Study on the chronic hypobaric hypoxia-induced alterations in locomotor activity, learning/memory ability, responses to scopolamine and clonidine and the chemoprotection by catechins treatment in rodents
| Autor: | Kuo-Chi Chang, 張國基 |
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| Rok vydání: | 2007 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 95 Hypoxia has been reported to lead to neuronal death, neural cytoarchitecture alterations and neurotransmitter receptor modifications. In the current study, we examined the effects of long-term hypobaric hypoxia (7-28 days, 15 h/day, 380 Torr) on locomotor activity, learning and memory, pain tolerance and cardiovascular function in rodents. In addition, selected neurotransmitter receptor agonist or antagonist was used to test for the potential underlying involvement of neurotransmitter receptor in hypoxia-induced alterations. In the open field test, mouse locomotor activity was increased in the groups those were exposed to 7 and 14 days hypobaric hypoxia but reduced back to control level in groups those exposed to 21 and 28 days hypobaric hypoxia. Mouse memory was tested with Morris Water Maze. Memory was impaired in 7 and 14 days exposure groups and similar to control level in 21 and 28 days groups. Learning was improved in 28 days exposure group. Mice were also treated with muscarinic receptor antagonist scopolamine; the scopolamine treatment increased the locomotor activity in control group. However, the effect was reduced in mice exposed to 28 days of hypobaric hypoxia. Moreover, mouse memory was impaired by scopolamine treatment and the effect was also reduced in mice exposed to 28 days of hypobaric hypoxia. There were also increased potency for clonidine to inhibit locomotor activity and increased pain tolerance measured by hot-plate test in 28 days exposure group. In another set of experiment with rats, blood pressure was increased after 28 days of hypobaric hypoxia exposure along with increased alpha-2 adrenoceptor (α-2AR) expression in the locus coeruleus neurons. Furthermore, catechins such as (-) epicatechin-3-gallate (ECG) and (-) epigallocatechin-3-gallate (EGCG) reduced the impairment of learning and memory as well as the increased locomotor activity resulted from 7 days hypobaric hypoxia. These data suggest that there are two phases of reactions for mice and rats exposed to hypobaric hypoxia: (1) acute injury phase in 7-14 days exposure: Animals have impaired memory and increased locomotor activities. The animals also became ameliorated when treated with anti-oxidative reagent such as ECG and EGCG, which indicates an oxidative brain injury occurred in this phase; (2) chronic adaptive phase after 28 days exposure: Animals showed increased learning speed, reduced effects of scopolamine and increased effects of clonidine. The results indicate adaptive responses in that hypoxia tolerance has built up in this chronic phase. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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