Biomedical subjects

J H Weishaupt

Publications and source records attributed to J H Weishaupt.

5 recordsLinked to original sources

PubMed2001

Reduction of potassium currents and phosphatidylinositol 3-kinase-dependent AKT phosphorylation by tumor necrosis factor-(alpha) rescues axotomized retinal ganglion cells from retrograde cell death in vivo.

Tumor-necrosis-factor-alpha (TNF-alpha) prevented secondary death of retinal ganglion cells (RGCs) after axotomy of the optic nerve in vivo. This RGC rescue was confirmed in vitro in a mixed retinal culture model. In accordance with our previous findings, TNF-alpha decreased outward potassium currents in RGCs. Antagonism of the TNF-alpha-induced decrease in outward potassium currents with the potassium channel opener minoxidilsulfate (as verified by electrophysiology) abolished neuroprotection. Western blot analysis revealed an upregulation of phospho-Akt as a consequence of TNF-alpha-induced potassium current reduction. Inhibition of the phosphatidylinositol 3-kinase-Akt pathway with wortmannin decreased TNF-alpha-promoted RGC survival. These data point to a functionally relevant cytokine-dependent neuroprotective signaling cascade in adult CNS neurons.

Animals↗

PubMed2001

Transection of the optic nerve in rats: studying neuronal death and survival in vivo.

Transection of the optic nerve (ON) in the adult rat, as a model of fiber tract lesion in the adult mammalian CNS, results in delayed, mainly apoptotic death of 80--90% of retinal ganglion cells (RGCs) within 14 days post-lesion. Because of good surgical accessibility of the retina and the optic nerve, the retino-tectal projection represents not only a convenient model to study the molecular mechanisms underlying neuronal death but also serves as a suitable system for investigating potential neuroprotective agents in vivo. In the present report, we provide a detailed protocol for this model including retrograde labeling of RGCs, ON lesion, assessment of the number of surviving neurons, and tissue preparation for several standard techniques like immunohistochemistry, reverse transcription--polymerase chain reaction (RT--PCR), enzyme assays and Immunoblot.

Animals↗

PubMed2000

Brain-derived neurotrophic factor-mediated neuroprotection of adult rat retinal ganglion cells in vivo does not exclusively depend on phosphatidyl-inositol-3'-kinase/protein kinase B signaling.

The neurotrophin brain-derived neurotrophic factor (BDNF) serves as a survival, mitogenic, and differentiation factor in both the developing and adult CNS and PNS. In an attempt to identify the molecular mechanisms underlying BDNF neuroprotection, we studied activation of two potentially neuroprotective signal transduction pathways by BDNF in a CNS trauma model. Transection of the optic nerve (ON) in the adult rat induces secondary death of retinal ganglion cells (RGCs). Repeated intraocular injections of BDNF prevent the degeneration of RGCs 14 d after ON lesion most likely by inhibition of apoptosis. Here, we report that BDNF activates both protein kinase B (PKB) via a phosphatidyl-inositol-3'-kinase (PI-3-K)-dependent mechanism and the mitogen-activated protein kinases extracellular signal-regulated kinase 1 (ERK1) and ERK2. Furthermore, we provide evidence that BDNF suppresses cleavage and enzymatic activity of the neuronal cell death effector caspase-3. Distinct from our recent study in which inhibition of the PI-3-K/PKB pathway attenuated the survival-promoting action of insulin-like growth factor-I on axotomized RGCs (Kermer et al., 2000), it does not in the case of BDNF. Thus, we assume that BDNF does not depend on a single signal transduction pathway exerting its neuroprotective effects on lesioned CNS neurons.

Animals↗

PubMed1997

Sublethal oxygen-glucose deprivation alters hippocampal neuronal AMPA receptor expression and vulnerability to kainate-induced death.

Recent studies have suggested that rats subjected to transient global brain ischemia develop depressed expression of GluR-B in CA1 hippocampal neurons. The present study was performed to determine whether a similar change in AMPA receptor expression could be triggered in vitro by sublethal oxygen-glucose deprivation in rat hippocampal neuronal cultures. mRNA was extracted from individual hippocampal neurons via patch electrodes and amplified by RT-PCR 24-48 hr after sublethal oxygen-glucose deprivation. Compared with controls, insulted neurons expressed increased levels of GluR-D flop. As an indication that this change in receptor expression was functionally significant, insulted cultures exhibited increased AMPA- or kainate-induced 45Ca2+ accumulation sensitive to Joro spider toxin and increased vulnerability to kainate-induced death. These data support the hypothesis that exposure to ischemia may enhance subsequent hippocampal neuronal vulnerability to AMPA receptor-mediated excitotoxicity by modifying the relative expression of AMPA receptor subunits in a manner that promotes Ca2+ permeability.

Animals↗

PubMed1997

NR2A subunit expression shortens NMDA receptor synaptic currents in developing neocortex.

NMDA receptors play important roles in learning and memory and in sculpting neural connections during development. After the period of peak cortical plasticity, NMDA receptor-mediated EPSCs (NMDAR EPSCs) decrease in duration. A likely mechanism for this change in NMDA receptor properties is the molecular alteration of NMDA receptor structure by regulation of NMDA receptor subunit gene expression. The four modulatory NMDAR2A-D (NR2A-D) NMDA receptor subunits are known to alter NMDA receptor properties, and the expression of these subunits is regulated developmentally. It is unclear, however, how the four NR2 subunits are expressed in individual neurons and which NR2 subunits are important to the regulation of NMDA receptor properties during development in vivo. Analysis of NR2 subunit gene expression in single characterized neurons of postnatal neocortex revealed that cells expressing NR2A subunit mRNA had faster NMDAR EPSCs than cells not expressing this subunit, regardless of postnatal age. Expression of NR2A subunit mRNA in cortical neurons at even low levels seemed sufficient to alter the NMDA receptor time course. The proportion of cells expressing NR2A and displaying fast NMDAR EPSCs increased developmentally, thus providing a molecular basis for the developmental change in mean NMDAR EPSC duration.

Aging↗