Biomedical subjects

T Tenkova

Publications and source records attributed to T Tenkova.

14 recordsLinked to original sources

PubMed2003

Ethanol-induced neuronal apoptosis in vivo requires BAX in the developing mouse brain.

A single episode of ethanol intoxication triggers widespread apoptotic neurodegeneration in the infant rat or mouse brain. The cell death process occurs over a 6-16 h period following ethanol administration, is accompanied by a robust display of caspase-3 enzyme activation, and meets ultrastructural criteria for apoptosis. Two apoptotic pathways (intrinsic and extrinsic) have been described, either of which may culminate in the activation of caspase-3. The intrinsic pathway is regulated by Bax and Bcl-XL and involves Bax-induced mitochondrial dysfunction and release of cytochrome c as antecedent events leading to caspase-3 activation. Activation of caspase-8 is a key event preceding caspase-3 activation in the extrinsic pathway. In the present study, following ethanol administration to infant mice, we found no change in activated caspase-8, which suggests that the extrinsic pathway is not involved in ethanol-induced apoptosis. We also found that ethanol triggers robust caspase-3 activation and apoptotic neurodegeneration in C57BL/6 wildtype mice, but induces neither phenomenon in homozygous Bax-deficient mice. Therefore, it appears that ethanol-induced neuroapoptosis is an intrinsic pathway-mediated phenomenon involving Bax-induced disruption of mitochondrial membranes and cytochrome c release as early events leading to caspase-3 activation.

Animals↗

PubMed2001

Neurotransmitters and apoptosis in the developing brain.

In the immature mammalian brain during a period of rapid growth (brain growth spurt/synaptogenesis period), neuronal apoptosis can be triggered by the transient blockade of glutamate N-methyl-d-aspartate (NMDA) receptors, or the excessive activation of gamma-aminobutyric acid (GABA(A)) receptors. Apoptogenic agents include anesthetics (ketamine, nitrous oxide, isoflurane, propofol, halothane), anticonvulsants (benzodiazepines, barbiturates), and drugs of abuse (phencyclidine, ketamine, ethanol). In humans, the brain growth spurt period starts in the sixth month of pregnancy and extends to the third year after birth. Ethanol, which has both NMDA antagonist and GABA(A) agonist properties, is particularly effective in triggering widespread apoptotic neurodegeneration during this vulnerable period. Thus, maternal ingestion of ethanol during the third trimester of pregnancy can readily explain the dysmorphogenic changes in the fetal brain and consequent neurobehavioral disturbances that characterize the human fetal alcohol syndrome. In addition, there is basis for concern that agents used in pediatric and obstetrical medicine for purposes of sedation, anesthesia, and seizure management may cause apoptotic neuronal death in the developing human brain.

Animals↗

PubMed2001

Apoptosis in the in vivo mammalian forebrain.

Apoptosis is a word originally introduced by Kerr, Wyllie, and colleagues for a cell death process they defined in terms of its ultrastructural appearance in nonneuronal cells from various tissues. There are very few studies providing detailed ultrastructural criteria for recognizing neuronal apoptosis in the in vivo mammalian brain. In the absence of such criteria, the Kerr/Wyllie description pertaining to nonneuronal cells has served as a reference standard. However, contemporary neurobiologists typically rely on cell culture models for studying neuronal apoptosis, and these models are rarely validated ultrastructurally; rather they are assumed to be appropriate models based on unvalidated biochemical tests for apoptosis. Relying on evidence generated in such cell culture models or on nonspecific cytochemical tests applied to brain tissue, many authors have recently suggested that an apoptotic mechanism may mediate neuronal death in a wide variety of human neurodegenerative diseases. Whether the cell death process in neurodegenerative diseases meets ultrastructural criteria for apoptosis has been given very little consideration. Recently, several methods have been described for triggering extensive apoptotic neurodegeneration in the developing in vivo mammalian brain. These methods include head trauma or treatment with several types of drugs (NMDA antagonists, GABAA agonists, or ethanol). We have performed an ultrastructural analysis of the neuronal cell death process triggered in the cerebral cortex and thalamus by these several methods and compared it with physiological cell death (PCD), a prototypic example of neuronal apoptosis that occurs naturally in the developing brain. Our findings, which are reviewed herein, demonstrate that the types and sequence of changes induced by each of the above methods are identical to those that characterize PCD. This confirms that each of these methods produces bona fide in vivo apoptotic neurodegeneration, and it signifies that our description of this neuronal apoptotic process, which differs in some respects from the Kerr/Wyllie description of nonneuronal apoptosis, can serve as a useful reference standard for recognizing the characteristic changes that in vivo neurons undergo when they are dying by an apoptotic mechanism.

