[Antidromic action potentials in the spinal cord motor neurons of the chick embryo].

Antidromic action potentials of chick embryonic hindlimb motoneurons were studied intracellularly in the isolated perfused spinal cord during the second half of the incubation period. Although the microelectrode penetration produced damage of most of cells, some of them could restore their conditions. The amplitude and time-to-peak of action potentials and the presence of components reflecting activation of the initial axon segment and somadendritic membrane as well as values of resting potentials did not show any age dependence in these cells from the 11th to 18th day of the embryonic development and were similar to those in adult birds and mammals while impulse conduction velocities of motor axons increased from 0.3-0.5 m/s in 10-day embryos to 2-4 m/s in 18-day embryos. These results do not support the hypothesis based on the study of newborn mammalian neurons in situ, which points to rather late postnatal maturation of action potential mechanisms. The early onset and maturation of action potentials in the chick embryonic motoneurons is in agreement both with the phylogenetic anciency of this mechanism and with the recent studies performed on different isolated preparations of developing CNS of warm-blooded animals.