Technic for Intravascular Injection and Bleeding of Newborn Rats and Mice. ∗

Abstract

Recent quantitative studies of immunological tolerance have focused attention on the need for special technics of bleeding and injection of embryonic and neonatal animals. Billingham and Brent(1) found that a higher proportion of tolerant mice was produced when homologous cells were injected by the intravenous route into the newborn than by other routes of administration. Their method of intravenous injection requires considerable skill and is not suitable for bleeding neonatal mice. Terasaki and Cannon(2) have devised an ingenious technic for cross-transfusion of blood in embryonic chicks. An intravascular method of injection for rat embryos of 13 to 17 days was described by Grazer and Clemente(3) but it has a relatively high mortality rate. The intracardiac technic described here for bleeding and injection of newborn rats and mice was accompanied by mortality of less than 5% in over 600 newborn rats, and 40 newborn mice. This technic has been advantageously employed in studies of transplantation immunity (4), and heterologous tumor cell tolerance.

Methods and materials. The animal is immobilized on an injecting board ventral side up (Fig. 1) with masking tape. It is important to stretch the subject as it is masked down, which helps to bring the heart closer to skin surface. The injecting equipment consists of a mounted Luer Lock Tuberculin syringe connected to a 15-inch length of P 50 polyethylene tubing by means of a plastic tubing adapter (Clay Adams size A). The 15-inch length can be conveniently calibrated for volumes up to 0.1 ml. A small length (1/2inch) of P 10 tubing is slipped inside the distal end of the P 50 tubing to serve as an adapter for the 30 gauge needle stock which is obtained by cutting off the hub of a 30 gauge needle.