Objective: The onset of schizophrenia symptoms in late adolescence implies a neurodevelopmental trajectory for the disease. Indeed, the γ-aminobutyric acid (GABA) inhibitory system shows protracted development, and GABA-ergic deficits are widely replicated in postmortem schizophrenia studies. The authors examined expression of several interneuron markers across postnatal human development and in schizophrenia to assess whether protracted development of certain interneuron subpopulations may be associated with a particular vulnerability in schizophrenia.
Method: RNA was extracted postmortem from dorsolateral prefrontal cortex of individuals from age 6 weeks to 49 years (N=68) and from a cohort of normal comparison subjects and schizophrenia patients (N=74, 37 pairs). Expression levels of parvalbumin, cholecystokinin, somatostatin, neuropeptide Y, calretinin, calbindin, and vasoactive intestinal peptide were measured by quantitative reverse transcription-polymerase chain reaction. Changes in calretinin protein levels were examined by Western blot.
Results: Interneuron marker genes followed one of three general expression profiles: either increasing (parvalbumin, cholecystokinin) or decreasing (somatostatin, calretinin, neuropeptide Y) in expression over postnatal life, with the most dramatic changes seen in the first few years before reaching a plateau; or increasing to peak expression in the toddler years before decreasing (calbindin, vasoactive intestinal peptide). mRNA expression of all genes, with the exception of calbindin (which increased), showed a reduction (8%-31%) in schizophrenia. Somatostatin showed the most dramatic reduction (31%) in schizophrenia.
Conclusions: It appears that a heterogeneous population of interneurons is implicated in schizophrenia. Further studies are needed to determine whether specific interneuron subpopulations are altered or whether common or distinct upstream pathways are responsible for interneuron deficits in schizophrenia.