Recent studies show that a reduced effect of inhibitory transmitter system in the visual cortex may underlie aged visual function degradation. Whether excitatory transmitter system changes with age and hence affects intracortical excitation-inhibition balance is not clear. To explore this issue, we used Nissl staining and immunohistochemical methods as well as Image-Pro Express software to examine the density of Nissl-stained neurons, Glutamie acid-immunoreactive （Glu-IR） neurons and T-Aminobutyric acid-immunoreactive （GABA-IR） neurons in the primary visual cortex of young adult and aged cats. The results showed that there was no significant difference in the density of Nissl-stained neurons between young and old cats （2〉0.05）. However, the density of Glu-IR neurons and GABA-IR neurons in the primary visual cortex of aged cats was significantly lower than that of young ones （P〈0.01）. The ratio between Glu-IR neurons and GABA-IR neurons was significantly increased in old cats compared to that in young adult ones （P〈0.01）. These results indicated that the effect of excitatory transmitter system in the old visual cortex was increased relative to the inhibitory transmitter system, which might cause an imbalance between cortical excitation and inhibition and might be an important factor mediating the visual function decline during aging.
目的比较青年猫和老年猫上丘浅层(superricial Superior Colliculus,sSC)GABA能神经元及其表达的年龄相关性变化,探讨老年个体视觉功能衰退的相关神经机理。方法Nissl染色显示上丘浅层结构及神经元、免疫组织化学ABC法标记GABA免疫阳性神经元。光镜下观察,采集图像,并利用图像分析软件对带状层、浅灰质层和视层神经元及GABA免疫阳性神经元及其灰度值进行分析统计。结果GABA免疫阳性神经元、阳性纤维及其终末在青年猫及老年猫上丘浅层均有分布。与青年猫相比,老年猫上丘浅灰质层、视层神经元和GABA免疫阳性神经元密度及其GABA免疫阳性反应强度均显著下降(P<0.01)(免疫反应强度与平均灰度值成反比);带状层神经元密度也显著下降(P<0.01),但其GABA免疫阳性神经元密度无显著变化(P>0.05)。结论衰老过程中猫上丘浅层GABA能神经元的丢失和GABA表达的下降,可能是在上丘水平上导致老年个体视觉功能衰退的重要因素之一。
Psychological studies on human subjects show that contrast detection learning promote learner＇s sensitivity to visual stimulus contrast. The underlying neural mechanisms remain unknown. In this study, three cats （Felis catus） were trained to perform monocularly a contrast detection task by two-altemative forced choice method. The perceptual ability of each cat improved remarkably with learning as indicated by a significantly increased contrast sensitivity to visual stimuli. The learning effect displayed an evident specificity to the eye employed for learning but could partially transfer to the naive eye, prompting the possibility that contrast detection learning might cause neural plasticity before and after the information from both eyes are merged in the visual pathway. Further, the contrast sensitivity improvement was evident basically around the spatial frequency （SF） used for learning, which suggested that contrast detection learning effect showed, to some extent, a SF specificity. This study indicates that cat exhibits a property of contrast detection learning similar to human subjects and can be used as an animal model for subsequent investigations on the neural correlates that mediate learning-induced contrast sensitivity improvement in humans.
