Modified thin GRIN setup

[Auptain]

Hi,

We are using the 0.5mm diameter GRIN lenses to image about 2.5mm deep and I am unclear about how the relay lens interfaces with the objective lens. I don't want to have to insert the 2.0mm relay lens into the brain and cause damage, but the photos show that it is protruding several millimeters beneath the base plate. Can someone show a full setup of a modified thin lens configuration? Additionally, what are the exact specifications needed for the 2.0mm lens? Will a GRIN lens from Edmunds be able to mesh with Grintech lenses? Thank you.

Best,
Alex

[Daniel Aharoni]

Hi Alex,
We will work on more detailed tutorial for doing dual GRIN lens imaging but in the meantime I will try to explain everything here. Below I will be referring to the thin GRIN lens as the 'relay lens' and the larger 2mm (or 1.8mm) diameter GRIN lens as the 'objective lens'.

You will implant the relay lens into the the brain with the bottom of the lens withing a couple hundred micrometers from the region you want to image. The relay lens should extend above the skull by a millimeter or two so it can be cemented/glued to the skull. After 2 to 3 weeks from implanting the relay lens we come back to cement the baseplate to the skull. We attach a Miniscope to a baseplate and connect the scope it to the DAQ software on the computer. Holding the Miniscope+baseplate with a micro-manipulator we lower them above the implanted relay lens until we see a nice image. There will be between a 100um and 500um gap between the top of the relay lens and the bottom of the objective lens (you are correct that the objective lens will extend a little below the baseplate). Once the Miniscope+baseplate are in a position where a good image can be seen we build up cement from the skull to the baseplate. The baseplate will be 3mm to 5mm above the skull of the animal. Once the cement sets you can remove the Miniscope and the baseplate will remain fixed to the skull.

A nice overview of imaging with a relay GRIN lens + objective GRIN lens can be found in this Nature Protocols paper by Resendez et al, http://www.nature.com/nprot/journal/v11/n3/full/nprot.2016.021.html. While the approach outlined in this paper is centered around the commercial nVista system from Inscopix, it is directly applicable to our modified Miniscope system with mounted 0.25 pitch objective GRIN lens.