d-Amphetamine-induced increase in catecholamine synthesis in the corpus striatum of the rat: Persistence of the effect after tolerance

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Abstract
The effect ofd-amphetamine onin vivo catecholamine synthesis in four regions of rat brain was determined by measuring the accumulation of dopa after inhibition of dopa decarboxylase. In doses up to 2.5 mg/kg,d-amphetamine caused dose-dependent increases in striatal dopa accumulation to a maximum of 280% of control; further increases in dose resulted in smaller effects until 10 mg/kgd-amphetamine was not significantly different from control.d-Amphetamine did not alter dopa accumulation in telencephalon, in diencephalon-mesencephalon, or in pons-medulla oblongata.d-Amphetamine did not affect either dopamine levels in striatum or NE levels in pons-medulla oblongata; at high doses,d-amphetamine did reduce norepinephrine levels in telencephalon and in diencephalon-mesencephalon. Daily administration of pre-session but not of post-sessiond-amphetamine produced tolerance to the effects ofd-amphetamine on milk consumption in rats. The ability ofd-amphetamine to increase striatal catecholamine synthesis was not altered by the development of tolerance tod-amphetamine. These results suggest that tolerance tod-amphetamine is not related to its effect on catecholamine synthesis but instead occurs via changes in aspects of catecholamine metabolism other than synthesis via change in catecholamine release, reuptake, or receptor sensitivity, or via changes in non-catecholaminergic mechanisms.