Road casualties in work-related and private contexts: occupational medical impact. Results from the ESPARR cohort.

BACKGROUND: Road accidents may impact victims' physical and/or mental health and socio-occupational life, notably including return to work. OBJECTIVES: To assess whether the occupational medical consequences sustained by subjects injured in road accidents occurring in a work-related context differ from those associated with private accidents. METHODS: 778 adults who were in work or occupational training at the time of their accident were included. Two groups were distinguished: 354 (45.5%) injured in road accidents occurring in a work-related context (commuting or on duty) and 424 (54.5%) injured in a private accident. The groups were compared on medical and occupational factors assessed on prospective follow-up at 6 months and 1 and 3 years. Multivariate analysis explored for factors associated at 6 months and 1 year with sick leave following the accident and duration of sick leave. RESULTS: There were no significant differences between groups for demographic data apart from a slightly higher injury severity in private accidents (32.5% of private accidents with MAIS3+(Maximum Abbreviated Injury Scale greater or equal to 3) vs. 23.7% for work-related accidents, p = 0.007). Victims of work-related accidents were more often on sick leave (OR = 1.8; 95% CI, 1.1-2.9). Although the length of sick leave is higher for work-related accidents that for private accidents, multivariate analysis showed that the injury severity and the post-traumatic stress disorder (PTSD) are significant factors to explain the time to return to work. There were no significant differences according to occupational impact during follow-up, notably including sick-leave duration, number of victims returning to work within 3 years and number of victims out of work due to incapacity. CONCLUSIONS: In the ESPARR (follow-up study of a road-accident population in the Rhône administrative county: Etude de Suivi d'une Population d'Accidentés de la Route dans le Rhône) cohort, the fact that a road accident occurred in a work-related context did not affect the occupational consequences.

Neurons derived from patients with bipolar disorder divide into intrinsically different sub-populations of neurons, predicting the patients' responsiveness to lithium.

Bipolar disorder (BD) is a progressive psychiatric disorder with more than 3% prevalence worldwide. Affected individuals experience recurrent episodes of depression and mania, disrupting normal life and increasing the risk of suicide greatly. The complexity and genetic heterogeneity of psychiatric disorders have challenged the development of animal and cellular models. We recently reported that hippocampal dentate gyrus (DG) neurons differentiated from induced pluripotent stem cell (iPSC)-derived fibroblasts of BD patients are electrophysiologically hyperexcitable. Here we used iPSCs derived from Epstein-Barr virus-immortalized B-lymphocytes to verify that the hyperexcitability of DG-like neurons is reproduced in this different cohort of patients and cells. Lymphocytes are readily available for research with a large number of banked lines with associated patient clinical description. We used whole-cell patch-clamp recordings of over 460 neurons to characterize neurons derived from control individuals and BD patients. Extensive functional analysis showed that intrinsic cell parameters are very different between the two groups of BD neurons, those derived from lithium (Li)-responsive (LR) patients and those derived from Li-non-responsive (NR) patients, which led us to partition our BD neurons into two sub-populations of cells and suggested two different subdisorders. Training a Naïve Bayes classifier with the electrophysiological features of patients whose responses to Li are known allows for accurate classification with more than 92% success rate for a new patient whose response to Li is unknown. Despite their very different functional profiles, both populations of neurons share a large, fast after-hyperpolarization (AHP). We therefore suggest that the large, fast AHP is a key feature of BD and a main contributor to the fast, sustained spiking abilities of BD neurons. Confirming our previous report with fibroblast-derived DG neurons, chronic Li treatment reduced the hyperexcitability in the lymphoblast-derived LR group but not in the NR group, strengthening the validity and utility of this new human cellular model of BD.

Cognitive and behavioural post-traumatic impairments: what is the specificity of a brain injury ? A study within the ESPARR cohort.

