RESUMO
A new concept in the design of a push-pull cannula device for localized perfusion of brain tissue in the conscious and/or unrestrained animal is described. A catheter, consisting of a single strand of polyethylene tubing, contains an internal dividing septum which runs longitudinally throughout its length. The orifice of each lumen is of equal diameter and provides an integrated system for simultaneous delivery and withdrawal of a perfusate from the perfusion locus. The principal features of the new cannula system are: its simplicity of fabrication due to its all-plastic construction; multiple tip configurations adapted for a specific anatomical requirement including V-shaped, slanted, horizontal and side-by-side opening; direct visualization of the perfusate monitor bubble through the wall of the transparent catheter; since there are no joints, lack of leakage of perfusate and occlusion of pull channel; ease of sterilization by liquid or gas methods; and infrequency of damage because of catheter flexibility. Using radiolabeled dopamine and norepinephrine, prototype experiments carried out with 3 flow rates and 3 tip configurations revealed differences in substrate exchange which depend upon a given experimental parameter. The practical advantages are discussed of the new perfusion system in comparison with dialysis needles as well as with more commonly used concentric, metallic push-pull cannulae. Finally, technical applications are presented of the methods for the rat and other animals in which either the pharmacological delivery of a drug over a specified interval, or recovery of a neurotransmitter released into the cerebral parenchyma is a principal experimental objective.