S100 brain protein: correlation with behavior.

The brain-specific acidic protein, S100, in the pyramidal nerve cells of the hippocampus was investigated as a possible correlate to learning during transfer of handedness in rats. The amount of S100 increased during training. Intraventricular injection of antiserum against the S100 protein during the course of training prevented the rats from further increases in learned behavior but did not affect motor function in the animals. Antibodies against the S100 protein could be localized after injection by immunofluorescence, in hippocampal structures, penetrating presumably through slight ependymal lesions caused by the injection. By contrast, control animals subjected to the same training and injected with S100 antiserum that had been absorbed with S100 protein or with other antisera against gamma-globulins showed no decrease in their ability to learn. The conclusion is that the brain-specific protein, S100, is linked to the learning process, at least within the training used.