Cationic Composition of Rat Cerebral Cortex Slices. Comparative Study During Development

Slices of cerebral cortex isolated from 20‐day‐old rats, when incubated in an appropriate oxygenated saline, show only a slight increase in weight (± 0.4 per cent of initial fresh wt.). At 30 days, under the same conditions, this increase in weight is 12.4 per cent. This is similar to the value observed in adult animals (13.6 per cent). Modifications of the cationic content of slices in the case of 20‐day‐old animals are very slight while in 30‐day‐old animals they are greater and similar to those observed with adults. The inulin space of 20‐ and 30‐day‐old rats are the same. The swelling exhibited by the slices isolated from 30‐day‐old animals may reasonably be attributed to a cellular uptake of extracellular fluid. This is accompanied by an increase of the Naf concentration and by a decrease of the K+ concentration. The values observed are similar to those observed with adult rats. Comparing our results with previous histological and histochemical data, it may be suggested that the modifications of cationic content, as well as the swelling of slices isolated from 30‐day‐old rats or adult animals, are solely attributable to changes affecting glial cells and more specifically the astrocytes.