Exposure to Morphine During Early Adolescence Sensitizes Rats as Adults

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A study conducted at Emory University School of Medicine indicates that exposure to morphine during adolescence may increase sensitivity to the drug during adulthood. Drs. Stephen Holtzman and David White first established that both periadolescent (7 to 10 days before puberty onset) and adult male rats receiving 10 mg/kg/day of morphine for 1 day or 3 consecutive days exhibited similar increases in locomotor activity relative to age-matched rats receiving only saline. When the researchers reexposed the animals to morphine 5 weeks later, significant age- and exposure-related differences emerged. All of the rats were more active, but a relatively small dose of morphine (0.3 mg/kg) triggered significantly more activity in the rats that previously were exposed to morphine for 3 days as periadolescents, relative to their 1-day and unexposed counterparts. By contrast, rats previously exposed for 3 days as adults required 10 times that dose to exhibit more activity than those in the 1-day and unexposed groups. The findings suggest that, during adolescence, even a relatively low level of exposure to morphine can have profound, long-lasting effects.

European Journal of Pharmacology 528(1-3):119-123, 2005. [Abstract]