Biomedical subjects

J Mariani

Publications and source records attributed to J Mariani.

At least 19 recordsLinked to original sources

PubMed1999

Afferent-target cell interactions in the cerebellum: negative effect of granule cells on Purkinje cell development in lurcher mice.

Lurcher (Lc) is a gain-of-function mutation in the delta2 glutamate receptor gene that results in a large, constitutive inward current in the cerebellar Purkinje cells of +/Lc mice. +/Lc Purkinje cells fail to differentiate fully and die during postnatal development. In normal mice, interactions with granule cells promote Purkinje cell dendritic differentiation. Partial destruction of the granule cell population in young +/Lc mice by x irradiation resulted in a significant increase in Purkinje cell dendritic growth and improved cytoplasmic structure but did not prevent Purkinje cell death. These results indicate two components to Purkinje cell abnormalities in +/Lc mice: a retardation/blockade of dendritic development that is mediated by interactions with granule cells and the death of the cell. Thus, the normal trophic effects of granule cell interaction on Purkinje cell development are absent in the +/Lc cerebellum, suggesting that granule cells are powerful regulators of Purkinje cell differentiation.

Afferent Pathways↗

PubMed1998

Severe atherosclerosis and hypoalphalipoproteinemia in the staggerer mouse, a mutant of the nuclear receptor RORalpha.

BACKGROUND: Hypoalphalipoproteinemia is the most common lipoprotein abnormality in patients with coronary artery disease, yet its causes are unknown. METHODS AND RESULTS: We show that the homozygous staggerer (sg/sg) mutant mouse, which carries a deletion within the nuclear receptor RORalpha gene, develops severe atherosclerosis when maintained on an atherogenic diet. In addition, sg/sg mice display a profound hypoalphalipoproteinemia, which is associated with decreased plasma levels of the major HDL proteins, apolipoprotein (apo) A-I and apoA-II. This decrease in HDL levels in sg/sg mice is due to lowered apoA-I gene expression in the intestine but not in the liver. ApoA-II gene expression is unaffected. CONCLUSIONS: These results suggest that the RORalpha gene contributes to the plasma HDL level and susceptibility to atherosclerosis.

Animals↗

PubMed1998

Abnormal IL-1beta cytokine expression in the cerebellum of the ataxic mutant mice staggerer and lurcher.

To assess the extent to which interleukin-1beta (IL-1beta) may contribute to the development and/or progression of neurodegenerative processes, we have examined the levels of IL-1beta in the brain of two types of neurological mutant mice, staggerer and Lurcher. Using a quantitative immunological method (enzyme-linked immunosorbent assay, ELISA), we measured IL-1beta in the cerebellum, hippocampus and cerebral cortex of mutant mice at baseline and after peripheral LPS treatment. Two types of IL-1beta expression abnormalities were found in the mutant cerebella: higher basal level in Lurcher and a response to peripheral administration of LPS in staggerer. The association of IL-1beta expression abnormalities with the only brain structure where a massive neurodegeneration occurs supports the role of proinflammatory cytokines in this process.

Animals↗

PubMed1998

Role of the cerebellum in exploration behavior.

Compared to +/+ mice, Lurcher (+/Lc) mutant mice whose cerebellar cortex is lacking almost all Purkinje cells and granule cells, exhibit a low level of exploration; this deficit is not due to a low level of activity but to both a decreased motivation to explore a novel environment and to spatial deficits. The characteristics of exploration in cerebellectomized +/+ and +/Lc mice suggest that the cerebellum is involved not only in cognitive but also in motivational processes.

Animals↗

PubMed1998

Sustained delivery of immunoglobulins from polymer microsources on a narrow surface of the developing rat brain.

Studies of postnatal neurogenesis have benefited from the use of a relatively non-invasive method for chronic delivery of bioactive substances to a restricted area of cortex. This method consists of the implantation of an Elvax polymer microsource of active substances close to the targeted brain surface. Receptor ligands, as well as macromolecules such as proteins, peptides and enzymes have been shown to be released by the implants in a sustained manner over weeks. Here we describe the kinetics and immunoreactivity of different immunoglobulins released in vitro and in vivo by Elvax polymer. In vitro, the immunoglobulins first diffuse during a burst phase from the pore network of the polymer matrix. Release continues during a slow phase depending on loading, porosity and volume of the matrix but also on intrinsic properties of immunoglobulins. Elvax microsources loaded either with anti-TAG-1 or with anti-HNK-1 antibodies according to the release data in vitro, are implanted on the posterior cerebellar cortex of postnatal rats during the period when the targeted antigens are expressed by the differentiating cells. After several days, the released immunoreactive antibodies are located at the antigenic sites within the cerebellar cortex close to the implants. The sustained local delivery of immunoglobulins using the Elvax implant method allows access to cell surface and matrix molecules and thereby to the mechanisms they control during postnatal neurogenesis.

