Effects of tissue trauma on the characteristics of microdialysis zero-net-flux method sampling neurotransmitters.

Microdialysis has been used for studying neurochemistry in brain regions that respond to afferent inputs or administered drugs. As the knowledge derived from and concerning microdialysis grows, so do the concerns over its invasiveness and, hence, the credibility of resulting data. Recent experimental and theoretical studies impugned the validity of the microdialysis zero-net-flux (ZNF) method in measuring brain extracellular neurotransmitters, suggesting that the tissue trauma resulting from probe implantation seriously compromises its worth. This paper developed a theoretical model to study the influences of two categories of tissue trauma on microdialysis ZNF operation: (1) morphological alterations in tissue extracellular structure and (2) physiological impairment of neurotransmitter release and uptake processes. Model results show that alterations of tissue extracellular structure negligibly affect the accuracy of the ZNF method in determining the basal level of extracellular neurotransmitter but do affect the fundamental characteristics of microdialysis: the extraction efficiency and relative recovery. An inhibited or damaged neurotransmitter uptake process always decreases the efficiency of microdialysis extraction, but rise of the relative recovery of neurotransmitters with the same uptake inhibition/damage occurs only when there is far more damage to the neurotransmitter release than to the uptake process in the tissue. A criterion for this rising trend of microdialysis relative recovery is discussed in terms of trauma parameters and neurotransmitter uptake inhibition.