Prior to conducting your first fiber photometry experiment, you are going to need a patch cord. While Neurophotometrics does not currently manufacture patch cords, we are happy to provide guidance so that your selection is the most compatible with your fiber photometry system and experimental setup.
The most important thing when choosing a patch cord is ensuring you have the correct numerical aperture (NA). Neurophotometrics systems come with an objective that has a 0.37 NA. To maximize your signal, the patch cord (and fiber optic cannulae) should match this NA. Matching the NA will ensure that there is no light loss from the excitation or emission side. Having mismatched NAs at any of these points will cause significant light loss, giving you less than optimal signal — or none at all!
Next, you must choose the ferrule and core diameters of the patch cord. These can vary between experiments, but must match specifications of the fiber optic cannula(e) that you will implant into the animal. Common ferrule diameters are 1.25mm and 2.5mm. Common core diameters are 200um and 400um. The most popular combination is 1.25mm ferrule diameter with a 200um core diameter. You can pick any combination to fit your experiment — just be sure that the patch cord matches the fibers.
Another consideration for your patch cord is the connection to the system. The Neurophotometrics fiber photometry system comes with an FCM connector, so we suggest purchasing a patch cord that also has an FCM connector. However, if you prefer to use an SMA connector and patch cord, this is an easy swap. Just let us know and we can provide an adaptor for you.
The patch cord also must connect to the animal subject, of course, so you will need to specify this type of connection as well. This connection type should be MF, followed by the size of your ferrule. For example, if you are using fiber optic cannulae with 1.25mm ferrules, the connection would be “MF1.25.”
Patch cords come in a variety of lengths. We recommend a length of 2-3 meters. This will make multiplexing the system and managing the patch cord easier. The longer the patch cord, the more resistant it will be to twisting (i.e. it can absorb a higher number of twists before the signal starts to attenuate). However, a longer patch cord will also lower your efficiency, as you will lose signal as a function of distance.
Patch cords can also have several branches. The number of branches you choose is completely up to you and dependent on your experimental needs. How many animals and/or brain regions you wish to record from at once will influence this choice. We recommend starting with at least two branches, even if you are only recording from one brain region to start. You can simply cover up one the unused core with tape during the experiment.
Once you’ve determined what kind of patch cord you need, we recommend buying that patch cord from Doric Lenses. Please note, however, that they can have quite long lead times; you’ll want to place your order at least 6 weeks before you plan to do any experiments.
Here at Neurophotometrics, we use the Branching Fiber-optic Bundle Design patch cords (1.25mm/200um/0.37NA). On the left you can see an example of how to specify what qualities you want in your patch cord when ordering from Doric. In this example, I have chosen a 2 branch, 3 meter long patch cord.
Some labs that are just beginning to do fiber photometry might already have patch cords. A common question we receive is whether or not these pre-existing patch cords will work for fiber photometry experiments, even if the NA, ferrule size, and/or core diameter don’t perfectly match their new system or fiber optic implants. We highly recommend that you purchase a patch cord that will perfectly match up with the system. There will be a significant amount of emission loss when these qualities are mis-matched, resulting in a diminished signal. Patch cords with higher or lower NAs can be used for testing and getting comfortable with recording, but ideally would not be used for experiments. It is always a good idea to double check the specs of your patch cord before recording, especially if you have multiple patch cords.
If you are performing experiments that require long recording periods, it is tempting to purchase a rotary joint or commutator as well. However, most rotary joints that are used for optogenetics are not optimized for fiber photometry. They can cause a loss of light at the connection point of the rotary joint and patch cord. Additionally, it is not currently possible to record from multiple regions while using a rotary joint due to their rotating nature. It would be impossible to keep the correct orientation of multiple cores, resulting in confounded data. We advise that you start recording without one, and add one only if necessary. If you decide that you need a rotary joint, Doric makes a pigtail commutator that is compatible with fiber photometry. These are very expensive (around $850), and make it impossible to record from multiple brain regions.
This second example order is for a pigtail commutator. It will also need to have an NA of 0.37 and match the ferrule and core diameters of your fibers.
This post was written by Savanna Howard.