A link is found between morphine addiction and the tendency to explore

February 21, 2006

A team of researchers from the UAB has found experimental evidence in rats showing a link between addiction to morphine and the tendency to explore perseveringly. This is the first time a direct relationship has been found without other psychological characteristics, such as anxiousness, that might affect results. Published in Behavioural Brain Research, the results of this study are useful for planning preventative strategies in the risk population.

The tendency to use drugs depends on each individual person. Not all those who have access to drugs become addicts, therefore there may be personality characteristics that influence their use. One such characteristic is the pursuit of new sensations found in people that like looking for risk at all times. Although some studies have already suggested a link between these people and a higher probability of becoming drug addicts, shopaholics or gambling addicts, until now no study has objectively found a direct relationship without the influence of other psychological factors, such as anxiousness.

A team of researchers from the Institute of Neuroscience, the Department of Psychobiology and Health Sciences Methodology and the Department of Cellular Biology, Physiology and Immunology, directed by Roser Nadal and Antonio Armario, has shown scientifically through experiments with rats that addiction to morphine is related to a tendency to explore perseveringly and to search for new sensations. Using mazes and cages, the scientists observed in their experiments that the animals with a greater tendency to explore are more inclined towards an addiction to morphine.

The researchers had classified the rodents according to whether they had a tendency to explore repeatedly a new situation (persevering explorers) or they became disinterested in the new situation within a short amount of time. This was done by placing them in a circular corridor they had never seen before and observing their behaviour. Only the persevering animals that persistently explored their new environment had a preference for being administered morphine. It was also observed that other personality characteristics in the rats, such as anxiousness or fear, are unrelated to morphine addiction. This is the first time a relationship has been observed between addiction and a tendency to explore without other characteristics appearing that could also increase the likelihood of an addiction.

Experimental research into addictions often uses rodents, rats and mice. According to Roser Nadal, "the animal model used is extremely reliable, giving us thorough, methodical results that can to a certain extent be applied to humans without the need to experiment directly upon them".

This research, published in Behavioural Brain Research, may help to focus preventative strategies against addiction towards those most at risk, according to their personality. "The results could be particularly useful in prevention campaigns for children, who are going through the period with the highest risk," explains Doctor Nadal.

To determine a rat's level of addiction to morphine, the researchers used the place-conditioning technique. In these tests, a special cage is used that has two very different compartments, with a distinct colour, feel and smell. The animal is placed in a compartment after being injected with the drug and is left to experiment the effects of the drug and associates them with the specific characteristics of the the compartment of the cage. On a different day, the animal is injected only with a placebo (the liquid that was used to dissolve the drug, eg, water and salt) and is placed in the other compartment of the cage. When this has been done several times over the period of a few days, the rat is left free and we observe which of the two compartments it prefers. The more the animal likes morphine, the more time it will spend in the compartment that it associated with the effects of this drug, and this gives us an indication of the rat's addiction to the drug.
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The UAB research group is part of a Spanish nationwide research network into addictive behaviours that is part of the Fondo de Investigaciones Sanitarias (FIS), a network of basic, clinical and epidemicological aspects on addiction, with 22 member groups from various disciplines.

Universitat Autonoma de Barcelona

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