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Biomedical subjects

M Bähr

Publications and source records attributed to M Bähr.

At least 91 records · Page 5Linked to original sources
PubMed1997

Fate of developing astrocytes in the optic nerve of the myelin-deficient rat.

There is considerable debate on the development of a glial cell line in the rat optic nerve, which is characterized by the specific expression of the A2B5 and HNK-1 epitopes. This cell line has been assumed to give rise to oligodendrocytes and so-called type 2 astrocytes. However, it is doubtful that the latter cell type really exists in vivo. In the present study, we have addressed this question by investigating the development of astrocytes in the myelin-deficient (md) rat, which is characterized by dysmyelination and loss of oligodendrocytes. Defective oligodendrocytes were observed by the third postnatal day, well before the generation of type 2 astrocytes. Consequently, the number of type 2 astrocytes was reduced in cultures prepared from optic nerves of md rats vs. controls. This finding was not paralleled in vivo; i.e., no dying astrocytes were observed in md sections by conventional electron microscopy. However, immunoreactivity against the HNK-1 epitope was enhanced in md compared to control sections. Ultrastructurally, HNK-1 immunoreactivity was detected predominantly on the axonal surface at astroaxonal contact sites, which were found only at the nodes of Ranvier within controls but extended to the whole axonal surface in md animals. Only a minor portion of the immunoreactivity derived from glial cells, presumably from oligodendrocytes at the paranodal region in controls. Thus, the HNK-1 epitope is not a useful antigen for distinguishing astrocytes in the rat optic nerve. Accordingly, our results do not provide evidence for the existence of specialized type 2 astrocytes in vivo. In vitro, these cells are probably only oligodendrocytes that mimic some astroglial features if grown in serum-containing media.

Animals↗
PubMed1997

Expression of c-Jun protein in degenerating retinal ganglion cells after optic nerve lesion in the rat.

Axonal lesions to the optic nerve (ON) induce c-Jun expression in retinal ganglion cells (RGCs) of the rat in vivo. Detailed investigations using retrograde tracers, and double labeling studies for c-Jun and regeneration-associated factors, such as the growth-associated protein GAP-43, have suggested that this upregulation of c-Jun is part of a cell body response in an abortive attempt of affected RGCs to survive and regenerate an axon. On the other hand, prolonged expression of c-Jun protein has in several paradigms of neurodegeneration been linked to the induction of apoptotic cell death. In the present study, we examined the time course and subcellular localization of c-Jun protein by immunocytochemistry on retinal sections after optic nerve crush and carried out double labeling for c-Jun protein and DNA strand breaks to detect apoptosis on the same sections. Several days after ON lesion, a subpopulation of RGCs was detected in which c-Jun protein was not confined to the nucleus, but also located in the cytoplasm. In addition, RGCs were seen that displayed morphological signs of apoptosis, DNA strand breaks, and c-Jun immunoreactivity at the same time. Therefore, c-Jun expression is not confined to intact or regenerating ganglion cells, but also occurs in cells that are destined to die. Our results suggest that the decision to undergo either fate depends on additional signaling events that modulate the transcriptional actions of c-Jun.

Animals↗
PubMed1997

[Sympathetic reflex dystrophy in circumscribed stenosis of the abdominal aorta. Case report and discussion of pathophysiologic principles].

Reflex sympathetic dystrophy (RSD) is a pain syndrome characterized by somatosensory and motor disturbances, as well as by autonomic and trophic changes. The term is used in a descriptive sense and does not imply specific mechanisms of pathogenesis. We report on a patient who fulfilled the clinical criteria of RSD and who also displayed increasing impairment of peripheral blood supply. Angiography revealed a circumscribed stenosis of the abdominal aorta adjacent to the bifurcation. Disturbances in peripheral circulation as a potential cause of RSD are discussed.

Aorta, Abdominal↗
PubMed1997

Growth characteristics of ganglion cell axons in the developing and regenerating retino-tectal projection of the rat.