OBJECTIVE: The variety and extent of impairments occurring after traumatic brain injury vary according to the nature and severity of the lesions. In order to better understand their interactions and long-term outcome, we have studied and compared the cognitive and neurobehavioral profile one year post onset of patients with and without traumatic brain injury in a cohort of motor vehicle accident victims. METHOD: The study population is composed of 207 seriously injured persons from the ESPARR cohort. This cohort, which has been followed up in time, consists in 1168 motor vehicle accident victims (aged 16 years or more) with injuries with all degrees of severity. Inclusion criteria were: living in Rhone county, victim of a traffic accident having involved at least one wheel-conducted vehicle and having occurred in Rhone county, alive at the time of arrival in hospital and having presented in one of the different ER facilities of the county. The cohort's representativeness regarding social and geographic criteria and the specificities of the accidents were ensured by the specific targeting of recruitment. Deficits and impairments were assessed one year after the accident using the Neurobehavioral Rating Scale - Revised and the Trail-Making Test. Within our seriously injured group, based on the Glasgow Score, the presence of neurological deficits, aggravation of neurological condition in the first 72hours and/or abnormal cerebral imaging, we identified three categories: (i) moderate/severe traumatic brain injury (n=48), (ii) mild traumatic brain injury (n=89), and (iii) severely injured but without traumatic brain injury (n=70). RESULTS: The most frequently observed symptoms were anxiety, irritability, memory and attention impairments, depressive mood and emotional lability. While depressive mood and irritability were observed with similar frequency in all three groups, memory and attention impairments, anxiety and reduced initiative were more specific to traumatic brain injury whereas executive disorders were associated with moderate/severe traumatic brain injury. DISCUSSION-CONCLUSION: The presence and the initial severity of a traumatic brain injury condition the nature and frequency of residual effects after one year. Some impairments such as irritability, which is generally associated with traumatic brain injury, do not appear to be specific to this population, nor does depressive mood. Substantial interactions between cognitive, affective and neurobehavioral disorders have been highlighted.

Krox20 inactivation in the PNS leads to CNS/PNS boundary transgression by central glia.

CNS/PNS interfaces constitute cell boundaries, since they delimit territories with different neuronal and glial contents. Despite their potential interest in regenerative medicine, the mechanisms restricting oligodendrocytes and astrocytes to the CNS, and Schwann cells to the PNS in mammals are not known. To investigate the involvement of peripheral glia and myelin in the maintenance of the CNS/PNS boundary, we have first made use of different mouse mutants. We show that inactivation of Krox20/Egr2, a master regulatory gene for myelination in Schwann cells, results in transgression of the CNS/PNS boundary by astrocytes and oligodendrocytes and in myelination of nerve root axons by oligodendrocytes. In contrast, such migration does not occur with the Trembler(J) mutation, which prevents PNS myelination without affecting Krox20 expression. Altogether these data suggest that maintenance of the CNS/PNS boundary requires a new Krox20 function separable from myelination control. Finally, we have analyzed a human patient affected by a congenital amyelinating neuropathy, associated with the absence of the KROX20 protein in Schwann cells. In this case, the nerve roots were also invaded by oligodendrocytes and astrocytes. This indicates that transgression of the CNS/PNS boundary by central glia can occur in pathological situations in humans and suggests that the underlying mechanisms are common with the mouse.

Boundary cap cells are highly competitive for CNS remyelination: fast migration and efficient differentiation in PNS and CNS myelin-forming cells.

During development, boundary cap cells (BC) and neural crest cell (NCC) derivatives generate Schwann cells (SC) of the spinal roots and a subpopulation of neurons and satellite cells in the dorsal root ganglia. Despite their stem-like properties, their therapeutic potential in the diseased central nervous system (CNS) was never explored. The aim of this work was to explore BC therapeutic potential for CNS remyelination. We derived BC from Krox20(Cre) x R26R(Yfp) embryos at E12.5, when Krox20 is exclusively expressed by BC. Combining microdissection and cell fate mapping, we show that acutely isolated BC are a unique population closely related but distinct from NCC and SC precursors. Moreover, when grafted in the demyelinated spinal cord, BC progeny expands in the lesion through a combination of time-regulated processes including proliferation and differentiation. Furthermore, when grafted away from the lesion, BC progeny, in contrast to committed SC, show a high migratory potential mediated through enhanced interactions with astrocytes and white matter, and possibly with polysialylated neural cell adhesion molecule expression. In response to demyelinated axons of the CNS, BC progeny generates essentially myelin-forming SC. However, in contact with axons and astrocytes, some of them generate also myelin-forming oligodendrocytes. There are two primary outcomes of this study. First, the high motility of BC and their progeny, in addition to their capacity to remyelinate CNS axons, supports the view that BC are a reservoir of interest to promote CNS remyelination. Second, from a developmental point of view, BC behavior in the demyelinated CNS raises the question of the boundary between central and peripheral myelinating cells.

