Smith D O
Department of Physiology, University of Wisconsin, Madison 53706.
Exp Gerontol. 1988;23(4-5):399-412. doi: 10.1016/0531-5565(88)90045-9.
Three characteristic features of aging in the nervous system are reviewed: deficits in the regulation of nerve-cell calcium levels, increased leakage of synaptic transmitters and changes in neuronal arborization. In hippocampal cells and motor nerve terminals, the rate of calcium clearance from the immediate vicinity of the membrane decreases with age. There is further evidence of decreased rates of transmembrane Ca2+ flux in synaptosomal preparations from aged animals. Stimulation-evoked transmitter release, which is calcium dependent, appears to increase at some neuromuscular junctions during aging; in contrast, high-K+-induced release in brain tissue appears to decline. A much more consistent age-related increase in "basal" transmitter efflux, under nonstimulated conditions, has been observed in both the peripheral and the central nervous system. This may be related to increased nerve-terminal arborization, which occurs in actively used muscles during aging. Likewise, dendritic branching becomes more extensive with moderate age; at advanced age, though, branching decreases. Furthermore, motor nerve terminal branching also decreases with age in muscles subject to disuse. This variability among morphologic features during aging illustrates the need to standardize ages and preparations when comparing these types of data.
神经细胞钙水平调节缺陷、突触递质泄漏增加和神经元分支变化。在海马细胞和运动神经末梢，膜附近钙清除率随年龄增长而降低。有进一步证据表明，老年动物突触体标本中跨膜Ca2+通量速率降低。刺激诱发的递质释放依赖于钙，在衰老过程中，一些神经肌肉接头处的释放似乎增加；相反，脑组织中高钾诱导的释放似乎下降。在非刺激条件下，在周围和中枢神经系统中均观察到“基础”递质外流与年龄相关的更为一致的增加。这可能与神经末梢分支增加有关，神经末梢分支增加发生在衰老过程中活跃使用的肌肉中。同样，树突分支在中年时变得更加广泛；然而，在老年时，分支减少。此外，在废用的肌肉中，运动神经末梢分支也随年龄增长而减少。衰老过程中这些形态学特征的变异性表明，在比较这些类型的数据时，需要对年龄和标本进行标准化。