Animals↗

PubMed2000

Apolipoprotein E isoform-dependent amyloid deposition and neuritic degeneration in a mouse model of Alzheimer's disease.

Apolipoprotein E (apoE) alleles determine the age-adjusted relative risk (epsilon4 > epsilon3) for Alzheimer's disease (AD). ApoE may affect AD pathogenesis by promoting deposition of the amyloid-beta (Abeta) peptide and its conversion to a fibrillar form. To determine the effect of apoE on Abeta deposition and AD pathology, we compared APP(V717F) transgenic (TG) mice expressing mouse, human, or no apoE (apoE(-/-)). A severe, plaque-associated neuritic dystrophy developed in APP(V717F) TG mice expressing mouse or human apoE. Though significant levels of Abeta deposition also occurred in APP(V717F) TG, apoE(-/-) mice, neuritic degeneration was virtually absent. Expression of apoE3 and apoE4 in APP(V717F) TG, apoE(-/-) mice resulted in fibrillar Abeta deposits and neuritic plaques by 15 months of age and substantially (>10-fold) more fibrillar deposits were observed in apoE4-expressing APP(V717F) TG mice. Our data demonstrate a critical and isoform-specific role for apoE in neuritic plaque formation, a pathological hallmark of AD.

Alzheimer Disease↗

PubMed2000

Ethanol-induced apoptotic neurodegeneration and fetal alcohol syndrome.

The deleterious effects of ethanol on the developing human brain are poorly understood. Here it is reported that ethanol, acting by a dual mechanism [blockade of N-methyl-D-aspartate (NMDA) glutamate receptors and excessive activation of GABA(A) receptors], triggers widespread apoptotic neurodegeneration in the developing rat forebrain. Vulnerability coincides with the period of synaptogenesis, which in humans extends from the sixth month of gestation to several years after birth. During this period, transient ethanol exposure can delete millions of neurons from the developing brain. This can explain the reduced brain mass and neurobehavioral disturbances associated with human fetal alcohol syndrome.

Animals↗

PubMed2000

Apolipoprotein E facilitates neuritic and cerebrovascular plaque formation in an Alzheimer's disease model.

The epsilon4 allele of apolipoprotein E (ApoE) is an important genetic risk factor for Alzheimer's disease (AD). Increasing evidence suggests that this association may be linked to the ability of ApoE to interact with the amyloid-beta (Abeta) peptide and influence its concentration and structure. To determine the effect of ApoE on Abeta and other AD pathology in vivo, we used APPsw transgenic mice and ApoE knockout (-/-) mice to generate APPsw animals that carried two (ApoE +/+), one (ApoE +/-), or no copies (ApoE -/-) of the normal mouse ApoE gene. At 12 months of age, Abeta deposition was present in the cortex and hippocampus and was also prominent within leptomeningeal and cortical blood vessels of all APPsw ApoE +/+ mice. Importantly, although Abeta deposition still occurred in APPsw ApoE -/- mice, no fibrillar Abeta deposits were detected in the brain parenchyma or cerebrovasculature. There was also no neuritic degeneration associated with Abeta deposition in the absence of ApoE. These data demonstrate that ApoE facilitates the formation of both neuritic and cerebrovascular plaques, which are pathological hallmarks of AD and cerebral amyloid angiopathy.

Alzheimer Disease↗

PubMed1999

Excitotoxic cell death dependent on inhibitory receptor activation.

Although excitotoxic cell death is usually considered a Ca(2+)-dependent process, in certain neuronal systems there is strong evidence that excitotoxic cell death is independent of Ca2+ and is instead remarkably dependent on extracellular Cl-. We have shown (in isolated chick embryo retina) that at least some of the lethal Cl- entry is through GABA and glycine receptors. Here we show that when all the GABA and glycine receptors are blocked by using an appropriate cocktail of inhibitors, agonist-induced excitotoxic cell death can be completely prevented. To determine if ligand-gated Cl- channels contribute to excitotoxic cell death in other neurons, we examined KA-induced cell death in cultured rat cerebellar granule cells. GABA receptor blockade with either a competitive or noncompetitive antagonist provides complete neuroprotection. KA stimulates Cl- uptake by the granule cells, and this is blocked by the GABA antagonists. Granule cell cultures take up [3H]GABA and release it in response to KA treatment. A subpopulation of neurons in the cultures is shown to have GAD and high concentrations of GABA, and this presumably is the source of the GABA that leads to receptor activation and lethal Cl- entry. Finally, we show that retinal cell death due to 1 h of simulated ischemia (combined oxygen and glucose deprivation) is completely prevented by blocking the inhibitory receptors. These results indicate that, paradoxically, excitotoxic cell death is completely dependent on activation of inhibitory receptors, in at least some neuronal systems, and this pathological process may contribute to disease.

