Considerations in the determination by microdialysis of resting extracellular amino acid concentrations and release upon spinal cord injury

• Published in: Neuroscience Vol. 86; no. 3; pp. 1011 - 1021
• Main Authors: Xu, G.-Y, McAdoo, D.J, Hughes, M.G, Robak, G, de Castro, R
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.10.1998; Elsevier
• Subjects: Amino Acids - blood; Amino Acids - cerebrospinal fluid; Amino Acids - metabolism; Animals; Biological and medical sciences; Blood-Brain Barrier; depletion; Evans Blue; excitotoxicity; Fundamental and applied biological sciences. Psychology; General aspects. Models. Methods; Glutamic Acid - metabolism; Hippocampus - metabolism; interstitial amino acid concentrations; Male; Microdialysis; Nerve Fibers - metabolism; Rats; Rats, Sprague-Dawley; Spinal Cord - metabolism; Spinal Cord Injuries - blood; Spinal Cord Injuries - cerebrospinal fluid; Spinal Cord Injuries - physiopathology; Vertebrates: nervous system and sense organs; depletion; blood–brain barrier; AIB, α-aminoisobutyric acid; interstitial amino acid concentrations; ISF, interstitial fluid; excitotoxicity; ACSF, artificial cerebrospinal fluid; CSF, cerebrospinal fluid; Spinal cord; Rat; Rodentia; Central nervous system; Blood brain barrier; Extracellular; Vertebrata; Mammalia; Microdialysis; Aminoacid; Lesion; Release; Brain (vertebrata)
• ISSN: 0306-4522; 1873-7544
• 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