Biomedical subjects

Anja U Bräuer

Publications and source records attributed to Anja U Bräuer.

14 recordsLinked to original sources

PubMed2006

Inherited cortical HCN1 channel loss amplifies dendritic calcium electrogenesis and burst firing in a rat absence epilepsy model.

While idiopathic generalized epilepsies are thought to evolve from temporal highly synchronized oscillations between thalamic and cortical networks, their cellular basis remains poorly understood. Here we show in a genetic rat model of absence epilepsy (WAG/Rij) that a rapid decline in expression of hyperpolarization-activated cyclic-nucleotide gated (HCN1) channels (I(h)) precedes the onset of seizures, suggesting that the loss of HCN1 channel expression is inherited rather than acquired. Loss of HCN1 occurs primarily in the apical dendrites of layer 5 pyramidal neurons in the cortex, leading to a spatially uniform 2-fold reduction in dendritic HCN current throughout the entire somato-dendritic axis. Dual whole-cell recordings from the soma and apical dendrites demonstrate that loss of HCN1 increases somato-dendritic coupling and significantly reduces the frequency threshold for generation of dendritic Ca2+ spikes by backpropagating action potentials. As a result of increased dendritic Ca2+ electrogenesis a large population of WAG/Rij layer 5 neurons showed intrinsic high-frequency burst firing. Using morphologically realistic models of layer 5 pyramidal neurons from control Wistar and WAG/Rij animals we show that the experimentally observed loss of dendritic I(h) recruits dendritic Ca2+ channels to amplify action potential-triggered dendritic Ca2+ spikes and increase burst firing. Thus, loss of function of dendritic HCN1 channels in layer 5 pyramidal neurons provides a somato-dendritic mechanism for increasing the synchronization of cortical output, and is therefore likely to play an important role in the generation of absence seizures.

Action Potentials↗

PubMed2006

Environmental manipulations early in development alter seizure activity, Ih and HCN1 protein expression later in life.

Although absence epilepsy has a genetic origin, evidence from an animal model (Wistar Albino Glaxo/Rijswijk; WAG/Rij) suggests that seizures are sensitive to environmental manipulations. Here, we show that manipulations of the early rearing environment (neonatal handling, maternal deprivation) of WAG/Rij rats leads to a pronounced decrease in seizure activity later in life. Recent observations link seizure activity in WAG/Rij rats to the hyperpolarization-activated cation current (Ih) in the somatosensory cortex, the site of seizure generation. Therefore, we investigated whether the alterations in seizure activity between rats reared differently might be correlated with changes in Ih and its channel subunits hyperpolarization-activated cation channel HCN1, 2 and 4. Whole-cell recordings from layer 5 pyramidal neurons, in situ hybridization and Western blot of the somatosensory cortex revealed an increase in Ih and HCN1 in neonatal handled and maternal deprived, compared to control rats. The increase was specific to HCN1 protein expression and did not involve HCN2/4 protein expression, or mRNA expression of any of the subunits (HCN1, 2, 4). Our findings provide the first evidence that relatively mild changes in the neonatal environment have a long-term impact of absence seizures, Ih and HCN1, and suggest that an increase of Ih and HCN1 is associated with absence seizure reduction. Our findings shed new light on the role of Ih and HCN in brain functioning and development and demonstrate that genetically determined absence seizures are quite sensitive for early interventions.

Animals↗

PubMed2006

Improved outcome of facial nerve repair in rats is associated with enhanced regenerative response of motoneurons and augmented neocortical plasticity.

Within a recent study on the vibrissae motor performance after facial nerve repair in strains of blind (SD/RCS) and sighted (SD) rats we found that, despite persisting myotopic disorganization in the facial nucleus, the blind animals fully restored vibrissal whisking. Here we searched for morphological substrates of better recovery in the regenerating motoneurons and in the cerebral motor cortex. Expression analyses of the neurite growth-related proteins f-actin, neuronal class III beta-tubulin and plasticity-related gene-1, and stereological estimates of growth cone densities revealed a more vigorous regenerative response in the proximal nerve stump of blind SD/RCS rats compared with SD animals at 5-7 days after buccal nerve transection. Using c-Fos immunoreactivity as a marker for neuronal activation, we found that the volume of the cortex acutely responding to nerve transection (facial muscles reactive volume, FMRV) in both hemispheres of intact sighted rats was twofold smaller than that measured in blind animals. One month after transection and suture of the right facial nerve (FFA) we found a twofold increase in the FMRV in both rat strains compared with intact animals. The FMRV in SD/RCS animals, but not in SD rats, returned to the values in intact rats 2 months after FFA. Our findings suggest that enhanced plasticity in the CNS and an augmented regenerative response of the injured motoneurons contribute to better functional recovery in blind rats.

