Science : Adoring mums raise calmer pups

日期:2019-02-27 02:19:02 作者:松蔓 阅读:

By Bob Holmes RATS born to attentive mothers grow up more adventurous and less sensitive to stress, say researchers in Canada. Their study, which measured the rat pups’ hormonal responses to stress, is the first to show that natural differences in mothers’ behaviour can have lasting effects on the physiology of their offspring. Dong Liu and his colleagues at McGill University’s Douglas Hospital Center in Verdun, Quebec, observed nine female rats rearing their litters without any outside interference. The researchers found a wide range in maternal attentiveness. The most attentive mothers spent about 40 per cent more time nursing their pups and almost twice as much time grooming and licking them as the least attentive. Once the pups reached adulthood, Liu tested their stress responses by confining each rat in a narrow plastic tube for 20 minutes. In all the offspring, the experience raised the blood levels of two important stress hormones, ACTH (adrenocorticotrophic hormone) and cortisone. However, the stress hormone response was weaker and shorter-lived among those rats with more attentive mothers. The team also found that rats reared by more attentive mothers were more likely to explore an unfamiliar setting and were quicker to calm down enough to begin eating. These results add weight to the findings of earlier, but more artificial, experiments by Michael Meaney, Liu’s supervisor. Meaney deliberately altered mother rats’ behaviour by removing pups from them for 15 minutes every day. Paradoxically, this increases maternal care, because the mothers lavish so much attention when reunited with their pups that it more than compensates for the time apart. Such pups show milder stress responses as adults. In part, this may be because they have more stress-hormone receptors in the hippocampus, the part of the brain responsible for shutting off the stress response once it begins, so they can dampen down the response more rapidly. The increased number of receptors makes it easier for hippocampal neurons to detect cortisone, which makes the brain reduce the output of ACTH,