Brain serotonin metabolism in hibernation.

It has been shown that notwithstanding 2-fold decreased monoamine oxidase (MAO) activity in brain of hibernating ground squirrels (Citellus erythrogenys major, Brandt), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels in most of the brain areas studied were not significantly different from the ones in active ground squirrels. However, marked changes were revealed in 5-HT and 5-HIAA brain level in entering hibernation (body temperature 11-9 degrees C) and arousing (body temperature 22 degrees C) animals. In entry into hibernation an increase in brain 5-HT, decrease in 5-HIAA level and lowered MAO activity was found. In arousal from hibernation 5-HT was decreased, 5-HIAA was increased and MAO activity was found to be increased to the level of the active ground squirrels.