In vivo neurochemical monitoring by microdialysis and capillary separations

doi:10.1016/S1367-5931(02)00373-3

Current Opinion in Chemical Biology

Volume 6, Issue 5, 1 October 2002, Pages 659-665

https://doi.org/10.1016/S1367-5931(02)00373-3 Get rights and content

Abstract

Microdialysis is valuable for studying the neurochemical changes underlying behavior. Recent advances include the application of the high-sensitivity methods of capillary electrophoresis and capillary liquid chromatography with mass spectrometry to dialysate analysis. These methods have improved temporal resolution, spatial resolution, multi-analyte capability and potential for compound discovery.

Introduction

One of the greatest challenges facing science is understanding the brain, how it controls behavior, how it malfunctions in mental illness and how such malfunctions might be corrected. As the brain is composed of neurons and glial cells that communicate via chemicals released into the extracellular space, it is of interest to monitor these chemical messengers in vivo. This is a daunting task as over 100 compounds including amino acids, simple amines and peptides have been identified as neurotransmitters and their levels can change rapidly in localized brain regions. Methods that enable in vivo neurotransmitter monitoring include positron emission tomography, sensors and sampling methods such as microdialysis. These methods have been influential in brain research because they enable identification of intracranial chemical changes associated with behavior and facilitate discovery of targets for pharmacological interventions. This article provides an overview of in vivo neurochemical monitoring using microdialysis and reviews recent advances based on coupling high sensitivity techniques such as capillary electrophoresis (CE) and capillary liquid chromatography (LC) to microdialysis probes.

Section snippets

Examples of microdialysis studies

Microdialysis is one of the most popular approaches for studying in vivo brain chemistry because of its convenience and high informing power. In microdialysis, a semi-permeable membrane, typically 1–4 mm long and 0.2–0.4 mm in diameter, is fashioned into a probe such that the interior of the probe can be perfused at 0.1 to 2 μl/min. When the probe is implanted into the brain, analytes present in the extracellular space diffuse to the probe according to their concentration gradient and become

Microdialysis with capillary electrophoresis

CE has been recognized as an attractive analytical method to couple to microdialysis mainly because of the potential for improved temporal resolution. Temporal resolution is important as neurochemical levels and behaviors can change rapidly. Indeed, the dopamine study discussed above was unable to distinguish among some roles for dopamine because temporal resolution was limited to 5 min. With microdialysis, temporal resolution is usually limited by mass sensitivity of the analytical method

CE–LIF coupled on-line to microdialysis

Although CE–LIF has the sensitivity to monitor analytes in nanoliter fractions, routine use of such small fractions is problematic because of the tremendous throughput needed to analyze the samples. Consider that at 6 s fraction collection intervals, 600 samples would be generated during 1 h of experimentation. One way to avoid this problem is to take advantage of the automatability and high-speed capability of CE to perform on-line measurements.

Successful design of an on-line method requires

Microdialysis with capillary LC–MS²: peptides, neuroproteomics and more

One of the most challenging problems in neurochemical monitoring in vivo is detecting neuropeptides. The difficulty stems from the low in vivo concentration of peptides (1–100 pM), which is ∼10⁶-fold lower than amino acid neurotransmitters. Thus, the detection method for peptides must be sensitive enough to quantify attomolar levels in microliter sample volumes.

Analytical methods developed to address this challenge include LC–radioimmunoassay [20], capillary LC–electrochemistry [21], CE [22]

Conclusion

In vivo neurochemical monitoring is a fertile field for research. Continued advances in analytical techniques have enabled significant improvements in temporal resolution, spatial resolution, multi-analyte capability and compound discovery. The present state of development of these methods is such that they require a substantial investment in training and novel instrumentation to be implemented for neuroscience applications. An important goal over the next few years will be to develop the

Acknowledgements

Our work in this area was supported by NIH NS38476.

References and recommended reading

Papers of particular interest, published within the annual period of review, have been highlighted as:

• of special interest
•• of outstanding interest

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ReviewIn vivo neurochemical monitoring by microdialysis and capillary separations

Abstract

Introduction

Section snippets

Examples of microdialysis studies

Microdialysis with capillary electrophoresis

CE–LIF coupled on-line to microdialysis

Microdialysis with capillary LC–MS2: peptides, neuroproteomics and more

Conclusion

Acknowledgements

References and recommended reading

J Chromatogr

J Chromatogr

J Chromatogr

Brain Res

J Chromatogr

J Neurosci Methods

J Chromatogr A

J Neurosci Methods

Brain Res

Peptides

J Chromatogr

J Chromatogr

J Chromatogr

J Neurosci Methods

Estimation of in vivo neurotransmitter release by brain microdialysis: the issue of validity

Behav Pharmacol

Behaviorally relevant measures of glutamate transmission?

Behav Pharmacol

Increased dopamine release in the human amygdala during performance of cognitive tasks

Nat Neurosci

Reversal of phenylcyclidine effects by a group II metabotropic glutamate receptor agonist in rats

Science

Capillary zone electrophoresis with laser-induced fluorescence detection for the determination of nanomolar concentrations of noradrenalin and dopamine: application to brain microdialysate analysis

Anal Chem

An integrated decoupler for capillary electrophoresis with electrochemical detection: application to analysis of brain microdialysate

Anal Chem

Investigation of the metabolism of substance P at the blood-brain barrier using capillary electrophoresis with laser-induced fluorescence detection

Electrophoresis

Continuous in vivo monitoring of amino acid neurotransmitters by microdialysis sampling with on-line derivatization and capillary electrophoresis separation

Anal Chem

Review
In vivo neurochemical monitoring by microdialysis and capillary separations

Microdialysis with capillary LC–MS²: peptides, neuroproteomics and more