Action Potentials↗

PubMed1998

Disseminated corticolimbic neuronal degeneration induced in rat brain by MK-801: potential relevance to Alzheimer's disease.

Blockade of N-methyl-D-aspartate (NMDA) glutamate receptors by MK-801 induces neuronal degeneration in the posterior cingulate/retrosplenial cortex and other corticolimbic regions although damage in the latter has not been adequately characterized. This disseminated corticolimbic damage is of interest since NMDA hypofunction, the mechanism that triggers this neurodegenerative syndrome, has been postulated to play a role in the pathophysiology of Alzheimer's disease (AD). Several histological methods, including electron microscopy, were used to evaluate the neurotoxic changes in various corticolimbic regions of rat brain following MK-801 or a combination of MK-801 plus pilocarpine. We found that MK-801 triggers neuronal degeneration in a widespread pattern similar to that induced by phencyclidine and that females showed more damage than males. The neurotoxic reaction involved additional brain regions when muscarinic receptors were hyperactivated by administering pilocarpine with MK-801. Ultrastructural evaluation revealed that a major feature of the neurotoxic action involves degeneration of dendritic spines which entails loss of synaptic complexes. The ultrastructural appearance of degenerating neurons was generally inconsistent with an apoptotic mechanism, although evidence equivocally consistent with apoptosis was observed in some instances. The cell death process evolved relatively slowly and was still ongoing 7 days posttreatment. Relevance of these results to AD is discussed.

Alzheimer Disease↗

PubMed1997

Vacuolar H+-ATPase in ocular ciliary epithelium.

The mechanisms controlling the production of aqueous humor and the regulation of intraocular pressure are poorly understood. Here, we provide evidence that a vacuolar H+-ATPase (V-ATPase) in the ocular ciliary epithelium is a key component of this process. In intracellular pH (pHi) measurements of isolated ciliary epithelium performed with 2',7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF), the selective V-ATPase inhibitor bafilomycin A1 slowed the recovery of pHi in response to acute intracellular acidification, demonstrating the presence of V-ATPase in the plasma membrane. In isolated rabbit ciliary body preparations examined under voltage-clamped conditions, bafilomycin A1 produced a concentration-dependent decrease in short-circuit current, and topical application of bafilomycin A1 reduced intraocular pressure in rabbits, indicating an essential role of the V-ATPase in ciliary epithelial ion transport. Immunocytochemistry utilizing antibodies specific for the B1 isoform of the V-ATPase 56-kDa subunit revealed localization of V-ATPase in both the plasma membrane and cytoplasm of the native ciliary epithelium in both rabbit and rat eye. The regional and subcellular distribution of V-ATPase in specific regions of the ciliary process was altered profoundly by isoproterenol and phorbol esters, suggesting that change in the intracellular distribution of the enzyme is a mechanism by which drugs, hormones, and neurotransmitters modify aqueous humor production.

Animals↗

PubMed1997

Age-related distribution of cones and ON-bipolar cells in the rd mouse retina.

PURPOSE: Retinal dystrophic (rd) mice lose most of their rod photoreceptors within the first three weeks after birth. We determined the age-related distribution of peanut agglutinin lectin (PNA)-labeled cones during the first 12 months of age. We also investigated whether the density of ON-bipolar cells expressing L7 protein was affected by their loss of photoreceptor inputs. METHODS: rd mice were selected from a transgenic strain which expresses an L7-beta-galactosidase fusion gene localized to ON-bipolar cells. Cones were stained with PNA and ON-bipolar cells with bluo-gal (halogenated indolyl-beta-D-galactoside). Retinas were flat-mounted and observed at 1, 2, 3, 6 and 12 months of age. RESULTS: PNA-labeled cones are distributed unevenly across the retina at 1 month postnatal. Their concentration decreases first in the central and far peripheral retina, leaving a ring of labeled cells in the midperipheral region. At 3 months, a larger patch of cones remains in the supero-temporal midperipheral region and a smaller patch in the infero-nasal retina. By 6 months, few cones remain in the infero-nasal retina; by 1 year approximately 100 cones remain in the entire retina, localized to the superior midperipheral region. ON-bipolar cells appear evenly distributed at 1 month. By 2-3 months, relatively more bluo-gal staining is seen in the midperipheral regions underlying dense cone populations. At 6-12 months, bluo-gal label is distributed in a spotty pattern with little or no staining seen in areas of apparent neovascularization. CONCLUSIONS: (1) PNA-labeling of cones in the rd retina deteriorates in a distinct spatial pattern with the longest cone survival in the midperipheral superior retina. (2) ON-bipolar cells are more densely labeled in regions of high cone density during the early months of cone degeneration and, in later stages, show relative decreases in regions of apparent neovascularization.

