Decreased number of cells in the inferior olivary nucleus of the adult mouse (+/sg) heterozygous for the staggerer gene

RORalpha, a pivotal nuclear receptor for Purkinje neuron survival and differentiation: from development to ageing

RORalpha (Retinoid-related Orphan Receptor) is a transcription factor belonging to the superfamily of nuclear receptors. The spontaneous staggerer (sg) mutation, which consists of a deletion in the Rora gene, has been shown to cause the loss of function of the RORalpha protein. The total loss of RORalpha expression leads to cerebellar developmental defects, particularly to a dramatic decreased survival of Purkinje cells and an early block in the differentiation process. This review focuses on recent studies which position RORalpha as a pivotal factor controlling Purkinje cell survival and differentiation, from development to ageing.

Regional brain variations of cytochrome oxidase activity inRelnrl-orl mutant mice

Cell malpositioning has been described in laminated structures of the spontaneous mutation, reeler, including the cerebellum, the hippocampus, and the neocortex. Despite the ectopic positions of different neuronal populations, the specificity of synaptic connections is maintained. The metabolic consequences of this form of neuropathology were examined in Reln(rl) mutant mice by quantitative measures of cytochrome oxidase (CO) activity, a mitochondrial enzyme essential for oxidative metabolism in neurons. Despite severe tissue disorganization but in line with the intact synaptic organization, the reeler mutation did not affect global metabolic activity of the laminated structures of the brain. CO activity, however, was altered in specific subregions of the cerebellum, hippocampus, and neocortex, as well as in septum and various brainstem (medial pontine, paramedial reticular, paragigantocellular reticular) regions anatomically related to these structures, attesting to large functional alterations in Reln(rl-orl) brain. Metabolic activity variations were also detected in the ventral tegmental area and ventral neostriatum of the mesolimbic dopaminergic pathway. The results are discussed and compared to the regional CO variations found in other ataxic mice, in regard to the structural defects, the integrity of the connections, and the mutation-specific effects.

Cell Counts of Purkinje and Inferior Olivary Neurons in the 'Hyperspiny Purkinje Cells' Mutant Mouse

The mutant mouse 'hyperspiny Purkinje cells' (hpc) has morphologically abnormal Purkinje cells and below normal intracerebellar calbindin-D28k, a calcium-binding protein that, in the cerebellum, is found only in the Purkinje cells. We counted the Purkinje cells on serial sections stained with thionin or labelled with anti-calbindin-D28k antibodies to investigate whether the depletion of the cerebellar content of calbindin-D28k was correlated with a reduced number of Purkinje cells. We also counted the inferior olivary neurons, as they are one of the major afferents of the Purkinje cells and also contain calbindin-D28k. The hpc mutant mice had 27% fewer cerebellar Purkinje cells and 12% fewer inferior olivary neurons than did controls. Their Purkinje cells were evenly immunostained but slightly atrophic. These data suggest that the depleted cerebellar calbindin-D28k content could be explained both by the loss of some Purkinje cells and the reduced size of the remaining ones.

Cerebellar contributions to instrumental learning

There is emerging evidence that the cerebellum is involved in spatial and nonspatial instrumental learning tasks. Cerebellar-lesioned animals have deficits in water maze learning tasks that may be explained by two-way interactions with higher order brain regions. There is suggestive evidence that cerebellar modulation extends to shock avoidance and discrimination learning. Although this evidence needs to be confirmed by a wider range of lesion methods and choice of learning tasks, it is in line with the hypothesis that the cerebellum affects cognitive processes and is not strictly concerned with motor control and the acquisition and retention of conditioned reflexes.

Analysis of protein variations in adult and postnatal day 11 staggerer and lurcher mutant mice

As an initial attempt at uncovering the molecular basis of cerebellar synaptogenic defects in the lurcher and staggerer mutant mice, the pattern of protein expression was compared between cerebellar and non-cerebellar tissues, between normal and mutant mice and between early postnatal and adult developmental stages. While cerebellar and mutation-specific alterations in the expression of proteins could be easily observed in adult tissues, no such alterations were observed in early postnatal lurcher mice and only one qualitatively unique protein species could reproducibly be identified in early postnatal staggerer mice.

