TYROSINE-HYDROXYLASE ACTIVITIES IN THE BRAINS OF WILD NORWAY RATS ANDSILVER FOXES SELECTED FOR REDUCED AGGRESSIVENESS TOWARDS HUMANS

Tyrosine hydroxylase (TH) activity was measured in brains from Norway rats and silver foxes showing wild type aggressiveness and from their counterparts selected over 20-25 generations for reduced aggressivenes s towards humans (tameness), TH activity in the brain stem and cortex was increased in tame animals of both species compared with aggressive counterparts. Selection increased hypothalamic TH activity in foxes, but decreased it in rats. There was no difference in TH activity in co rpus striatum between the tame and aggressive animals. Fetal TH activi ty in the posterior part of the brain was higher in tame than aggressi ve rats at day 20 of embryogenesis. Increased TH activity in the brain stem and cortex of adult aggressive rats was observed after treatment of their mothers with hydrocortisone on the days 16 and 18 of pregnan cy. This elevation in TH activity was associated with attenuation of t he defense behavior of aggressive rats, The data suggested that altera tions in neural TH activity in tame rats and foxes may be part of the neurochemical basis of their behavioral phenotype which is developed b y selection. (C) 1994 Wiley-Liss, Inc.