Peripheral-type benzodiazepine receptors in diagnostic subtypes of schizophrenic patients

The peripheral-type benzodiazepine receptor (pBZD-R; also called the omega-3 receptor or the mitochondrial benzodiazepine receptor) seems to play a critical role in the production of neurosteroids, which are able to alter the electrical properties of neuronal membranes and thus the firing patterns of neurons. Putative endogenous ligands are the diazepam-binding inhibitor and its processing products, as well as porphyrins, some of them, in the case of porphyria, are well known to give rise to certain aspects of neuropsychiatric disorders, such as schizophrenic-like symptoms. Previous findings of altered benzodiazepine binding sites in post-mortem brain samples and platelets from small samples of schizophrenic patients have been inconclusive. Therefore we investigated characteristic binding parameters (Bmax, Kd) of the granulocytic pBZD-R by using the selective ligand PK11.195 in 53 subjects, fulfilling ICD-10 and DSM-IV criteria of schizophrenia. The binding parameters in our total group of 53 schizophrenic patients did not differ from those in healthy subjects. However, Bmax values were significantly reduced in schizophrenic patients with predominantly negative symptoms (residual type) compared to schizophrenic patients with predominantly positive symptoms, i.e. paranoid (-50%) and catatonic subtype (-38%). Moreover, only residual type schizophrenics exhibited a significantly reduced binding capacity compared to healthy subjects (-38%). More studies are warranted to clarify the functional significance of this binding site in the pathogenesis of negative symptoms.