Neuronal cell loss in heterozygous staggerer mutant mice: a model for genetic contributions to the aging process

Staggerer is a neurological mutation of mice that causes a severe ataxia correlated with digenesis of the cerebellar cortex. The Purkinje cell population in the homozygous mutant is reduced in size with a near total atrophy of dendritic structure. Further, the cells are ectopic and are reduced in number by about 75%. All of these phenotypes have been shown to be direct effects of the staggerer gene on the Purkinje cell itself. As an indirect consequence of gene action, virtually all of the cerebellar granule cells die as do 60% of the cells of the inferior olive. The mutation is described as recessive because of the heterozygote, +/sg, is behaviorally normal and the mature cerebellum shows none of the defects described in the homozygous mutant. We report here that, as the +/sg mouse advances in age, a syndrome of cell losses is observed. While these losses are not as severe as in the homozygote, by 12 months of age 35% of the Purkinje cells are gone, as are 35% of the granule cells and 40% of the cells in the inferior olive. We propose that these results illustrate a synergy between the aging process and the heterozygous genotype. Neither alone is sufficient to cause the cell loss. This interaction suggests that the +/sg represents a new model for the genetic contribution to regressive CNS changes during aging.

Peripheral macrophage abnormalities in mutant mice with spinocerebellar degeneration

We recently reported hyperproduction of interleukin-1 (IL1) and hyperexpression of IL1 beta mRNA, after in vitro activation by lipopolysaccharide (LPS) in peripheral macrophages of several neurological mutant mice, i.e. staggerer, lurcher, pcd and reeler, that exhibit patterns of neuronal degeneration in the cerebellum; in the present study, we investigated the expression of several cytokine mRNA in peripheral macrophages of other mutants with neuronal degeneration in the cerebellum or in the spinal cord to determine whether this genetic dysregulation is specific for IL1 beta or whether it reflects a generalized hyperexcitability of these macrophages. Hyperexpression of IL1 beta mRNA was present in the cerebellar mutants nodding and nervous, but not in weaver. A similar phenomenon was found, but to a lesser extent, in the spinal mutants dystonia musculorum, wobbler and motor neuron degeneration. On the contrary, no hyperexpression of IL1 beta mRNA was found in non-genetic models of neuronal degeneration (Wistar rats treated with X irradiation or with 3-acetyl-pyridine). In the heterozygote staggerer +/sg, which exhibits a late onset of cerebellar neuronal loss, hyperexpression was found not only in 12-month old animals but also in 2-month old ones, i.e. when the number of cerebellar neurons is still normal. Synthetic molecules (muramyl dipeptides) like MDP or murabutide (Mu), known as macrophage activators, were also efficient in inducing IL1 hyperexpression in sg/sg macrophages. Hyperexpression of two other cytokine mRNA, i.e. IL1 alpha and tumour necrosis factor alpha mRNA, was also detected in LPS-stimulated macrophages of staggerer and lurcher mutant mice. These data led us to conclude that the macrophages of spinal and cerebellar mutants are in a state of general hyperexcitability. Work is in progress to establish whether the cytokine abnormalities result from a defect intrinsic to the macrophages of the mutant mice or are secondary to the degenerative process ultimately leading to neuronal loss.

