Presence and induction of Fos B-like immunoreactivity in neural, but not non-neural, cells in adult rat brain.

The presence and induction of Fos B, a novel growth factor-activated gene, was investigated in adult rat brain using an antiserum to Fos B and immunocytochemical methods. In normal rat brain immunoreactivity was detected in the nuclei of nerve cells scattered in the cerebral cortex, striatum, amygdala, hippocampus and dentate gyrus. This immunostaining was not present in adjacent brain sections incubated with anti-Fos B serum preadsorbed with the Fos B peptide. Furthermore, Fos B-like immunoreactivity was induced in neurons by two treatments (focal brain injury and haloperidol injection) that are known to induce Fos, however, whereas Fos levels returned to baseline 24 h after these treatments, Fos B-like immunoreactivity remained elevated at this time point. Also, although focal brain injury and rolipram injections induced Fos in ependymal and glial-like cells in rat brain, Fos B-like immunoreactivity was not detected in these non-neural cells. The implications of these results for the presence of Fos B in adult neurons is discussed.