A. B. Schmitt

Spontaneous longitudinally orientated axonal regeneration is associated with the Schwann cell framework within the lesion site following spinal cord compression injury of the rat.

Spontaneous cellular reorganisation at the lesion site has been investigated following massive spinal cord compression injury in adult rats. By 2 days post operation (p.o.), haemorrhagic necrosis, widespread axonal degeneration, and infiltration by polymorphnuclear granulocytes and OX42‐positive macrophages were observed in the lesion site. By 7 days p.o., low affinity nerve growth factor receptor‐positive Schwann cells, from activated spinal roots, were identified as they migrated far into the lesion. Between 7 and 14 days p.o., the overlapping processes of Schwann cells within the macrophage‐filled lesion formed a glial framework which was associated with extensive longitudinally orientated ingrowth by many neurofilament‐positive axons. Relatively few of these axons were calcitonin gene‐related peptide (CGRP)‐, substance P (SP)‐, or serotonin (5HT)‐positive; however, many were glycinergic or gamma aminobutyric acid (GABA)ergic. At 21 and 28 days p.o. (the longest survival times studied), a reduced but still substantial amount of orientated Schwann cells and axons could be detected at distances of up to 5 mm within the lesion. Glial fibrillary acidic protein (GFAP) immunoreactivity demonstrated the slow formation of astrocytic scarring which only became apparent at the lesion interface between 21 and 28 days p.o. The current data suggest the possibility of developing future therapeutic strategies designed to maintain or even enhance these spontaneous and orientated regenerative events. J. Neurosci. Res. 53:51–65, 1998.

Lesion-induced changes of electrophysiological properties in astrocytes of the rat dentate gyrus

Reorganization of the adult dentate gyrus following unilateral entorhinal cortex lesion (ECL) is a well‐established model for studying mechanisms of trauma‐induced neuronal plasticity. The lesion induces deafferentiation of the outer molecular layer, which is accompanied by a strong astroglial reaction. This glial response is thought to contribute to subsequent repair processes, but the underlying mechanisms are poorly understood. In this study we addressed the question whether denervation leads to modifications in the electrophysiological properties of astrocytes, assuming that such changes might be involved in the remodeling of neural circuitry. Patch‐clamp recordings were obtained from astrocytes in the dentate gyrus of adult rats that underwent ECL and compared to corresponding data from control animals. We observed a significant reduction of inward rectifier K+ current densities, a positive shift of resting potentials, and an increase in input resistance in astrocytes of the denervated molecular layer. Current densities were reduced between 6 and 19 days postlesion (dpl), reaching a minimum at 10 dpl. Voltage‐gated outward K+ currents were not affected by the lesion. Inward rectifier K+ currents increase with maturation in astrocytes. Thus, our results provide evidence that, following ECL, mature astrocytes dedifferentiated and readapted an immature current pattern. Presumably, these changes lead to stronger and prolonged depolarization of glial cells and neurons in response to activity‐dependent K+ release, which in turn might enhance the synthesis of neurotrophic factors and contribute to a permissive environment for neuronal reorganization. GLIA 28:166–174, 1999.

Identification of regeneration-associated genes after central and peripheral nerve injury in the adult rat

BackgroundIt is well known that neurons of the peripheral nervous system have the capacity to regenerate a severed axon leading to functional recovery, whereas neurons of the central nervous system do not regenerate successfully after injury. The underlying molecular programs initiated by axotomized peripheral and central nervous system neurons are not yet fully understood.ResultsTo gain insight into the molecular mechanisms underlying the process of regeneration in the nervous system, differential display polymerase chain reaction has been used to identify differentially expressed genes following axotomy of peripheral and central nerve fibers. For this purpose, axotomy induced changes of regenerating facial nucleus neurons, and non-regenerating red nucleus and Clarkes nucleus neurons have been analyzed in an intra-animal side-to-side comparison. One hundred and thirty five gene fragments have been isolated, of which 69 correspond to known genes encoding for a number of different functional classes of proteins such as transcription factors, signaling molecules, homeobox-genes, receptors and proteins involved in metabolism. Sixty gene fragments correspond to genomic mouse sequences without known function. In situ-hybridization has been used to confirm differential expression and to analyze the cellular localization of these gene fragments. Twenty one genes (~15%) have been demonstrated to be differentially expressed.ConclusionsThe detailed analysis of differentially expressed genes in different lesion paradigms provides new insights into the molecular mechanisms underlying the process of regeneration and may lead to the identification of genes which play key roles in functional repair of central nervous tissues.

