Studies On Age-Related Morphological Changes In The Lateral Geniculate Nucleus Of Cats

The lateral geniculate nucleus (LGN) is an important relay station in the visual pathway of higher-order mammals and plays a key role in the regulation of visual information processing. The senescence-related structural and functional change of LGN is possibly, considering at the visual circuit level, one of the important factor that leads to the visual function decline in the aged. This thesis makes a comparative study of the age differences between the young cats and the old cats at the level of LGN.1. Apply the Nissl dyeing method to show the laminar structure of LGN and the cell components of each layer. The statistical result demonstrated that the thickness, neuronal density and cell size in each laminae of LGN showed no significant difference between young adult and old cats. This indicates that the neuronal composition in LGN stays quite stable during aging. This result is consistent with the result observed in the primary cerebral cortex, but varied with that in retina. It can be concluded that the declines of old animals'visual functions cannot be simply attributed to the loss of neurons in visual brain. The stability of LGN neuronal composition is beneficial to the transmission and regulation of visual information.2. Apply the immunohistochemical ABC method to show the GABA-IR neuron in the young and old cats'LGN. The statistical data and the analysis result show that there are GABA immunoreactive neurons in each layer of LGN of both old cats and young adults. Compared with young adult cats, the GABA immunoreactivity in old cats'LGN was obviously weakened, and the density and cell size of GABA-IR neurons were decreased to different extent. This indicates that a compromised GABA suppression at the level of LGN is one of the important factor that leads to the decline of visual function.3. Apply the immunohistochemical ABC method to show the immunoreactive structure of S100 protein and glial fibrillary acidic protein (GFAP) both in old cats'and young cats'LGN, for the purpose of comparing the activities of astrocyte in old cats'and young cats'LGN. Statistical data and analysis result show that the S100 protein and GFAP immunity positive reactions exist at each layer of both old cats'and young cats'LGN. Compared with that in young cats', the reaction intensity of old cats'was remarkably increased to varying degree, which indicates the existence of astrocyte reactive gliosis in old cats'LGN and may exert positive or negative influence on visual functions of senescent individuals.