Presence of NF-kappaB-like and IkappaB-like immunoreactivities in postsynaptic densities.

The distributions of IkappaB and NF-kappa B 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 IkappaB or NF-kappa B. Both IkappaB alpha and NF-kappa B 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-kappa B to the kappa B DNA elements. These results suggest that the NF-kappa B/IkappaB system or a similar mechanism may play a role in signal transmission from synapses to the nucleus.