[Consequences for children involved in a road traffic accident: one year of observation and follow-up in the Rhone county]. / Consequénces des accidents de la circulation chez les enfants: suivi pendant un an dans le département du Rhône.

Children aged 6 to 11 who have been injured in a traffic accident were observed over a one year period, in parallel with a control group of children. More than one-third of the injured children had been hospitalized (for periods ranging anywhere between 1 and 47 days). One year later, one injured child out of ten was still suffering from pain, and/or still being treated for injuries resulting from the accident. Many other factors were linked to the initial overall level of severity of the injuries, contrary to that of pain, such as the rate and duration of hospitalization, the duration of care provided, the number of medical consultations, and absenteeism from school. Children who had been injured in a road traffic accident were found to be more anxious and nervous, in general, as well as having a high prevalence of sleeping disorders in comparison to the children in the control group.

Hindbrain patterning: Krox20 couples segmentation and specification of regional identity.

We have previously demonstrated that inactivation of the Krox20 gene led to the disappearance of its segmental expression territories in the hindbrain, the rhombomeres (r) 3 and 5. We now performed a detailed analysis of the fate of prospective r3 and r5 cells in Krox20 mutant embryos. Genetic fate mapping indicates that at least some of these cells persist in the absence of a functional Krox20 protein and uncovers the requirement for autoregulatory mechanisms in the expansion and maintenance of Krox20-expressing territories. Analysis of even-numbered rhombomere molecular markers demonstrates that in Krox20-null embryos, r3 cells acquire r2 or r4 identity, and r5 cells acquire r6 identity. Finally, study of embryonic chimaeras between Krox20 homozygous mutant and wild-type cells shows that the mingling properties of r3/r5 mutant cells are changed towards those of even-numbered rhombomere cells. Together, these data demonstrate that Krox20 is essential to the generation of alternating odd- and even-numbered territories in the hindbrain and that it acts by coupling the processes of segment formation, cell segregation and specification of regional identity.

Effects of cannabinoids in Krox-24 targeted mice.

Krox-24 is an immediate early gene encoding a zinc-finger transcription factor implicated in several adaptive responses, and its induction by cannabinoids has been reported. We used mice targeted in the Krox-24 gene to specifically dissect the role of this protein in the acute and chronic central actions of cannabinoids. We report here on the ability of cannabinoids to activate G-proteins and to inhibit adenylyl cyclase, and to elicit behavioral responses in wild-type and mutant mice. The behavioral parameters and the biochemical correlates of abstinence after delta9-THC withdrawal were evaluated. We show that Krox-24 is not involved in the acute analgesic effects of delta9-THC and in the SR precipitated delta9-THC withdrawal syndrome.

Ablation of NF1 function in neurons induces abnormal development of cerebral cortex and reactive gliosis in the brain.

Neurofibromatosis type 1 (NF1) is a prevalent genetic disorder that affects growth properties of neural-crest-derived cell populations. In addition, approximately one-half of NF1 patients exhibit learning disabilities. To characterize NF1 function both in vitro and in vivo, we circumvent the embryonic lethality of NF1 null mouse embryos by generating a conditional mutation in the NF1 gene using Cre/loxP technology. Introduction of a Synapsin I promoter driven Cre transgenic mouse strain into the conditional NF1 background has ablated NF1 function in most differentiated neuronal populations. These mice have abnormal development of the cerebral cortex, which suggests that NF1 has an indispensable role in this aspect of CNS development. Furthermore, although they are tumor free, these mice display extensive astrogliosis in the absence of conspicuous neurodegeneration or microgliosis. These results indicate that NF1-deficient neurons are capable of inducing reactive astrogliosis via a non-cell autonomous mechanism.

Krox-20 patterns the hindbrain through both cell-autonomous and non cell-autonomous mechanisms.

The Krox-20 gene encodes a zinc finger transcription factor, which has been shown previously, by targeted inactivation in the mouse, to be required for the development of rhombomeres (r) 3 and 5 in the segmented embryonic hindbrain. In the present work, Krox-20 was expressed ectopically in the developing chick hindbrain by use of electroporation. We demonstrate that Krox-20 expression is sufficient to confer odd-numbered rhombomere characteristics to r2, r4, and r6 cells, presumably in a cell-autonomous manner. Therefore, Krox-20, appears as the major determinant of odd-numbered identity within the hindbrain. In addition, we provide evidence for the existence of a non cell-autonomous autoactivation mechanism allowing recruitment of Krox-20-positive cells from even-numbered territories by neighboring Krox-20-expressing cells. On the basis of these observations, we propose that Krox-20 regulates multiple, intertwined steps in segmental patterning: Initial activation of Krox-20 in a few cells leads to the segregation, homogenization, and possibly expansion of territories to which Krox-20 in addition confers an odd-numbered identity.