Evidence for a hyperexcitability state of staggerer mutant mice macrophages

We recently reported an abnormal production of interleukin-1 (IL-1) in peripheral macrophages of several neurological mutant mice that exhibit patterns of neuronal degeneration, especially in the cerebellum. After in vitro activation by lipopolysaccharide acid (LPS), these macrophages hyperexpress IL-1 beta mRNA and hyperproduce IL-1 protein in comparison with +/+ controls. In the present study, focused on the staggerer mutant mice, we investigate if this genetic dysregulation is specific for IL-1 beta or if it reflects a generalized hyperexcitability of these macrophages. The hyperexpression of IL-1 beta mRNA in sg/sg macrophages is present whatever the duration of LPS stimulation, even for periods as short as 15 min, although it reaches a maximum after 4 h of stimulation. The hyperinducibility of sg/sg macrophages is observed even when very low doses of LPS are used (0.01 microgram/ml) and reaches its maximum for 5 micrograms/ml LPS. Synthetic molecules (muramyl dipeptides), such as N-acetylmuramyl-L-alanyl-D-isoglutamine or murabutide, known as macrophage activators, are also efficient in revealing the cytokine hyperexpression in sg/sg macrophages. In addition, hyperexpression of two other cytokines, i.e., tumor necrosis factor-alpha and IL-1 alpha mRNAs, is also detected in LPS-stimulated macrophages of mutant mice. Finally, the effect of an inhibitor of protein synthesis, cycloheximide, is similar in +/+ and sg/sg macrophages. As a whole, these data lead us to conclude that the sg/sg macrophages are in a state of general hyperexcitability when compared with +/+ ones.

Olivary morphology and olivocerebellar topography in adult lurcher mutant mice

In adult lurcher mice, in which virtually all cerebellar Purkinje cells have degenerated as a direct consequence of mutant gene action, the inferior olivary complex suffers a severe retrograde transneuronal atrophy. Our analysis indicates a 63% cell loss in the lurcher inferior olive, homogeneously distributed between the medial and dorsal accessory, and principal olivary subdivisions. Olivary neurons are reduced in cross-sectional area by 30% in lurcher mice, compared to normal controls. All olivary subdivisions morphologically identifiable in normal mice are also found in the lurcher inferior olive. Analysis of olivocerebellar topography by retrograde transport of lectin-conjugated horseradish peroxidase and fluorogold, in both single and double labeling paradigms, reveals no abnormalities in the general organization of this highly ordered projection. This stability may be based on the initial establishment of the topographic pattern in late embryogenesis or early postnatal periods, prior to the onset of lurcher Purkinje cell degeneration, or, alternatively, the lurcher gene may not alter critical afferent and target characteristics at stages when the topographic relationship is being established. Once established, the olivocerebellar projection is apparently not dependent on the Purkinje cell for long-term maintenance of its general topographic organization.

Quantitative analysis of the Purkinje cell population during extreme ageing in the cerebellum of the Wistar/Louvain rat

The loss of neurons is viewed as one of several causes of the deterioration of neural function during ageing. However, the existing experimental evidence for an age-related decrease in the neuronal number may be misinterpreted due to the way the cells are counted and to the interference of unsuspected degenerative pathology of the animals studied. To reinvestigate this question we have quantified an easily identifiable population of neurons, the cerebellar Purkinje cells, in very old but healthy rats. The number of Purkinje cells in the cerebellum was assessed in two populations of rats: control (10 months) and old (42 months) rats from the Wistar/Louvain strain. In both groups, paraffin-embedded brains were cut serially in the sagittal plane. Purkinje cells were counted every 15 or 22 sections under the light microscope at a magnification of 1250 x. The raw value of cell counts were corrected according to the method of Hendry (21) in order to avoid the overestimation due to splitting of the nucleus during sectioning. The latero-lateral extent of the cerebellar cortex, obtained by multiplying the thickness of the section by the number of sections in which Purkinje cells were counted, was not statistically different (mean +/- standard deviation): 12.8 +/- 1.16 mm (n = 6) for the control rats and 12.0 +/- 1.02 mm for the old animals (n = 8) (Student's t-test, p = 0.18). The corrected number of the Purkinje cells (mean +/- standard deviation) was 330,350 +/- 35,448 cells (n = 6) for the control animals and 299,019 +/- 50,223 (n = 8) cells for the old rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 hyperproduction by in vitro activated peripheral macrophages from cerebellar mutant mice

