Experimental spinal cord injury induced an increase of extracellular ascorbic acid concentration in anesthetized rats: A microdialysis study

Ascorbic acid plays important roles in mammalian central nervous system. We employed an on-line analytical system to monitor the extracellular ascorbic acid concentrations in anesthetized rat spinal cord before and after the experimental injury. A microdialysis probe (216 μm od, 200 μm id, 3 mm in length) was implanted into an anesthetized rat spinal cord (Thoratic-12). Microdialysis perfusate (2 μl/min) was collected in the sample loop (20 μl) of an on-line injector for direct injection onto a High Performance Liquid Chromatography (HPLC) system equipped with an electrochemical detector. Normal ascorbic acid concentrations in the spinal cord extracellular fluids ranged from 1.8 μM to 10.8 μM (mean ± S.D. 5.6 ± 2.4 μM, n = 8). The experimental spinal cord injury, induced by a lesion at T-10, gradually yet significantly increased the extracellular ascorbic acid levels. The effect of exogenous glutamate perfusion (0.2 mM, 2 mM, and 20 mM) through the microdialysis probe also increased the extracellular ascorbic acid concentrations in a dose dependent manner. These results suggested that the injury-induced ascorbic acid accumulation may result from elevated extracellular glutamate levels that are commonly observed in spinal cord injury. This on-line, continuous and automatic monitoring system can be applied to future investigations on the roles of ascorbic acid in spinal cord injuries.