The landmark study, which was carried out by a team at Imperial College London and CNWL, was the first study in the world to image the opiate system in the brain of pathological gamblers.
Dysregulation within the opioid receptor system is increasingly recognised in substance dependence, with higher mu-opioid receptor (MOR) availability reported in alcohol, cocaine and opiate addiction. It was expected that the same would be found in pathological gamblers whose condition is also recognised as a behavioural addiction.
To see if pathological gamblers showed a similar pattern, 14 pathological gamblers and 15 healthy volunteers underwent two positron emission tomography (PET) scans before and after an oral administration of 0.5mg/kg of d-amphetamine which releases ‘natural' opioids in the brain called endorphins. The study is the first in the world to measure this directly in addiction.
The results showed "significant blunting of opioid release" compared with the healthy volunteers and "blunted amphetamine-induced euphoria and alertness compared with HV (healthy volunteers)." However no difference was seen in baseline MOR availability.
This study differs from alcohol, cocaine or opiate dependence where higher MOR is seen.
The study is the first to show blunted opioid release in the brain an addiction; such blunting is consistent with some models of alcoholism.
One of the team - Dr Henrietta Bowden-Jones from CNWL's Problem Gambling Clinic - said: "This is very exciting as it provides the first evidence of blunted endogenous opioid release in pathological gamblers.
"Our findings are consistent with a growing evidence base that dysregulation of endogenous opioids may have an important role in the pathophysiology of addictions. Our data also provides a challenge to how opiate blockers work since it was presumed that the opiate system was ‘over-active' in pathological gamblers. Our findings show the opposite."
The team was led by Prof Anne Lingford-Hughes, Consultant Psychiatrist at CNWL and Professor of Addiction Biology at Imperial and Prof David Nutt, The Edmond J Safra Chair in Neuropsychopharmacology at Imperial.
The study was conducted by Dr Liese Mick, also from Imperial College and CNWL's Problem Gambling Clinic.
The findings are published in Neuropsychopharmacology - the official journal of the American College of Neuropsychopharmacology.