Behavioral development in the absence of neural activity: effects of chronic immobilization on amphibian embryos

Embryos of Xenopus laevis and Ambystoma mexicanum were continually immobilized from premotile stages of development to stages at which normally reared embryos were swimming well. Immobilization was achieved through exposure to solutions of chloretone, lidocaine, or alpha-bungarotoxin. At a number of stages after recovery from the drugs, spontaneous and stimulated behaviors were extensively quantified. Immobilization of Ambystoma embryos resulted in temporary defects in musculoskeletal development. In contrast, treated Xenopus embryos could not be distinguished from controls by simple visual observation within minutes to hours after removal from the drug solutions. Quantifications of behavior revealed, however, a transient period of 24-48 hr during which treated embryos exhibited consistently reduced measures of stimulated swimming, while showing an increase in frequency of spontaneous movements. Detailed behavioral testing could detect no permanent effects of chronic immobilization in either species after this initial period of recovery. The results are discussed in reference to the classic works of Harrison (1904), Carmichael (1926, 1927), and Matthews and Detwiler (1926).