Tracer Molecule Delivery in the Cisterna Magna: A Method to Deliver Fluorescent Tracer Molecules via Direct Cannulation of the Cisterna Magna in Pig

The vertebrate brain contains a specialized fluid exchange system analogous to the lymphatic system, called the glymphatic system. In this system, cerebrospinal fluid or CSF enters the periarterial spaces, allowing solute exchange via specialized channels present in the astrocytic endfeet. The solute-carrying CSF flows into the perivenous space to flush the solutes from the brain. This pathway is significant for brain physiology and can be visualized using fluorescent tracer molecules.

To begin, prepare an anesthetized pig in the prone position with its head flexed upward. Make an incision below the occipital crest. Retract the muscles to expose the cisterna magna - an opening in the subarachnoid space between the cerebellum and medulla oblongata.

Carefully insert a cannula through the dura mater into the cisterna magna. Apply dental glue around the cannula. Allow it to harden. Thereafter, inject fluorescent tracer molecules suspended in artificial CSF at an appropriate rate. A visibly pulsating tracer solution at the cannula’s base confirms successful delivery.

Following injection, reposition the tissue layers and suture the incision. Place a wet cotton gauze over the incision to limit heat loss. Allow the tracer molecules to circulate for the desired period. When visualized under a fluorescence microscope, tracer molecules help visualize the CSF distribution in the glymphatic system.