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

Electroosmotic perfusion of tissue: sampling the extracellular space and quantitative assessment of membrane-bound enzyme activity in organotypic hippocampal slice cultures

This review covers recent advances in sampling fluid from the extracellular space of brain tissue by electroosmosis (EO). Two techniques, EO sampling with a single fused-silica capillary and EO push-pull perfusion, have been developed. These tools were used to investigate the function of membrane-bound enzymes with outward-facing active sites, or ectoenzymes, in modulating the activity of the neuropeptides leu-enkephalin and galanin in organotypic-hippocampal-slice cultures (OHSCs). In addition, the approach was used to determine the endogenous concentration of a thiol, cysteamine, in OHSCs. We have also investigated the degradation of coenzyme A in the extracellular space. The approach provides information on ectoenzyme activity, including Michaelis constants, in tissue, which, as far as we are aware, has not been done before. On the basis of computational evidence, EO push-pull perfusion can distinguish ectoenzyme activity with a ~100 μm spatial resolution, which is important for studies of enzyme kinetics in adjacent regions of the rat hippocampus.

Demonstration of low flow push-pull perfusion

Methods to follow in vivo chemical composition provide information regarding the processes of intercellular communication. There is a need for methods that provide chemical information from small volumes of the central nervous system (CNS) without sacrificing neurochemical recovery. One method that offers potential for providing such information is push-pull perfusion. In this study a low flow push-pull perfusion system is introduced that provides high (70-80%) in vitro recoveries. A concentric probe design is used with a 27-gauge stainless steel outer cannula for saline infusion and an inner fused silica capillary for fluid withdrawal. Flow rates of 10-50 nl/min were reliably generated and were well matched in vitro. Sampling was performed in the striatum of an anesthetized rat generating a 0.5 microl sample every 12 min. Capillary electrophoresis was used to determine glutamate levels in each sample; the basal level was found to be 1.97+/-0.70 microM. The method described was also demonstrated to deliver L-trans-pyrrolidine-2,4-dicarboxylic acid through the perfusion solution while sampling. Post-sampling histological analysis demonstrates little tissue disturbance to the sampled region. These data provide evidence that low flow push-pull method is a viable alternative for studying neurochemical signaling in the CNS.

Simultaneous comparison of cerebral dialysis and push-pull perfusion in the brain of rats: a critical review

Over the last 30 years, studies of the in vivo activity of neurotransmitters and other endogenous factors in the brain have comprised a major effort in the neurosciences. Historically, the technology of push-pull perfusion was utilized as a major approach to investigations in this field. In the last 10 years, cerebral dialysis has been used as an alternative method essentially for the same scientific purpose, since the perfusion technique was viewed as difficult and excessively damaging to tissue. This review considers the representative literature in which both systems have been used to study local neurochemical responses to a drug or other chemical factor, a physiological condition or other situation. In addition, new experiments have been undertaken to compare, in the same animal and at the same time, the utility and properties inherent in the techniques of push-pull perfusion and cerebral dialysis in terms of the profile of a neurotransmitter activity and their local histopathological effects. A miniaturized 33/26 ga push-pull needle and a 24 ga dialysis probe were implanted simultaneously in the left and right caudate nuclei, respectively, in the anesthetized rat. An artificial cerebrospinal fluid (CSF) was perfused simultaneously through both devices at a rate of 10 microliters/min in the push-pull cannula and at 1.0 or 2.0 microliters/min in the dialysis probe. Within a series of 8-10 successive perfusions, excess K+ ions in a concentration of either 30 or 60 mM were incorporated in the CSF and delivered simultaneously to both the push-pull cannula and dialysis probe. Samples of perfusate and dialysate were assayed chromatographically by coulometric HPLC detector and quantitated in terms of the pg/min efflux of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA). The results showed that the resting level of DA was almost undetectable in dialysate samples from either structure; in push-pull perfusates the recovery of DA ranged between 7.0 to 10.0 pg/min, which was increased threefold by excess K+ ions. The recovery of DA and the three metabolites in samples of push-pull perfusate was two to four times that in samples of dialysate during the condition of excess K+ ions. Post-mortem histological analysis of the sites of perfusion and dialysis revealed little or no differences in the cytological damage induced by either the perfusion needle or dialysis probe. Finally, the advantages and limitations of each of these two experimental approaches to in vivo analysis of neurotransmitter efflux are reviewed in relation to the selection of an open or closed system for the on-line study of in vivo neurochemical events.

Development of a sensitive and inexpensive micropush-pull technique for the continuous analysis of brain neurotransmitters and metabolites in vivo

A new, sensitive, convenient, inexpensive and low-maintenance miniaturized triple-cannula system (Zhange et al., 1990) for the push-pull perfusion of brain tissue has been constructed, and tested for its ability to exchange substances in rats, both in vitro and in vivo. In vitro: the cannula was immersed in a vial filled with 1.5 ml of a 1 microM standard solution of norepinephrine, dopamine, and their metabolites. Artificial cerebrospinal fluid was perfused through the system. Perfusate was collected at rates of 1, 2, 5, 10 and 20 microliters/min over 10 min. The recovery rate of the biogenic amines (using high performance liquid chromatography) at 10-min intervals for 60 min was consistent (57 +/- 1.31%) in low flow rate groups (1 approximately 10 microliters/ml). In vivo: [3H]choline (3 microCi, 35 nmol) was infused (6 min) into the lateral ventricle and collected by micropush-pull at 10-min intervals for 180 min, from the cerebellomedullary cistern and hippocampus. The highest [3H]choline count was reached within 10 min after infusion. Levels returned to baseline within 20 min following infusion of the tracer. The micropush-pull cannula was also adapted for chronic brain perfusion in vivo. Recovery of perfused fast green dye (0.00025%) was comparable (83 +/- 1.75%), using the same cannula for 3 sampling periods within 1 month in a freely moving rat. A cresyl violet analysis showed minimal damage to the brain tissue, with gliosis only evident in a narrow margin along the cannula track. Thus the micropush-pull technique is highly efficient in terms of exchange of material, causes minimal damage of brain tissue, and can be used chronically in awake animals. These data have been presented in preliminary form at the 1991 ASPET meetings (Zhang et al., 1991).