Sodium, phosphorus, sulphur, chlorine and potassium shifts in rat brain during embryonic development

Concentrations of sodium (Na), phosphorus (P), sulphur (S), chlorine (Cl) and potassium (K) and their variations during brain development were measured in freeze-dried thick sections from rat brain (16-20 micron). Sprague-Dawley rats were bred and the day of finding vaginal spermatozoa was considered as day zero of pregnancy. On days 12E, 13E, 14E, 16E, 19E, 21E (embryonic) and postnatal day one whole embryos or fetal heads were rapidly frozen in liquid Freon 22 cooled with liquid nitrogen (-180 degrees C), sectioned in a cryostat (-20 to -40 degrees C), and processed for X-ray microanalysis on pure carbon plates. Concentrations of Na and Cl differed in the cells of the cerebral cortex, ependyma, choroid plexus and cerebral spinal fluid (CSF). During cerebral development, Na and Cl concentrations appeared to be correlated, while K was more related to P. S was low and unchanged in all compartments during development and was thus considered as an internal control. K was inversely related to Na and Cl fluctuations within the choroid plexus epithelia. Sharp phase changes of elemental composition appeared in all tissues at specific growth stages, e.g. days 14E and 19E. These results demonstrate rhythmic changes in the inorganic components of developing rat brain cells and fluid environment presumably reflecting physiological fluctuations and cell cycle phenomena. Such changes may also be related directly or indirectly to known 'growth phase changes' in the developing rat.