Changes in density of calcium-binding-protein-immunoreactive GABAergic neurons in prefrontal cortex in schizophrenia and bipolar disorder

There is evidence that GABAergic neurotransmission is altered in mental disorders such as schizophrenia (SCZ) and bipolar disorder (BPD). The calcium-binding proteins (CBPs) calbindin (CB), calretinin (CR), and parvalbumin (PV) are used as markers of specific subpopulations of cortical GABAergic interneurons. We examined the postmortem prefrontal cortical region (Brodmann's area 9) of patients with SCZ and BPD, and of age-matched control subjects, excluding suicide cases. The laminar density of neurons immunoreactive (IR) for three CBPs, namely CB, CR, and PV, was quantified. The densities of CB-IR neurons in layer 2 and PV-IR neurons in layer 4 in the SCZ subjects decreased compared with those in the control subjects. When CBP-IR neurons were classified according to their size, a reduction in the density of medium CB-IR neurons in layer 2 in SCZ subjects and an increase in the density of large CR-IR neurons in layer 2 in BPD subjects were observed. These results suggest that alterations in specific GABAergic neurons are present in mental disorders, and that such alterations may reflect the vulnerability toward the disorders.