[Study of amphibian brain asymmetry during normal embryonic and larval development]

Amphibian embryos (Triturus vulgaris, Pleurodeles waltl, Hynobius keyserlingii, Ambystoma mexicanum, Rana temporaria, Bufo bufo, and Xenopus laevis) were investigated. We ascertained the morphological right-side asymmetry of the brain, which appears at the neurula stage and is preserved during the postembryonic (larval) development. In T. vulgaris, P. waltl, H. keyserlingii, and X. laevis, we observed right-side asymmetry of peripheral analyzers, such as the retina, ganglia of nerve VIII, and olfactory placodes. Structural analysis of the forebrain in A. mexicanum has shown that in the larvae, the pallium prevails on the left side of the cerebral hemisphere. During metamorphosis, left-side asymmetry is replaced by right-side, which is then preserved. We propose that the brain asymmetry arose at the early stages of evolution as a result of embryonic formation of the nervous system.