Retinal ganglion cell (RGC) axons from the temporal retina project to the anterior superior colliculus (SC), whereas nasal retinal axons project to the posterior SC. The stripe assay has shown that temporal retinal axons avoid growing on membrane stripes from the posterior SC but nasal retinal axons show no growth preference. Several putative guidance molecules have been identified in target tissues for these axons during development in vertebrates. Regenerating axons from adult rat retinae also possess the capacity to recognize appropriate target cells and to form functional connections in vivo and in vitro. However, the expression of information for axonal guidance and target recognition in mammals and birds seems to be limited to the period when central nervous system projections develop during embryogenesis. Nevertheless, the deafferented adult rat SC re-establishes target information recognizable by embryonic rat retinae, although the re-expression of guidance factors after deafferentation does not seem to be a mere recapitulation of their normal developmental expression pattern. The roles of astrocytes and microglia in axon guidance are also discussed.

Animals↗
PubMed1997

The c-Jun transcription factor--bipotential mediator of neuronal death, survival and regeneration.

Axon interruption elicits a complex neuronal response that leaves neurons poised precariously between death and regeneration. The signals underlying this dichotomy are not fully understood. The transcription factor c-Jun is one of the earliest and most consistent markers for neurons that respond to nerve-fiber transection, and its expression can be related to both degeneration and survival including target re-innervation. In vitro experiments have demonstrated that expression of c-Jun can kill neonatal neurons but, in the adult nervous system, c-Jun might also be involved in neuroprotection and regeneration. The functional characteristics of c-Jun offer a model for the ability of a single molecule to serve as pivotal regulator for death or survival, not only in the response of the cell body to axonal lesions but also following neurodegenerative disorders. In this model, the fate of neurons is determined by a novel transcriptional network comprising c-Jun, ATF-2 (activating transcription factor-2) and JNKs (c-Jun N-terminal kinases).

Animals↗
PubMed1997

Up-regulation of Bax protein in degenerating retinal ganglion cells precedes apoptotic cell death after optic nerve lesion in the rat.

Retrograde degeneration of retinal ganglion cells as a consequence of optic nerve lesion has been shown to fulfil the criteria of apoptosis. In the present study, we investigated the time course of ganglion cell apoptosis following intraorbital crushing of the optic nerve in adult rats using morphological criteria and applying a terminal transferase technique (TUNEL) for in situ detection of DNA strand breaks. In addition, we examined expression patterns of the anti-apoptotic proteins Bcl-2 and Bcl-X and the cell death-promoting protein Bax in retinae after crushing the optic nerve. Apoptotic nuclei were detected in the ganglion cell layer in the first 3 weeks after optic nerve crush, with a peak after 6 days. Bcl-2 and Bcl-X proteins were expressed in ganglion cells at low levels. Expression of Bcl-2 decreased further during the days following crush. Bcl-X expression was initially increased, followed by a decline over the following days. In contrast, Bax protein, which was expressed in most ganglion cells at moderate baseline levels, was sharply increased as early as 30 min after crush, reached peak levels after 3 days, and remained up-regulated for at least 1 week thereafter. Double labelling for Bax and TUNEL in retinal sections, however, did not reveal colocalization of the two signals in individual retinal ganglion cells, consistent with the idea that increases in Bax precede apoptosis after optic nerve lesion. Thus, retinal ganglion cell death might be prevented by ablation of Bax protein in these cells, or by up-regulation of Bax-antagonists such as Bcl-2 or Bcl-X.

Animals↗
PubMed1996

Retinal ganglion cell axons recognize specific guidance cues present in the deafferented adult rat superior colliculus.

During development, retinal ganglion cell axons establish a topographically ordered projection from the retina to the superior colliculus (SC). The putative guidance activities for retinal axons that operate during embryonic development are not detectable in the normal adult SC. However, these cues reappear upon transection of the optic nerve of adult rats. In the present study, we used a modified version of the "stripe assay," in which membranes from either anterior or posterior SC alternated with laminin stripes. Temporal embryonic retinal axons consistently avoid membranes from embryonic posterior SC, but only rarely from adult deafferented SC. However, they are attracted to membranes from both embryonic and adult deafferented anterior SC. Nasal retinal axons only show a significant preference for membranes from posterior SC after deafferentation. When retinal axons were offered a choice to grow on membranes either from their embryonic or their deafferented target regions, they showed a preference for the deafferented SC. On carpets consisting of laminin and membranes from normal SC (not deafferented) or nontarget regions (inferior colliculus), temporal and nasal axons grow either in a random fashion or show preferences for the laminin stripes. Our modified version of the classic stripe assay shows specific growth preferences of embryonic retinal axons for membrane lanes from their appropriate embryonic or deafferented adult target regions. These findings suggest that the deafferentation of the SC in adult rats triggers the reexpression of specific guidance activities for retinal axons. Those "attractive" guidance cues appear to be differentially expressed in the developing and deafferented SC.

