Presence of NF-κB-like and IκB-like immunoreactivities in postsynaptic densities

THE distributions of IκB and NF-κB immunoreactivities were examined immunohistochemically in the rat brain by the electron microscopy. Antibodies were raised against synthetic peptides with the sequences specific to the human MAD-3 type IκB or NF-κB. Both IκBa and NF-κB immunoreactivities were localized in the dendrites including the spines and, particularly, the postsynaptic densities (PSDs) of the hippocampus and the cerebral cortex. The PSD fraction prepared from the rat brain contained an activity that inhibited the binding of NF-κB to the κB DNA elements. These results suggest that the NF-κB/IκB system or a similar mechanism may play a role in signal transmission from synapses to the nucleus.