Microdialysis and Fiber Photometry are both powerful techniques for monitoring the concentrations
of neurotransmitters in vivo, but each technique has very different advantages. Amuza is the only company that provides both types of equipment to the neuroscience community, putting us in a unique position to help you determine when microdialysis or fiber photometry would be the best choice.
|Multiple analytes||Many analytes can be measured in each sample with the little added difficulty||Data processing and experimental protocol are both more difficult|
|Types of analytes||Most types of molecules.||Limited by available fluorescent sensors|
|Type of measurement||Absolute concentration or % change relative to baseline||% Change relative to baseline|
|Data analysis||Relatively simple||Often quite complex|
|Sampling period||~30 seconds to hours||Milliseconds|
|Sampling duration||Days||Days, but difficult to monitor slow changes|
|Targeting||Brain region/structure||The brain region, specific projection, cellular subtype, axon vs cell body|
|Animal movement||Tether required||Tether or wireless headstage|
It is routine to measure many different neurotransmitters or amino acids in each microdialysis sample using HPLC chromatography and electrochemical detection. Samples can also be split and stored before analysis so that additional analytes can be added to the protocol at a later date. Commercially available assays also allow panels of multiple peptides and proteins to be measured in each sample.
Measuring multiple analytes simultaneously using fiber photometry is possible, but it requires expressing multiple fluorescent sensors at the target and the data analysis also becomes much more complex
Types of analytes
Microdialysis is extremely flexible and has been used to measure many types of analytes including amino acids, proteins, peptides, neurotransmitters, sugars, and more. If you can assay for it, you can probably sample for it using microdialysis.
Fiber photometry can now measure most of the principal neurotransmitters but is limited by the fluorescent sensors available. The number of sensors is increasing rapidly, but the options are still smaller than those available to microdialysis users.
Type of measurement
Microdialysis allows the monitoring of absolute concentrations or concentrations relative to basal levels in every sample.
Fiber photometry data yields a change in fluorescence data (∆F/F0). This correlates with changes in the concentration of the analyte relative to baseline but typically isn’t used to determine absolute concentrations.
HPLC software packages already include all of the functions required to automate the processing of microdialysis data, allowing the monitoring of many analytes simultaneously over time. The analysis can be easily taught to new users. In contrast, fiber photometry data processing is still usually a complex operation, with most labs using multiple software packages and writing their own scripts to deconvolve and analyze multiple streams of data. (TeleFipho photometry data only uses fluorescence data from one wavelength, and is easier to process)
Sampling Period and Duration
While sample times can be as short as 30 seconds, microdialysis excels in measuring long-lasting changes in extracellular concentrations, and for determining absolute concentrations for baseline levels. It is quite routine to continuously sample for many hours or even days during a microdialysis experiment. Furthermore, the microdialysis probe can be removed and replaced with a dummy probe for days or weeks between sampling sessions.
Fiber photometry is at the opposite extreme: fluorescence is measured every 1 to 10 ms, allowing it to record events lasting less than a second. But drift, noise, and photobleaching during fiber photometry experiments complicate observation of slow changes over time.
Both microdialysis and fiber photometry are used to target a discrete region or structure within the brain. Fiber photometry also allows retrograde or anterograde targeting, so that only specific projections are monitored. Viral vectors that only express the sensor in a specific cellular subtype or target either the axon or cell body can further narrow the scope of the events recorded.
Microdialysis and fiber photometry both typically require a tether during the experiment. TeleFipho is the exception and uses a wireless rechargeable headstage to gather and transmit fiber photometry data.
Do you have a question about microdialysis or fiber photometry?