In vivo stimulation of nerve cells by phytohemagglutinin. I. Alterations of some cytological aging parameters in rat brain cells.

Phytohemagglutinin P (PHA-P) was administered in form of intralumbar injection to old (24-27 months) female Wistar rats. PHA-P has an inductive effect also on the nerve cells. The thermal denaturation characteristics of the DNA in situ as well as the numerical density of perichromatin granules being connected to the extranucleolar RNA synthesis returned practically to the young levels in the large brain cortical cells and in the cerebellar granular cells 20 h after the injection. The reversal of these aging phenomena was accompanied by a significant decrease of intranuclear and intracytoplasmic K+ content measured by X-ray microanalysis in the dry mass, whereas Na+ and Cl- remained unchanged. If PHA-P causes also some (1-2%) rehydration of the old neurons, the total ionic strength in the cell due to the monovalents may even reach the young level. The possible regulatory role of the ionic strength and the Na+/K+ ratio in the chromatin function is discussed on the basis of experimental data. It is the first time that the reversibility of some cytological aging parameters has been demonstrated in vivo.