Rethinking depression

Associate Professor Rohan Walker is advancing a scientific premise that could transform treatment for mood disorders.

Rohan Walker on stairs 

Associate Professor Rohan Walker is part of a growing international band of scientists whose work is challenging conventional thinking about the neurochemical causes of depression. Walker leads a research group investigating brain cell inflammation as a primary cause of psychological disorders. Their research looks into the role of microglia cells, a key part of the immune defence of the central nervous system, and how those cells can be manipulated to mediate the effects of chronic stress.

Traditional drugs prescribed for severe depression act by adjusting the levels of neurotransmitters in the brain but the specific role neurotransmitters play in the development or treatment of clinical depression is not clearly understood by the medical or scientific fields. Also, these common anti-depressants – taken by an estimated one million Australians – often produce side effects and their efficacy varies considerably.

"As scientists we would like to design better medications but the major roadblock is that there is no solid understanding of the precise changes in the brain that lead to mood disorders," Walker maintains. "What has motivated me to take my research down this new path is the compelling body of evidence emerging from around the world that suggests inflammatory processes are strongly involved in depression."

Walker's interest in inflammatory processes in the brain was inspired by his postdoctoral research into the neurobiological mechanisms of stress and the factors that determine vulnerability to mood disorders. His studies drew a parallel between the behaviours that people display when they have a physical ailment such as a cold and those commonly reported by people who are depressed – symptoms such as fatigue, loss of appetite and libido, disrupted sleep and demotivation.

"It seemed more than a striking coincidence that the two were so similar," Walker says. "We know from previous work that sickness behaviours are influenced by microglia, so that prompted me to start thinking about whether microglia could be involved in regulating depression and psychological illness."

Although only three years into the research program, Walker and his colleagues have already made a novel discovery that has advanced the neuroinflammation hypothesis. Their research established that exposure to chronic stress changes the behaviour of microglia in the brain and that chemically inactivating microglia can reduce stress-related emotional response. Their findings were published last year in the high-level journal Cerebral Cortex, a publication that has increased the international profile of their work and opened up collaborations withresearch groups at other institutions, including the University of Queensland and La Trobe University.

Walker completed both his undergraduate and doctoral studies at the University of Newcastle and has worked full-time in research since being awarded his PhD in 2006. He received a Peter Doherty Early Career Fellowship from the National Health and Medical Research Council (NHMRC) in 2007. He is the convenor of the Affective and Addictive Disorders Program within the University's Centre for Brain and Mental Health and his research into neuroinflammation and novel anti-depressant strategies is supported by a NHMRC grant of more than $346,000.

"The Centre is a fantastic network of more than 100 academics and I collaborate with neuroscience researchers at the University and within the Hunter Medical Research Institute group," Walker states. "It is a very supportive and intellectually challenging environment in which to work."

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