© 1978 by The Society for Integrative and Comparative Biology
Aspects of Mauthner Cell Differentiation in the Axolotl, Ambystoma mexicanum
Departments of Neuroscience and Anatomy, Albert Einstein College of Medicine of Yeshiva University Bronx, New York 10461
SYNOPSIS. In premetamorphic amphibians, the Mauthner cells (M-cells), a single pair of large neurons, are present in the medulla. M-cells differentiate early, are easily recognized morphologically, and in the axolotl embryo, may be approached experimentally: This system is a unique one for the study of neuronal development.
The withdrawal of a neuron from the cell division cycle is an early event in its differentiation. Gastrulae, neurulae and tailbud embryos were each given a single injection of 3H-thymidine. Radioautographs of larvae showed label over M-cell nuclei when injections were made before the end of gastrulation, but not when injections were made at later stages. Thus, the cells that give rise to M-cells cease DNA synthesis during late gastrulation.
Unilateral rotations of prospective hindbrain through 180° were performed to see if M-cell axes are specified during neurulation. Rigid axial polarization of the M-cell does not appear to occur in the neurula: The rotated cell regulates and develops normally with respect to its axes.
A major source of input to the M-cell is from the ipsilateral vestibular system. To study the interaction of the M-cell with ingrowing axons, unilateral implants of otic vesicles were made anterior to the otic vesicle in host midtailbud embryos. Preliminary data suggests a mechanism for the formation of specific neuronal connections not dependent upon position-time relationships: The ectopic vestibular axons enter the medulla and course caudad to terminate in the region of the ipsilateral M-cell. Whether these axons actually form synapses on the M-cell remains to be established.