A neurophysiological analysis of the effects of hypercapnia on the embryonic spinal cord

Progressive hypercapnia in the normal chick embryo late in incubation (14-19 days) is temporally associated with a gradual decline in motor activity and the corresponding frequency of polyneuronal (burst) activity in the spinal cord. We have studied the possible correlation between the increasing hypercapnia and the declining frequency of burst activity seen during these later stages of incubation by systematic manipulation of CO2 levels. Burst frequency was seen to decrease as a result of a 5-min exposure to different carbon dioxide environments at all ages studied. The magnitude of this inhibition and the ability to recover from consecutive bouts of hypercapnia (pulses) is pulse and age dependent. These short-term (less than 5.0 min) changes differ qualitatively from the long-term (greater than 2.5 h) effects of subsequent hypercapnic episodes. This evidence suggests a role for metabolic factors in the normal developmental changes in motility and electrophysiological activity in the chicken embryo spinal cord.