Multilayer cannula for long-term infusion of unrestrained rats

A multilayer cannula was constructed from a long, thin inner cannula of siliconized rubber tubing with an outer collar of siliconized rubber tubing held in place by three "rubber bands" made from the same tubing as the collar. This multilayer cannula has been used for long term infusion studies of unrestrained rats and has several advantages over those described in the literature. It is easily secured into place without bending near the entry to the vein, or constricting the lumen. The use of a collar also insures that the correct length of cannula is inserted into the vein of the size rat being used.