New triple microbore cannula system for push-pull perfusion of brain nuclei of the rat

A new miniaturized triple-barreled cannula system has been developed for the push-pull perfusion of a circumscribed area of brain tissue and/or simultaneous microinjection of a drug or other chemical substance at the same site. A three-lumen, microbore glass capillary tube is drawn to a length of 10-15 mm with a tip diameter of 150-190 microM and connected by lengths of PE tubing to a multichannel peristaltic pump. An artificial CSF is then perfused through either one or two tubes at a rate of 5.0-10.0 microliters/min at a selected site. Thus, a pharmacological receptor agonist and/or antagonist, for example, can be delivered simultaneously to the tissue quantitatively to achieve steady-state levels over time. Alternatively, a single volume of a given drug can be micro-injected at the perfusion site during the course of a push-pull perfusion, simply by replacing one push channel with an injection tube. In both cases, aliquots of CSF perfusate from the pull channel(s) are collected on ice for assay by HPLC or other procedures. Because of the diminutive size of the triple-bore cannula system, it is now possible to perfuse an individual nucleus in the hypothalamus or lower brainstem not only with minimal cytopathological damage but also with a punctate dispersion of the perfusion medium. The large number of possible in vivo manipulations which can be undertaken using this cannula system is illustrated experimentally by recovery studies of [14C]glutamate and 45Ca from the nucleus tractus solitarius and hypothalamus of the rat.