A requirement for the immediate early gene Zif268 in the expression of late LTP and long-term memories.

The induction of long-term potentiation (LTP) in the dentate gyrus of the hippocampus is associated with a rapid and robust transcription of the immediate early gene Zif268. We used a mutant mouse with a targeted disruption of Zif268 to ask whether this gene, which encodes a zinc finger transcription factor, is required for the maintenance of late LTP and for the expression of long-term memory. We show that whereas mutant mice exhibit early LTP in the dentate gyrus, late LTP is absent when measured 24 and 48 hours after tetanus in the freely moving animal. In both spatial and non-spatial learning tasks, short-term memory remained intact, whereas performance was impaired in tests requiring long-term memory. Thus, Zif268 is essential for the transition from short- to long-term synaptic plasticity and for the expression of long-term memories.

Forward signaling mediated by ephrin-B3 prevents contralateral corticospinal axons from recrossing the spinal cord midline.

To investigate Eph-ephrin bidirectional signaling, a series of mutations were generated in the ephrin-B3 locus. The absence of both forward and reverse signaling resulted in mice with mirror movements as typified by a hopping locomotion. The corticospinal tract was defective as axons failed to respect the midline boundary of the spinal cord and bilaterally innervated both contralateral and ipsilateral motor neuron populations. A second mutation that expresses a truncated ephrin-B3 protein lacking its cytoplasmic domain did not lead to hopping, indicating that reverse signaling is not required for corticospinal innervation. Ephrin-B3 is concentrated at the spinal cord midline, while one of its receptors, EphA4, is expressed in postnatal corticospinal neurons as their fibers pathfind down the contralateral spinal cord. Our data indicate ephrin-B3 functions as a midline-anchored repellent to stimulate forward signaling in EphA4-expressing axons.

Control of the migratory pathway of facial branchiomotor neurones.

Facial branchiomotor (fbm) neurones undergo a complex migration in the segmented mouse hindbrain. They are born in the basal plate of rhombomere (r) 4, migrate caudally through r5, and then dorsally and radially in r6. To study how migrating cells adapt to their changing environment and control their pathway, we have analysed this stereotyped migration in wild-type and mutant backgrounds. We show that during their migration, fbm neurones regulate the expression of genes encoding the cell membrane proteins TAG-1, Ret and cadherin 8. Specific combinations of these markers are associated with each migratory phase in r4, r5 and r6. In Krox20 and kreisler mutant mouse embryos, both of which lack r5, fbm neurones migrate dorsally into the anteriorly positioned r6 and adopt an r6-specific expression pattern. In embryos deficient for Ebf1, a gene normally expressed in fbm neurones, part of the fbm neurones migrate dorsally within r5. Accordingly, fbm neurones prematurely express a combination of markers characteristic of an r6 location. These data suggest that fbm neurones adapt to their changing environment by switching on and off specific genes, and that Ebf1 is involved in the control of these responses. In addition, they establish a close correlation between the expression pattern of fbm neurones and their migratory behaviour, suggesting that modifications in gene expression participate in the selection of the local migratory pathway.

Hindbrain patterning: FGFs regulate Krox20 and mafB/kr expression in the otic/preotic region.

Krox20 and mafB/kr are regulatory genes involved in hindbrain segmentation and anteroposterior (AP) patterning. They are expressed in rhombomeres (r) r3/r5 and r5/r6 respectively, as well as in the r5/r6 neural crest. Since several members of the fibroblast growth factor (FGF) family are expressed in the otic/preotic region (r2-r6), we investigated their possible involvement in the regulation of Krox20 and mafB/kr. Application of exogenous FGFs to the neural tube of 4- to 7-somite chick embryos led to ectopic expression in the neural crest of the somitic hindbrain (r7 and r8) and to the extension of the Krox20- or mafB/kr-positive areas in the neuroepithelium. Application of an inhibitor of FGF signalling led to severe and specific downregulation of Krox20 and mafB/kr in the hindbrain neuroepithelium and neural crest. These data indicate that FGFs are involved in the control of regional induction and/or maintenance of Krox20 and mafB/kr expression, thus identifying a novel function for these factors in hindbrain development, besides their proposed more general role in early neural caudalisation.

