Mohamed Doulazmi

Cerebellar purkinje cell loss during life span of the heterozygous Staggerer mouse (Rora+/Rorasg) is gender‐related

The staggerer mutation causes dysgenesis of the cerebellar cortex in the homozygous mutant (Rorasg/Rorasg). The mutation acts intrinsically within the Purkinje cells (PCs), leading to cytological abnormalities and a severe deficit in the number of these cells. In contrast, in the heterozygous staggerer (Rora+/Rorasg), the cytoarchitecture of the cerebellar cortex appears to be normal, but quantitative studies have revealed a significant loss of cerebellar neurons with advancing age. In the heterozygous reeler (+/rl), another mutant presenting a PC loss with age, we have found that only males were affected (Hadj‐Sahraoui et al., 1996). In the present study, we have investigated whether a similar gender effect exists in the heterozygous staggerer during life span. PCs were counted on cerebellar sagittal sections in male and female Rora+/Rorasg and in their Rora+/Rora+ littermates at 1, 3, 9, 13, 18, and 24 months of age. In the Rora+/Rora+, the number of PCs remained stable until 18 months, but there was a 25% significant loss in 24‐ month‐old mice of both genders. During life span, Rora+/Rora+ males had slightly more PC than females. In the Rora+/Rorasg of both genders, the deficit in PC number was similar at 13 months but it appeared earlier in males, beginning between 1 and 3 months, and was aggravated regularly up to 13 months. By contrast, the decline was delayed and more abrupt in Rora+/Rorasg females, from a value still normal at 9 months to its maximal extent at 13 months. In view of these results, the heterozygous (Rora+/Rorasg) mouse offers an interesting model to test the interaction between sex, age, and genetic background on the development and maintenance of cerebellar neuronal populations. J. Comp. Neurol. 411:267–273, 1999.

RORα, a pivotal nuclear receptor for Purkinje neuron survival and differentiation: From development to ageing

RORα (Retinoid-relatedOrphanReceptor) is a transcription factor belonging to the superfamily of nuclear receptors. The spontaneousstaggerer (sg) mutation, which consists of a deletion in theRora gene, has been shown to cause the loss of function of the RORα protein. The total loss of RORα 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 RORα as a pivotal factor controlling Purkinje cell survival and differentiation, from development to ageing

Specific inhibition of the JNK pathway promotes locomotor recovery and neuroprotection after mouse spinal cord injury.

Limiting the development of secondary damage represents one of the major goals of neuroprotective therapies after spinal cord injury. Here, we demonstrate that specific JNK inhibition via a single intraperitoneal injection of the cell permeable peptide D-JNKI1 6h after lesion improves locomotor recovery assessed by both the footprint and the BMS tests up to 4 months post-injury in mice. JNK inhibition prevents c-jun phosphorylation and caspase-3 cleavage, has neuroprotective effects and results in an increased sparing of white matter at the lesion site. Lastly, D-JNKI1 treated animals show a lower increase of erythrocyte extravasation and blood brain barrier permeability, thus indicating protection of the vascular system. In total, these results clearly point out JNK inhibition as a promising neuroprotective strategy for preventing the evolution of secondary damage after spinal cord injury.

A comparative study of Purkinje cells in two RORα gene mutant mice: staggerer and RORα−/−

The staggerer (Rora(sg/sg)) mutation is a deletion in the RORalpha gene, one member of a family of nuclear receptor genes related to the retinoic acid receptor. Recently Steinmayr et al. (Proc. Natl. Acad. Sci. USA 95 (1998) 3960) generated a RORalpha null-mutant mouse (Rora(-/-)) by using a targeting vector in which a beta-Gal gene replaces the second finger of the DNA-binding domain of RORalpha. The Rora(-/-) cerebellum is qualitatively a phenocopy of the Rora(sg/sg) one, but the two strains differ slightly in their motor skills. To address the question whether the morphological defects in the Rora(-/-) cerebellum are identical to the Rora(sg/sg) one, we compared number and size of Purkinje cells in both staggerer and RORalpha null-mutant mice, using calbindin (CaBP) immunohistochemistry and revelation of beta-Gal activity. Compared to control cerebella the Rora(sg/sg) cerebellum has 82% fewer CaBP-positive cells. In Rora(-/-) mouse, all the the beta-Gal-positive Purkinje cells also expressed CaBP, but the cerebellum contained 78% less CaBP-positive cells than control, a deficit not different from the one observed in Rora(sg/sg). We show similar mediolateral compartments in Purkinje cell number and cytological abnormality in Rora(sg/sg) and Rora(-/-) mice. These results provide quantitative support for the hypothesis that the cerebellar phenotype in the homozygous Rora(sg/sg) is due to the lack of function of the RORalpha gene.

