Nycthemeral variation in brain monoamines of Syrian hamsters: relation to activity and energy homeostasis.

No significant time-of-day variations were found in whole brain content of various monoamines and metabolites of sedentary Syrian hamsters. In a second experiment, norepinephrine and serotonin levels in diencephalon were higher in the morning than the evening of both sedentary and voluntarily exercising hamsters. In telencephalon, levels of most transmitters were elevated in the evening, with the most dramatic rises in the metabolites 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid. Again, in most instances, there was no difference between sedentary and exercise conditions.