Development of spinal cord bioelectric activity in spinal chick embryos and its behavioral implications.

Embryonic behavior of the chick is the product of spontaneous multiunit burst discharges within the ventral spinal cord. The present study describes the ontogeny of spinal cord burst discharges in embryos which were deprived of brain input by removing several neural tube segments of 2-day embryos at cervical or mid-thoracic levels. Characteristics of bioelectric activity present in both intact and chronically transected cords are: (a) the appearance of spike discharges; (b) the organization of unit discharges into synchronized multiunit bursts; (c) the establishment of intracord synchronization of burst discharges over wide expanses of cord tissue; (d) an increase in burst duration and complexity at 7 days due to the appearance of the burst afterdischarge; (e) an increase in the amount of burst activity from 6 to 13 days followed by a decline until hatching at 21 days; (f) a shift from periodic to irregular patterns of burst activity at 13 days; and (g) the existence of the cord burst discharge as a correlate of embryonic movement. Several differences were found between burst activity from chronic spinal and intact embryos: (a) cervical spinal embryos were significantly less active than controls from 15 through 19 days; and (b) long sequences of unusual repetitive burst afterdischarges appeared in chronic spinal embryos by 13 days. The results indicate that the transected embryonic spinal cord is remarkably autogenous in function, although patterns of activity unique to the transected cord appear and increase in prominence during later stages of incubation.