| 其他摘要 | 1. Visual cortical neuron response to pattern contrast and its latency characteristics in senescent rhesus monkeys: It is well known that visual function is affected significantly by normal aging, such as decreased spatial and temporal contrast sensitivity as well as prolonged visual information processing. Although some of declines of visual function are related to the optical changes of eyes, these changes can not explain most of the aging-related visual deficits. The results from our previous studies and other data indicate that the visual function declines are underpinned mainly by the functional changes of the central visual system. Therefore, in the present study, we used single-unit recording technique to compare the contrast response property of neurons in the primary visual cortex (V1) between young and old rhesus monkeys, and also the response latency and its variability of neurons in the V1 and the middle temporal cortex (MT). The results showed that the contrast sensitivity of old monkey V1 neurons decreased, accompanied by reduced signal-to-noise ratios when compared with that of young adult monkey V1 neurons, and as well that response latency and its variability of old monkey V1 and MT neurons increased when compared with those of young adult monkey V1 and MT neurons. However, the mean difference in response latency of V1 neurons between young adult and old animals was larger than that of MT neurons, indicating that MT neurons could compensate the aging effects by unclear mechanisms. Additionally, there were the positive correlations between response latency and variability of neurons in V1 area in both age groups, but no correlations in MT area in either the young group or the old group. These findings suggest that the response properties of contrast and latency of the cortical neurons generate alterations which may be related to a degeneration of inhibitory intracortical circuits in the central visual system, but the underlying molecular mechanisms and neural circuits remain unclear. In conclusion, these results provide a new clue for a better understanding about the neural mechanisms underlying the decreased spatial and temporal contrast sensitivity, and also prolonged visual information processing of aged human. 2. Researches on the effects of the extremely-low frequency magnetic fields on brain function and cognitive function of orbitofrontal cortex: The aims of these studies were (1) to investigate the effects of the extremely low-frequency (ELF) magnetic field (20 Hz, 14 mT) exposure during morphine treatment on dopamine D2 receptor density in the rat dorsal hippocampus following withdrawal; (2) to evaluate the effects of the ELF magnetic field (50 Hz, 2 mT) exposure during the early adolescent period of mice on spatial memory performance; (3) to preliminarily investigate the role of orbitofrontal cortex (OFC) in the novelty-seeking behavior of rats. In Experiment 1, we used the immunohistochemical approach to examine the alterations of the dopamine D2 receptor density in the rat dorsal hippocampus. The results showed that the density of dopamine D2 receptor in morphine-treated rats was significantly lower than that of the saline control group during early withdrawal days, and that the combination of ELF magnetic field exposure and morphine treatment strengthened this downregulation. However, the D2 receptor density tended to normalize as morphine withdrawal days increased. These findings suggest that withdrawal from chronic morphine treatment may lead to neuroadapatation of the hippocampus dopamine system, and that the combination of ELF magnetic field exposure and morphine treatment may strengthen this adaptation, which provides a possible neural mechanism underlying the potentiating effect of ELF magnetic field exposure on morphine-induced conditioned place preference observed in our previous behavioral studies. In Experiment 2, we used the two-trial Y-maze and Morris water maze tasks to investigate the effects of the ELF magnetic field exposure in the early adolescent period of mice on spatial memory performance. The results showed that the magnetic field exposure did not affect Y-maze performance, but improved spatial learning acquisition and memory retention in the water maze task. Under the present experimental conditions, our data indicate the task-specific effects of chronic exposure to the ELF magnetic field during early adolescence on spatial memory performance. In Experiment 3, we used both the open-field and Y-maze behavioral paradigms to examine the role of orbitofrontal cortex in the novelty-seeking behavior of rats. Male Sprague-Dawley rats received bilateral electrolytic lesions of the OFC or sham lesions. The results showed that OFC lesions did not impair neuromotor ability of rats, but rats with lesions of the OFC exhibited reduced ambulation distance and numbers of rearing, and also reduced duration and number of visits in the novel arm when compared with the sham controls. The findings suggest that the intact OFC is crucial for the novelty-seeking behavior of rats, which may be related to the implications of the OFC in memory or decision-making on behavior. |
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