Annual and daily changes in brain serotonin content in differentially housed mice.

The annual and daily variations of brain serotonin and 5-hydroxyindolacetic acid have been studied over a 6-year period in normally grouped and isolated mice. The results obtained indicate that differences exist between normally grouped and isolated animals, especially when referred to the annual changes to which brain serotonin and 5-hydroxyindolacetic acid undergo. The results suggest that the outcome of the experiments on neurochemistry, neuropharmacology and behavior can change according to the month of the year and they can further be modified by differential housing of mice.