Changes With Age in Water and Extra‐cellular Space in Incubated Brain Tissue

Abstract— (1) Incubation in physiological saline at 37º caused brain slices from chick embryos to lose water (shrink), whereas slices from young chicks gained water (swell). Shrinkage decreased with age in embryonic brain, and swelling increased with age in chick's brain. (2) Incubation at 0º diminished shrinkage in 8‐day old embryos, caused an increasing degree of swelling in older embryos, and enhanced swelling in young chick's brain slices. (3) Inulin equilibrated more rapidly with tissue water in embryonic than in young adult brains. Measured ‘inulin space’ values at 37º changed little with age, whereas 0º‘inulin space’ values significantly decreased with age. Calculated zero time ‘inulin space’ values also decreased with age. (4) The measured ‘inulin space’ at 0º was larger than that measured at 37º (but not of the calculated zero time ‘inulin space’) in young embryos, then became progressively smaller, so that in young chicks the situation was reversed. (5) The calculated extracellular space ranges from about 37 per cent (8‐day old embryos) to about 14 per cent (15‐day old chicks). (6) Incubation in the absence of glucose had more effect on brain slices from young chicks than from embryos. The opposite was true when a hypotonic medium or a medium containing d‐glutamate was used.