Morphine stimulation of mesolimbic and mesocortical but not nigrostriatal dopamine release in the rat as reflected by changes in 3-methoxytyramine levels.

Morphine was shown to enhance dopamine release in the rat olfactory tubercle, nucleus accumbens, prefrontal cortex and pyriform cortex, as assessed by increased 3-methoxytyramine (3-MT) levels and 3-MT accumulation after pargyline treatment. In contrast, both 3-MT levels and accumulation after pargyline were unaffected by morphine in the rat striatum. These data suggest that the mesolimbic and mesocortical dopaminergic projections in the rat can be activated by opiates and lead to changes in cortical function which may be involved in some of the complex behavioral actions of opiates and opioid peptides.