Aging↗

PubMed1998

Quantitative analysis of cerebellar lobulation in normal and agranular rats.

Cerebellar pattern formation was investigated in rats treated with DNA modifying agents. Animals were subjected to combinations of daily injections of methylazoxymethanol acetate (MAM) for the last 6 days gestation and/or localised X-irradiation of the hindbrain on postnatal days 1 and 5 (P1 and P5). Animals were analysed on embryonic day 18 (E18), P0, P3, P7, and P14. Five parameters of the cerebellum were recorded from midsagittal sections: the number of primary lobules; the thickness of the external germinal layer (EGL); the density of cells in the internal granule cell layer (IGL) region; and the midsagittal area and perimeter. In addition, the laterolateral cerebellar distance was calculated. The data demonstrate that pre- and postnatal reduction of the EGL results in reduced cerebellar growth and folding. Cessation of the treatment at birth results in a recovery and eventual overproduction of EGL, but cerebellar growth and the development of fissures lags behind that of normal rats. Pre- and postnatal destruction of the EGL severely limited cerebellar growth and fissuration, and the cerebella contained only five primary lobules at P14. Rats subjected to postnatal X-irradiation alone had a similar low density of granule cells relative to those treated with a combination of prenatal MAM injections and postnatal X-irradiation, and yet the cerebella contained deeper fissures and more lobules (nine at P14). The data indicate that there are two phases of cerebellar folding: the establishment of five lobules that arise independent of granule cell production, and the granule cell-dependent expansion and partitioning of these five principal lobules during postnatal development. We propose that the lack of correlation between the severity of the granule cell loss and degree of lobulation in agranular rats indicates that granule cells exert an inductive influence over lobulation that is in part independent of the forces generated by their production and differentiation.

Abnormalities, Drug-Induced↗

PubMed1998

staggerer phenotype in retinoid-related orphan receptor alpha-deficient mice.

Retinoid-related orphan receptor alpha (RORalpha) is a member of the nuclear receptor superfamily. To study its physiological role we generated null-mutant mice by targeted insertion of a lacZ reporter gene encoding the enzyme beta-galactosidase. In heterozygous RORalpha+/- mice we found beta-galactosidase activity, indicative of RORalpha protein expression, confined to the central nervous system, skin and testis. In the central nervous system, the RORalpha gene is expressed in cerebellar Purkinje cells, the thalamus, the suprachiasmatic nuclei, and retinal ganglion cells. In skin, RORalpha is strongly expressed in the hair follicle, the epidermis, and the sebaceous gland. Finally, the peritubular cells of the testis and the epithelial cells of the epididymis also strongly express RORalpha. Recently, it was reported that the ataxic mouse mutant staggerer (sg/sg) is caused by a deletion in the RORalpha gene. The analysis of the cerebellar and the behavioral phenotype of homozygous RORalpha-/- mice proves identity to sg/sg mice. Although the absence of RORalpha causes dramatic developmental effects in the cerebellum, it has no apparent morphological effect on thalamus, hypothalamus, and retina. Similarly, testis and skin of RORalpha-/- mice display a normal phenotype. However, the pelage hair of both sg/sg and RORalpha-/- is significantly less dense and when shaved shows reluctance to regrow.

Animals↗

PubMed1998

Postnatal expression of Hu-bcl-2 gene in Lurcher mutant mice fails to rescue Purkinje cells but protects inferior olivary neurons from target-related cell death.

