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Tauopathies are a class of neurodegenerative diseases resulting from the pathological aggregation of tau protein in brain. The best known of these disorders is Alzheimer’s disease, where tau protein is deposited within neurons in the form of neurofibrillary tangles, which are formed by hyperphosphorylation of this microtubule-associated protein. Good animal model that mimic this form of age-related disease is still missing. Such a model should be characterized by: over expression, hyperphosphorylation and different cellular compartmentalization of tau in neurons, breakdown of cytoskeleton and malfunctioning of neuronal transport, and impairment of cognitive processes. We propose to develop such a model by local administration of full length tau directly into CA1 area of hippocampus in rats. Using specific pore-forming agent poly-APS we delivered tau protein through the membrane into the neurons where it is metabolized and may influence cognitive processes. Additional chronic administration of okadaic acid, a specific phosphatase inhibitor, caused tau hyperphosphorylation. Because tauopathies are age-related disorders, in our experiment we used several age-groups of animals to determine the age, in which we can provoke the morphological and cognitive impairments characteristic for tauopathy. Cognitive and neurodegenerative changes were examined with behavioral test and immunohistochemical techniques. Our data indicate that use of poly-APS enables for neuronal tau incorporation at selective brain site resulting in accelerated neurofibrillary tangle-like pathology. The major advance in the development of current tauopathy model is the determination of critical age at which it is possible to trigger morphological and cognitive impairments. This model mimics several pathologies observed in progressive dementia and could be successfully used in drug discovery to support therapeutic strategies.
Filamentous inclusions of tau protein are hallmarks of tauopathies including Alzheimer’s disease. Here a rat model for tauopathies was developed using pore-forming halitoxin Poly-APS. Tau protein was delivered through the membrane into the neurons where it is metabolized. Rats were injected with recombinant human Tau441 only (controls), Tau+Poly-APS (double) and Tau+PolyAPS+Okadaic Acid (triple). Cognitive and neurodegenerative changes were examined with Morrris water maze behavioral test and immunohistochemistry, respectively. Acquisition of the spatial reference memory was unaffected by administration of Tau or Tau+Poly-APS. However, enhanced phosphorylation of exogenously delivered tau with the triple infusion impaired learning. Hippocampal tau was visualized using antibodies against Tau441 and phosphorylated Tau-S404. The higher intensity of Tau441 immunostaining in double and triple groups suggests that exogenous tau is sequestered from the infusion solution into the cells. With respect to phospho-tau izoform we observed different cellular compartmentalization of P-Tau-S404 in double and triple treated rats. In double treated rats P-TauS401 was distributed both in the cell bodies and neuronal fi bers, while in triple group presence of OA caused redistribution of phospho-tau staining from neuronal processes to the perikaryon. This is similar to age-dependent tau redistribution between cellular compartments and could be a result of hyperphosphorylation.
A defi cit in the cholinergic system of the basal forebrain (BF) is thought to contribute to the development of cognitive symptoms of dementia. Forebrain cholinergic neurons are highly dependent on nerve growth factor (NGF) for phenotype maintenance. Attempts to prevent age-associated cholinergic vulnerability and deterioration therefore represent a crucial point for pharmacotherapy in the elderly. The pharmacological induction of endogenous NGF synthesis in the brain could be an elegant way to overcome application problems. Therefore, the present experiment was undertaken to determine the infl uence of prolonged pharmacological stimulation of NGF biosynthesis on learning and memory in aged rats. To address these issues we used young (4-month-old) and aged (28-month-old) rats in which we stimulated endogenous NGF biosynthesis by treatment with clenbuterol (β2-adrenergic receptors agonist). The cognitive behavior of the young and aged rats was assessed in the long-lasting “Non-Matching to Position Test”. Our data suggest that in aged rats, clenbuterol positively affects cognitive processes related to formation of associations established in recognition memory and discrimination tasks. In addition, NGF signifi cantly improved morphological parameters of BF cholinergic cells in aged rats. These data suggest that endogenous NGF induction restores the age-related decline of the cholinergic system activity in rats, resulting in improvement of water maze performance in old animals.
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