Pns, from P10; (ii) a lower density of synaptic contacts between Pn dendrites and parallel or climbing fibers, from P5; (iii) a lower density of synaptic contacts between basket cells and Pns, from P5; and (iv) a lower density of mossy fiber rosettes, from P10. Our results demonstrate that Reelin profoundly affects the structure and synaptic connectivity of post-natal mouse cerebellum.

In Vivo Analysis of Cell Proliferation and Apoptosis in the CNS

The balance between cell proliferation and death is fundamental in several morphogenetic processes and ultimately determines the mass, shape, and function of the various tissues and organs that form the animal body. Apoptosis is a gene-regulated process of programmed cell death (PCD) that plays fundamental roles in several normal and pathological conditions (56,126). This form of “cell suicide” is most often detected during embryonic development, but is also found in normal cell and tissue turnover (26,77,81,133). Although the nervous tissue is traditionally regarded as being fundamentally constituted by postmitotic nonproliferating cells, analysis of cell proliferation and apoptosis in vivo has recently gained an increasing importance mainly considering that: (i) proliferative and/or apoptotic events have been extensively characterized not only during embryonic development but also in several areas of the postnatal and adult brain (9,10, 46,63–65,79,97,101); (ii) trophic factor deprivation often results in apoptotic cell death of target neurons (25,82,131); and (iii) links have been hypothesized between apoptosis and signal transduction (31,60).

Immuno-electromicroscopic approach for the study of neural stem cell niches

Immuno-electromicroscopic approach for the study of neural stem cell niches L. Bonfanti & P. Aimar & G. Ponti & N. Canalia Published online: 7 August 2008 # Springer Science + Business Media B.V. 2008

The Rabbit Subventricular Zone (SVZ): An Ultrastructural and Immunocytochemical Study

The subventricular zone (SVZ) is a germinative layer persisting throughout life within the mammalian telencephalon (Gage, 2000). In all species studied, the SVZ generates neuronal precursors which migrate toward the olfactory bulb, where they differentiate into interneurons (Lois and Alvarez-Buylla, 1994). In laboratory rodents, cell migration occurs in the form of chains of neuroblasts wrapped with an astrocytic sheath referred to as ‘glial tubes’ (Bonfanti and Theodosis, 1994; Peretto et al., 1997). Studies carried out in Primates have hypothesized that some SVZ-generated cells could also reach other cortical regions (Gould et al., 1999; Bernier et al., 2002). In a recent work performed on the rabbit telencephalon (Luzzati et al., 2003) we described the existence of ‘parenchymal chains’ localized between the SVZ and the cerebral cortex, which could theoretically be linked with such hypothesis. In the present study, we addressed the issue of rabbit SVZ internal arrangement. Using confocal and electron microscopy, we performed a detailed analysis of the young and adult rabbit SVZ, to identify its cell types and to investigate their mutual relationships.

Context-dependent toxicity of amyloid-β peptides on mouse cerebellar cells.

Alzheimers disease (AD) is the major cause of dementia in old people. AD pathology is characterized by amyloid-β (Aβ) deposits in several regions of the brain, and links have been hypothesized between Aβ toxicity and apoptosis. Cerebellar granule cells (CGCs) have been widely used as in vitro tools for molecular studies correlating apoptosis with AD, although the cerebellum is a relatively spared area of the brain in vivo. We have used mixed neuronal-glial cerebellar cultures (NGCCs) and organotypic cerebellar cultures (OCCs) obtained from postnatal mice to assess the toxic effect of the Aβ oligomer 1-40 (Aβ1-40) after propidium iodide uptake in vitro. Our results demonstrate that NGCCs, which are primarily composed of CGCs, are resistant to Aβ1-40 challenge (5-10 μM) when cultured in physiological (5 mM) extracellular KCl ([K+]e) concentrations, i.e., in a condition in which CGCs undergo full maturation. Conversely, when 10 μM Aβ1-40 is given to NGCCs cultured in elevated (25 mM) [K+]e (and thus maintained in an immature state), there is a statistically significant increase in cell death. Cell death is by apoptosis, as demonstrated by ultrastructural examination. OCCs are resistant to Aβ challenge in any of the conditions tested (variation of [K+]e, presence or absence of serum, or addition of the neprilysin blocker phosphoramidon). Altogether these observations lead us to conclude that cerebellar cells in an organotypic context may be less susceptible to damage by Aβ, raising the question whether isolated CGCs are a reliable assay in drug discovery studies of AD.

Immunocytochemical Labeling Methods and Related Techniques for Ultrastructural Analysis of Neuronal Connectivity

We describe a series of techniques based on the use of immunocytochemical labeling methods for the study of the neurochemistry and connectivity of cells within the central nervous system (CNS). According to our current view, neurons communicate to each other mainly at the level of synapses. Although it is now widely accepted that nonsynaptic neuron-to-neuron communication and neuron-to-glia crosstalk also occur, ultrastructural localization of transmitters–modulators at synapses and analysis of neuronal connections still remain major challenges for a correct understanding of the way in which neuronal networks are organized and operate.