MODIFICATION OF ADRENAL TYROSINE HYDROXYLASE ACTIVITY IN RATS FOLLOWING MANIPULATION IN INFANCY

Abstract

The activity of some of the enzymes synthesizing the adrenal catecholamines is affected by the animal's genetic endowment. Activity of these enzymes is also affected by environmental variables. Mice that have received the combined psychosocial stimulation of maternal separation during infancy and isolation after weaning have reduced activity of adrenal tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT), while animals that are group housed after weaning have increased activity of these enzymes. In rats, infant handling modifies the response to later stressful situations. This manipulation consists of removing infant pups from the mother and placing them in individual containers and then returning them to the maternity cage. The procedure might be repeated for any length of time up to weaning. When the adrenocortical response to a novel environment is examined in later life, animals that have been handled in infancy have lower plasma levels of corticosterone and return to “resting” levels rapidly than non-handled animals.