A novel ex vivo Huntington's disease model for studying GABAergic neurons and cell grafts by laser microdissection

Organotypic brain slice cultures have been recently used to study neurodegenerative disorders such as Parkinson’s disease and Huntington’s disease (HD). They preserve brain three-dimensional architecture, synaptic connectivity and brain cells microenvironment. Here, we developed an innovative model of Huntington’s disease from coronal rat brain slices, that include all the areas involved in the pathology. HD-like neurodegeneration was obtained in only one week, in a single step, during organotypic slice preparation, without the use of neurotoxins. HD-like histopathology was analysed and after one week, a reduction of 40% of medium spiny neurons was observed. To analyse new therapeutic approaches in this innovative HD model, we developed a novel protocol of laser microdissection to isolate and analyse by RT-qPCR, grafted cells as well as surrounding tissue of fresh organotypic slices. We determined that laser microdissection could be performed on a 400μm organotypic slice after alcohol dehydration protocol, allowing the analysis of mRNA expression in the rat tissue as well as in grafted cells. In conclusion, we developed a new approach for modeling Huntington's disease ex vivo, and provided a useful innovative method for screening new potential therapies for neurodegenerative diseases especially when associated with laser microdissection.

1,25-dihydroxyvitamin D3 regulates the synthesis of gamma-glutamyl transpeptidase and glutathione levels in rat primary astrocytes

Astrocytes play a pivotal role in CNS detoxification pathways, where glutathione (GSH) is involved in the elimination of oxygen and nitrogen reactive species such as nitric oxide. We have previously demonstrated that the specific activity of gamma-glutamyl transpeptidase (gamma-GT), an enzyme of central significance in GSH metabolism, is regulated in vivo in astrocytes by 1,25-dihydroxyvitamin D3 (1,25-D3). The aim of the present work was to investigate, in primary cultures of newborn rat astrocytes, the effects of this hormone on gamma-GT synthesis and on GSH and nitrite levels after lipopolysaccharide (LPS) treatment. This study demonstrates that both gamma-GT gene expression and specific activity, induced by LPS, are potentiated by 1,25-D3. In contrast, 1,25-D3 does not regulate the expression of other enzymes involved in astrocyte detoxification processes, such as superoxide dismutase or GSH peroxidase. In parallel, 1,25-D3 enhanced intracellular GSH pools and significantly reduced nitrite production induced by LPS. Taken together, these results suggest that gamma-GT, GSH, and 1,25-D3 play a fundamental role in astrocyte detoxification pathways.

Low affinity NGF receptor expression in the central nervous system during experimental allergic encephalomyelitis

In the central nervous system (CNS), p75, or low-affinity nerve growth factor receptor (LNGFR), is assumed to play a critical role in mediating the effects of neurotrophins on neuronal survival. Recent studies have shown that nerve growth factor (NGF) can act also on immune cells through its binding to p75. Using immunohistochemistry, we have investigated the expression of the p75 receptor in the CNS during chronic relapsing experimental allergic encephalomyelitis (EAE) of the Lewis rat, an animal model of multiple sclerosis (MS). We report here a sequential expression of p75, first in Purkinje cells during the first attack, and secondly on both endothelial and perivascular cells in the latter stages of the disease. Moreover, starting from the second attack, p75 was also expressed on glial ensheathing cells, likely myelinating cells, located primarily in the dorsal roots. These data suggest that during EAE, LNGFR may play an important role in leukocyte-endothelial cell interactions and in the maintenance of Purkinje cells survival.

