Effect of different environmental temperatures on the serotonin concentration and turnover in the brain stem of a hibernator.

The serotonin (5-HT) and 5-hydroxyindoleacttic acid (5-HIAA) levels and 5-HT turnover were studies in the brain stem of warm- (+30 degrees C) and cold- (+6 degrees C) acclimated golden hamsters, exposed for 3 hours to temperatures of +6 degrees C, +30 degrees C and +37 degrees C, respectively. In war-acclimated hamsters kept under conditions the 5-HT level in the brain did not change significantly during the year. The 5-HIAA level was slightly higher in the winter. The 5-HT turnover varied within limits of 0.071 to 0.180 mug/g/hour-1. Three hours' exposure of warm-acclimated golden hamsters to cold (6 degrees C) increased the concentrations of 5-HT and 5-HIAA and the 5-HT turnover in the brain. After long-term adaptation to cold (6 degrees C) the 5-HT level, and the 5-HT turnover returned to the original level. Three hours' exposure of golden hamsters to higher environmental temperatures (warm-acclimated individuals to 37 degrees C and cold-acclimated individuals to 30 degrees C) also increased the 5-HT turnover. The concentrations of 5-HT and 5-HIAA increased in cold-acclimated golden hamsters exposed to 30 degrees C and was not changed in warm-acclimated ones, exposed to 37 degrees C. Although the elevated temperatures induce greater changes in serotonin metabolism than lowered temperatures, the serotonin pathways in the brain do not seem to be affected by short-term temperature changes specifically. The findings are rather indicative that changes in 5-HT turnover may be the primary reaction to stressful conditions.