The Lurcher mutant has been extensively studied as a model for cell-autonomous and target-related cell death, yet there are still many unknowns concerning the mechanisms of neuronal degeneration in this mutant. As a key regulator of apoptosis, a bcl-2 transgene has been overexpressed in the heterozygous Lurcher mutant to investigate the effects of BCL-2 on two types of in vivo neuronal cell loss in Lurcher: cell-autonomous Purkinje cell degeneration and target-related olivary neuron death. Six adult +/Lc mutants expressing a human bcl-2 transgene (Hu-bcl-2) were generated by crossing +/Lc mutants with NSE71 Hu-bcl-2 transgenic mice. Analysis of these brains showed that bcl-2 overexpression did not prevent +/Lc Purkinje cell degeneration, but it did rescue most olivary neurons from target-related cell death. Although the number of olivary neurons was equivalent to wild-type numbers, the inferior olive nucleus was significantly shorter in its rostrocaudal extent, suggesting that olivary neurons are atrophied. We propose that Lurcher gene action causes Purkinje cell degeneration independently of a BCL-2-mediated pathway. Furthermore, although bcl-2 overexpression rescues olivary neurons from target-related cell death, it does not prevent the atrophy associated with the loss of target-related trophic support.

Animals↗

PubMed1998

Immature chemodifferentiation of Purkinje cell synapses revealed by 5'-nucleotidase ecto-enzyme activity in the cerebellum of the reeler mouse.

During postnatal development of the rodent cerebellum, a transient enzyme activity of ecto-5'-nucleotidase has been shown in the asymmetrical synapses of Purkinje cells. The alterations of the afferent circuitry and microenvironment of the ectopic Purkinje cells present in the cerebellum of the reeler mutant mouse could enlighten parameters that influence the synaptic 5'-nucleotidase activity of these cells. Ecto-enzyme cytochemistry reveals intense 5'-nucleotidase activity in 43% of synapses of the Purkinje cells throughout the cortex and the core of the reeler cerebellar vermis, although the molecular layer displays large areas with less than 1% of labelled synapses. However, enzymatic labelling is found in considerably more Purkinje cells synapses (73%) throughout the granular layer and the subcortical mass. Climbing fiber synapses of monoinnervated Purkinje cells are labelled by 5'-nucleotidase activity in the molecular layer, as well as asymmetrical synapses made on the subjacent ectopic Purkinje cells by the multiple climbing fibers and by the heterologous afferences. The non-innervated dendritic spines of these cells are also labelled, suggesting that 5'-nucleotidase activity at postsynaptic sites of reeler Purkinje cells does not depend on the presynaptic innervation. Rather, 5'-nucleotidase enzyme activity is enhanced at theses sites when the Purkinje cells have not achieved chemodifferentiation but have conserved immature wiring, i.e., low parallel fiber and multiple climbing fiber inputs.

5'-Nucleotidase↗

PubMed1998

The cerebellum and postural sensorimotor learning in mice and rats.

Animals with cerebellar damage caused by gene mutations, surgical ablations and irradiation by X-rays during developmental stages are impaired in maintaining posture and equilibrium. For most tests, even in animals with total cerebellectomy, postural sensorimotor learning is not abolished. Simpler compensatory movements may be adopted. The acquisition of simple sensorimotor skills occurring after massive damage of the cerebellar cortex may be explained by the modulatory role of the cerebellar deep nuclei during learning processes or by the influence of extracerebellar regions taking over lost cerebellar function.

Animals↗

PubMed1998

Eradication of cerebellar granular cells alters the developmental expression of trk receptors in the rat inferior olive.

Granule cells which relay the mossy fibre afferent system to the cerebellar cortex are generated postnatally in mammals. In their absence, the climbing fibres, i.e. the second afferent system to the cerebellum originating in the inferior olivary nucleus, remain in an immature stage, and substantial elimination of redundant synapses they establish on the Purkinje cells does not occur in the rat between day five (P5) and day fifteen (P15). It is generally assumed that synapse elimination is partly regulated by electrical activity which modulates the competition among afferent fibres for the uptake of a limited amount of trophic factors released by the target. The neurotrophins, whose expression is developmentally regulated in the cerebellum, especially in granule cells, could be this retrograde signal. Using RT-PCR, we studied the expression of their trk receptors in the inferior olivary nucleus of developing and adult rats, and its alteration after eradication of the granule cell precursors by X-irradiation on P5. From P0 to P90, the amount of trkA mRNA is low and remains stable in control rats; the high levels of trkB and C mRNAs detected at P0 markedly decrease in parallel from P5 and reach their minimal values at P15, when the process of synapse elimination is completed in the cerebellum. X-irradiation of the cerebellum decreases the level of expression of the three trks, but a transient upregulation of trkC occurs at P10. The down-regulation of trkB and C expression in the inferior olivary nucleus, contemporary with the altered expression of neurotrophins in the cerebellum, suggest that NT-3 and/or BDNF/NT-4/5 could be involved in the remodelling of olivocerebellar relationships during development. In addition, the transient overexpression of trkC after granule cells eradication is consistent with a paracrin effect exerted on the olivary cells by granule cells release of NT-3, at the time when the climbing fibres invest the growing Purkinje cell dendrites in the molecular layer.