Attempted endogenous tissue repair following experimental spinal cord injury in the rat: involvement of cell adhesion molecules L1 and NCAM?

It is widely accepted that the devastating consequences of spinal cord injury are due to the failure of lesioned CNS axons to regenerate. The current study of the spontaneous tissue repair processes following dorsal hemisection of the adult rat spinal cord demonstrates a phase of rapid and substantial nerve fibre in‐growth into the lesion that was derived largely from both rostral and caudal spinal tissues. The response was characterized by increasing numbers of axons traversing the clearly defined interface between the lesion and the adjacent intact spinal cord, beginning by 5 days post operation (p.o.). Having penetrated the lesion, axons became associated with a framework of NGFr‐positive non‐neuronal cells (Schwann cells and leptomeningeal cells). Surprisingly few of these axons were derived from CGRP‐ or SP‐immunoreactive dorsal root ganglion neurons. At the longest survival time (56 days p.o.), there was a marked shift in the overall orientation of fibres from a largely rostro‐caudal to a dorso‐ventral axis. Attempts to identify which recognition molecules may be important for these re‐organizational processes during attempted tissue repair demonstrated the widespread and intense expression of the cell adhesion molecules (CAM) L1 and N‐CAM. Double immunofluorescence suggested that both Schwann cells and leptomeningeal cells contributed to the pattern of CAM expression associated with the cellular framework within the lesion.

Major histocompatibility complex class II expression by activated microglia caudal to lesions of descending tracts in the human spinal cord is not associated with a T cell response.

Abstract Lesion-induced microglial/macrophage responses were investigated in post-mortem human spinal cord tissue of 20 patients who had died at a range of survival times after spinal trauma or brain infarction. Caudal to the spinal cord injury or brain infarction, a strong increase in the number of activated microglial cells was observed within the denervated intermediate grey matter and ventral horn of patients who died shortly after the insult (4–14 days). These cells were positive for the leucocyte common antigen (LCA) and for the major histocompatibility complex class II antigen (MHC II), with only a small proportion staining for the CD68 antigen. After longer survival times (1–4 months), MHC II-immunoreactivity (MHC II-IR) was clearly reduced in the grey matter but abundant in the white matter, specifically within the degenerating corticospinal tract, co-localising with CD68. In this fibre tract, elevated MHC II-IR and CD68-IR were still detectable 1 year after trauma or stroke. It is likely that the subsequent expression of CD68 on MHC II-positive microglia reflects the conversion to a macrophage phenotype, when cells are phagocytosing degenerating presynaptic terminals in grey matter target regions at early survival times and removing axonal and myelin debris in descending tracts at later survival times. No T or B cell invasion or involvement of co-stimulatory B7 molecules (CD80 and CD86) was observed. It is possible that the up-regulation of MHC II on microglia that lack the expression of B7 molecules may be responsible for the prevention of a T cell response, thus protecting the spinal cord from secondary tissue damage.

Distribution of B-50(GAP-43) mRNA and protein in the normal adult human spinal cord.

Abstract B-50(GAP-43) is a phosphoprotein mainly found in the nervous system which plays a major role in neurite growth during development and regeneration as well as in synaptic remodelling. In the mature intact central nervous system, intense B-50 immunoreactivity (B-50-IR) can still be detected in regions which maintain residual capacity for structural re-organization. B-50 expression has been studied extensively in laboratory animals; however, its distribution and regulation in the human spinal cord is largely unknown. As a first step to analyze lesion-induced structural alterations, we investigated the distribution of B-50 protein and mRNA in the normal adult human spinal cord and dorsal root ganglia. Intense B-50-IR was localized to the superficial laminae of the dorsal horn at all segmental levels, the intermediolateral nucleus at thoracic levels and Onuf’s nucleus at sacral levels. Scattered neurons, particularly in the ventral horn of lumbar and sacral segmental levels (and occasionally also in Clarke’s nucleus) displayed intense B-50-IR in close apposition to the perikaryal and proximal dendritic surfaces. Nonradioactive in situ hybridization indicated that B-50 mRNA could also be detected in neurons of the ventral horn and also in the intermediolateral nucleus. The distribution of B-50 mRNA and protein in the normal human spinal cord shows a marked similarity to that reported in experimental animals, including the selective labelling of Onuf’s nucleus. However, the strong B-50-IR on the surface of some large anterior horn motor neurons has not been observed in other mammals. This finding might reflect a particular state of readiness for synaptic plasticity.

