The effect of antiserum to S 100 protein on behavior and amount of S 100 in brain cells.

Since antiserum raised against the S 100 protein has an impairing effect on acquisition in behavioral tests, when interacting with S 100 on hippocampal cells, the effect of S 100 antiserum was studied in rats on the S 100 content of the hippocampus and thalamus, as well as on behavior. The operant reversal of handedness test and a light discrimination test were used. S 100 antiserum, 2 X 30 mu l, was injected intraventricularly before and during the sessions of two different learning tests. The S 100 protein was determined by quantitative immunoelectrophoresis. In the antiserum-injected animals, the levels of S 100 protein was increased by up to 30%, the incorporation values of 3H-valine increased in proteins of high molecular weight. Further acquisition was inhibited compared to controls, in which antiserum absorbed with pure S 100 protein was injected intraventricularly. The stimulation of S 100 synthesis, probably by the glia, may have occurred by a negative feedback effect, as has been observed in thymocytes.