The role of supraspinal input in embryonic motility: a re-examination in the chick.

The present experiments represent an attempt to further clarify the role of the brain in embryonic motility and behavior. By making high chronic cervical transections ("gaps") at early prefunctional stages of incubation (i.e., 40-50 hours) and studying the subsequent emergence of motility in the chick it has been possible to determine that supraspinal input is not functional until about the tenth day of incubation. Acute cervical transection results in a modification of the temporal pattern (rhythm) of motility without affecting the frequency of activity. Qualitatively the movements of spinal embryos are indistinguishable from controls up to 16-17 days. At that time there are detectable differences in the character of spontaneous movements, in reflex responsivity and in hatching behavior; spinal embryos are not able to initiate the coordinated Type III movements necessary for escape from the shell. Injection of strychnine into chronic cervical and control embryos at 10 days and at 16-17 days indicates that certain aspects of the typical strychnine response are lost following removal of brain input to the spinal cord. Finally, chronic thoracic gaps result in a clear modificaect at this age. These data suggest that propriospinal integration is present at least several days prior to the onset of supraspinal input in the chick spinal cord.