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--------------------------------------------------------------------- Mother's Love Linked to Brain Chemicals --------------------------------------------------------------------- NEW YORK (Reuters) -- Studies in rats suggest that a woman's maternal affection for her newborn may depend on the production of a specific brain chemical during the birthing process. When that chemical 'switch' is not thrown, new mothers may be indifferent to the care of their young. "We have to be open to the possibility that some instances of human neglect, abuse or postpartum depression could involve the failure of such a mechanism," said Boston geneticist Dr. Michael Numan, commenting in the magazine New Scientist. Numan was responding to the results of a new study conducted by Drs. Steven Thomas and Richard Palmiter of the University of Washington in Seattle. According to a New Scientist report on the study, the researchers studied the nurturing behaviors of a group of female mice, each of whom lacked a gene responsible for initiating a process ending in the production of the neurotransmitter norepinephrine. Norepinephrine is thought to help 'prime' the brains of rodent mothers-to-be for the demanding task of caring for their young. The study found that just 35% of newborn mice pups born to gene-deficient mothers survived into adulthood. The pups were left scattered, uncleaned, and unfed, the researchers report. When pups were 'adopted' by normal mothers, survival rates climbed to a healthy 85%. Thomas and Palmiter subsequently tried to see if gene-deficient mothers injected with a norepinephrine-producing drug would fare any better at caring for their newborns. They found that injecting the mothers early in pregnancy effected no change in behavior. However, if the injection was administered during the actual birth process, the maternal nurturing response 'kicked in' soon after birth, and pup survival rates climbed to 75%. "It makes sense that maternal instincts would be reinforced in the brain just before they're needed," said Thomas. Studies have not yet confirmed that what works in mice might someday work in humans, but Numan points out that the nurturing response seems to originate in the hypothalamus, a primitive area of the mammalian brain that has remained remarkably unchanged through millennia. In any case, experts say the study leaves open the possibility that a carefully timed dose of norepinephrine-stimulating drugs during childbirth could someday help eliminate the rejection of newborns by human mothers as well. SOURCE: New Scientist (December 13, 1997, p. 4) 1997, Reuters Health eLine http://www.medscape.com/reuters/fri/t1211-2f.html janet [log in to unmask]