Chick embryos, incubated at 38–39°C to stages 8–11 (Hamburger-Hamilton staging), were injected (under the vitelline membrane) with ten MLD (mice) per 0.05 ml of tetanus toxin or with avian physiological saline solution. Seventeen hours after the injection the embryos were harvested and fixed in Bouin's solution. Selected control and experimental specimens were sectioned for histological study.
Observations of gross specimens show that open neural folds of younger embryos are more susceptible than are the more extensively closed tubes of older embryos. The progressively more caudal restriction of toxin-susceptible sites with increasing age is a manifestation of this correlation with the degree of closure at injection time.
Study of serial sections establishes the concentration of lesions almost exclusively in neural tissue, especially in the alar region of the neuraxis. Tetanus-induced lesions include encephaloschisis, myeloschisis and platyneury at various levels of the neural tube. These basic defects are comparable to those reported after treatment with many CNS teratogens.
Suggestions are made concerning the possible effect of tetanus toxin on biochemical interactions that might lead to aberrations from the normal morphogenesis of the central nervous system.