Fluid compartmentation and electrolytes of cat cerebral cotex in vitro. 3. Ontogenetic and comparative aspects.

Abstract

SUMMARYStudies on swelling and fluid compartmentation have been carried out in vitro on incubated slices of cerebral cortex from kittens 1.5‐120 days post‐natal age and on incubated sections of corpus callosum and slices of liver and kidney cortex from adult cats. The findings have been compared with analogous data for incubated slices of adult cat cerebral cortex, studied under identical conditions (Bourke and Tower, 1966a, b), in order to identify the probable morphological correlates of fluid and electrolyte distribution.Incubated cortical slices from neonatal (1.5‐4‐day‐old) kittens exhibit none of the relevant characteristics of slices from adult cerebral cortex. By 1 month post‐natal age, K+‐dependent swelling of slices becomes demonstrable, and the K+ and Na+ contents of slices approximate adult levels. Both these developments coincide with the morphological and physiological maturation of cortical neurons. At 3 months post‐natal age, slice swelling accessible to C1− but not to sucrose becomes observable and the dependence of sucrose space size on time, during incubation, of solute addition becomes demonstrable. Both these developments follow completion of axonal myelination in the cortex but coincide with the period of cortical glial cell proliferation.Incubated sections of corpus callosum from adult cats exhibit none of the relevant characteristics observed for cortical slices under identical conditions. Tissue swelling is minimal and uninfluenced by K+ concentrations of incubation media. Tissue fluid spaces accessible to sucrose are approximately twice the size of spaces accessible to inulin. In general, qualitatively similar results have been obtained for incubated slices of cat liver or kidney cortex or for incubated sections of rat diaphragm under the same conditions. A behaviour for glial cells (? astrocytes) in cerebral cortex under such in vitro conditions distinctly different from behaviour of subcortical glial cells is suggested.