Science Cannabis

The Effects of Cannabis on the Central Nervous System 107cuits is thought to be critical in the laying down of memory circuits inthe brain. When cannabinoids are added to the incubating solution theydisrupt this potentiation.Another behavioral test that can be employed both in rodents or inmonkeys is the delayed matching to sample task. When using this test inmonkeys an animal is confronted with a number of alternative panels ona touch screen. At the start of the experiment one of these panels isilluminated and the screen then goes dead, preventing the animal frommaking any immediate response. After a delay, usually of 30-90 secondsall the panels on the screen are illuminated and the animal has to rememberwhich one was illuminated earlier and press it to obtain a foodreward. After daily training sessions animals become proficient at suchtasks and make few errors. THC and other cannabinoids again disruptbehavior in these tests of working memory. Similar results have beenobserved in rats using a variant of this task.The results of a recent study suggest the possibility that the ongoingrelease of endogenous cannabinoids in the brain may play a role in modulatingworking memory; the study employed an unusual memory taskinvolving a social recognition. When adult rats or mice are exposed forthe first time to a juvenile animal they spend some time contacting andinvestigating it. If the adult is exposed to the same juvenile within 1 hourof the first encounter it appears to recognize that it has already encounteredthis juvenile and will spend less time investigating it. If the delaybetween trials is increased to 2 hours, however, the adult seems to havelargely forgotten the original encounter and investigates the juvenile animalthoroughly once more. This short-term memory appears to relymainly on olfactory cues. Researchers at the Sanofi company in Francefound that animals treated with low doses to the cannabinoid antagonistSR141716A showed improved memory function in this test, and wereable to retain the social recognition cues for 2 hours or more. They alsoshowed that the performance of aged rats, who had difficulty in rememberingfor even as long as 45 minutes, could be significantly improved bytreatment with the antagonist drug (Terranova al., 1996). This raises theintriguing possibility that cannabinoid receptor antagonists could possiblyhave beneficial effects in elderly patients who suffer from memory loss.