Afferent Pathways↗
PubMed1996

Antibody that neutralizes myelin-associated inhibitors of axon growth does not interfere with recognition of target-specific guidance information by rat retinal axons.

During development, many CNS projection neurons establish topographically ordered maps in their target regions. Myelin-associated inhibitors of neurite growth contribute to the confinement of fiber tracts during development and limit plastic changes after CNS projections have been formed. Neutralization of myelin-associated growth inhibitors leads to an expansion of the retinal innervation of the superior colliculus (SC). In the lesioned adult mammalian CNS, these long projection neurons are usually unable to regrow axons over long distances after lesion due to myelin-associated inhibitors, which interfere with axonal growth in vivo and in vitro. Application of a specific antibody directed against myelin-inhibitors (IN-1) promotes regrowth of corticospinal tract or retinal ganglion cell axons. In the present study, we asked whether application of an antibody to myelin-associated growth inhibitors would lead to disturbances of target-specific axon guidance. To examine this issue, we used an in vitro model, the "stripe assay", to examine the behavior of rat retinal ganglion cell axons on membranes from embryonic and deafferented adult rat SC. On membrane preparations from embryonic rat SC, retinal fibers avoid posterior tectal membranes, possibly due to the presence of a repulsive factor. Nasal retinal axons show a random growth pattern. On membranes prepared from the deafferented adult rat SC, temporal and nasal axons prefer to grow on membranes prepared from their specific target region, which suggests the involvement of target-derived attractive guidance components. The results of the present study show that retinal axons grow significantly faster in the presence of IN-1 antibody that neutralizes myelin-associated growth inhibitors present in the membrane preparations from the adult rat SC. IN-1 antibody, however, does not interfere with specific axonal guidance. This suggests that axonal guidance and specific target finding are independently regulated in retinal axons.

Afferent Pathways↗
PubMed1996

Acute and chronic effects of troglitazone (CS-045) on isolated rat ventricular cardiomyocytes.

Freshly isolated and primary cultured adult rat cardiomyocytes were used to elucidate the mechanism of action of the new oral antidiabetic agent (+/-)-5-[4-(6-hydroxy-2, 5, 7, 8-tetramethyl-chroman-2-yl-methoxy)benzyl]-2,4-thiazolidinedione (troglitazone) on the heart. Interaction with protein kinase C (PKC) and regulation of glucose transport were evaluated as possible sites of drug action. Acute treatment (30 min) of cardiomyocytes with troglitazone did not affect the phorbolester-induced membrane association of PKC-delta and PKC-epsilon, which represent the major isoforms present in these cells. However, under these conditions the phorbolester-mediated increase in membrane associated PKC activity was inhibited by 43 +/- 4% (n = 4) without affecting the basal distribution of PKC activity. In contrast to these findings, troglitazone had no acute effect on basal or insulin-stimulated glucose transport in freshly isolated cardiomyocytes; even after 120 min treatment an unaltered release of lactate was determine in the presence of the drug. After 20 h in serum-free culture troglitazone induced a dose-dependent increase in 2-deoxyglucose uptake reaching a 40-fold stimulation at 5 mumol/l. This was paralleled by a dose-dependent increase of glucose transporter-1 (GLUT1) and GLUT4 protein expression to 320 +/- 80 and 156 +/- 15% of control, respectively. In addition, chronic exposure to troglitazone increased the GLUT4 abundance in a plasma membrane fraction about twofold. These data show that troglitazone exerts multiple effects on cardiomyocytes involving inhibition of PKC and regulation of glucose transporter expression and distribution. We suggest that an increased glucose supply may be beneficial for the diabetic heart and that modulation of PKC-activity could be relevant for improving insulin action in muscle tissue.

3-O-Methylglucose↗
PubMed1996

[Gene therapy of neurologic diseases. Experimental approaches and clinical perspectives].

