What happens to the brain’s ‘reward pathways’ when a person takes an addictive drug? And why do some people who try drugs walk away while others try it again?
The answers to those seemingly simple questions are complex, but figuring them out could point to new ways of tackling drug dependence.
Circuits of reward
Our understanding of what happens to brain information circuits or pathways has taken big steps forward, according to Dr Stella (Styliani) Vlachou, assistant professor in psychology at Dublin City University (DCU). However, there is plenty of work left to tease out what different types of drugs do to the brain, and figure out ways to help tackle addiction.
“For a number of decades, some circuits in the brain have been identified that tend to be activated by drugs of abuse,” explained Vlachou, who heads the Behavioural Neuroscience Laboratory at DCU’s School of Nursing and Human Science. “These pathways can also change their function because of the presence of drugs of abuse molecules.”
The brain’s reward pathways and other circuits are linked to the addictiveness of a substance and difficulties in withdrawing from it, but figuring out exactly what is going on in the addicted or withdrawing brain is no easy task.
“Each drug of abuse has different mechanisms of action,” noted Vlachou, who has mostly concentrated her own research on nicotine and cannabis. “Some substances have many things in common; they can either directly or indirectly activate brain reward pathways, but they can do that in different ways.”
Nicotine and cannabis
Smoking has obvious negative impacts on a person’s health, and nicotine is addictive because it binds to receptors on brain cells. “The molecule binds specific receptors of the brain, and these receptors are in many different areas of the brain, including areas of the brain reward system,” explained Vlachou.
Her research in animal models has looked at ways to try and change the effects of nicotine on the brain. She is particularly interested in targeting GABAB receptors in the hope of developing new ways to support people while they stop smoking, but there can be issues around side effects. “We are still in the process of trying to find more safe compounds acting on this GABAB system. It is still something that needs a lot of research,” she said.
Cannabis also binds to specific receptors in the brain, and Vlachou has been looking at what happens if the brain is exposed to cannabinoids and other stimulants or drugs at the same time.
While the nuts and bolts of the biochemistry provide plenty to think about, Vlachou is also looking at how other aspects of behaviour, age and personality might contribute to whether a brain is more or less likely to develop an addiction.
“I’m looking at how caffeine and nicotine can affect brain reward mechanisms, but taking into account whether factors like personality traits, impulsivity, attention and age may have an effect,” she said.
“Age is really important to think about, because numerous studies have shown stronger effects in individuals who have been exposed to compounds and drugs at around adolescent age when areas of the brain such as the pre-frontal cortex [involved in decision-making] are still developing.”
Prevention better than cure
To date, Vlachou’s journey in research has taken her from her native Greece, where she did a PhD at the University of Crete, to the US where she worked as a researcher at the University of California, San Diego. She moved to DCU in 2011, set up her own group there and she has been building collaborations in Ireland and abroad.
Ultimately, the goal is to develop new ways to help to tone down the dependence on addictive substances, but Vlachou is passionate about prevention.
“I do hope we will reach a stage where we have identified a number of substances, natural or synthetic, that can be used for dealing with drug dependence, and I would love to have contributed – even with a small stone, as we say back home – a small piece of the puzzle into a substance that could be used for smoking cessation, or managing the use of substances to help people with diseases,” she said.
“But what is really important is that I always try to educate young people, including the students, about the importance of prevention – that is something we really need to support.”
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