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Addicted to finding a cureMonash researchers have been trying to identify why some people become addicted to drugs, while others can more easily say no. ALLISON HARDING reports Just say “no” to drugs, advise the public awareness campaigns – but it might not be that easy for some, according to researchers at Monash’s Victorian College of Pharmacy.
They have been investigating, with the aim of identifying, neurological differences that are responsible for making some people more susceptible to opiate addiction than others. And if they can identify or develop a drug that can suppress the neurochemical craving for some opiates, the war against illegal drugs might become easier to win. Dr David Taylor, senior lecturer in the Department of Pharmaceutical Biology and Pharmacology, has been working with drugs of addiction and their mechanism of action for more than 20 years. His studies have involved researching the physiological and behavioural changes induced by cannabis, cocaine and morphine, and have even included investigating the reasons why some people experience an increase in appetite for novel foods after using cannabis. Dr Taylor and his team are now focusing on identifying the chemical changes that occur in the brain when morphine is ingested. Other members of the team with expertise in neurotransmitter receptor systems, second messenger systems and molecular biology are assisting in the search. “It is clear that drugs of abuse are pharmacologically diverse – some are stimulants, some are depressants, and people take them for a range of reasons,” Dr Taylor says. “But the curious thing is that not everybody has a compulsion to take them again – those who do are the ones who have become psychologically and perhaps physically dependent.” Scientists define the physical dependency on a drug of addiction as the adaptive state of the body to a drug. However, psychological dependency relates to the craving for the drug – experienced in the ‘pleasure centre’ of the brain – as well as the desire to avoid the discomfort of withdrawal. Dr Taylor points out that physical dependence on opiate drugs is “relatively easy” to treat – for instance, those trying to break a heroin habit can be prescribed methadone. But it is overcoming the psychological commitment to the drug – or the craving – that is the crucial factor. At present, Dr Taylor says, the only weapons to break that bond are counselling and willpower. “The craving is the hard part to decipher, so we’re looking at that neurochemical process – at what’s occurring in the brain to drive somebody to take opiates,” he says. “We need to find the common elements among opiates that create the dependence.” Dr Taylor and his team are excited by early results from laboratory rats, exposed to a sucrose solution containing morphine. In time-consuming experiments conducted over many weeks, the rats drank the solution for three weeks – the time it takes for an addiction to develop. The rats were then given a choice of a plain sucrose solution to drink or the sucrose solution that included morphine. While some of the rats wouldn’t touch the morphine solution, an astounding 25 to 45 per cent of the animals went straight for the drug. “They actually went for the pharmacological action of the solution,” Dr Taylor says. “They would go back and back and back for the drug – and while the non-morphine favouring rats would only drink about a teaspoon of fluid, the ‘junkie rats’ drank from 40 to 150 millilitres (about half a glass) a day. “Since rats will not normally voluntarily consume morphine solution, it appears that the exposure to morphine had actually triggered some change in them.” And when they examined the brains of the ‘junkie rats’, Dr Taylor and PhD student Mr Henry Skupek discovered what the change was. “To our surprise, we found that the morphine released more dopamine, a natural stimulant, from the brains of the ‘junkie rats’ than the abstainers,” Dr Taylor said. “The region of the brain where this occurs is the ‘pleasure centre’, where dopamine is a natural stimulant.” Studies of the central nervous system show that morphine increases dopamine release and also increases the number of dopamine receptors. This happens in the ‘reward’ centre of the brain. “This centre is normally involved in reward processes, but in addicts it is implicated in the craving properties of drugs of abuse,” Dr Taylor says. “It’s significant that morphine releases a greater amount of dopamine in the brains of morphine-preferring rats compared to morphine-abstaining rats. This fundamental difference could explain why some animals are susceptible to opiate self-administration. “It is not unreasonable to assume that the same underlying difference dictates susceptibility to opiate abuse in humans.” The researchers are now using the ‘morphine-preferring’ model to investigate the predisposition to opiate abuse. “And that will help us develop a specific drug for opiate dependence,” Dr Taylor says. He believes that if the components of the drug are already clinically available, human trials might not be too far away. “Drug addiction impacts negatively on communities in Australia and around the world in so many ways – finding a drug that treats opiate dependence would undoubtedly be a significant breakthrough,” Dr Taylor says. ACTION: Organisations interested in supporting or finding out more about research into opiate addiction at the Victorian College of Pharmacy can contact Dr David Taylor on +61 3 9903 9568 or visit www.vcp.monash.edu.au/pharmacology/research.html |
The
researchers believe they are close to discovering the reason why some
people so readily say “yes” to potentially fatal drugs of addiction
such as heroin.