Expression of inducible nitric oxide synthase during rat brain inflammation: regulation by 1,25-dihydroxyvitamin D3

This study, based on in situ hybridization and immunolabeling experiments, presents the time-course and cellular distribution of inducible NO synthase (iNOS) expression in a rat model of brain inflammation. Both intrahippocampal injection of lipopolysaccharide (LPS) or of buffer (stab lesion) induce an early, transient, and restricted expression of iNOS mRNA and immunoreactivity in the rat CNS. The topographic and phenotypic characteristics of iNOS-producing cells are distinct. After stab lesion, iNOS mRNAs, expressed at 5 h mainly in cells in the interventricular junction and in a few cells in brain parenchyma, were no more detectable from 15 h onwards, whereas the protein was faintly expressed in parenchymal cells at 15 h and 24 h. In contrast, after LPS injection, iNOS-mRNAs were detected from 5 to 24 h. iNOS-immunoreactivity was highly induced and sequentially observed first in choroid plexus and ependymal cells at 5 h, in monocytes and activated/reactive microglia at 15 h and 24 h, and finally in astrocytes at 72 h. In order to investigate potential regulatory effects of 1,25-dihydroxyvitamin D3 (1,25-D3) on iNOS expression, we have delivered this hormone with LPS or buffer into the rat hippocampus. 1,25-D3 significantly inhibits iNOS expression, at both the mRNA and immunoreactive protein levels, 15 h and 24 h after LPS injection, in the cells of the monocyte lineage. Moreover, 72 h after LPS injection, the addition of 1,25-D3 leads to a 6-fold increase in the number of macrophages around the lesion site, that correlates with a decrease in the proportion of apoptotic cells. Since 1,25-D3 can be produced by activated macrophages/microglia and since NO stimulates 1,25-D3 synthesis by macrophages, our results support the hypothesis that this hormone might be synthesized endogenously during CNS inflammatory reactions, thus explaining the transient and restricted iNOS expression observed after LPS intracerebral injection.

Early events of the inflammatory reaction induced in rat brain by lipopolysaccharide intracerebral injection: relative contribution of peripheral monocytes and activated microglia

We have previously demonstrated that lipopolysaccharide (LPS) intracerebral injection induced only minimal inflammatory reaction in rat brain, apart from an increased number of 'brain macrophages' observed 24 h after LPS administration [Montero-Menei et al., Brain Res., 653 (1994) 101-111]. However, the nature of these 'brain macrophages' in the inflammatory response is still unclear. The present study focused on the early time-points (from 5 h to 24 h) after LPS injection or stab-lesion, and was aimed at the identification of the peripheral (monocytes) or parenchymal (microglia) origin of these 'brain macrophages'. OX42- and ED1-labeling did not clearly discriminate between monocytes/macrophages and reactive microglia, both cell types being immunoreactive. In other experiments, rats were made aplasic by irradiation prior to lesioning. These experiments clearly demonstrated that LPS induces an intense monocyte recruitment and, to a lesser extent, microglial activation since about 80% of the cells present 24 h after LPS injection consisted of recruited monocytes not observed in aplasic rats. Interestingly, our data show that LPS exerts a sequential dual action by first inhibiting the monocyte recruitment observed 5 h after stab lesion and then enhancing it at 15 h and 24 h after injection. A possible involvement of cytokines, chemokines and adhesion molecules in the mechanisms occurring in the early events of brain inflammatory reaction is discussed.

Lipopolysaccharide intracerebral administration induces minimal inflammatory reaction in rat brain

An inflammatory reaction, essential for defence against infection and for wound repair, may also induce irreversible tissue damage. It appears that the central nervous system has developed its own immunosuppressive strategy in order to limit the destructive effects of inflammation. To clarify this point, we have characterized in one unique model of inflammation induced in the rat by intracerebral lipopolysaccharide injection the kinetics of the inflammatory reaction, the participation of immunitary and glial cells and of three growth factors. Among these molecules, brain-derived neurotrophic factor mRNA expression was found decreased following LPS injection. No striking differences were observed in the brain parenchyma after stab lesion or inflammatory lesion apart from an increase in the number of monocytes/macrophages recruited early to the lesion area. Macrophages were later accumulated around the lesion when astroglia and microglia reactions occurred. Some of the macrophages and microglia expressed major histocompatibility complex class II antigens on their surface whereas no T or B lymphocytes were observed in the brain parenchyma. However, a subpopulation of CD3- and CD4-negative CD8-positive cells, likely natural killer cells, was observed around the lesion site; this recruitment was inhibited by the highest dose of LPS. This study therefore supports the hypothesis of a suppression of some aspects of cell-mediated immunity in the brain, mechanisms which need to be further characterized.