2 Neuroscience2.3 Basic techniques in neuroscience
2.3.1.4 Microdialysis
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Written by Resident Doctor Committee · Published
Principle
Microdialysis pumps physiological fluid through a stereotactically placed probe, so soluble molecules diffuse across its semipermeable membrane with nearby extracellular fluid.
Shorter collection intervals improve timing but yield less analyte.
Reverse dialysis delivers a drug locally by adding it to the perfusate.
What the dialysate shows
Assays detect transmitters such as dopamine, glutamate and gamma-aminobutyric acid, and metabolites such as homovanillic acid and 5-hydroxyindoleacetic acid.
Concentration reflects release, uptake, metabolism, diffusion and membrane exchange, so a rise does not prove increased vesicular release or show which cells contributed.
Recovery
Relative recovery is dialysate concentration divided by concentration outside the membrane. In vivo it is usually below one, so raw values underestimate local concentration.
Calibration cannot fully reproduce living tissue.
Factor | Effect on recovery |
|---|---|
Membrane area | More area raises recovery |
Pore size and chemistry | Decide which molecules pass |
Flow rate | Slower flow raises recovery but shrinks samples |
Molecular size | Affects passage |
Analysis
Microlitre samples need sensitive assays, such as high-performance liquid chromatography with electrochemical detection for monoamines or fluorescence after derivatisation for amino acids.
Liquid chromatography mass spectrometry adds selectivity by mass-to-charge ratio.
Limits and human use
Probe insertion damages tissue, and settling time cannot fully remove the reaction.
Sampling is highly local, and collection over minutes misses rapid release. Fast-scan cyclic voltammetry is faster for selected electroactive compounds.
Human intracerebral use is mainly in neurointensive care, such as metabolic monitoring after brain injury.
Animal findings suggest mechanisms but cannot show that the same process causes a psychiatric disorder.