Several mutations in mice produce complex patterns of neuronal degeneration of the cerebellum and of its afferent pathways. In the staggerer (sg/sg) mutant, atrophy of the lymphoid organs and immunological abnormalities have been described. To search for a possible link between the neurological and the immune disorders in this mutant, we studied the production by its peripheral macrophages of interleukin-1 (IL-1), which roles in both immune and nervous systems are well established. Suspensions of peritoneal and/or spleen macrophages from mutants and their appropriate controls were stimulated in vitro by lipopolysaccharide. Northern and dot blots, performed with murine IL-1 cDNA probes, revealed a clear-cut hyperexpression of IL-1 mRNA in staggerer macrophages. An IL-1 bioassay using the IL-1-responsive D10.G4 cell line also revealed a sixfold increase of IL-1 activity in the macrophage supernatants of staggerer mutant mice. The hyperproduction was found in 3-week to 1-year-old staggerer and also in heterozygous (+/sg) mice. A similar phenomenon existed in cerebellar mutants lurcher, Purkinje cell degeneration (pcd), and to a lesser extent reeler and wobbler, but was absent in the neurological mutants weaver, jimpy, and motor end plate disease (medH). These observations establish that in several point mutations in mice, central nervous degeneration is associated with dysregulation of IL-1 production by peripheral macrophages.

Glutamate dehydrogenase in cerebellar mutant mice: gene localization and enzyme activity in different tissues

Many similarities of both the inheritance pattern and the neuropathology can be observed between olivopontocerebellar atrophies, or so-called multiple system atrophies (MSAs), and murine cerebellar mutations like Purkinje cell degeneration, nervous, staggerer, weaver, and reeler. Our study aimed to test whether the glutamate dehydrogenase (GDH) deficiency observed in some MSA patients could be found also in any of the murine mutants. GDH activity was assayed in several organs of these mutants, and no general deficiency was detected. By contrast, the level was found to be elevated in the cerebellum. The GDH gene was localized on mouse chromosome 14 and does not map close to any known neurological mutation in the mouse. We conclude, for the moment, that none of these cerebellar mutant mice can be considered as an animal model for GDH-deficient MSA.

Regional and topographic organization of the olivocerebellar projection in homozygous staggerer (sg/sg) mutant mice: an anterograde and retrograde tracing study

The purpose of this investigation was to examine the organization of the olivocerebellar projection in the homozygous staggerer mouse. The adult stagger cerebellum is devoid of most Purkinje cells which are the primary target neurons for olivocerebellar fibers. Many of the remaining Purkinje cells are ectopic. In the first experiments, a small injection of a tritiated amino acid was placed into the staggerer inferior olivary complex. In coronal sections, longitudinal strips of labeled axons and olivocerebellar fiber terminals were separated by similarly oriented regions that contained little or no olivocerebellar fiber label. Within a given orthogonal band, olivocerebellar fiber terminal label was visualized around Purkinje cell soma and primary dendrites. The labeled olivocerebellar fiber axons were usually located just ventral to these labeled olivocerebellar fiber terminals. Analysis of the distribution of olivocerebellar fiber terminals in the staggerer cases indicated the presence of 10-11 distinct zones, which is slightly less than that reported in normal mice. In the next set of experiments, a small injection of horseradish peroxidase conjugated with wheat germ agglutinin was made into different mediolateral cerebellar regions. These results demonstrated that staggerer olivocerebellar fibers are entirely contralateral and are also organized topographically in a manner similar to the pattern seen in the normal animal. Thus, severe depletion and ectopia of staggerer Purkinje cells does not greatly alter olivocerebellar fiber organization.

Stability of inferior olivary neurons in rodents. I. Moderate cell loss in adult Purkinje cell degeneration mutant mouse

A light microscopic study and cell counts of the inferior olivary nucleus (ION) were performed in the Purkinje cell degeneration mutant mouse (pcd/pcd). Six groups of animals aged from 24 to 210 days were studied and compared to age matched (+/+) C57Bl.6J mice. A cell deficit of about 30% was found in the youngest animals studied; it did not change significantly with age. The deficit affects the 4 subnuclei of the ION, but predominates clearly in the medial accessory olive. This cell loss is already established at the moment when the massive loss of Purkinje cells that has been reported in this mutant occurs. Thus it is not yet known if the ION represents a primary site of gene action or if the deficit is secondary to another cellular event, presumably the loss of Purkinje cells.