Columns:: The inside dope: Study by UGA scientists reveals that laboratory rats ‘under the influence’ find it hard to concentrate

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Columns::September 15, 2003

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Co-authors of a paper based on the study were (from left) psychologist Jonathon Crystal, laboratory research coordinator Kenneth Maxwell and assistant professor of psychology Andrea Hohmann. (Photo by Peter Frey)

The inside dope
Study by UGA scientists reveals that laboratory rats ‘under the influence’ find it hard to concentrate

By Phil Williams
phil@franklin.uga.edu

Sustained attention to timing-tasks was substantially altered in laboratory rats when they were given a synthetic cannabinoid--a compound similar to the one which occurs naturally in marijuana, according to a recent study by scientists at UGA. The research team, headed by psychologist Jonathon Crystal, showed that rats “under the influence” had difficulty distinguishing between long and short periods of time during tasks for which they had previously been trained.
“In the real world, this suggests that someone smoking marijuana might well be able to do a task briefly, but over time there could be serious attention problems,” says Crystal. The implication is that users of marijuana could be lulled into thinking they are capable of using the motor skills for such actions as driving when in fact there could be serious long-term attention-span problems.
The research was published in the journal Behavioural Brain Research. Coauthors of the paper are Andrea Hohmann, assistant professor of psychology, and laboratory research coordinator Kenneth Maxwell. The study was funded by a grant from the National Institute on Drug Abuse.
The rats used in the study were placed in a box equipped with a speaker and two retractable levers. A sound was presented to the rats for either a short period (four seconds, for example) or a long period (16 seconds). The rat could obtain a pellet of food by pressing one of the two levers following short sounds and by pressing the other lever following long sounds.
“Under these circumstances, animals will typically learn to press the correct lever with high accuracy,” the researchers say.
The research team then played sounds of intermediate length in order to identify the midpoint, at which rats were equally likely to respond as if the sound were “short” or “long.”
After the rats learned the right levers to press, they were injected with a synthetic cannabinoid, and their sensitivity to time was measured. Cannabinoids produce a substantial decline in sensitivity to time through a specific brain receptor mechanism.
Crystal’s team used a synthetic compound rather than tetrahydrocannabinol (THC), the “active” ingredient in marijuana, because the synthetic cannabinoid is more powerful and easier to use in laboratory settings. It is so close chemically to THC, however, that the findings can be equated with the effects of THC.
Using computer models to interpret the data, the scientists found that the general ability to maintain attention was altered by exposure to the cannabinoid. The cannabinoid disrupted performance of the task by producing a disorder of attention.

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