Animals↗

PubMed1998

Overexpression of a Hu-bcl-2 transgene in Lurcher mutant mice delays Purkinje cell death.

Cerebellar Purkinje cells in the heterozygous Lurcher mutant undergo cell autonomous degeneration beginning in the second week of postnatal development and becoming almost total around 30-45 days. The Lurcher mutation was recently identified as gain-of-function defect in the delta 2 glutamate receptor causing a constitutive current leak, suggesting that +/Lc Purkinje cells die by an excitotoxic mechanism. In previous studies we have shown that overexpression of bcl-2, a key regulator of cell death, in the heterozygous Lurcher mutant does not prevent +/Lc Purkinje cell death. To investigate further the mechanisms of +/Lc Purkinje cell death, we have crossed +/Lc mutants with a second line of Hu-bcl-2 transgenics (NSE73a) that shows an earlier onset of transgene expression and higher expression levels. Analysis of eight +/Lc-NSE73a mutants (4 at 2 months and 4 at 5-6 months) showed that Hu-bcl-2 overexpression delayed, but ultimately could not prevent +/Lc Purkinje cell death.

Animals↗

PubMed1998

Differential roles of cerebellar cortex and deep cerebellar nuclei in learning and retention of a spatial task: studies in intact and cerebellectomized lurcher mutant mice.

Lurcher mutant mice (+/Lc) exhibit a massive loss of neurons in the cerebellar cortex and the inferior olivary nucleus, while deep cerebellar nuclei are essentially intact. To discriminate the relative participation of the cerebellar cortex and deep structures in learning and memory, 3 to 6-month-old +/Lc mice were subjected to a spatial learning task derived from the Morris water escape. They were able to learn to escape as well as their strain-matched controls (+/+). Seven days later, their scores showed that they had memorized the spatial environment but not as accurately as +/+ mice. Cerebellectomy before training did not significantly alter the escape learning capabilities of either group, whereas cerebellectomy performed after learning completely abolished retention in +/+, as well as in +/Lc, mice. These results suggest that the cerebellum, although not necessary for learning a spatial task, plays a crucial role in its retention, and that the storing structure of spatial information differs in +/+ and +/Lc mice.

Analysis of Variance↗

PubMed1998

An animal model of autism: behavioural studies in the GS guinea-pig.

Autism is a human behavioural pathology marked by major difficulties in abnormal socialization, language comprehension and stereotypic motor patterns. These behavioural abnormalities have been associated with corticocerebral and cerebellar abnormalities in autistic patients, particularly in vermal folia VI and VII. Progress in understanding this disease has been hindered by the absence of a non-primate animal model. GS guinea-pigs are a partially inbred, non-ataxic guinea-pig strain with cerebellar and corticocerebral abnormalities similar to those reported to exist in human patients with autism. In order to determine if GS guinea-pigs represent an animal model of autism, their behaviour was compared with that of Hartley strain guinea-pigs. GS animals learned a motor task significantly more rapidly than Hartley guinea-pigs, but performed it in a more stereotypic manner and were less influenced by environmental stimuli than Hartleys. GS animals exhibited significantly less exploratory behaviour in a novel environment and were significantly less responsive to 50-95 dBA pure tones than Hartley guinea-pigs. In a social interaction assay, GS guinea-pigs interacted significantly less frequently with each other or with Hartley guinea-pigs than Hartleys did under the same conditions. GS behaviour thus exhibits autistic-like behaviour patterns: motor stereotypy, lack of exploration and response to environment and poor social interaction. Coupled with the neuropathological findings, this abnormal behaviour suggests that GS guinea-pigs could be a useful animal model of autism.

Acoustic Stimulation↗

PubMed1998

Neurotrophin-3 promotes cerebellar granule cell exit from the EGL.