CEREBELLAR PURKINJE CELL LOSS IN HETEROZYGOUS RORA +/- MICE: A LONGITUDINAL STUDY

The staggerer (sg) mutation is a spontaneous deletion in the Rora gene that prevents the translation of the ligand-binding domain (LBD), leading to the loss of RORα activity. The homozygous Rorasg/sg mutant mouse, whose most obvious phenotype is ataxia associated with cerebellar degeneration, also displays a variety of other phenotypes. The heterozygous Rora+/sg is able to develop a cerebellum that is qualitatively normal but which suffers a significant loss of cerebellar neuronal cells with advancing age. A truncated protein synthesized by the mutated allele may play a role both in Rorasg/sg and Rora+/sg. To determine the effects during life span of true haplo-insufficiency of the RORα protein, derived from the invalidation of the gene, we compared the evolution of Purkinje cell numbers in heterozygous Rora knock-out males (Rora+/−) and in their wild-type counterparts from 1 to 24 months of age. We also compared the evolution of Purkinje cell (PC) numbers in Rora+/− and Rora+/sg males from 1 to 9 months. The main finding is that in Rora+/− mice, for which only one-half the normal amount of protein is produced, the deficit was established as early as 1 month and did not change during the animals’ adult lifespans. Thus, the effects of aging on PC number were apparent much earlier in Rora+/− than in Rora+/sg, although at 24 months of age the degrees of deficit were similar.

DIMINISHING PURKINJE CELL POPULATIONS IN THE CEREBELLA OF AGING HETEROZYGOUS PURKINJE CELL DEGENERATION BUT NOT HETEROZYGOUS NERVOUS MICE

Mice homozygous for the recessive, cerebellar affected mutations nervous and Purkinje cell degeneration display an almost complete loss of Purkinje cells during their first two postnatal months. We have recently shown a progressive and age-related loss of Purkinje cells in mutant mice heterozygous for mutations apparently recessive, such as staggerer and reeler , and have thus chosen to investigate whether a similar Purkinje cell loss occurred with aging in +/ nr and +/ pcd heterozygous mice. Purkinje cells were counted on serial sections heterozygous mice. Purkinje cells were counted on serial sections stained with thionin obtained from 17-month-old male and female heterozygous mice and their respective wild-type controls. In the case of the +/ nr wild-type mice, no difference in cell counts was observed. However, +/ pcd mice had significantly fewer (−18%) Purkinje cells (143.700±5.400) than control wild-types (175.100±2.300); p<0.0001) at 17 months. These results extend our previous findings and further support the idea that apparently recessive neurological mutations may exert, at the heterozygous state, a deleterious effect upon Purkinje cells during the aging process.

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.

Fragile X Mental Retardation Protein and Dendritic Local Translation of the Alpha Subunit of the Calcium/Calmodulin-Dependent Kinase II Messenger RNA Are Required for the Structural Plasticity Underlying Olfactory Learning

