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The flu virus could affect your brain processes to make you feel sad as well as physically ill, a new study on mice shows.
By
Yasmin Noone

21 Apr 2016 - 8:31 AM  UPDATED 21 Apr 2016 - 8:31 AM

If having the flu makes you feel extra sorry for yourself, don’t worry. According to a new German study, a brain protein associated with the early stages of sickness could be to blame for your viral moodiness.

Two researchers from the University of Freiburg have attempted to determine why common illnesses induce sadness by studying how mice react after being injected with a virus causing symptoms similar to the human flu.

The scientists observed the mice and found that the infection increased the mice’s immobility: a behavioural sign of despair in vermin.

The study, published this week in the journal Immunity, also determined why the sick mice became depressed, noting that an antiviral protein compound in their brains, called CXCL10, had been activated.

“Our findings suggest that preventing the release of CXCL10 or blocking its receptors at an early phase should eliminate at least the initial stages of sickness behaviour, seen in response to viral infection,” cellular and molecular neuroimmunology expert and the study’s lead author, Dr Thomas Blank tells SBS.

Previous studies show that the flu and other viral infections often cause mood changes such as depressive-like behavior, cognitive deficits, sleepiness, and headache.

This study is the first to explain how the flu chemically induces sadness and determine the underlying mechanisms behind a low mood.

But to-date, there’s been little evidence to explain why an immune system impairment affects our psychology and cognition. This study is the first to explain how the flu chemically induces sadness and determine the underlying mechanisms behind a low mood.

“Whenever the body faces some kind of infection, certain proteins called cytokines are produced,” Dr Blank says.

“These compounds are essential for effective host defense against infections.”

According to the study’s results, once a body is infected with a virus like the flu, the cells lining the brain’s blood vessels produce the cytokine compound, CXCL10.

The protein is known to impair neuronal firing in the hippocampus – a brain region important in learning, memory, and mood.

“The trouble starts as soon as these proteins have access to the brain and the concentration increases.

“These compounds can induce so called sickness behavior, which makes you feel sad and gives you a hard time concentrating.”

Dr Blank says now that the scientific world understands why being sick makes mice – and possibly humans – sad, people can acknowledge the source of their temporary depression and better cope with it.

“The good news is that the whole misery is only transient.

“Sometimes, it might even be helpful to realise that feeling down while having the flu is just an unpleasant side effect of the infection, which interferes with your brain function and ultimately with your mood.

“As soon as the cytokine level in your brain is back to normal, the neurons are fine again and relay messages between each other as before.”

According to beyondblue, depression is the leading cause of disability worldwide.

Previous studies show that the flu and other viral infections often cause mood changes such as depressive-like behavior, cognitive deficits, sleepiness, and headache.

It’s estimated that around 45 per cent of all Australians will experience a mental health condition in their lifetime. In any year, one million Australian adults will have depression.

Although this study was conducted on mice and focused on the flu virus, Dr Blank says the findings could be used in future therapy studies to help people with other illnesses, who are battling the black dog.

“From our study, we learned that the compound causing depressive-like behaviour in mice after viral infection is the cytokine CXCL10 or IP10.

“Interestingly, increased expression levels of the protein CXCL10 were also found in depressed patients or in patients with bipolar depression during depressive episodes.”

Dr Blank is also hopeful that the research may be used in therapies against multiple sclerosis and hepatitis C, where patients are suffering from treatment side effects like depression and cognitive impairment.

But first, more research is also needed to develop new inhibitors of CXCL10 and clarify its role in humans.

If you are experiencing depression, want to talk to someone or are in need of support, contact Lifeline on 13 11 14 or beyondblue on 1300 22 46 36.

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