So far, it has not been possible to treat many neurological conditions causally. However, in the past few years underlying genetic defects have been characterized for a substantial number of neurodegenerative disorders. Experimental methods have been developed that allow for efficient gene transfer into defined regions of the mammalian CNS. Such techniques can be applied to deliver genes into target cells of a recipient organism or to transfer genetically modified cells into defined regions of the CNS. Candidate genes for gene therapy are those encoding for neurotrophins and neurotransmitters for symptomatic therapy and, in the case of neurodegenerative disorders with localized gene defects, the wild-type allele as a causal treatment approach. In this review article, we describe some of the most widely used strategies for gene transfer to the CNS. We also report on the results obtained with animal models for human disease, and discuss both the chances and problems of gene therapy approaches in clinical medicine.

Animals↗
PubMed1995

Insulin-dependent regulation of Glut4 gene expression in ventricular cardiomyocytes: evidence for a direct effect on Glut4 transcription.

The present study examined the effect of insulin on Glut4 transcription in isolated ventricular cardiomyocytes. Upon exposure to the hormone (2 x 10(-7) M) the cellular Glut4 mRNA content increased to 224 +/- 46% of control within 3.5 hours. Nuclear run-on analysis indicated a parallel increase of transcription of the Glut4 gene to 208 +/- 49% of control. Direct incubation of cardiac nuclei with insulin resulted in a comparably significant increase of Glut4 transcription. Cross-linkage experiments with 125I-labelled insulin demonstrated the absence of soluble nuclear insulin receptors, which were readily detected in plasma and microsomal membranes. These findings suggest that expression of the cardiac Glut4 gene is subject to regulation by insulin at the transcriptional level, a process possibly involving nuclear association of the hormone.

Animals↗
PubMed1995

Myelin from peripheral and central nervous system is a nonpermissive substrate for retinal ganglion cell axons.

In the CNS of mammals axonal regeneration is limited by inhibitory influences of the glial and extracellular environment. Myelin-associated inhibitors of neurite growth as well as some properties of so called "reactive astrocytes" which make the environment nonpermissive for axonal growth contribute to the inhibitory nature of the mammalian CNS. In contrast, the PNS is supportive of regeneration and Schwann cell surfaces and Schwann-cell-derived extracellular matrix provide suitable substrates for regenerating axons in vivo and in vitro. However, as the results presented here indicate, myelin derived from normal and axotomized sciatic nerves is a nonpermissive substrate for axonal regrowth. Addition of laminin to either CNS or PNS myelin or freezing of the myelin, however, allows reproducibly axonal growth. Membrane preparations from CNS or PNS tissue on the other hand allow axon outgrowth from retinal explants when adhesive substrates (e.g., polylysin) are available. This suggests that inhibitors of neurite growth are present in myelin from the CNS and PNS. Growth supportive substrates, which are present in large quantities after PNS but not after CNS injury, can overcome nonpermissive substrate properties.

Animals↗
PubMed1995

Astrocytes from adult rat optic nerves are nonpermissive for regenerating retinal ganglion cell axons.

We have directly compared the abilities of astrocytes from newborn and adult rats to support or inhibit the growth of regenerating axons in vitro. Astrocytes prepared from newborn rats were able to promote retinal ganglion cell (RGC) axon growth from embryonic and adult rat and from adult fish retinal explants. Retinal axons from E16 rat retinae grew significantly faster on astrocytes from neonatal rats than those from E18 or adult rat retinae with growth rates comparable to RGC axons from adult fish retinae. RGC regeneration from adult rat retinae was almost completely inhibited on adult rat optic nerve astrocytes. Only axons from adult fish retinae were able to extend onto monolayers from these reactive astrocytes, although their growth rates were significantly reduced. We conclude that the failure of mammalian RGC axons to regrow within the lesioned optic nerve environment is, at least in part, due to nonpermissive aspects of adult "reactive" optic nerve astrocytes. However, the cell intrinsic growth potential of RGCs also appears to influence their ability to extend axons on cellular substrates.

Age Factors↗
PubMed1995

Direct stimulation of myocardial glucose transport and glucose transporter-1 (GLUT1) and GLUT4 protein expression by the sulfonylurea glimepiride.

