A remote insertion technique for intracerebral microinjections in freely moving animals

This report describes two improvements to the typical double-cannula microinjection technique. (1) Intracerebral microinjections usually require holding the animal during the insertion of an injector through an implanted guide cannula; however, this is not necessary with the technique described. The injector is made of a long piece of fused silica capillary tubing (145 mm outer diameter x 21.2 cm) which is so small and flexible that it slips through a PE-20 tube (20 cm) that guides it into the implanted guide cannula and down to the desired brain site where it stops. (2) Connection to a microliter syringe is usually done with PE tubing which is leaky, expandable and represents a relatively large dead space that makes it difficult to deliver small, accurate volumes. This problem is avoided by making connection to the syringe via another piece of silica glass capillary tubing. Thus both the injector and its connection to the syringe are made of glass. With these modifications the injector can be inserted without touching the animal, and accurate volumes in the low nanoliter range can be delivered.