Schizophrenia remains a serious mental disorder without a fully effective medical cure. To better understand the molecular changes that occur in the schizophrenic brain, researchers at the University of Southern Denmark analyzed protein changes in the brains of rats exposed to a powerful hallucinogen. Their proteomics-based approach may point the way to new, more targeted treatments.
Schizophrenia affects a significant portion of the adult population and, despite centuries of study, clinicians still cannot diagnose the disorder through a definitive blood or tissue test. Diagnosis relies largely on behavioral observation, because the precise physiological causes and molecular markers remain unclear. Identifying reliable biological signatures in the brain would be a crucial step toward improved diagnostics and therapies.
Because it is difficult to examine living human brains at the molecular level, scientists use animal models to probe the biological processes that underlie psychiatric symptoms. Rat brains share many structural and biochemical features with human brains, making them useful models for investigating brain disorders, including schizophrenia.
Modeling schizophrenic-like symptoms with PCP
Phencyclidine (PCP), often known as “angel’s dust,” produces in humans a range of symptoms similar to those seen in schizophrenia. When administered to rats, PCP triggers comparable behavioral changes—altered movement patterns and impairments in cognition such as memory, attention, and learning—making PCP-treated rats a widely used model for studying schizophrenia-like states.
“When we give PCP to rats, the animals provide a valuable model for exploring the molecular events behind schizophrenia,” explains Ole Nørregaard Jensen, professor and head of the Department of Biochemistry and Molecular Biology at the University of Southern Denmark. Jensen and colleagues Pawel Palmowski, Adelina Rogowska-Wrzesinska and others report their findings in the Journal of Proteome Research.
Because PCP is rapidly taken up by the brain and cleared within a few hours, the research team examined brain tissue at short, well-defined intervals after injection to capture immediate molecular responses. Using advanced mass spectrometry facilities available at the University of Southern Denmark, the researchers mapped protein expression and phosphorylation changes across the cortex at multiple time points.
Proteomic discovery: 352 proteins linked to PCP response
The proteomic analysis identified 2,604 proteins in the rat frontal cortex. Of these, 352 proteins exhibited changes in phosphorylation or abundance that correlated with PCP exposure. Many of these proteins switched “on” or “off” abnormally in response to the drug, triggering downstream disturbances across cellular pathways.
These disturbed proteins are implicated in a variety of neuronal processes: calcium balance, substance transport across membranes, cellular metabolism, and cytoskeletal structure. Such disruptions can alter neuronal signaling and synaptic function, plausibly contributing to the behavioral changes observed in the PCP model and, by extension, to some of the molecular dysfunctions present in schizophrenia.
“These 352 proteins appear to drive the behavioral and physiological responses to PCP in rats,” says Jensen. “If similar protein changes are confirmed in human schizophrenia, they could become targets for new drugs designed to prevent or correct the molecular events that lead to symptoms.”
The protocol and mass spectrometry workflow developed by Jensen’s team constitute one of the most extensive proteomics data sets applied to the PCP model to date. The methods are broadly applicable and can be used to study other brain disorders that involve rapid and complex molecular changes.
The project was a collaboration between the University of Southern Denmark, the Danish Technological Institute, and NeuroSearch A/S.
Experimental details
In the experiment, twelve rats were divided into two groups: six received PCP injections (10 mg/kg body weight) and six received saline as controls. At 15, 30, and 240 minutes after injection, pairs of animals from each group were euthanized. Within two minutes of euthanasia, temporal lobe tissue samples were collected and rapidly frozen in liquid nitrogen to preserve transient phosphorylation states.
All procedures complied with Danish and EU guidelines for the care and treatment of laboratory animals. The frozen tissue samples underwent mass spectrometric analysis to detect changes in protein phosphorylation and abundance. Interpretation of the complex proteomic data indicates that PCP produces rapid and extensive alterations in intracellular signaling, calcium regulation, transport processes, metabolic pathways, and the cytoskeleton.
This research was supported by the Villum Foundation and the Danish Ministry of Higher Education and Science (Grant No. 08-034107, Innovation Consortium “New drugs”).
Contact: Ole Nørregaard Jensen – University of Southern Denmark
Source: University of Southern Denmark press release
Image Source: Image credited to S. B. Raymond et al/PLOS ONE (Creative Commons attribution)
Original Research: Abstract for “Acute Phencyclidine Treatment Induces Extensive and Distinct Protein Phosphorylation in Rat Frontal Cortex” by Pawel Palmowski, Adelina Rogowska-Wrzesinska, James Williamson, Hans C. Beck, Jens D. Mikkelsen, Henrik H. Hansen, and Ole N. Jensen in Journal of Proteome Research. Published online February 12, 2014 (doi: 10.1021/pr4010794)