1. The selection of 20 generations of Norway rats for a domesticated type of behavior led to disappearance of the reaction to a glove and a decrease in aggressiveness induced by electropain stimulation but did not change the intraspecies aggression of males and the predatory aggression of rats toward mice. 2. Selection of gray rats for taming is accompanied by changes in the level and metabolism of monoamines in the brain. Beginning with the 15th to 16th generations of selection, in the tamed rats an increase in the level of 5-hydroxyindoleacetic acid was noted in the hypothalamus, in the 20th generation an increase in the serotonin content in the hypothalamus and midbrain, and in certain generations of selection an increased level of norepinephrine was noted in the hypothalamus in comparison with wild rats.
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