BACKGROUND In the adult brain, structural plasticity allowing gain or loss of synapses remodels circuits to support learning. In fragile X syndrome, the absence of fragile X mental retardation protein (FMRP) leads to defects in plasticity and learning deficits. FMRP is a master regulator of local translation but its implication in learning-induced structural plasticity is unknown. METHODS Using an olfactory learning task requiring adult-born olfactory bulb neurons and cell-specific ablation of FMRP, we investigated whether learning shapes adult-born neuron morphology during their synaptic integration and its dependence on FMRP. We used alpha subunit of the calcium/calmodulin-dependent kinase II (αCaMKII) mutant mice with altered dendritic localization of αCaMKII messenger RNA, as well as a reporter of αCaMKII local translation to investigate the role of this FMRP messenger RNA target in learning-dependent structural plasticity. RESULTS Learning induces profound changes in dendritic architecture and spine morphology of adult-born neurons that are prevented by ablation of FMRP in adult-born neurons and rescued by an metabotropic glutamate receptor 5 antagonist. Moreover, dendritically translated αCaMKII is necessary for learning and associated structural modifications and learning triggers an FMRP-dependent increase of αCaMKII dendritic translation in adult-born neurons. CONCLUSIONS Our results strongly suggest that FMRP mediates structural plasticity of olfactory bulb adult-born neurons to support olfactory learning through αCaMKII local translation. This reveals a new role for FMRP-regulated dendritic local translation in learning-induced structural plasticity. This might be of clinical relevance for the understanding of critical periods disruption in autism spectrum disorder patients, among which fragile X syndrome is the primary monogenic cause.

Sleep Apnea in Elderly Adults with Chronic Insomnia

To the Editor: Insomnia and sleep apnea syndrome (SAS) are common in elderly adults. SAS may generate insomnia complaints by repeatedly interrupting sleep, altering sleep quality, and producing perceptions of unrestored sleep. Only a few studies have focused on the characteristics of SAS in elderly adults with insomnia. Polysomnography (PSG) is the criterion standard for SAS diagnosis but is not systematically indicated in individuals with insomnia, yet identifying SAS in people with insomnia is crucial because the therapeutic management of SAS is different from that of insomnia. Over a period of 29 months, outpatients aged 60 and older who consulted with physicians specializing in sleep for insomnia complaints—difficulty initiating or maintaining sleep, waking up too early, experiencing nonrestorative or poor quality sleep despite adequate opportunity and circumstances for sleep, and experiencing daytime functional consequences, at least three times per week for at least 6 months—were selected. The prevalence, characteristics, and predictors of SAS were examined in these individuals using clinical interviews, overnight ambulatory PSG (including 6 electroencephalogram (EEG) leads, electrooculogram, chin and leg electromyogram, nasal canula, thoracic and abdominal bands and pulse oximeter) and multiple sleep latency tests (MSLTs). Apnea was defined as a complete absence of nasal airflow for at least 10 seconds. Hypopnea was defined as an event lasting at least 10 seconds with a 50% or greater decrease in the airflow or a 30% or greater decrease in airflow accompanied by a 3% or greater decrease in oxyhemoglobin saturation or an EEG arousal. Flow limitation was a decrease of 30% or less in the form of classic flattening of the airflow limb for at least two consecutive breaths, lasting 10 s or longer and ending in an EEG arousal. SAS was defined as an apnea, hypopnea, flow limitation index (AHI) of 15/hour or greater. Individuals with night time sleep recorded less than 3 hours were excluded. The Charles Foix Hospital institutional review board approved this study. Multilinear regression analyses were tested using stepwise backward selection of the explicative variables. Of 64 participants included (mean age 72, range 60 91; 40 women), 44 (68.7%) had SAS (mean AHI = 33.6 ± 13.9/hour), and 41 (64%) were taking a benzodiazepine or a benzodiazepine receptor agonist (BRA). Fourteen participants did not report any of three cardinal symptoms of SAS (snoring, observed apnea, and excessive daytime sleepiness), but six had an AHI of 15/ hour or more. The SAS group had more participants who reported snoring symptoms (P = .03), had higher (P = .002) but still moderate body mass indices (BMI), and had a shorter (P = .006) but subnormal MSLT value (Table 1). Logistic analysis showed that SAS was positively associated with BMI (odds ratio (OR) = 1.33; P = .01) and negatively associated with MSLT value (OR = 0.87; P = .03). Multiple regression analysis showed that age (P = .03), BMI (P = .01), sleep onset latency (P = .049), snoring (P = .03), and BRA use (P = .004) were positively