Actins↗

PubMed2005

Functional significance of HCN2/3-mediated I(h) in striatal cells at early developmental stages.

Hyperpolarization-activated cAMP-gated cation currents (I(h)) were recently linked to pre- and postnatal developmental processes in several brain regions, including the ventral telencephalon. To evaluate the role of I(h) in striatal development, we used short-term cultured cells from the lateral ganglionic eminence at embryonic day 14 (E14) and postnatal days 1-3 (P1-3) as well as the embryonic striatal progenitor cell line ST14A. Western blot analysis of the I(h) underlying subunit proteins HCN1-4 revealed strong HCN2 expression in proliferating ST14A cells and weak expression in postmitotic ST14A cells and in cells from the developing brain. We also found HCN3 expression only in ST14A cells at both proliferative and nonproliferative stages but not in short-term cultured striatal cells. In all cases, HCN1 and HCN4 transcripts were below the detection level. Despite the selective protein expression, RT-PCR analysis showed stable expression of HCN2-4 but not HCN1 mRNA in all short-term-cultured striatal cells and in the ST14A cell line. Consistent with the strong protein expression, an I(h) was recorded with features of an HCN2-mediated current in ST14A cells at the proliferative stage and in short-term-cultured E14 cells. Of particular importance is that we detected no currents upon hyperpolarization in the ST14A cells at the nonproliferative stage when only HCN3 protein was present. These results suggest the potential importance of ST14A cells in defining the molecular mechanisms regulating I(h) expression and function.

Animals↗

PubMed2005

Neurotractin/kilon promotes neurite outgrowth and is expressed on reactive astrocytes after entorhinal cortex lesion.

The IgLON subgroup of the immunoglobulin superfamily consists of four members that are thought to be important in neural cell-cell recognition. Here, we cloned and characterized the murine IgLON subgroup member neurotractin/kilon, in the context of brain development and axonal regeneration. Neurotractin/kilon was found to be upregulated during brain development and is expressed on neurites of primary hippocampal neurons. To elucidate a potential role for neurotractin/kilon during regeneration in the CNS, we performed lesions in the entorhinal cortex, and showed that the expression of neurotractin/kilon is induced on reactive astrocytes. Notably, the expression on reactive astrocytes appears specifically in the denervated outer molecular layer of the dentate gyrus, where regenerative axon sprouting occurs. In vitro assays demonstrated that neurotractin/kilon attracts hippocampal axons in the stripe assay and that astroglial neurotractin/kilon promotes neurite outgrowth. These results suggest a function for neurotractin/kilon as a trans-neural growth-promoting factor for outgrowing axons following hippocampal denervation.

Animals↗

PubMed2004

Identification of macrophage/microglia activation factor (MAF) associated with late endosomes/lysosomes in microglial cells.

Damage to the central nervous system triggers rapid activation and specific migration of glial cells towards the lesion site. There, glial cells contribute heavily to secondary neuronal changes that take place after lesion. In an attempt to identify the molecular cues of glial activation following brain trauma we performed differential display reverse transcription-polymerase chain reaction screenings from lesioned and control hippocampus. Here we report on the identification of the macrophage/microglia activation factor (MAF), a new membrane protein with seven putative transmembrane domains. Expression analysis revealed that MAF is predominantly expressed in microglial cells in the brain, and is upregulated following brain lesion. Overexpression of MAF in non-glial cells shows an intracellular codistribution with the lysosomal marker endosome/lysosome-associated membrane protein-1 (lamp-1). Furthermore, MAF-transfected cells show that MAF is primarily associated with late endosomes/lysosomes, and that this association can be disrupted by activation of protein kinase C-dependent pathways. In conclusion, these results imply that MAF is involved in the dynamics of lysosomal membranes associated with microglial activation following brain lesion.

Amino Acid Sequence↗

PubMed2004

Selenium and brain function: a poorly recognized liaison.

Molecular biology has recently contributed significantly to the recognition of selenium (Se)2 and Se-dependent enzymes as modulators of brain function. Increased oxidative stress has been proposed as a pathomechanism in neurodegenerative diseases including, among others, Parkinson's disease, stroke, and epilepsy. Glutathione peroxidases (GPx), thioredoxin reductases, and one methionine-sulfoxide-reductase are selenium-dependent enzymes involved in antioxidant defense and intracellular redox regulation and modulation. Selenium depletion in animals is associated with decreased activities of Se-dependent enzymes and leads to enhanced cell loss in models of neurodegenerative disease. Genetic inactivation of cellular GPx increases the sensitivity towards neurotoxins and brain ischemia. Conversely, increased GPx activity as a result of increased Se supply or overexpression ameliorates the outcome in the same models of disease. Genetic inactivation of selenoprotein P leads to a marked reduction of brain Se content, which has not been achieved by dietary Se depletion, and to a movement disorder and spontaneous seizures. Here we review the role of Se for the brain under physiological as well as pathophysiological conditions and highlight recent findings which open new vistas on an old essential trace element.

