A new technique for studying potential changes in nephrons of chick embryo kidneys in vivo.

To make the chick embryo accessible to electrophysiological measurements in its mesonephric kidney during the period between embryonic days (e.d.) 5 and 10, a special "chick-embryo-incubation bath" was constructed. It consists of an aerated chamber covering the egg and maintaining the gas exchange across the shell, and of a warmed reservoir of the incubation medium, into which the embryo is pulled out of the egg through a window in the shell. The two compartments are separated with a rubber membrane tightly fitting to the edges of the shell-window. The incubation medium contains a modified Krebs-Henseleit-Ringer solution and anesthetic Tricaine (Sigma). Access to the mesonephric nephrons is achieved by surgical excision of the body wall on the right side performed at e.d. 5. On average only about 35 percent of the operated embryos survive till the third day after surgery but during the next two days a mortality rate recedes to zero. The tolerance of short-term survival of embryos placed in the incubation bath was tested for up to 4 1/2 h. It was very good in embryos of age 5 to 7 e.d. as assessed by a steady heart rate and the presence of arterio-venous differences. A modified differential amplifier containing circuits for frequency compensation of the two channels was used for high-fidelity registration of voltage changes in the embryonic nephron with a single double-barrel microelectrode.