From: NORML California <canorml@igc.org>
Newsgroups: alt.drugs
Date: 16 Apr 92 23:51 PDT
Subject: 3 Things Pot Doesn't Do (1)
Nf-ID: #N:cdp:1301300139:000:3737
Nf-From: cdp.UUCP!canorml    Apr 16 23:51:00 1992



THREE THINGS MARIJUANA DOESN'T DO
 from California NORML Reports, April 1992
(1) NO BRAIN DAMAGE SEEN IN MARIJUANA-EXPOSED MONKEYS
   Two new scientific studies have failed to find evidence 
of brain damage in monkeys exposed to marijuana, undercutting 
claims that marijuana causes brain damage in humans.
    The studies were conducted by two independent 
research groups.  The first, conducted by Dr. William Slikker, 
Jr. and others at the National Center for Toxicological Research 
in Arkansas  examined some 64 rhesus monkeys, half of which 
were exposed to daily or weekly doses of marijuana smoke for 
a year.  The other, by Gordon T. Pryor and Charles Rebert at SRI 
International in Menlo Park, California,  which is still 
unpublished, looked at over 30 rhesus monkeys that had inhaled 
marijuana one to three times a day over periods of 6 to 12  
months.  Neither study found evidence of structural or 
neurochemical changes in the brains of the monkeys when 
examined a few months after cessation of smoking.
   The new results cast doubt on earlier studies 
purporting to show brain damage in animals.  The most famous 
of these was a study by Dr. Robert Heath, who claimed to find 
brain damage in three monkeys heavily exposed to  cannabis.  
Heath's results failed to win general acceptance in the 
scientific community  because of the small number of subjects, 
questionable controls, and heavy doses.  
   Subsequent rat experiments by Dr. Slikker and others 
reported persistent structural changes in the brain cells of 
rats chronically exposed to THC.  The studies did not show that  
pot kills brain cells, as alleged by some pot critics, but they 
did show degeneration of the nerve connections between brain 
cells in the hippocampus, where THC is known to be active.   
   Although scientists have regarded the animal evidence 
as inconclusive, some critics have cited it as proof that pot 
causes brain damage in humans.  Thus Andrew Mecca, the  
director of California Department of Alcohol and Drug Abuse, 
recently stated on the Ron Reagan, Jr. talk show (Sep. 2, 1991) 
that marijuana "leaves a black protein substance in the 
synaptic cleft" of brain cells, a claim apparently based on 
Heath's monkeys.  When asked by a NORML member for his 
evidence, Mecca sent a list of three references, none of which 
turned out to have anything to do with brain damage.
   Although the new monkey studies found no physical 
brain damage, they did observe behavioral changes from 
marijuana.  Slikker's group found that monkeys exposed once a 
day to the human equivalent of four or five joints showed 
persistent effects throughout the day.  Slikker says that the 
effects faded gradually after they were taken off marijuana, 
and were not detectable seven months later, when they were 
sacrificed.  Autopsies did reveal lingering chemical changes in 
the immune cells in the lungs of monkeys that had inhaled THC.   
However, Slikker's group concluded that experimental exposure 
to marijuana smoke "does not compromise the general health of 
the rhesus monkey."
   References:  William Slikker, Jr. et al, "Chronic 
Marijuana Smoke Exposure in the Rhesus Monkey," Fundamental 
and Applied Toxicology  17: 321-32 (1991)
    Guy Cabral et al, "Chronic Marijuana Smoke Alters 
Alveolar Macrophage Morphology and Protein Expression, 
Pharmacology Biochemistry and Behavior 40: 643-9 (1991)
   Merle Paule et al., "Chronic Marijuana Smoke Exposure 
in the Rhesus Monkey II: Effects on Progressive Ratio and 
Conditioned Position Responding,"  Journal of Pharmacology and 
Experimental Therapeutics 260: 210-22 (1992)

(from California NORML Reports:  4/92
2215-R Market  St#278, San Francisco, CA (415) 563-5858)

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