EFFECTS OF SINGLE AND REPEATED INJECTION OF METHAMPHETAMINE ON THE TISSUE CATECHOLAMINE OF RABBIT

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Abstract
The effects of the single and repeated injections of methamphetamine on the content of tissue catecholamine in association with the behavioral changes of the intact rabbits were studied. The first two injections of methamphetamine produced progressive decreases in the atrial and adrenal catecholamine, but further injections did not result in more decrease. In the brain stem, the significant decrease of norepinephrine was observed only in response to the first injection of methamphetamine. The second and further injections of methamphetamine induced much less decrease of norepinephrine. In the brain cortex, the single injection of methamphetamine did not significantly affect the content of norepinephrine. Further repetition of the injection resulted in slight and somewhat variable changes. Though the depletion of catecholamine was subjected to a tachyphylactic phenomenon after repetitive injections of methamphetamine, the behavioral exictements including the increase in heart rate and spontaneous motor movements appeared as usual for every injection. It is suggested that the behavioral excitements of the animal in response to the first injection of methamphetamine derive from the direct effects of it plus indirect effects which the norepinephrine released by methamphetamine exerts, while the large parts of the behavioral excitements including tachycardia in response to more than 2 injections of methamphetamine derive mainly from the direct effects of the drug, independently the level of endogenous catecholamine.