Age Factors↗

PubMed1997

Photoreceptor transplants increase host cone survival in the retinal degeneration (rd) mouse.

Retinal transplants offer a potentially interesting approach to treating human retinal degenerations, but so far little quantitative data are available on possible beneficial effects. We isolated photoreceptor layers from normal-sighted mice and grafted them into the subretinal space of retinal degeneration (rd) mice lacking rod photoreceptors. At 2 weeks after surgery, the numbers of residual host cone photoreceptors outside the graft zone were quantified following specific labelling. Examination of operated retinas revealed highly significantly greater numbers of surviving cones (mean of 38% more at 2 weeks) within the central field compared to sham-operated paired control retinas (p < 0.01). These are the first quantified data indicating a trophic effect of transplanted photoreceptors upon host cone cells. As cone cells are responsible for high acuity and colour vision, such data could have important implications not only for eventual therapeutic approaches to human retinal degenerations but also to understanding underlying interactions between retinal photoreceptors.

Animals↗

PubMed1993

Sympathetic hyperinnervation protects vascular smooth muscle cells from necrosis in stroke-prone spontaneously hypertensive rats.

Sympathetic nerve fiber distribution and vascular smooth muscle morphology were investigated in the ophthalmic artery of stroke-prone spontaneously hypertensive rats (SHRSP) and were compared with those of normotensive Wistar Kyoto (WKY) rats at the age of 120 days. The distribution of fluorescent noradrenergic (NA) nerve fibers was examined by the glyoxylic acid method. The ophthalmic artery was divided into two portions according to the size of the outer diameter, that is into a proximal portion (above 100 microns) and a distal portion (30-70 microns). The distribution densities of noradrenergic nerve fibers were measured by quantitative image analysis using the Interactive Bild-Analyse System (IBAS). The distribution densities of NA nerve fibers in both portions of the ophthalmic artery were significantly higher (p < 0.01) in SHRSP than that in WKY rats. The difference in the density of NA fibers of the ophthalmic arteries between SHRSP and WKY rats was 1.9 times in the proximal portion and 1.5 times in the distal portion. The vascular smooth muscle cells of the ophthalmic arteries in SHRSP were observed by scanning electron microscope to examine the trophic effect of NA nerve fibers on the vascular smooth muscle cells. The smooth muscle cells of both portions of the ophthalmic arteries in SHRSP showed a smooth surface texture and no necrosis, and were very similar to those of WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic Fibers↗

PubMed1990

Internalized gap junctions in ciliary epithelium of rabbit and rat. A transmission electron-microscopic study.

Transmission electron microscopy was used to examine internalized gap junctions (IGJ) in rabbit and rat ciliary epithelial cells. A prominent feature of all the specimens studied was the presence of different images of IGJ membrane that entrapped a portion of an adjoining cell. We documented and analyzed more than 500 gap junction (GJ) vacuoles and invaginations, the latter comprising less than 20% of all the structures examined. With ten exceptions found in non-pigmented cells, all the IGJ were unidirectionally internalized within the cytoplasm of pigmented epithelial cells. Morphological signs of autophagic degradation of GJ vacuoles were observed. An essential finding was that once a GJ membrane started to invaginate, a "lucidation" of a part of the protruding cytoplasm occurred; no planar GJ membranes exhibited such an alteration. The present finding suggest that IGJ derived from the epithelium of ciliary processes arise through an invagination-endocytosis mechanism and are degraded autophagically. This phenomenon may be relevant to aqueous humor production.

Animals↗

PubMed1988

Golgi-cilium complex in rabbit ciliary process cells.

We report here on a structural association of single cilia, via their striated rootlets, with the Golgi complex in epithelial cells and stromal fibroblasts of rabbit ciliary processes of the eye. The structure is designated a Golgi-cilium complex and its likely role in aqueous humor production is discussed.

Animals↗