Aging And Sex Associated Functional Degradation Of Visual Cortical Cells In Rats

Visual functions deteriorate gradually during normal aging process, such as the decrease of visual acuity and contrast sensitivity, impairment in the ability of orientation discrimination and motion direction as well as reduction of eyes summation and temporal processing speed. Age related visual function declines can not be attributed completely to changes in optical media and retinal morphology. Considerable visual functions impairment in the old may result from neuronal morphological changes or transmitter pathways degeneration (such as weakened GABA inhibition) in the visual processing centers, such as the primary visual cortex. To uncover the neural mechanism underlying the visual function degradation is of great practical importance to how to improve life quality for the old population and to slow down the aging process in human beings.Using in vivo field potentials recording and extracellular single-unit recording techniques, we compared the short-term synaptic plasticity of geniculo-cortical visual pathway in aged and young rats. The response properties of primary visual cortical cells to flash stimuli in aged and young rats were also examined. Moreover, we investigated the sexual difference of visual cortex's function in aged rats. The density of GABA-immunoreactive neurons in primary visual cortex was quantitatively studied by immunohistochemistry method. Main results are as following:1. We compared the short-term synaptic plasticity of geniculo-cortical visual pathway in five aged rats and six young rats. Our results showed either the pair-pulse depression ratio with interstumilus intervals from 25 ms to 1000ms or the frequency depression ratio at 10 Hz~40 Hz were significantly high in aged rats. The decreased short-term depression suggests the degradation of inhibition system in cortex of aged rats, which may be related to the degradation of GABAergic system during aging.2. Response properties of primary visual cortical cells to 1, 2, 4, 8 Hz flash stimuli...