Xu G Y, McAdoo D J, Hughes M G, Robak G, de Castro R
Marine Biomedical Institute, Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston 77555-1069, USA.
Neuroscience. 1998 Oct;86(3):1011-21. doi: 10.1016/s0306-4522(98)00063-3.
The following issues are further addressed: (1) Is there considerable leakage of amino acids from the circulation into the space around microdialysis probes, or are amino acid concentrations naturally much higher in the interstitial space than is generally thought? (2) Do observed high interstitial concentrations or depletion of substances in the intracellular space by microdialysis affect release measurements upon spinal cord injury? Amino acid concentrations around microdialysis fibres in the spinal cord of rats were found to approach those in the circulation and to be much higher than interstitial concentrations previously estimated in the CNS. However, much lower concentrations of amino acids were derived in the hippocampus by analogous experiments. Considerable Evans Blue/albumin leaked from the circulation into the interstitial space in the spinal cord immediately after fibre insertion. However, this movement diminished considerably by 4 h later, demonstrating substantial resealing of the blood-brain barrier, at least to large molecules. There is either substantial damage-induced movement of amino acids from the circulation into the dialysis zone after insertion of a microdialysis probe, or there is much less impediment to movement of amino acids across the blood-brain barrier in the spinal cord than in the brain. At low flow rates through the fibre, adding concentrations of amino acids to the inside of the fibre equal to the concentrations around the fibre to prevent their depletion by removal through the microdialysis fibre did not affect increases in concentrations of amino acids in microdialysates following injury. Thus the high concentrations of amino acids present around microdialysis fibres following their insertion do not seem to disturb measurements of amino acid release upon spinal cord injury.
（1）氨基酸是否会大量从循环系统渗漏到微透析探针周围的间隙中，或者间隙中的氨基酸浓度是否天然就比通常认为的要高得多？（2）微透析所观察到的间隙中高浓度物质或细胞内空间中物质的消耗是否会影响脊髓损伤后的释放测量？研究发现，大鼠脊髓中微透析纤维周围的氨基酸浓度接近循环系统中的浓度，且远高于先前在中枢神经系统中估计的间隙浓度。然而，通过类似实验在海马体中测得的氨基酸浓度要低得多。纤维插入后，相当数量的伊文思蓝/白蛋白立即从循环系统渗漏到脊髓的间隙中。不过，4小时后这种渗漏显著减少，表明血脑屏障至少对大分子物质实现了大量重新封闭。要么是插入微透析探针后损伤导致氨基酸从循环系统大量进入透析区域，要么是脊髓中氨基酸穿过血脑屏障的阻碍比大脑中要小得多。在低流速通过纤维时，向纤维内部添加与纤维周围浓度相等的氨基酸以防止其通过微透析纤维被清除而耗尽，这并不会影响损伤后微透析液中氨基酸浓度的增加。因此，微透析纤维插入后其周围存在的高浓度氨基酸似乎不会干扰脊髓损伤后氨基酸释放的测量。