Pattern of expression of the transcription factor Krox-20 in mouse hair follicle.

We examined the pattern of expression in hair follicles of the transcription factor gene Krox-20. During embryogenesis, Krox-20 is first expressed in the upper portion of the hair bud, then in the hair canal, in the sebaceous glands and in the outer root sheath. In the mature follicles, Krox-20, like Shh and TGFbetaRII, is also expressed in a sub-population of matrix keratinocytes located in a ring-like fashion in vibrissal follicles and clustered on one side of the papilla in pelage follicles. This polarized pattern rotates around the papilla as a result of sequential gene expression by individual groups of matrix cells. This peculiar pattern is not linked to follicle angling.

Targeting of the EphA4 tyrosine kinase receptor affects dorsal/ventral pathfinding of limb motor axons.

The Eph family of tyrosine kinase receptors has recently been implicated in various processes involving the detection of environmental cues such as axonal guidance, targeted cell migration and boundary formation. We have inactivated the mouse EphA4 gene to investigate its functions during development. Homozygous EphA4 mutant animals show peroneal muscular atrophy correlating with the absence of the peroneal nerve, the main dorsal nerve of the hindlimb. This phenotype is also observed, although with a lower penetrance, in heterozygotes. During normal hindlimb innervation, motor axons converge towards the sciatic plexus region at the base of the limb bud, where they must choose between dorsal and ventral trajectories within the limb. Among the axons emerging from the sciatic plexus, dorsal projections show higher levels of EphA4 protein than ventral axons. In EphA4 mutant mice, presumptive dorsal motor axons fail to enter the dorsal compartment of the limb and join the ventral nerve. Our data therefore suggest that the level of EphA4 protein in growing limb motor axons is involved in the selection of dorsal versus ventral trajectories, thus contributing to the topographic organisation of motor projections.

A dual role of erbB2 in myelination and in expansion of the schwann cell precursor pool.

Neuregulin-1 provides an important axonally derived signal for the survival and growth of developing Schwann cells, which is transmitted by the ErbB2/ErbB3 receptor tyrosine kinases. Null mutations of the neuregulin-1, erbB2, or erbB3 mouse genes cause severe deficits in early Schwann cell development. Here, we employ Cre-loxP technology to introduce erbB2 mutations late in Schwann cell development, using a Krox20-cre allele. Cre-mediated erbB2 ablation occurs perinatally in peripheral nerves, but already at E11 within spinal roots. The mutant mice exhibit a widespread peripheral neuropathy characterized by abnormally thin myelin sheaths, containing fewer myelin wraps. In addition, in spinal roots the Schwann cell precursor pool is not correctly established. Thus, the Neuregulin signaling system functions during multiple stages of Schwann cell development and is essential for correct myelination. The thickness of the myelin sheath is determined by the axon diameter, and we suggest that trophic signals provided by the nerve determine the number of times a Schwann cell wraps an axon.

Nab proteins mediate a negative feedback loop controlling Krox-20 activity in the developing hindbrain.

The developing vertebrate hindbrain is transiently subdivided along the anterior-posterior axis into metameric units, called rhombomeres (r). These segments constitute units of lineage restriction and display specific gene expression patterns. The transcription factor gene Krox-20 is restricted to r3 and r5, and is required for the development of these rhombomeres. We present evidence that Krox-20 transcriptional activity is under the control of a negative feedback mechanism in the hindbrain. This regulatory loop involves two closely related proteins, Nabl and Nab2, previously identified as antagonists of Krox-20 transcriptional activity in cultured cells. Here we show that in the mouse hindbrain, Nab1 and Nab2 recapitulate the Krox-20 expression pattern and that their expression is dependent on Krox-20 function. Furthermore, misexpression of Nab1 or Nab2 in zebrafish embryos leads to alterations in the expression patterns of several hindbrain markers, consistent with an inhibition of Krox-20 activity. Taken together, these data indicate that Krox-20 positively regulates the expression of its own antagonists and raise the possibility that this negative feedback regulatory loop may play a role in the control of hindbrain development.