Freshly isolated and primary cultured cardiac myocytes from adult rats were used to elucidate acute and chronic effects of the sulfonylurea drug glimepiride on basal and insulin-stimulated glucose transport and on expression of the transporter isoforms glucose transporter-1 (GLUT1) and GLUT4. A 30-min incubation with glimepiride (100 microM) was unable to modify the initial rates of 3-O-methylglucose transport in freshly isolated cardiocytes, both in the absence or presence of insulin (10(-7) M). Cells were then kept in serum-free culture for 20 h in the presence of glimepiride (10 microM) and a physiological insulin dose. Under these conditions, the sulfonylurea induced an increase in 2-deoxyglucose uptake to 186% of control. This drug effect was dose dependent and could also be demonstrated in the absence of insulin during the culture period. The acute action of insulin on glucose transport was additive to the effect of glimepiride, and the insulin responsiveness of glucose transport remained unaltered in sulfonylurea-treated cultures. Western blot analysis of crude membrane fractions obtained from cultured cardiocytes showed that glimepiride increased the expression of both GLUT1 and GLUT4 to 164% +/- 21% and 148% +/- 5% of control, respectively. We concluded that glimepiride increases cardiac glucose uptake by an insulin-independent pathway, probably involving an increased protein expression of GLUT1 and GLUT4. The increased expression of GLUT4 may have a therapeutic impact on the treatment of insulin-resistant states.

3-O-Methylglucose↗
PubMed1994

Differential regulation of c-JUN expression in rat retinal ganglion cells after proximal and distal optic nerve transection.

In adult rats, the distance between the site of axotomy and the cell body influences the ability of retinal ganglion cells (RGCs) to survive and regenerate an axon. Optic nerves of adult rats were transected 2 mm or 6 mm from the optic bulb and RGCs labeled with the fluorescent marker fluorogold. The time course of c-JUN expression was monitored immunocytochemically between 3 days and 4 weeks after axotomy. c-JUN expression began later and declined faster after distal axotomy than after proximal transection of the optic nerve. However, at the same time significantly more RGCs survived after distal than after proximal axotomy 3 and 4 weeks after axotomy. These findings suggest that survival and expression of c-JUN in rat RGCs are independently regulated by the length of the optic nerve stump after lesion.

Animals↗
PubMed1994

Regulation of immediate-early gene expression in rat retinal ganglion cells after axotomy and during regeneration through a peripheral nerve graft.

To determine mechanisms of structural plasticity in adult CNS neurons, we investigated the expression of immediate early genes (IEGs) in the rat retina. Gene products of different IEG families (JUN and FOS proteins) and cAMP-responsive element binding protein (CREBP) were examined by immunohistochemistry under three different paradigms. Normal rats which were not axotomized were compared with axotomized animals, were retinal ganglion cells (RGCs) were axotomized by intraorbital optic nerve cut and retrogradely labeled with fluorogold (FG). Under these circumstances, RGCs show only transient sprouting, followed by continuous retrograde RGC degeneration. In the third group, after the optic nerve lesion, adult rats additionally received a sciatic nerve graft to the transected optic nerve stump. This allows some RGCs to regenerate an axon into the grafted nerve. In both groups, the time course of RGC survival and JUN, CREB, and FOS protein expression was monitored. In normal animals, JUN-Immunoreactivity (JUN-Ir) was not detectable in the retinal ganglion cell layer. JUN-Ir was induced in about 70% of all FG-positive RGCs 5 days after axotomy. The expression of JUN-Ir stated to decline 8 days after axotomy. Only a few JUN-Ir-positive RGCs were found after 2 weeks. In transplanted animals, however, the numbers of JUN-Ir-positive RGCs were significantly higher 2 and 3 weeks after transplantation compared to animals that exclusively received axotomy. Furthermore, in grafted rats, about 70% of the regenerating RGCs expressed JUN-Ir 2 weeks after grafting as compared to only 38% JUN-positive RGCs among the surviving but not regenerating RGCs. In normal animals CREBP-Ir was constitutively expressed in nearly all cells of the retinal ganglion cell layer. The decline in number of CREBP-Ir-positive cells paralleled the axotomy-induced RGC death. FOS-Ir-positive cells were not found in the ganglion cell layer at any time. These results demonstrate a selective and transient JUN expression of RGCs after axotomy which is sustained during axonal regeneration. This suggests that sciatic nerve grafts are able to regulate the expression of JUN proteins in axotomized RGCs of adult rats.

Activating Transcription Factor 2↗