Administration of d-amphetamine sulfate (7.5 mg/kg i.p.) twice daily to cats produces an initial large increase in both locomotion and behavioral stereotypy. As this regimen continues beyond three days, however, both measures show large significant decreases. We hypothesize that this tolerance to the behavioral effects of amphetamine is attributable to the concomitant decrease (approx. 70%) in presynaptic stores of dopamine and norepinephrine.
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