New "micro push-pull" catheter system for localized perfusion of diminutive structures in brain.

A new double-lumen micro-catheter has been adapted for use in an integrated push-pull cannula system for perfusion of brain tissue of the unrestrained animal. The catheter consists of a single strand of polyethylene tubing available in sizes with an external diameter ranging from 280-480 microns. A microcapillary pipette is drawn and inserted into each lumen of the two channels. The pipettes are then connected by polyethylene tubing to calibrated gas-tight syringes mounted on the reciprocating decks of an infusion-withdrawal pump. Since the diameter of the orifice of each lumen is equal, the simultaneous delivery and withdrawal of an osmotically balanced artificial CSF at a perfusion site is assured. In prototype experiments, the tissue exchange of 3H-norepinephrine and 14C-dopamine incorporated into the CSF perfusate was examined simultaneously at hypothalamic sites in the rat. At perfusion rates of 12.5 and 25.0 microliter/min, the mean recovery of the catecholamine neurotransmitters in terms of the radio-label residual in the perfusate ranged between 85-88 percent. The principal advantages of the new system are its flexibility, ease of sterilization and its diminutive size which enables perfusion, for the first time, of individual nuclei or fiber tracts in the brain of a laboratory animal such as the rat. Thus, a more precise delivery of a drug or other chemical agent to the site of perfusion as well as the collection of a released transmitter substance from the same anatomical locus can now be accomplished.