EFFECT OF STRESS ON THE DISPOSITION OF CATECHOLAMINES LOCALIZED IN VARIOUS INTRANEURONAL STORAGE FORMS IN THE BRAIN STEM OF THE RAT

Abstract— The utilization of ³H]norepinephrine newly taken up or newly synthesized from ³H]tyrosine was studied in the brain stem of normal and stressed rats up to 5 h after the intracistemal injection of ³H]norepinephrine or ³H]tyrosine. The biphasic disappearance of the exogenous as well as of the endogenously synthesized ³HJnorepinephrine revealed that the amine is localized in at least two main compartments (A and B). The half-life of the amine newly taken up or newly synthesized, mainly localized in compartment A, is of short duration (between 15 and 30 min); the amine stored for a longer period of time and mainly distributed in compartment B is utilized more slowly (half-life, 180 to 260 min). A stress of short duration (15 min) induced by electric shocks applied to the feet increased the utilization of ³HJnorepinephrine newly taken up or newly synthesized from ³H]dopamine or ³H]tyrosine, but has no effect on the ³H]norepinephrine stored for a longer time period, indicating that the amine in compartment A is released in preference to that stored in compartment B. A stress of longer duration (180 min) increased the utilization of ³H] norepinephrine in both compartments and induced a sustained increased in norepinephrine synthesis as shown by the enhanced formation of ³H]norepinephrine from ³H]tyrosine in brain stem slices in vitro. The electrical stress was without effect on ³H]norepinephrine uptake. As for ³H]norepinephrine, the 15 min of stress enhanced the utilization of ³H] dopamine newly taken up or newly synthesized from ³H]tyrosine and had no effect on ³H]dopamine stored for a longer time period. These results suggest an increased release of both ³H]dopamine and ³H]norepinephrine from noradrenergic terminals of the rat brain stem. Finally, the 15 min of stress appeared to have no effect on the utilization of ³H] serotonin newly synthesized from ³H]tryptophan in serotonergic neurons of the brain stem, whereas the 180 min of stress increased the utilization of 5-HT in this structure.