A method for quick and simple construction of push-pull cannulae and their use in recovery of hippocampal amino acids

Abstract

Push-pull cannulae have been extensively employed for the in vivo perfusion of discrete brain regions and investigation of perfusate contents (Gaddum, 1961; Szerb, 1967; Yaksh and Yamamura, 1974; Errington et al., 1983). We wish to report a highly simplified and quick technique for the construction of push-pull cannulae. The outer barrel of the cannula consists of 24-gauge stainless-steel tubing cut to a length of 52 mm and finished to a blunt end (Popper and Sons, New Hyde Park, NY); the inner cannula, obtained from the same source, consists of 32-gauge stainless-steel tubing cut to a length of 65 mm. Tygon (R-3603 plastic) microbore tubing with an internal diameter of 0.19 mm (Cole-Parmer: TV-7626-72) is stretched over one end of the outer barrel to a distance of approximately 6 mm (Figure IA). The Tygon tubing is then bent to 90” at the end of the outer barrel, and the inner barrel is slowly pushed through from the free end of the outer barrel to perforate the Tygon tubing (Figure IB). The inner barrel is then adjusted so that it protrudes the desired distance (e.g., 0.5 mm) beyond the outer barrel tip of the cannula (Figure IC). The other end of the inner barrel, protruding from the Tygon tubing, is then fitted to another length of the same-sized Tygon tubing and all tubing-metal connections are overtied with surgical thread (Figure ID). From start to finish, the whole construction process takes approximately 5 min. A larger size of tubing can be used for the outer barrel, but the advantage of the smaller interior diameter plastic tubing is a reduced delay from sampling site to collection tube. At first appearances the 32-gauge steel tubing should plug the small interior diameter plastic tubing to the outer barrel, but this does not occur due to the stretching of the plastic tubing over the 24-gauge steel tubing. The junction points of Tygon tubing with inner and outer cannulae are then covered with Dow-Corning Silastic (Figure ID) and cured under a forced convection dryer for 2 hr. After further curing overnight, cannulae are ready to use. Cannulae are held in a clamp on a stereotaxic apparatus for acute implantation. In practice, we often clamp a metal recording electrode immediately adjacent (Figure IE) to