The Development of Fundulus heteroclitus Embryos in Solutions of Metrazol

Abstract

Speidel 1 has attempted to ascertain the specific effect of metrazol on the nervous system by immersing frog tadpoles in aqueous solutions of it and by studying, by direct microscopic and ciné-photomicrographic methods, the outgrowth of living nerve fibers in the tadpoles'tails. Using a 2% solution for approximately 20 minutes, Speidel found that the growing nerve endings degenerated during the period of immersion, but recovered and subsequently regenerated when the tadpoles were returned to pond-water.

The present communication reports the results of studying the development of certain aspects of gross behavior in whole embryos (Fundulus heteroclitus) which were immersed in solutions of metrazol at different stages of development and which remained in them for varying periods of time. The investigation was undertaken with the possibility in mind that subjecting embryos to treatment at various stages of development might produce alterations of structure and function in the central nervous system which could be correlated with the particular fiber-tracts being laid down during the period of treatment.

Over 500 eggs of Fundulus heteroclitus were treated with aqueous solutions of metrazol (Pentamethylentetrazol, Bilhuber-Knoll Corporation). Solutions, made in distilled water, were used in strengths of either 0.1% or 2 %. The embryos were introduced into the solutions at stages varying between 6 and 34 (Oppenheimer 2 ), and remained in them for periods varying from a few hours to 14 days. In some cases they remained in the solutions until fixation; in others they were transferred to tap- or sea-water. Some embryos were dechorionated before treatment, others were left in their chorions throughout; still others were dechorionated during the course of treatment or recovery. All embryos were observed at least twice daily; those which survived treatment were preserved and are being prepared for histological study.