O2 tension in the spinal cord of the avian embryo.

A small recessed-tip O2 microelectrode was used to construct frequency distributions of PO2 in the chicken embryonic spinal cord during the last week of development (15-20 days). PO2 was remarkably low and stable at a given spinal locus. Electrode movement led to little change in the absolute level of tissue PO2 for a given day in the development. Spontaneous fluctuations occurred, predominantly in the motor columns, whose frequencies were dependent on the stage of incubation. PO2 decreased progressively; the most significant decline occurred between 16 and 17 days in ovo [19.2 +/- 1.7 (SD) to 11.5 +/- 2.7 Torr, respectively]. This decline in tissue PO2 at 16 days precedes dramatic alterations in spinal cord electrical activity and the resulting embryonic behavior.