Retrograde reactions of Clarke's nucleus neurons after human spinal cord injury

Successful axon regeneration depends on the expression of regeneration‐associated genes by axotomized neurons. Here, we demonstrate, for the first time to our knowledge, the expression of regeneration‐associated genes by axotomized human CNS neurons. In situ hybridization and immunohistochemistry showed a transient induction of GAP‐43 and c‐jun in Clarkes nucleus neurons caudal to traumatic human spinal cord injury. These results support experimental data that nonregenerating central nervous system neurons can temporarily upregulate regeneration‐associated genes, reflecting a transient regenerative capacity that fails over time. Ann Neurol 2003;54:534‐539

Regulation of stearoyl-CoA desaturase-1 after central and peripheral nerve lesions.

BackgroundInterruption of mature axons activates a cascade of events in neuronal cell bodies which leads to various outcomes from functional regeneration in the PNS to the failure of any significant regeneration in the CNS. One factor which seems to play an important role in the molecular programs after axotomy is the stearoyl Coenzyme A-desaturase-1 (SCD-1). This enzyme is needed for the conversion of stearate into oleate. Beside its role in membrane synthesis, oleate could act as a neurotrophic factor, involved in signal transduction pathways via activation of protein kinases C.ResultsIn situ hybridization and immunohistochemistry demonstrated a strong up-regulation of SCD at mRNA and protein level in regenerating neurons of the rat facial nucleus whereas non-regenerating Clarkes and Red nucleus neurons did not show an induction of this gene.ConclusionThis differential expression points to a functionally significant role for the SCD-1 in the process of regeneration.

Works Councils, Quits and Dismissals in Germany

We examine the relationship between works councils and two different types of employment separation – dismissals by the firm and voluntary quits by employees. On the basis of representative data from the German Socio-Economic Panel, we find a negative relationship between works councils and both kinds of separation. This is particularly true for skilled blue collar as well as qualified white collar workers compared with employees in other job categories.

Aktuelle Aspekte der Neuroregeneration nach Rückenmarktrauma

ZusammenfassungAusgeprägte Rückenmarktraumen führen regelmäßig zu einem persistierenden Querschnittsyndrom mit entsprechender lebenslanger Behinderung. Ursache ist eine funktionell unzureichende Regeneration durchtrennter Nervenfasern im zentralen Nervensystem. In den vergangenen 20 Jahren konnten eine Reihe zellulärer und molekularer Mechanismen der abortiven Nervenregeneration und der komplexen Reorganisation nach Rückenmarktrauma tierexperimentell identifiziert werden. Auf der Grundlage dieser Erkenntnisse konnten im Rahmen zahlreicher experimenteller Therapiestrategien partielle funktionelle Restitutionen erzielt werden. Eine klinische Anwendung dieser Behandlungskonzepte bei querschnittgelähmten Patienten ist jedoch noch nicht absehbar. Die folgende Übersicht fasst die wichtigsten neurobiologischen Aspekte der Regeneration nach Rückenmarktrauma zusammen und skizziert die Prinzipien der experimentellen Behandlungsstrategien.AbstractIn recent years, our neurobiological knowledge of the various cellular mechanisms that mediate successful peripheral nerve regeneration, and also of those that prevent repair of damaged nerve fibre pathways following traumatic injury to the central nervous system (CNS), has become more precise. On the basis of this knowledge, a range of experimental therapies for promoting axonal regeneration and functional recovery after spinal cord injury have been developed in animal models. Such intervention strategies focus on the molecular inactivation of glial-associated growth-inhibitory factors and on the application of trophic molecules and cellular substrates that enhance the postlesional regenerative capacity of intrinsic CNS neurons. At present, these experimental therapies cannot be applied in the clinical situation for the treatment of spinal cord-injured patients. This overview briefly summarizes current progress in the neurobiology of spinal cord trauma.