EFFECTS OF STRESS ON THE METABOLISM OF NOREPINEPHRINE, DOPAMINE AND SEROTONIN IN THE CENTRAL NERVOUS SYSTEM OF THE RAT. I. MODIFICATIONS OF NOREPINEPHRINE TURNOVER

Abstract

The effect of stress on the metabolism of norepinephrine (NE), dopamine and serotonin (5-hydroxytryptamine; 5HT) in the central nervous system of the rat has been examined. Estimations of turnover of NE have been made by following the changes in NE specific activity after labeling the endogenous stores of NE by intracisternal injection of H 3 -NE. Stress induced by mild electric shocks to the feet did not significantly affect the endogenous content of NE but did markedly increase the turnover of this amine in central NE-containing neurons, mainly in the brainstem-mesencephalon and in the spinal cord. The disappearance of H 3 -dopamine in the striatum and brainstem-mesencephalon was not affected under these conditions. This stress increased the synthesis of 5HT in the brainstem-mesencephalon as seen by the greater increase of endogenous 5HT after monoamine oxidase inhibition but did not affect the disappearance of intracisternally administered H 3 -5HT. Changes in NE turnover regulation induced by electric foot shocks were studied in various conditions. There was an enhanced turnover of NE in the brainstem-mesencephalon when higher intensities of stimulation were used; this was associated with an increased accumulation of H 3 -normetanephrine; no modification was seen when the frequency of stimulation was increased. NE turnover during an acute stress session was enhanced to a greater degree when rats were previously subjected to many stress sessions. The initial accumulation of H 3 -NE in the brainstem-mesencephalon was decreased just after an acute stress and increased 24 hr after the last electric shock stress session of a chronic stress treatment.