Ch 4 Flashcards
Have previous papers used TFs for depth resolved monitoring?
Yes, Pisano 2019 show the first use of the TFs for monitoring fibre photometry signals where they assess dopamine signals in the striatum as mice perform a behaviour task.
To my knowledge, nobody else has publishable results using these.
What are the main findings of Pisanello 2014?
Pisanello 2017?
- gold plated TF with windows to deliver light
- establih what angles of light are required for multomode derlivery of light regions fat away from the tip
- light derluvery length increases with increased NA and decreased TA
- the smaller the angle of entre the light will come out the top of TF, the larger, it will reflect inside and propagate
- illustrated site illumination in FITC and brain slices
- shown site with multi wavelength in dual fluorescent solution
- checked if shaking/twisting patch effected the light
- in vivo in striatum with silicon probe showed site detective excitation
)_____-
to show it could be whole brain or region specific optogenetics
- TF with no fold plating
- did ray simulations to confirm light patterns
- monitored inflammationn
- see increased modulation over intentiy and depth compared to FF
- implemented the galvo mittor for continuous sweeping
site directed opto in striatum
What are the main findings of Pisano 2019?
- did raster scanning along tf in FITC and monitored response with two hotodetectors to determine signal collection field
- found unform and depth specific collection field in fitxc and human tissue
- equalised power density along TF
- monitored in vivo dopamine in striatum woth depth-resolved differences.
How exactly is the TF made?
A heat and pull process where the tip of the fibre is heated and stretched until the ti is ~500 nm,
They set this with a NA of 0.37 and taper of ~2.4
How can the TF record fluorescence?
There is a change in the refractice index (the light refeaction level) from tissue to TF which makes it couple into the fibre.
Then the modes of light pass the same way as they fo on the way down – the site of entry is correlated with the angle of light entering the TF.
How does the taper angle determine the active region?
the tpaer angle decreased will increase the length of th e active region.
Pisanello found that increasing this shortened it most likely because the internal reflectance was too hgih.
How were those images of the fibres acquired?
The fibres were placed into a solution of high concentration fluorescein in a cuvette.
Then light was delivered through the system.
A camera was set up focussed though the cuvette and images were taken.
Why on the images are there some spects of fluorescence?
It is most likley the fact these fibres have been previously used so there may be some residue on them.
What was the function of the galvo mirror?
As we have 1.8mm of TF to work with, we needed a way to modulate where the light was being propagated out each depth of the fibre instead of it being along the whole shank.
This mirror modulates the direction of the laser beam in order to change where the light enters and leaves the TF.
Why for this system did you need to use a laser?
Because we are changing the focus of light on a rapid time scale and lasers are known to have a more focussed beam and a faster operation speed.
Why have you now got an additional photodetector channel?
Because lasers are more unstable than LEDs and can fluctate due to head differences. We also found that perhaps the way the laser was being driven - through the DAQ was causing an unstable power voltage and therefore, we implemented a photodetector to monitor this read out.
Did you use the 405 nm read out for analysis?
No, as we had out control group we did not use this. Also the changes were minor so shouldn’t have effected this profiles.
Why did the original laser deterioate?
This was purchased from a cheaper supplier so it is thought that there was some electrical faults that were perhaps not picked up as they do not have as vigiourous quality control.
Also, this laser was not based on a heat-sink which is important for temperature control in order to prevent damage.
Why was a glass slide ok for focussing onto a detector and not a lens for 405 nm channel?
Because the signals on here were very high as it was direct from the laser so even capturing a small part of this signal would be high enough.
What is a neutral density filter and what type did you use?
Why did you use this?
This is a filter that across all wavelengths, will reduce the light power at equal amounts.
*** need to check system
We used this because this laser was very high power and produced alot of light. To reduce it to working and safety limit we used this.
Why didi you use an aspheric lens that was length 50 mm focal length?
To generate a focal spot of <500 um and the appropriate distance of the system.
Why are some of the focal length of lenses different throughout the system?
As some were being coupled into the fibre they needed to be smaller.
What mirrors were used for first reflection in the system?
Broadband mirrors. These will reflect all wavelengths with equal transmission. These allow direction of the light path.
How is the light directed towards the photodetectors?
The light passes back through the fibre before reaching a 425 short pass mirror where light below 425 will pass and light above will be reflected. This removes the excitation light from our emission channels.
Then the light passes a 525 nm short pass dichroic mirror where light above 525 nm will be reflected before passing a 550 nm bandpass filter which is focused onto the photodetector by an aspheric lens. Light below 525nm will pass through the mirror before a 440 nm bandoass filter and being focussed onto a PD.
How is the light seperated for each photodetector? Is this not a mirror instead of a filter?
Yes, the diagram is wrong.
The light is seperated using a 525 nm shortpass mirror.
This seperates the light pass for 440 and 550 nm.
Why did you have a 1.25 mm ferrule setting for this system?
This is the setting that the TF can be made in and it works better as they are lightweight for the chronically implanted headcap.
Why did you have a 470 laer in the first system?
Because at first we discussed the possibility of using this as the control as this system was deisgned before we established the system needed reconfigured.
Why do you need to focus light onto the galvo mirror with a lens?
To make the beam focussed so that the light path is modulated appropriately.
What does the heat sink do?
The heat sink works as a fan to remove heat by dissapating it into air.
Therefore, it prevents the overheating of the laser and damage.