Neuronal potentialities of cells in the optic nerve of the chicken embryo are revealed in culture.

Neuronal potentialities in neuroepithelial cells of the chicken embryonic optic nerve were studied in culture by using neurofilament antibodies as neuronal markers. Embryonic day-4 and -5 (E4 and E5) optic stalks were explanted in vitro. Within the first few days of culture, numerous morphologically identifiable neurons extending long neurites developed. These neurons and their processes were specifically labeled with neurofilament antibodies. Similar results were obtained by explanting only the medial portion of E7 optic stalks away from possibly contaminating cerebral or retinal tissue. To determine whether neuronal potentialities persisted at later embryonic stages, cultures of dissociated optic stalks were established at E11, E15, and E18. Neurons labeled with the various neurofilament antibodies appeared in all cultures of E11 and E15 optic stalks. However, typical neurons could not be recognized in cultures of E18 optic nerves. These results indicate that cells with neuronal potentialities are present in the embryonic optic nerve from early stages of development and persist until at least E15. Since the adult optic nerve is devoid of nerve cell bodies, our observations are consistent with the hypothesis that axons of retinal ganglion cells, which course through the optic stalk, repress neuronal potentialities within a subpopulation of precursor cells during normal development.     

Femoral block provides superior analgesia compared with intra-articular ropivacaine after anterior cruciate ligament reconstruction

BACKGROUND AND OBJECTIVES: Arthroscopic anterior cruciate ligament (ACL) reconstruction of the knee is a painful procedure requiring intensive postoperative pain management. This prospective study investigates analgesic quality after a femoral block as compared with intra-articular injection of local anesthetic. METHODS: Eighty patients scheduled for elective ACL repair under general anesthesia were included in our study. Upon completion of surgery, the patients were randomly assigned into 1 of 2 groups: femoral group (n = 40) received a femoral block with 20 mL 1% ropivacaine; intra-articular group (n = 40) received 20 mL 1% ropivacaine injected intra-articularly. During the first 24 hours after surgery, all patients received 2 g propacetamol and 100 mg ketoprofen, intravenously. Additional postoperative analgesia was available with parenteral morphine if required. Analgesic duration was defined as the time from end of surgery to the first requirement for a supplemental analgesic. Data collection included patient demographics, visual analog scale (VAS) scores, analgesic duration, and morphine use. Analysis of variance (ANOVA) test was used to compare the 2 groups. RESULTS: VAS score in the recovery room and during rehabilitation was higher in the intra-articular group than in the femoral group (P <.001). Morphine use was lower in the femoral group than in the intra-articular group (P <.001). Similarly, analgesic duration was longer in the femoral group than the intra-articular group (P <.0001). CONCLUSIONS: Compared with intra-articular injection of local anesthetic, femoral nerve block (FNB) provides better analgesia and allows a significant morphine-sparing effect after ACL repair.     

Initial expression of neurofilaments and vimentin in the central and peripheral nervous system of the mouse embryo in vivo

The appearance of neurofilaments (NFs) and vimentin (Vim) in the nervous system of the mouse embryo was documented using immunohistochemical techniques. The three NF protein subunits appear early and simultaneously in central and peripheral neurons at 9 to 10 days of gestation. The onset of NF expression is concomitant with axon elongation and correlates extremely well with neurofibrillar differentiation and, in the case of autonomic ganglia, with the expression of adrenergic neurotransmitter properties. In the central and peripheral nervous system, NF expression is preceded by that of Vim, and both types of intermediate filaments coexist within the same cell for a short period of time.     

Dynamic friction and the origin of the complexity of earthquake sources

We study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid to understand the origin of seismic source heterogeneity in the presence of nonlinear rate- and state-dependent friction. All the mechanical properties of the medium and friction are assumed homogeneous. Friction includes a characteristic length that is longer than the grid size so that our models have a well-defined continuum limit. Starting from a heterogeneous initial stress distribution, we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for a few 1000 events. The style of seismicity produced by this model is determined by a control parameter associated with the degree of rate dependence of friction. For classical friction models with rate-independent friction, no complexity appears and seismicity is perfectly periodic. For weakly rate-dependent friction, large ruptures are still periodic, but small seismicity becomes increasingly nonstationary. When friction is highly rate-dependent, seismicity becomes nonperiodic and ruptures of all sizes occur inside the fault. Highly rate-dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop. Partial stress drop produces large variations in the state of stress that in turn produce earthquakes of different sizes. Similar results have been found by other authors using the Burridge and Knopoff model. We conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity.     

Pulmonary oedema in scuba-diving: frequency and seriousness about a series of 19 cases

Objectives

Pulmonary oedema in self-contained underwater breathing apparatus diving is an accident whose risk factors, conditions of occurrence and incidence are not well-known. The aim of this study was to evaluate the frequency, the risk factors and the evolution of this accident.

Study design

Retrospective case study and prospective frequency study.

Patients and methods

Study covering the Brittany region and performed in two steps with distinct objectives: a review of cases diagnosed between 2002 and 2007, and a one-year study of cases reported by emergency physicians. Diagnosis was based on the history, a respiratory distress, auscultation and radiologic features.

Results

Nineteen cases were reported, of which one was recurrent. The mean age of patients was 49 years. Divers without heart disease were involved, as well as divers with hypertension (eight cases) or valve abnormalities (three cases). Stress and/or physical exertion were involved. Dyspnoea, cough and haemoptysis were the most common symptoms; in addition, two cases of cardiac arrest and three of loss of consciousness were observed. Chest radiography was unsensitive (normal in four cases), contrasting with abnormal thoracic CT scan in all cases. Symptoms resolved rapidly with oxygen, except for two divers who died. We identified five cases over one year, one of which lethal.

Conclusion

This accident is not a rare event and may have serious consequences. Oldest divers submitted to stress and/or effort are at higher risk.