Animals↗

PubMed2004

Molecular cloning and expression regulation of PRG-3, a new member of the plasticity-related gene family.

Phospholipid-mediated signalling on neurons provokes diverse responses such as neurogenesis, pattern formation and neurite remodelling. We have recently uncovered a novel set of molecules in the mammalian brain, named plasticity-related genes (PRGs), which mediate lipid phosphate phosphatase activity and provide evidence for their involvement in mechanisms of neuronal plasticity. Here, we report on a new member of the vertebrate-specific PRG family, which we have named plasticity-related gene-3 (PRG-3). PRG-3 is heavily expressed in the brain and shows a specific expression pattern during brain development where PRG-3 expression is found predominantly in neuronal cell layers and is already expressed at embryonic day 16. In the mature brain, strongest PRG-3 expression occurs in the hippocampus and cerebellum. Overexcitation of neurons induced by kainic acid leads to a transient down-regulation of PRG-3. Furthermore, PRG-3 is expressed on neurite extensions and promotes neurite growth and a spreading-like cell body in neuronal cells and COS-7 cells. In contrast to previously described members of the PRG family, PRG-3 does not perform its function through enzymatic phospholipid degradation. In summary, our findings feature a new member of the PRG family which shows dynamic expression regulation during brain development and neuronal excitation.

Amino Acid Sequence↗

PubMed2004

An impaired neocortical Ih is associated with enhanced excitability and absence epilepsy.

Neuronal subthreshold excitability and firing behaviour are markedly influenced by the activation and deactivation of the somato-dendritic hyperpolarization-activated cation current (Ih). Here, we evaluated possible contributions of Ih to hyperexcitability in an animal model of absence seizures (WAG/Rij rats). We investigated pyramidal neurons of the somatosensory neocortex, the site of generation of spike-wave discharges. Ih-mediated functions in neurons from WAG/Rij rats, Wistar rats (sharing the same genetic background with WAG/Rij, but less epilepsy-prone) and ACI rats (an inbred strain, virtually free of seizures) were compared. We complemented whole-cell recordings from layer 2-3 pyramidal neurons with immunohistochemistry, Western blot and RT-PCR analysis of the h-channel subunits HCN1-4. The fast component of Ih activation in WAG/Rij neurons was significantly reduced (50% reduction in the h-current density) and four times slower than in neurons from nonepileptic Wistar or ACI rats. The results showing decreases in currents corresponded to a 34% reduction in HCN1 protein in the WAG/Rij compared to the Wistar neocortex, but HCN1 mRNA showed stable expression. The other three Ih subunit mRNAs and proteins (HCN2-4) were not affected. The alterations in Ih magnitude and kinetics of gating in WAG/Rij neurons may contribute to augmented excitatory postsynaptic potentials, the increase in their temporal summation and the facilitation of burst firing of these neurons because each of these effects could be mimicked by the selective Ih antagonist ZD 7288. We suggest that the deficit in Ih-mediated functions may contribute to the development and onset of spontaneously occurring hyperexcitability in a rat model of absence seizures.

2-Amino-5-phosphonovalerate↗

PubMed2004

Molecular actions of selenium in the brain: neuroprotective mechanisms of an essential trace element.

In addition to acting as an essential nutrient for the immune system and overall body function, it is apparent that selenium also plays a critical role in the operation of the nervous system. Selenium itself is a constituent of selenoproteins, which are primarily involved in antioxidant function and redox status. However, apart from its covalent incorporation into these proteins, selenium also performs neuroprotective actions independent of translational processes. Furthermore, low selenium intake has detrimental effects on proper brain function, such as epileptic episodes and neuronal cell death, which have, in turn, been shown to be mitigated by higher selenium levels. Understanding the mechanisms of selenium action will be crucial to determining its potential as a preventive and therapeutic agent against excitatory brain damage.

Animals↗

PubMed2003

Molecular analysis of Nogo expression in the hippocampus during development and following lesion and seizure.

