Brain-imaging studies conducted on animals by American scientists have provided clues as to why an increasingly popular recreational drug that causes hallucinations and motor-function impairment in humans is abused.
Scientists at the Department of Energy's Brookhaven National Laboratory have discovered that the brains of the primates show a behaviour similar to the extremely fast and brief "high" observed in humans upon receiving Salvia divinorum (salvia), a Mexican mint plant that can be smoked in the form of dried leaves or serum.
Writing about their study in a paper published online in the journal NeuroImage, the researchers claimed that they were the first to look at how salvia travels through the brain.
"This is probably one of the most potent hallucinogens known," said Brookhaven chemist Jacob Hooker, the lead author of the study.
"It's really important that we study drugs like salvia and how they affect the brain in order to understand why they are abused and to investigate their medicinal relevance, both of which can inform policy makers," he added.
During the study, the technique of positron emission tomography (PET) was used to watch the distribution of salvinorin A in the brains of anaesthetized primates.
The subjects received a radioactively labelled form of salvinorin A, and were put under the scanner to track site-specific concentrations of the substance in various regions of their brains.
Within 40 seconds of administration, the researchers found a peak concentration of salvinorin A in the brain, nearly 10 times faster than the rate at which cocaine enters the brain.
The effect of the drug was essentially gone about 16 minutes later.
The researchers say that this pattern is similar to the effects described by human users, who experience an almost immediate high that starts fading away within five to 10 minutes.
Hooker's team also observed that high concentrations of the drug were localized to the cerebellum and visual cortex, which are parts of the brain responsible for motor function and vision, respectively.
Analysing the results of their own study as well as published data from human use, the researchers came to the conclusion that just 10 micrograms of salvia in the brain was needed to cause psychoactive effects in humans.
Hooker has revealed that salvia does not cause the typical euphoric state associated with other hallucinogens like LSD.
The researcher says that the drug targets a receptor that is known to modulate pain, and may be important for therapies as far reaching as mood disorders.
"Most people don't find this class of drugs very pleasurable. So perhaps the main draw or reason for its appeal relates to the rapid onset and short duration of its effects, which are incredibly unique. The kinetics are often as important as the abused drug itself," Hooker said.
The researchers said that further steps in their research would include studies pertaining to salvia's abuse potential, and attempts to develop radioactive tracers that can better probe the brain receptors to which salvia binds.
They believe that such studies may open the door for therapies for chronic pain and mood disorders.