Modified ontogenesis of enkephalin and sunstance P containing neurons after perinatal exposure to morphine

The development of met-enkephalin (ME) and substance P (SP) neurons has been studied in rats exposed to morphine during the perinatal period up to day 30 of life. Both peptides levels were measured by specific radioimmunoassays. ME developmental pattern is markedly affected by morphine in the pons-medulla oblongata, while SP does not seem to be influenced. It is suggested that the well known inhibitory effects of opiates on brain growth and maturation might take place by altering the developmental pattern of the endogenous opioid system.