The Nogo gene encodes an integral membrane protein mainly responsible for the neurite inhibition properties of myelin. Here, we analyzed the expression pattern of Nogo-A, Nogo-B, and Nogo-C and Nogo-66 receptor (Ng66R) mRNA during hippocampal development and lesion-induced axonal sprouting. Nogo-A and Nogo-B and Ng66R transcripts preceded the progress of myelination and were highly expressed at postnatal day zero (P0) in all principal hippocampal cell layers, with the exception of dentate granule cells. Only a slight Nogo-C expression was found at P0 in the principal cell layers of the hippocampus. During adulthood, all Nogo splice variants and their receptor were expressed in the neuronal cell layers of the hippocampus, in contrast to the myelin basic protein mRNA expression pattern, which revealed a neuronal source of Nogo gene expression in addition to oligodendrocytes. After hippocampal denervation, the Nogo genes showed an isoform-specific temporal regulation. All Nogo genes were strongly regulated in the hippocampal cell layers, whereas the Ng66R transcripts showed a significant increase in the contralateral cortex. These data could be confirmed on protein levels. Furthermore, Nogo-A expression was up-regulated after kainate-induced seizures. Our data show that neurons express Nogo genes with a clearly distinguishable pattern during development. This expression is further dynamically and isoform-specifically altered after lesioning during the early phase of structural rearrengements. Thus, our results indicate a role for Nogo-A, -B, and -C during development and during the stabilization phase of hippocampal reorganization. Taken together with these data, the finding that neurons in a highly plastic brain region express Nogo genes supports the hypothesis that Nogo may function beyond its known neuronal growth inhibition activity in shaping neuronal circuits.

Animals↗

PubMed2003

Identification of neuronal cell death in a model of degeneration in the hippocampus.

Neuronal cell death and microglial changes are both hallmarks of neurodegenerative disorders. Therefore, analysis of degenerating neurons related to microglial changes are addressed in many studies of neurosciences. Here we compared different lesion models and two markers for neurodegeneration (Fluoro-Jade and propidium iodide) in an in vivo as well as an in vitro approach. Fluoro-Jade is a specific and selective marker to identify neurons undergoing degeneration. We also tested this marker to analyze neurodegeneration in organotypic hippocampal slice cultures. We could show that activation of microglia is followed by neuronal cell death. Most degeneration markers, such as propidium iodide, only stain the neuronal cell body excluding the axonal and dendritic processes. Fluoro-Jade is able to stain the distal portion as well as the proximal portion of the dissected axon including the axotomized neuron, as so called anterograde and retrograde degeneration after axotomy. To analyze the specificity of Fluoro-Jade, we used primary microglial and BV-2 cells, a well-described murine microglial cell line. Treatment of microglial and BV-2 cells with an excess of L-glutamate induces cell death which could be detected by propidium iodide staining, but not by Fluoro-Jade, demonstrating its specificity to monitor neuronal cell death.

Animals↗

PubMed2003

A new phospholipid phosphatase, PRG-1, is involved in axon growth and regenerative sprouting.

Outgrowth of axons in the central nervous system is governed by specific molecular cues. Molecules detected so far act as ligands that bind to specific receptors. Here, we report a new membrane-associated lipid phosphate phosphatase that we have named plasticity-related gene 1 (PRG-1), which facilitates axonal outgrowth during development and regenerative sprouting. PRG-1 is specifically expressed in neurons and is located in the membranes of outgrowing axons. There, it acts as an ecto-enzyme and attenuates phospholipid-induced axon collapse in neurons and facilitates outgrowth in the hippocampus. Thus, we propose a novel mechanism by which axons are able to control phospholipid-mediated signaling and overcome the growth-inhibiting, phospholipid-rich environment of the extracellular space.

Amino Acid Sequence↗

PubMed2002

Selenium deficiency increases susceptibility to glutamate-induced excitotoxicity.

Excitotoxic brain lesions, such as stroke and epilepsy, lead to increasing destruction of neurons hours after the insult. The deadly cascade of events involves detrimental actions by free radicals and the activation of proapoptotic transcription factors, which finally result in neuronal destruction. Here, we provide direct evidence that the nutritionally essential trace element selenium has a pivotal role in neuronal susceptibility to excitotoxic lesions. First, we observed in neuronal cell cultures that addition of selenium in the form of selenite within the physiological range protects against excitotoxic insults and even attenuates primary damage. The neuroprotective effect of selenium is not directly mediated via antioxidative effects of selenite but requires de novo protein synthesis. Gel shift analysis demonstrates that this effect is connected to the inhibition of glutamate-induced NF-kappaB and AP-1 activation. Furthermore, we provide evidence that selenium deficiency in vivo results in a massive increase in susceptibility to kainate-induced seizures and cell loss. These findings indicate the importance of selenium for prevention and therapy of excitotoxic brain damage.

Animals↗