Effects of handling during infancy on the sympathetic–adrenal medullary system of rats

We examined the effects of daily handling and maternal separation (5 min per day) on the responsiveness of the sympathetic-adrenal medullary system of Sprague-Dawley rats before weaning and in adulthood. Plasma levels of norepinephrine (derived primarily from sympathetic nerves) and epinephrine (released from the adrenal medulla) were elevated in handled pups compared to unhandled controls at 14 and 18 days of age but not at 6 and 10 days of age. When tested in adulthood, previously handled and control rats did not differ with respect to basal or stress-induced increments in plasma levels of norepinephrine and epinephrine. These results indicate that brief daily episodes of handling and maternal separation are attended by an increase in sympathetic-adrenal medullary tone in 14-18-day-old rats. However, the enhanced response of the sympathetic-adrenal medullary system of separated rats may not persist into adulthood.