Diazepam binding inhibitor (DBI) processing: immunohistochemical studies in the rat brain.

Diazepam Binding Inhibitor (DBI) is an endogenous 11-kDa peptide originally isolated from rat brain. In rat brain DBI coexists with at least three different processing products and the members of this peptide family have been shown to displace benzodiazepines and beta carbolines from recognition sites located on the allosteric modulatory centers of GABAA receptors. Immunocytochemical methods were used to study the location of DBI and two of the processing products, octadecaneuropeptide (ODN) DBI 33-50 and triakontatetraneuropeptide (TTN) DBI 17-50, in rat brain. DBI-LI was found in selected neuronal perikarya and in many glia and glial-like cells. All circumventricular organs displayed a strong DBI like immunoreactivity (LI). The distribution and cellular location of the ODN-LI and TTN-LI differed from that of DBI because they were preferentially associated with DBI in neurons, but not in glia or glial-like cells. The presence of DBI, but not of its processing products, in glial cells, circumventricular organs, and cells of peripheral tissues suggests that the function of this peptide may extend to other yet unknown function in addition to an action on the allosteric modulatory center of GABAA receptors located in neurons.