Rats learn risk of cannabis

[Lunar Loops]

This from Theage.com.au:

Rats learn risk of cannabis

Richard Macey
July 31, 2007

YOUNG rats high on cannabis suffer far greater memory loss and more lasting changes in brain function than doped-up adult rodents.
Research by Sydney scientists has also found the drug is a turn-off for grown-up rats. But the wisdom of age comes too late.
"Cannabis produces much greater long-term changes in adolescent than adult rat brains," said Iain McGregor, professor of psychopharmacology at the University of Sydney.
His research team used sophisticated cages more like three-room houses for the experiments. Each room was given different wallpaper and smells so the rats could tell them apart.
Adolescent and adult rats were locked in one room and injected 12 times over two weeks with tetrahydrocannabinol, or THC, the drug's active ingredient.
When the doors were opened, allowing the rats to roam from room to room, the researchers noticed something unusual.
"The adults avoided the room where they had been under the influence of THC," Professor McGregor said.
But the adolescents had no fear of the room.
Professor McGregor said the results reflected cannabis use patterns in humans.
"Studies show that most adult (humans) have given it away by the time they are 30 or 35."
The rats were left drug-free for two weeks, given blood checks to ensure they no longer had THC in their bodies, and then had their memories tested.
"The 'teenagers' that had received cannabis were still memory impaired two weeks later, while the adults were fine," Professor McGregor said. "The adolescents showed poor memory for what had happened an hour ago."
Finally the researchers examined the brains of the rats, looking for tell-tale protein changes in the hippocampus, the area responsible for memory.
The adolescents that had been given cannabis had three times as many changed proteins in this brain region as the adults given the same dose.
"It was a double whammy," Professor McGregor said. "The adolescents liked cannabis more, but it was worse for their brains and their memory."
Although Professor McGregor said he did not want to sound as if he was preaching that cannabis was "a drug of doom", he said it was "another cautionary study about heavy use" by young people, whose brains were still developing.
The findings appear in the journal Neuropsychopharmacology this month.