c-fos protein-like immunoreactivity: distribution in the human brain and over-expression in the hippocampus of patients with Alzheimer's disease.

c-fos protein-like immunoreactivity was investigated in the human brain post mortem, using a polyclonal antiserum raised against the N-terminal conserved peptide of c-fos protein. Immunostaining was found in the cerebral cortex, hippocampus, striatum, thalamus and cerebellum but not in the upper brainstem and the adrenal gland. c-fos-like immunoreactivity predominated in neuronal elements, but was also observed in neuropil and glial cells. In addition to a nuclear localization, the staining could be seen in neuronal dendrites (i.e. in the pyramidal cells of hippocampus or in some cortical areas). In order to analyse the effect of brain injury on c-fos expression, the characteristics of the immunostaining were analysed in the hippocampus of patients deceased with Alzheimer's disease known to be associated with a preferential vulnerability of the pyramidal neurons. No staining was observed in the senile plaques or in neurofibrillary tangles, the histopathological stigmata of the disease. Densitometric measurement of the intensity of c-fos-like staining revealed a significant increase in the hilus, the fimbria and the CA1 field of the pyramidal layer in brains of patients with Alzheimer's disease compared to controls. These modifications may result from a suffering stage of hippocampal cells or from a compensatory mechanism in the still surviving neurons not yet affected by the pathological process.