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Washington, Apr 20 (ANI): Exposure to marijuana or hashish during adolescence has a lasting impact on cognitive processes such as learning and memory, says a new study.

Lead researcher Dr. Peter Winsauer, from Louisiana State University suggests that illicit use of THC, an ingredient of marijuana or hashish, during adolescence produces persistent changes in the brain that sensitise females to the negative effects of THC later in life.

During the study, the research team examined a group of 12 female rats, who were 35 days old - an age equivalent to that of human teenagers about to undergo puberty.

They began to be exposed to THC chronically for 40 days. Half had had their ovaries removed when they were 30 days old, half retained their ovaries.

After the 12 females finished the period of exposure, they underwent an extensive training process consisting of pressing colored keys in a specific sequence in order to obtain food pellets.

Then, as adults, they were challenged with different dosages of THC and tested with a learning task.

They found that all rats given THC did worse on tests than did similar animals receiving saline.

All of them showed a dose-dependent reaction: the more THC, the worse they performed.

However, the rats that had been exposed to THC earlier in life performed significantly worse at the varying doses of THC than did the rats for which the adult exposure to THC was their first.

This was true whether the animals had ovaries or not. Because of their earlier THC exposure, having ovaries did not bestow any benefit when exposed to THC as adults.

The findings were presented at Experimental Biology 2009 as part of the scientific program of the American Society for Pharmacology and Experimental Therapeutics. (ANI)