Chloride compartments in embryonic brain tissue after intracerebral ouabain administration

The "chloride space" in brain tissue of 15- and 19-day-old chick embryos was studied during the 3 h following intracerebral administration of 3.4-10(-4) M ouabain. Total tissue water, dry substance, plasma and liquor and tissue chloride concentrations were determined. The chloride space in brain tissue was calculated on the basis of the brain-cerebrospinal fluid ratio and the brain-plasma ratio. The chloride concentration in blood plasma was generally unchanged after ouabain treatment. The chloride concentration in cerebrospinal fluid was lower in younger embryos during the whole 3-h period, whereas in 19-day-old embryos only during the 1st h. Tissue chloride concentration was generally elevated, but to a greater extent in younger embryos. Total brain tissue water increased for 3 h after ouabain treatment in 15-day-old embryos and for the first 2 h in 19-day-old embryos. The expansion of chloride space reached a new steady state during the 1st h after ouabain treatment and amounted to 12-15% of control values in 15-day-old embryos. The increase of chloride space in older embryos reached its maximum (14.8% of control values) within the 1st h and gradually decreased thereafter. The age-dependent changes of chloride compartmentation in embryonic brain tissue are discussed in relation to the previously investigated spongy state of the brain tissue in chick embryo.