Effects Of Aging On The Spatial Frequency Selectivity Of Visual Cortical Neurons And Activities Of Glial Cells

Our ability to discriminate fine morphological difference between objects, called visual acuity, decreases during aging. It's unclear if this visual acuity decrease relates to selectivity changes of visual cortical neurons to visual stimulus spatial frequencies. On the other hand, previous investigations on aged visual cortex show that functional degradation of visual cortical neurons are accompanied by a decreased expression of neurotransmitters, especially inhibitory ones. However, there is no study to report whether functional decline of visual cortical neurons is directly correlated with activity changes of glial cells. This research uses cats as subjects and investigate the selectivity change of V1 neurons to visual stimulus spatial frequencies with age as well as the impact of senescence on glial cells activity changes, trying to uncover the neural mechanisms that may underlie the reduced visual acuity and other visual ability declines in the aged individuals. The main results are as follows:1. We recorded respectively the tuning response of V1 neurons in both old and young adult cats to varied stimulus spatial frequencies using in vivo extracellular single-unit recording techniques. Our statistical analysis showed that the mean optimal spatial frequency value of visual stimuli that evoked the maximal response of V1 neurons in old cats was significantly lower than that in young adult cats. This result is consistent with that reported in the V1 of old monkeys, suggesting that age-related functional declines of visual cortical cells might be an important neural base mediating visual acuity reduction in senescent individuals.2. We comparatively observed the activity of GFAP-immunoreactive (GFAP-IR) astrocytes in the primary visual cortex of both old and young adult cats using general immunohistochemistry method. Our results showed that the mean density of GFAP-IR cells in each cortical layer and the white matter of V1 in old cats were significantly higher than in young adult cats (p<0.001). Compared with young adult cats, the mean diameter of astrocytes in both gray matter and white matter of old cats was significantly increased (p<0.0001). Further, GFAP immunoreaction intensity in the primary visual cortex of old cats was stronger than that of young adult ones. These results suggest that The functional degradation of neurons in the visual cortex of old cats is accompanied by an improved activity of astrocytes, which could be beneficial to communication between neurons and thus may compensate neuronal function declines during senescence.