Analysis of hypothalamic transmitter release during cardiovascular changes

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.

Peristaltic versus syringe pumps for push-pull perfusion: tissue pathology and dopamine recovery in rat neostriatum

The characteristics of performance were compared for two types of pump, peristaltic and infusion-withdrawal, commonly used for localized push-pull perfusion of brain tissue. Guide cannulae were stereotaxically implanted bilaterally in the caudate-putamen complex of the rat at homologous sites in the coronal plane. Consecutive 5.0 min push-pull perfusions were carried out simultaneously with one pump perfusing ipsilaterally while the other pump perfused the contralateral caudate nucleus. 3H-dopamine (DA) diluted with an artificial CSF was used as the radiotracer and was perfused at a rate of 25 microliters/min. Following the collection of 7-8 samples, the brain was fixed, removed, and histological sections taken through the sites of perfusion. Microscopic examination of the perfusion site showed that the circumscribed lesion at the tip of the cannula connected to either pump was generally indistinguishable. A comparison of the values of 3H-DA recovery in samples obtained with the peristaltic and infusion-withdrawal pumps demonstrated that: (1) the respective uptakes of the catecholamine into caudate tissue paralleled one another in most experiments, and (2) the content of 3H-DA in push-pull perfusates recovered from sample to sample varied independently of the pump used. Based on the results of histopathological examination and DA radioactivity values, it is concluded that the peristaltic pump as well as the syringe-driven push-pull pump can yield valid experimental observations which are comparable to one another.