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

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Abstract
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.