| 其他摘要 | 1 The function of primary visual cortex and GABA system during senescence The chapter reviewed studies on neuromorphology and neuroelectrophysiology about aging, and then reported our researches during my postgraduate period. With neuroelectrophysiology techoniques, we investigated changes in function of primary visual cortex (V1), as well as GABA system during senescence. In Experiment 1 and 2, with unit-recording techniques, the orientation and direction biases, spontaneous activities and peak responses were investigated in V1 cells in middle-aged monkeys, which were compared with those in young and old monkeys; the suppression indexes of surround region of the receptive field of V1 cells were also measured in young and old monkeys. In Experiment 3, we recorded the cortical EEG during pentobarbital (GABA agonist) or ketamine (NMDA antagonist indirectly activates GABAa receptor) anesthesia in young and aged rats. Our results are as follows: In Experiment 1, the direction biases and spontaneous activities in middle-aged monkey cells were in between young and old monkey cells. However, the orientation biases and peak responses were not correlated with age. In Experiment 2, in both age groups, the orientation biases decreased in cells that were biased for orientation when the optimal surround suppression was presented. However, cells showing no significant orientation selectivity more strongly reduced surround suppression indexes in old than in young monkeys. In Experiment 3, in both age groups, pentobarbital anaesthesia induced an increase in relative power in alpha and beta bands and a decrease in the theta band, but the degrees of these power variations were more marked in aged rats. Ketamine anaesthesia decreased relative power in the theta band, with aged rats showing more markedly decreased power. In brief, the functional deficits in visual cells appeared during the early stage of senescence, which may result from general degradation of intracortical inhibition with age. 2 Researches on the reward mechanism and the biological effects of the extremely low-frequency magnetic fields This chapter firstly reviewed the reward mechanism including natural rewards and drug addiction, the biological effects of the extremely low-frequency (ELF; 0–300 Hz) magnetic fields, and the influence of the ELF magnetic fields on the reward system. Secondly, we reported our studies during my postgraduate period. The studies assessed the activities of the orbitofrontal cortex (OFC) in rats during the process of food-related stimulus, and the effects of the ELF magnetic fields on spatial cognitive function in mice. In Experiment 1, we recorded EEG activity in the OFC in rats during the development of food reward and craving. In Experiment 2, the short- and long-term effects of 50 Hz and 25 Hz magnetic fields on spatial recognition memory in mice by using a two-trial recognition Y-maze that is based on the innate tendency of rodents to explore novel environments, in which no rewards are involved. Our results are as following: In Experiment 1, the EEG activity peaking in delta band (2-4 Hz) was significantly correlated with the stimulus in the food-related environment, increasing during food reward and decreasing during food craving when compared with that in the control environment; In Experiment 2, long-term exposure to 50 Hz fields reduced recognition of the novel arm. However, neither short- nor long-term exposure to magnetic fields affects the locomotor activity of mice in the Y-maze. In summary, the delta EEG activity in the OFC could be altered by the food reward, and still in this region the gamma activity has been found to correlate with opiate addiction. Thus, these studies suggested that the OFC may play differential effects during the process of drug addction and natural rewards. Additionally, the ELF magnetic fields impair spatial recognition memory in the Y-maze in mice depending on the field strength and/or duration of exposure. Our study demonstrates, for the first time, that long-term exposure to 50 Hz electromagnetic fields impairs spatial recognition memory in a task that does not involve reward. The ELF magnetic fields have been found to potentiate morphine-induced conditional place preferences in rats. Therefore, the ELF magnetic fields may take special biological effects on drug addiction. |
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