In the cerebellum, the mRNAs for neurotrophin-3 (NT-3) and its high-affinity tyrosine kinase receptor trkC are expressed by both the differentiated granule cells of the internal granule cell layer (IGL) and their precursors in the external germinal layer (EGL). We have investigated the effects of chronic application of exogenous NT-3 in vivo on cerebellar granule cell genesis and differentiation. NT-3 was applied to the posterior surface of the rat cerebellum from P6 onwards using Elvax implants. At P10 the EGL of cerebellar lobules VII and VIII was significantly reduced in thickness in NT-3 implanted rats when compared with controls. Immunocytochemical analysis of the EGL using antibodies to proliferating cell nuclear antigen (PCNA) revealed that the number of postmitotic, premigratory (PCNA-immunonegative) granule cell precursors was preferentially reduced in the NT-3 implanted rats. In situ DNA fragmentation labelling confirmed that this was not accompanied by increased cell death in the EGL. These results suggest that NT-3 promotes the differentiation of postmitotic, premigratory granule cell precursors, accelerating cell exit from the EGL.

Animals↗

PubMed1997

Transcriptional regulation of apolipoprotein A-I gene expression by the nuclear receptor RORalpha.

Since elevated concentrations of plasma high density lipoprotein (HDL) and its major apolipoprotein (apo), apoA-I, confer protection against atherosclerosis, considerable research efforts have focussed on the identification of factors regulating apoA-I gene expression in an attempt to increase its production. Nuclear receptors are interesting candidates because they are transcription factors whose activity is ligand-dependent. In the present study we identified the orphan receptor RORalpha1 as an activator of apoA-I gene transcription. In apoA-I-expressing intestinal Caco-2 cells, overexpression of the RORalpha1, but not the RORalpha2 or RORalpha3 isoforms, increased rat apoA-I gene transcription. Deletion and site-directed mutagenesis experiments identified a functional ROR-responsive element (RORE) in the rat and mouse apoA-I gene promoters, which overlaps with the TATA box. Gel shift experiments indicated that this RORE binds the RORalpha1 isoform, but not the RORalpha2 or RORalpha3 isoforms. Furthermore, compared with wild type mice, apoA-I mRNA levels were significantly lower in small intestines of staggerer mice homozygous for a deletion in the RORalpha gene. In addition, reverse transcriptase-polymerase chain reaction analysis revealed the expression of RORalpha in small intestinal epithelium and in Caco-2 cells. These data indicate a novel, physiological role for RORalpha1 in the regulation of genes involved in lipid and lipoprotein metabolism and possibly in the development of metabolic diseases, such as atherosclerosis.

Animals↗

PubMed1997

Fear decrease in transgenic mice overexpressing bcl-2 in neurons.

Neuronal destruction in the amygdala, hypothalamus and cerebellum provokes a diminution in anxiety and neophobia. In transgenic mice that express the human bcl-2 gene under the control of neuron specific enolase promotor (Hu-bcl-2), BCL-2 overexpression reduces the naturally occurring neuronal death, producing an increase of the number of neurons and brain size. Since BCL-2 over-expression has been observed in different parts of the brain and especially in the amygdaloid nuclei, the hypothalamus and the cerebellum, we studied the fear-related behavior of these transgenic mice. Hu-bcl-2 transgenic mice showed a decrease in anxiety and neophobia, indicating that, for this particular behavior, supernumerary neurons elicit the same modification as that observed after neuronal destruction.

Animals↗

PubMed1997

Hypersensitivity of lurcher mutant mice to the depressing effects of lipopolysaccharide and interleukin-1 on behaviour.

Lurcher mutant mice are characterized by a fast and almost total loss of olivocerebellar neurones during the first postnatal month, associated with a chronic inflammatory state. To test their brain sensitivity to proinflammatory cytokines, we assessed the behavioural responses of adult male Lurcher and wild type to an i.p. or i.c.v. injection of rat recombinant IL-1 beta, and lipopolysaccharide (LPS). IL-1 beta (15 micrograms kg-1, i.p. or 1 ng i.c.v.) decreased social exploration measured 2, 4 and 6 h later, and this decrease was significantly more pronounced in Lurcher than in wild type mice. LPS (60 micrograms kg-1, i.p. or 5 ng i.c.v.) decreased social exploration measured 2 and 4 h later, and this effect was also significantly more marked in Lurcher than in wild type mice. These results suggest that the chronic inflammatory state which characterizes Lurcher mice renders these animals more sensitive to the effects of cytokines such as IL-1 beta and LPS. This difference may be due to the higher reactivity of brain macrophages and glial cells to LPS and IL-1 in Lurcher mice than in wild type.

Animals↗