BRAIN MONOAMINES IN TEMPERATURE ACCLIMATION OF MICE

The brain 5‐hydroxytryptamine (5‐HT) and noradrenaline (NA) levels were determined fluorimetrically from mice during prolonged exposure to cold or heat. The NA level did not change until at extreme ambient temperatures, in which cases, especially in heat, a marked decrease was observed. In cold environment the 5‐HT level decreased after an initial short increase. However, within one day the initial control level was reached again. In warm environment the changes were reversed. Some depletion experiments, where an inhibitor of 5‐HT synthesis was used, showed that the activity of brain 5‐HT neurons decreased for some days in cold, but returned gradually to the control level after the animals had acclimated to cold. © 1969 Scandinavian Physiological Society